US2287716A - Fluid device - Google Patents

Description

J. E. WHITFIELD FLUID DEVICE June z3, 1942.

7 Sheets-Sheet 1 Filed April 22, 1941 June 23, 1942.v

J. E. WHITFIELD l FLUID DEVICE Filed Aiaril 22, 1941 '7 Sheets-Sheet 2 V INVE TOR Z5/2% A B mw- La ATTORNEY June 23, 1942. JQE. WHITFIELD FLUID DEVICE Filed April 22, 1941 '7 Sheets-Sheet 5 IIJ June 23, 1942-. JQE. WHITIELD FLU1D DEVICE 'T Sheets-Sheet 4 Filed April 22, i941 4, 6 QJM Y ,f 1/ y 12 2 1 J E .w y; @M w\;

June .23, 1942- J. E. WHITFIELD FLUID DEVICE Filed April 22, 1941 7 Sheets-Sheet 5 ATTORNEY June 23, 19424- J. E. WHITFIELD 2,287,716

FLUID DEVICE Filed April 22, 1941 7 sheets-sheet e ATTORNEY Patented June 23, 1 942 UNITED STATES. PATENT orrlc 2,281,716 FLUID nevica Joseph E. Whitfield, Grove City, Pa. Application April 22, 1941, serial No. 389,729

(cl. 23o-14a) 22 Claims.

This invention relates generally to uid pumps, motors. blowers, compressors and similar devices in which the rotary engaging members are provided with helical intermeshing threads, and more particularly to the novel structure of the rotary members, the case in which they operate and other associated parts making up any one of these devices.

These screw type iluid pumps, motors and the like have two or more helically threaded members rotatably supported with their axes parallel and with their complementary threads intermeshing to provide a continuous seal line for the full extent of their engagement. The casing encloses both of the members and the perimetral edge of each thread forms a seal therewith. Thus any flow of fluid from one end of the members 1 )to the other must pass through the grooves of the threaded members.

The threads must be complementary to permit rotation of the members. Thus one member has left hand threads while the other member has right hand threads.

One of the threaded members is referred to as the rotor andthe other as the gate. When rotated the rotor threads, in effect, act a continuous series of pistons which slide axially in the same direction through the grooves of the gate and produce a successive series of pockets which convey the uid from one end of the members to the other. The openings in the casing at the ends of the rotary members mag be either the inlet or the discharge, depending upon the direction of rotation of the members.

These types of screw pumps, motors and the like are old in the art but they are impractical commercially because they inherently possess a leakage path back through the screw members from the discharge to the inlet. The volume of this leakage path is substantially the same as the pump displacement which renders them impractical.

To make these pumps practical it is necessary to seal this leakage path and increase their eiciency so that they may compete commercially with other types of pumps. This object may be accomplished as disclosed herein, by partially closing and sealing one or both ends of the rotary members and by carefully selecting the character of the coactinghelical threads on the rotary members.

The most efficient combination of coacting helical threads on the rotary members is in the ratio of two to one. This thread ratio provides the largest capacity "for a given size of the members and the ends of the rotary members are easily sealed., 'I'he speed of the rotary member having the least number of threads must be greater, and the pitch of its threads must be less than the rotary member having the most threads in order that they may properly coact to produce a continuous sealing engagement between each other.

If the ratio of the threads is one to one the rotary members would have the same speed and the pitch of the threads would be the same. It is practically impossible to prevent an end to end backward or leakage flow in a structure of this character. To function the whole of the ends of the rotor membersmust be covered, leaving a very small size opening or port, the location of which is critical. This makes the device inoperative as a liquid pump and impractical as a gas pump or blower, since the capacity and the eiciency are very low.

With the threads on the members being in vthe ratio oftwo to one a larger port opening may bevused, which is an important advantage over a device where the threads have a one to one ratio.

Again if the ratio of the threads on the rotary members were two to five the capacity of the device is' decreased fr a given diameter of the rotary members which offsets what other advantages it might have.

After having selected the ratio of one to two for the threads of the rotary members it will be found advantageous to employ a plurality of parallel threads on both members because a greater number of independently sealed pockets may be produced in a shorter length of the rotary members.

The selection of two parallel threads for the rotor member provides a greater pumping capacity for a given diameter than three or more threads. The choice of two parallel threads on the rotor thus fixes thev number of threads on the gate to four. In order that these threads may roll together the pitch of the rotor threads must be less than the pitch of the gate threads and the first rotor thread slides through the odd gate troughs while the second rotor thread slides through the even gate troughs. This thread selection also fixes the speed ratio of the rotorand the gate at two to one respectively.

The accurately formed complementary threads of the members will operate as smoothly as a set of gears and one member can drive the other and transmit power therebetween. However it is preferable to provide a slight clearance between the members and between the perimetral edges of their threads and the casing to avoid wear. Timing gears are therefore employed to maintain the proper angular relation of the intermeshed threads.

The principal object of this invention is to' obtain a novel and commercially practical uid pump, motor and the like employing the above recited advantages.

Another object is the provision of a iiuid transier device through which the uid may travel in either direction.

Another object is the provision of an improved form oi casing structure -for screw type blowers, compressors. pumps, motors and the like.

Another object is the provision oi a iluid transfer device having a pair oi rotary members with complementary coacting threads, one member being smaller in diameter than the other and having a greater number of threads which are disposed at a steeper pitch `and wherein the coacting threaded surfaces of the members do not roll but slide relative to one another.

Another .Objectis the provision oi improved rotor and gate members having complementary helical threads in the ratio oi one to two and wherein the rotor threads extend through a helix of approximately 180 and the gate threads onehaif that amount.

Another object is the provision of rotor and gate members having intermeshing complementary helical threads wherein the helix angle of the threads change intermediate the ends of the members.

Another object is the provision of means for sealing the inherent leakage path through the rotary members.

Another object is the provision of means for varying the openingat the discharge end of the rotor and gate members to produce a variable rotary screw type compressor.

Another object is the provision of means for closing and maintaining a seal on the discharge ends of the rotor and gate members to prevent a succession of pockets from being prematurely opened to discharge when the seal line between the members has been interrupted as the pocket being discharged runs out.

Another object is the provision oi a relief for fluids entrapped in pockets as they are running out at the discharge of a iiuid pump.

Another object isthe provision of compleme tary helical threads that coact to produce equal exposed areas on each side of the gate troughs which balance each other and eliminate power consumption in the gate member.

Other objects and advantages appear in the following description.

In the accompanying drawings a practical embodiment, illustrating the principles of the invention is shownwherein:

Fig. 1 is a vertical sectional view taken through the axes of the rotary members of the device.

Fig. 2 is a view similar to Fig. 1 with the parts being partially disassembled to illustrate their correlation.

Fig. 3 is a vertical sectional view ofthe casing, with the rotary parts removed, taken on the line 3-3 of Fig. 4. A

Fig. 4 is a side elevation oi the casing shown in Fig. 3, part of which is shown in section along the lmet-4 oi' Fig. 3.

Fig. 5 is a horizontal sectional view taken through the axis oi' the rotary gate member and the casing along the line 5-5 of'Fig. 1.

Fig. 6 is a horizontal sectional viewt taken through the axis oi' the rotor member having a helical screw thread longer than that shown in Fig. l, one end of which member is completely exposed within the case while the other end is adjacent a port, the rotor being shown in full.

Fig. 7 is a'partial vertical sectional view taken through the axes of the rotary members and il-v lustrating variable port members at one endv of the device.

Fig. 8 is an end elevation oi tbedevice iii trating a iiuid pressure operated servomotorfor actuating the variable port members. shown in Fig. 7. v

Fig. 9 is a diagrammatic mustrauopora-helical thread ofja rotary'memberwherein the-flaitchfoi the thread is constant; v

Fig. 10 is a diagrammatic illustration ofa helical thread of a rotary member wherein the pitch of the thread changes progressively. vfrom one end to the other.

Fig. 11 is a diagrammatic illustration of a. helical thread of a rotary member wherein the pitch oi' the thread changes continuously from one end to the other.

Fig. 12 isan end view of the rotary members constructed coincidental with the pitch circles of their intermeshing gears.

Fig. 13 is an end view of the rotary members constructed with the gate member larger'in diameter than the pitch circle of its gear.

Fig. 14 is an end view of the rotary members constructed with the gate member smaller in dlameter than the pitch circle of its gear.

Fig. 15 is an end view of the rotary members showing a rotor thread proceeding intothe gate. Fig. 16 is an end view of the rotary members showing a rotor thread in full engagement with the gate. Y

Fig. 17 is an end view of the rotary members showing a rotor thread about to leave the gate. Fig. 18 is an end view of the rotary members showing a. rotor thread proceeding into the gatev and sealing' plates covering the trailing edges of the threads. A

Fig. 191s a view similar to-Fig. 18 vshowing `the rotor thread in full engagement with the gate.

Fig. 20 is a view similar to Fig. 19 showing the rotor thread about to leave the gate.

Fig. 21 is an end view of the rotary members showing a rotor thread proceeding into the gate .and illustrating the cutting away of-the leading face of the rotor threads to extend the. discharge.

Fig. 22 is a view similar to Fig. 2l showing the pocket being shut oi! from the discharge and opening up to a successive pocket.

Fig. 23 is a view similar to Fig. 2l showing the pocket being relieved by the cut away'portlon to a successive pocket.

Fig. 24 is a view similar to Fig. 15 showing a slot cut from the leading edge to adjacent the trailing edge of the rotor threads for relieving the pockets to discharge. f

Fig. 25 is a view similar to Fig. 24 showing the rotor thread in full engagement with the gate.

Fig. 26 is a view similar to Fig. 25 showing the slot relieving the pocket to discharge at its fully run out position. Fig. 27 is a side elevation of the rotor member shown in Figs. 21 to 2 3 showing the leading por-I tions of the threads cut away.

Fig. 28 is an end view of gate and. rotor members at the discharge end showing one gate thread in full engagement with a trough of the rotor.

-I 6 therebetween.

Fig. 31 is a side elevation of a rotor threadl designed to produce equal exposed Aareas on each side of the gate trough.

Referring to Figs. 1 to 5 of the drawings, the casing I of the pump contains two cylindrical chambers II and I2 disposed side by side in parallelism and merging into one another, forming a large chamber'th cross-section of which is somewhat in the form'of a ilgure 8. One end of the casing is provided with an integral chambered head I3 having an inner wal1 'I4 which forms one end wall of the chambers II and I2 and an outer wall I5 with a space or chamber The head I3 is provided with the tubular openings I'I and I8, concentrically disposed with respect to the axes of the cylindricalchambers II and I2, respectively, for receiving the bearing and sealing structure which supports the rotary members.

A portion .of the inner wall I4 is cut away to form the port which may be either the intake or exhaust port, depending upon the direction of rotation of the rotary members of the pump. This port connects the cylindrical chambers II and I2 with Vthe chamber I6. An opening 2| is provided in the wall of thecasing adjacent the head I3 for connecting the 4chamber I6 to a conduit external of the casing. The port 20 is extended along the side walls of the chambers II and I2 as indicated by the V-shaped ,wa1l22 which is Wide at the opening 2l and narrows down to the sharp edge 23 near the center of the casing which is formed by the juncture of the walls of the cylindrical chambers II and I2.

At the other end o'f the casing the chambers II and I2 are open to permit the assembly of the rotary members therein. After the rotary members are inserted in the casing it is closed by the removable head 26.- A port 24 is provided in the head 26 and is connected to without the casing by the opening 25. A second v-shaped wall 22 is provided in the sidewalls of the casing diagonally opposite to the port 28 and the opening 2I. The apices of the V-shaped walls 22 extend to points just short of one another as shown in Fig. fi.y

The removable head 26 may be made in one piecel but it is preferably constructed in two pieces 21 and 28 separable along the plane 38 which intersects the edges 23 of the casing. The removable head 26 is also provided with the spaced inner and outer Walls I4 and I5 forming the included chamber I6 that is connected with as they are connected to their respective chambers I6 in the heads of the casing.

The casing and the removable head are provided with suitable abutting ilanges for securing the latter in place. The exterior of the cas- 75 ing is reinforced by the ribs 3| to provide strength to the-walls of the casting which are of uniform thickness. The feet 32 may be formed integral with the casing and positioned at any convenient placewhich is determinedby the location of the exterior'connections of the ports 2l and 26, so that the pump as a unit may be properly adapted to other apparatus associated therewith. However it is advisable to arrange the feet so that the shafts of the rotary members lie horizontally, for obvious reasons..I

The rotary members which are mounted inthe casing comprise the mating helical screw thread members 33 and l34 which are arranged to operate in the cylindricalchambers I I and I2, respectively. For convenience the member 33 is referred to as the rotor and the member 34 as the gate. However as they may either act upon or are rotated by the fluid medium, they do not engage for the purpose of transmitting power.

The rotor 33, shown in Figs. l to 5. is provided 'with two matched and oppositely disposed screw threads 35 and 36, the contour of which is later discussed in detail. Each thread is helically disposed and extends through approximately 180 from one end of the rotor to the other. Thus the profile of the thread 35 is congruent with the prole of the thread 36 at opposite ends of the rotor, and vice versa. The perimetral surfaces or crests 3'I of these threads are cylindrical and snugly fit the cylindrical wall II of the casing. The rotor is preferablymade hollow to reduce its weight and mounted onthe shaft 38.

The gate 34 has four helical threads 40, 4I, 42 and 43, which are formed complementary to the threadsof the rotor. Each of these threads are helically disposed and extend through from one end of the gate to the other. Thus the prole of each thread at one end of the gate is con-l gruent with the profile of the next adjacent thread at the opposite end of the gate. The cylindrical crest surface 44 of the threads on the gate snugly fit the cylindrical wall I2 of the casing. The gate is mounted on the shaft 45.

As stated above the threads of the rotor and gate are complemental to one another and the threads of each member form grooves or troughs therebetween. The threads, of the rotor in this instance are disposed in a left hand helical path, whereas the threads of the gate are disposed in a right hand helical path and the overall diameter of the rotor is larger than the gate. l

The shafts 38 and 45 project beyond the ends of the rotor and gate, and since the drive is connected with the shaft 36 it extends vbeyond the head 26, as shown in Fig. 1, for receiving a pulley or gear to provide for the transmission of power to or from the device as the case may be.

The openings I1 and I8 in the heads are suiiiciently large to receive bearing assemblies which are mounted on the shafts before the rotary members are assembled in the casing. The bearing assemblies on the shafts 38 and 45, which are mounted in the head I3, are the same with the exception that the shaft 38 carries a small gear and the shaft 45 carries a hub for a large gear which cannot be passed through the opening I8.

Each of these bearing assemblies in the head I3 comprises the sleeve 46 which has a press t on the shaft. A seal ring 41 is placed over this sleeve. This ring has a` running t with the sleeve 46 and is provided with an internal annular groove 48 which is vented through a radial hole to the passageway 49 and thence to atmosphere, as shown in Figs.- 3 and 5. An annular groove 50 is formed on the outerend of each sealing ring.

A sleeve 5I is stepped over the sealing ring 41 and is provided with a radially extending flange 52 which abuts against the rotary member, An internal annular groove 53 is provided in the bore of the sleeve opposite to the groove 50 on the sealing ring.

An oil slinging disk 54 is placed on the shaft and held between the inner race of the bearing 55 and the end of the sleeve 41 and thus rotates with the shaft. The outer race of the bearing 55 engages a shoulder formed in the bore of the sleeve l5I and is held in place by the spanner nut 56.

The small gear 51 is keyed to the shaft 38 and abuts the inner race of the bearing 55, thus holding it in place. The mounting of the gear 51 completes the bearing assembly for the gear end of the rotor shaft 38. It will be noted in Fig. 2 that the gear 51 has ample clearance for passing through the tubular opening I1.

The gate shaft 45 has keyed thereto the gear hub 58 which is locked by the nut and washer indicated at 59. The gear hub 58 has ample clearance for passing through the tubular opening I8. The radially extending ange on the hub 56 is provided with a series of threaded openings 60. When the rotor and gate members are placed in mesh and the bearing assemblies are mounted in the head I3 through the tubular openings I1 and I8, the spanner nuts 6I are screwed on the outer ends of the threaded sleeves 5I to lock them in place and the gear 62 is slid in position in mesh with the gear 51 and is secured to the hub 58 by means of the bolts 63 as shown in Fig. 1.

A large oil slinger disk 64 is then mounted on the end of the shaft'38 by means of the washer and nut indicated at 65 in Fig. 1.

The left or gear end of the pump is thus completely assembled and a cover 66 is placed thereover to protect the gear and to provide an oil the sleeves 5I are connected by the radial pas-- sages 68 through the sleeves 5I to the passages 10 which lead back to the oil sump formed by the cover 66. Thus the oil that is picked up by the large slinger 64 splashes over the case and gears and finds its way to the bearings where itis again picked up by the small oil slingers 54 and is discharged into the grooves 53 and drains back through the passages 68 and 10 to the sump.

Thus one end of the sealing ring 41 discharges any fluid that has leaked past the sleeve 46 directly to atmosphere and the oil slinger disk 54 at the other end directs the lubricating oil back to the sump within the case. With this novel arrangement the uid and the oil are never permitted to mingle with one another.

The bearing assembly on the other end of the shafts 38 and 45 comprises the sleeves 1I which abut against the rotor and gate members at one end and are flush with a. shoulder on the shafts at the other end. The bearings 12 are sealed by the sleeves 1I and the inner race abuts the shoulder on the shaft and holds the sleeve in place. These bearings are locked in position by a sultable washer and nut asindicated at 13.

The sleeves 1I have a running t with the tubular openings I1 and -I8 in the head 26. Any leakage of the fluid past the sleeves 1I is permitted to escape directly to atmosphere.

Referring now to Fig. 6, in this instance the threads on the rotor 33 extend through 360 or one complete revolution, and the threads of the complementary gate member extend through Thus the rotary members in this view are equal in eiIect to twice the length of the rotary members shown in Figs. 1 to 5. The actual length of the rotary members shown in Fig. 6 need not be twice the length of the rotary members shown in Fig. 1, for the same effect may be obtained by reducing the pitch of the screw thread without altering its shape.

In the structure shown in Fig. 6 the inner wall I4 of one of the heads is eliminated. and the corresponding ends of the cylindrical chambers II and I2 thus open directly into the chamber I6. The-other head retains its inner wall with its port. As illustrated in the drawings, the wall I4 of the head I3 has been eliminated, thus converging the whole left end of the casing into the port 20. When the rotary screw members are rotated as indicated on the drawings, the uid is drawn in through the `opening 2| into the chamber I6 and is picked up by the rotary members and conveyed to the other end of the casing where it is discharged through the port 24 and the opening 25. When the threads of the rotor extend through 360 and the threads of the gate extend through 180 it is necessary to seal oi selected troughs of the gate at one end of the pump. 'I'hus the inner wall I4 of the head 26 with the port 24 are left intact at the right end of the casing as shown in this view.

Regardless of how many turns the threads of the rotor and gate are extended, it is necessary to partially seal off the rotors at one of the inner walls I4 of the heads I3 or 26. However the pump may be materially shortened bythe use of the oppositely disposed ports in the walls I4 as shown in Figs. 1 to 5, and operated at a higher eiliciency.

In the structure illustrated in Figs. 1 to 5 the radial edges 14 oi the ports 28 and 24, as indicated in Fig. 3, may be positioned at an angle approximately 30 from the plane which intersects the axes of the two rotary members, and in the structure illustrated in Fig. 6 the port 24 may retain the same degree of opening. To convert these structures into compressors the radial edges 14 are moved toward one another, thereby delaying the opening of the successive pockets. The distance that the radial surface 14 is extended determines the degree of delay in the opening of the pockets to the discharge side of the pump and thus determines the degree of compression of the iiuid within the pocket before it is discharged. If the port setting is the same as that shown in Figs. 1 to 5 and the System connected to the discharge of the pump is subjected to pressure, then, as each successive pocket opens to discharge, the uid under pressure rushes back into the pocket to equalize the pressure of discharge. This momentary back flow is a loss, and to be avoided the same radial edges 14 are advanced to a position where the fluid in the contracting pocket independently reaches the same pressure as that in the d harge as the pocket is opened to the discharge. It the pressure in the system varies, then provision must be made to control the advance or retraction oi the permitting it to discharge.

' radial edges 14 of the ports to regulate theinthe vdis- In Figs. 7 and 8 the tubular openings I1 and stant at which the pocket opens to charge.

tors 11 and 18 are formed integral with the innen end of the sleeves 15 and 16, respectively. The inner faces of these sectors abut against the ends of the rotarymembers andthe outer faces against the wall Il of the head 28 to prevent the passage of liquid. The space intermediate of the sleeve 15 and 18 in the plane of the sectors 11 and 18 is occupied by theiiller plate 80. l

The port 24 is formed' inthe head 28 in the .usual manner. However the edges of the arcuate sectors 11 and 18 provide the radial edges 1I of the port. l

'I'he intermeshing segmental gears 8| and 82 are secured to the outer ends of the sleeves 15 and 18 to. provide the proper movement of the radial edges 14 at opposite ends of the port 24. As shown in Fig. 8, one gear sector may be provided witli a radially extending arm 88 which is operably connected to a piston 484 by a link 85. 'Ihe piston is'arranged to reciprocate in the chamber 86 which is connected to the discharge 25 of thecompressor. Thus the fluid under pressure in the discharge-is effective on the piston for opening, or closing the ports in the Vcompressor against the force of a spring 81. By properly' selecting the spring 81 the pressure of the iluid in the discharge of the compressor may be eifective to set the edges 14 of the port to delay the opening of the pockets until the pressure of the uid therein reaches the pressure of the fluid in the discharge system.

The pitch oi the threads of the rotary members shown in Fig. 6 is different than the pitch of the threads of the rotary members shown in Fig. 1. However the `pitch ofeach set is uniform throughout its length. Fig. 9 is a diagrammatic View illustrating threads having a uniform pitch from one end of the rotary members to the other. Slight pulsations are produced by the discharge of the successivelyv formed pockets when the device is in operation. Thus each pocket being an independent conveying chamber for the fluid passing through the device produces a slight unbalance of the torque load. This unbalancing of the torque load may i be compensated for byvchanging the pitch of the threads of the rotary members intermediate of their length. 'I'hls change in pitch may be` made progressive or in steps, as illustrated diagrammatically in Fig. l0, or by continuously changing the pitch as illustrated in Fig. 1l.

It will be noted that inrFigs. 10 and 1l the pitch of the threads decreases as the threads approach the discharge end of the device. Thus the pockets withv the fluid therein travel at a lower rate of speed as they approach the discharge end. This structure is particularly advantageous for use in compressors wherein the delay of the opening of the pockets is made to compress the gas to'the proper pressure before The work expended in compressing the gas within the 'pocket is thus spread over a longer period of time, thereby reducing the peak of the torque load that is nor-v mally formed with threads of uniform pitch. In this manner the torquecurve is attened and bers.

the torque characteristics of the device are more uniform. If the compressor is to operate in both directions under the same conditions it is necessary to provide the same thread structure in that the end sections of the continuouslyv advancing thread have a similar pitch which is diii'erent than the pitch of the intermediate portion of the thread and corresponding points along the. generated curves ofA the threads in such case would be equidistant from a transverse plane passing -through the center of each member.

Figs. 12, 13 and 14 illustrate three different forms of the thread profiles of -the rotary memy These views are diagrammatic andthe speciflc'contours which they illustrate are too small to accurately portray the exact forms of the thread surfaces as these surfaces are generated curves and not true circles as they import. Since the rotor is provided with two threads andthe gate has four, the rotor travels at twice'the speed as the gate. Thus the ratio of the timing gears 61 and 8| is one to two. If the profiles of the threads of the rotary me bers are as shown in Fig. 12, the rotors will have' the same diameter as the pitch circles of the timing gears wherein 88 is the pitchcircle of the gear 51 and 9| is the pitch circle of the gear Q2. .With this construction the perimetralportions ofthe gate threads have a rolling contact with the hub of the rotor and in all three forms the sharp edges of the gate threads have a relative sliding action with the sides of the rotor threads.` -The normal rolling surfaces ofthe rotary members are equivalent in diameter to the pitch circles of their respective timing gears the dimensions of which are determined by the number and the axial pitch of threads of the respective members. It should be noted that this design provides a sharp intersection where the sides of the rotor teeth join the rotor hub, as indicated at 92. This sharp angle must be accurately formed to produce a .small clearance between the rotary members.

y diflicult to produce and provides a leakage path.

Again these two types of threads tend to roll and pack any foreign material rather than remove-it.

It has been discovered that by making the diameter of the gate 34 circle, as shown in Fig. 14, and the hub surface or root surface of the rotor larger in diameter than its pitch circle, any foreign material is wiped out rather than being pressed between the members. The edges defining gate thread surfaces 44 may be kept sharp and continuously seal along the rotor thread surfaces intersecting at 92 and the perimetral surfaces of the gate threads follow a reverse curve and still maintain the proper sealing relation between the rotary members. This reverse curve, shown smaller than its pitch in Fig. 14. is purposely lexaggerated to emphasize the radius at the intersection of the sides of the rotor threads with the hub surface indi- `cated at 92. The actual size of this radius is of course determined by the diameters of the gate" -and rotor members relative to the diameters In this preferred l of theirv true pitch circles. form of thread section the perimetral surfaces 44 of the gate must have a combined rolling and sliding movement relative to the hub or root surfaces ofthe rotor because of the difference between the diameter of these surfaces and their respective pitch circles. As stated above the sharp edges of the gate threads describe the curved sides of the rotor threads and conversely the edges of lthe crest of the rotor threads describe the curved sides of the troughs of the gate, producing the continuous sealing line .which is later described with reference to Figs. 29 and 30. It is apparent that the thread structures must be generated in this manner to produce the continuous sealing line described hereinafter.

It will be noted that the diameter of the rotor member is the same in Figs. l2, 13 and 14 and the hub of the rotor in Fig. 14 is larger than in the other two views, but the space or void created between the threads is larger because of the shape-of the sides 33 of the threads. Thus with this preferred form of thread the capacity of the pump is increased.

Again the void 94 formed between the gate and the rotor when they are in mesh, as shown, is smaller. These advantages are attributed to the fact that the diameter of the gate is smaller than the pitch circle of the gear. This is a very important discovery in this invention. It aids in providing a gate trough which is substantially circular in cross section and the bottom of the troughs do not have a hump, yet the extent of the perimetral surfaces 31 of the rotor threads is suilicient to provide an adequate seal. It is impossible to obtain these important advantages if the diameters of the rotary members are the same as the gear pitch circle.

As stated above, screw type pumps of this character inherently possess a leakage path from the discharge to the 4inlet e'nd of the pump. When two or more threads are employed on each member, the volume'of this leakage path is substantially as great as the pump displacement, thus rendering them impractical unless this leakage path is checked.

'I'his leakage path may be readily traced on Figures 29 and 30 which illustrate an elongated gate and rotor members of the same character as that shown in Fig. 1 These screwvmembers were made suiliciently long -to clearly show that added length will not seal oi the leakage path.

When the gate and rotor members are assembled in intermeshing relation, as shown in Fig. 28, their adjacent surfaces engage each-other along a continuous line 8B. which extends from one end of the members to the other. 'I'his continuous line of contact forms the sealing line between the two members and prevents any ilow of duid transversely between the members.

If the members were dipped in paint while intermeshed as shown in Fig. 28 and then separated, Vthe heavy continuous sealing line 88 would appear alongthe full length of each member as shown in Figs. 29 and 30. Since'the gate has a right hand thread and the rotor has a left hand thread the sealing line on these figures is correspondingly right and left handed, and if the drawing were folded to bring the figures face to face these sealing lines would match.

Assuming that the ends of the rotor and gate are fully exposed and the top of these figures represent the discharge end of the p'ump, fluid may ow from a through the gate trough between the threads 40 and 43 down in back of the screw to b where this trough again appears three-fourths of the way down Fig. 29. Further ow down this groove is checked by the seal line 88. However the uid may transfer from the gate groove to B on the rotor in Fig. 30 which is on the corresponding side of the seal line. B is in the rotor groove above the thread 36.

The iluid maythen flow up in back of the rotor screw to D where it appears on the opposite side ofthe seal line. 'I'he fluid then transfers from the rotor back to d between the threads 4|! and 4| on the gate and on the corresponding side of the seal line. 'I'hus the fluid upon making a complete circuit. down one gate trough across and up one of the rotor troughs and back 'to the gate, arrives in the next adjacent gate trough toward the inlet from which it started. The oftener the iluid circulates in this manner the nearer it approaches the inlet.

The fluid may then continue to ow down between the threads 40 and 4| from d to e, and if this trough is closed by the seal line, as illustrated in Fig. 29, it will make another circuit by transferring to E on the rotor and flow up to F and across to f on the gate and thence flow down between the gate threads 4| and 42 to g where it may pass directly to the inlet of the pump.

This leakage path has no restrictions whatsoever and it is quite evident that the volume per unit of time,.ilowing through this leakage path under given pressure and speed conditions, approaches the displacement output of the pump.

During the particular instant that the above leakage path has been traced the gate trough between the threads 42 and 43 is closed by the seal line below h in Fig. 29 andv the corresponding trough H on the rotor is connected to the discharge at A in Fig. -30. This path is thus blocked. v

Likewise the gate trough between the threads 4| and 42 is closed by the seal line below 7' and the corresponding trough J on the rotor is open to discharge.

The corresponding gate and rotor trough portions k and K represent a pocket that is running out at discharge.

Since the upper end of the gate and rotor is the discharge end of the pump the gate must rotate in a clockwise direction and the rotor in a counllerclockwise direction because of the direction of their threads. If the gate and ro'tor in Figs. 29 and 30 were rotated the sealing line on each gure would appear to continuously travel up the screw members and vanish at the top. The same effect may be obtained by sliding a transverse straight edge down over the figures.

By closely observing the seal line 88 in Figs. 29 and 30 it will be noted that the vertical straight section at the top is made between the cylindrical edge of the gate thread 40 and the adjacent,I

cylindrical trough of the rotor. The contacting surfaces being cylindrical this section of the seal vline must be straight. vThe bottom of this straight section intersects the bottom edge of the gate thread 40 and from thereon the edge of this thread seals across the upper face of the rotor .thread 35 to where the edges of both threads intersect, which occurs at the juncture 23 .cated by the dotted line 89. The seal then re- .traces the center line 89.until it intersects the A.lower edge of the rotor thread 35 which-seals across the right side of the gate trough to the 'point where the edges of the gate thread 4l and rotor thread 35 intersectat 23 on the opposite side of the casing. The zigzag line just described represents the sealing line made by the rotor thread extending into andx out of the gate trough. y

From the intersection 23 .the seal line continues down along the top of the gate thread 4| across the under side of the rotor thread 35 to the position where the cylindrical edge surface of the gate thread Il ointersects the cylindrical surface in the bottom of the .trough in the rotor. This represents a complete sealing path from one rotor trough to another which is duplicatedV down the faces of the rotary members from one end to the other. 7. v

When a horizontal straight edge is moved down over Figs. 29 and` 30 the sealing line 88 vanishes in the same manner that it would if the gate and rotorl members were rotated. As the straight edge proceeds down Figs. 29 and 30 it breaks the seal line 98 and the` upper part of the space d inthe gate and D in the rotor are open to discharge. The breakithus formed in the sealing-line is the void 94 which produces a leakage path'4 from the discharge to theinlet parallel tov the path starting at a as described above.

'Ihe leakage path `starting at a ceases the instant that the pocket formed-by Ic and K completely runs out and the gate groove between the threads 40 and 4l becomes the sole leakage path until the next void 94 Vis formed by breaking the sealing line. Thus for the short space.

the plane intersecting the axes of the members as shown in Figs. 3, and to 17 because the fluid is compressible. However when used as a liquid pump the port edges should be located as indicated in Fig. 28 so that there is no tendency to compress the liquid. 'The size and shape of the rotors in such a case would determine the exact position and contour of the port edges.

These rotary members may be made with little or no tolerance and then assembled in an operrfmachine where they can lbe operated to lap in their engaging surfaces. device 'is very large, a clearance of one thirty second .of an inch 4may produce a negligible leakage. in comparison to the volume of fluid transmitted therethrough. 'Ijhus tolerances and clearances are, as a practical questiom determined largely as to size and use to which the device is to be applied. y

The void 94 which is produced between the trailing side of the -rotor and the leading side of the gate threads after a thread of the rotor has entered a trough in the gate directly connects the discharge with the inlet when the roof time that the sealing line is broken the leakage path from a to b and B to D and back to d is short circuited and remains in vthis condition until the pocket formed by Ic and K runs out, at which time thespace d becomes in effect the space a described abve.

In order to stop this leakage path through the gate and rotor members, Where the threads extend through one or more complete turns, it is,

necessary to close one end of the members with a sealing wall or land covering the overlapping areas of the gate and rotor and extending'around the back thereof, as shown by the dotted line in Fig. 28. But for this area the ends of the rotor and gate are exposed and this exposed portion represents the dischargelport.

If the rotor threads are 4less than one complete turn, as illustrated in Fig. 1, it is then necessary to employ a sealing wall or land at both ends of the rotary members, one at the inlet and one at the outlet.- `These sealing walls are diagonally disposed to one another and extend over the areas illustrated by the port lines 20 and 24 shown in Figs. 3 and 15 to 17. When the end sealing walls are disposed in thismanner, the rotor'and the-gate may be made very short in length, which is an important advantage in this art.` The rotor threads must extend at least substantially one-half turn in order that a complete seal line is formed over one rotor thread which is necessary to seal the members. The curve of the seal line 88 thus extends through one complete cycle.

When used as a blower or compressor the port edges can be disposed substantially at 30 to tor and the gate members are provided with threads that extend only 180 and 90 respectively. 'I'his void may be closed 'by the arrangement of the sealing end walls as explained above or by the use of sealing plates fastened on the ends of the rotary members. The sealing end walls may be .arranged as shown in dotted lines in Figs. 1'6 and 17, wherein a single port at one end of the rotary members is divided into two openings separated by the land 95. .The land is an integral part of the inner wall IlA and its edges represent the uitimate port opening whether the ports are fixed or variable as described above. 'It will be noted that the land covers up the void 94 and'thus prevents a leak back.

The sealing plates are shown in Figs. 18,-19

and 20 at 96 and 91. The yplate 96 'is shown to have exactly the same profile as the rotor.

and the plate 9" is shown to have the exact proille as the gate. These sealing plates are mounted on the ends of the rotary members in an offset position sutllcient to cover the initial part of the void 94 formed by the rotary members.

The direction of the offset of these sealing. plates is inconsequential within the limits of the thickness of `the gate threads. It is preferable to extend the trailing edge of the rotor plate 96 over the void and thus overlap the gate thread to produce an effective seal. These sealing plates therewith. Thus the port 9B leaves a ,goodly part of the ends of the rotary members exposed.

Another important advantage lies in the fact that the whole of the rotary members may be made up of a series of such plates with the teeth portions beveled to the degree of pitch ofthe thread desired, as indicated in Fig. 9, and then mounted on a shaft with each succeeding plate angularly disposed with respect to the plate adjacent thereto to producea smooth continuous Again il' the thread. In this instance the end plates become the sealing plates and they are disposed at a greater angle relative to the next adjacent plate to cover the voids. However the edges of the sealing plates are preferably not beveled but normal to their faces.

Theoretically each pocket Ic, K completely runs out when thethread of the rotor is about to leave the trough of the gate, at which time they are completely covered by the sealing wall. `As a practical proposition the pockets may be kept vented to the discharge until the rotor thread approaches the full depth of the gate trough, as illustrated in Fig. 22. This is accomplished by cutting away the leading side of the rotor threads along an angularly disposed plane intersecting the radial line and bounded by the arcuate line |0| as shown inFigsf21 to 23 and 27. Thus the fluid is` permitted to escape from the pocket to the discharge up until these lines reach the sealing end wall. In Fig. 22' the port 98 is employed and is similar to the port shown in Figs. 3 and 18, the sealing plates being eliminated for the sake of simplicity. Immediately after the radial line |00 of the cut away portion passes behind the edge ofthe port 98 and thus seals the .included pocket from discharge, the outer end of the cut away portion defined by the arcuate line ||I| opens the pocket to the leading side of the thread and permits the iluid to escape. Thus as the pocket becomes smaller it is being continuously relieved until it completely runs out as the rotor thread passes from the gate trough.

If it is desired to continuously relieve the uid trapped in the pockets to the discharge of vthe pump up until the time that they completely run out, agroove |02 may be cut in the end -face of the rotor member as shown in Figs. 24 to 26.`

Just as the groove |02 is about to be opened to the space in front of the rotor thread, the other end oi the groove is sealed under the port 98. 'I'his represents the intimate position of the pocket as it runs out.`

A third method of avoiding the squeezing of the uid in the pocket as the latter runs out may be obtained by changing the pitch of the threads of the rotary members so that the pocket is completely run out when the rotary membersreach the edge of the port, in which case the whole of the pocket would be vented past the edge |00 `or the groove |02 when the rotor and gate are about to pass under the sealing end wall.

Fig. 31 shows a seal line so arranged and balanced that in each pocket the same amount of area is exposed to pressure on one side of the center line as on the other side of the center line, as indicated by the equivalent areas |03 and |04. Therefore, the pressure does not tend to resist rotation of the gate, nor does it tend to overrun the gate ahead of the rotor. This condition eliminates all gear loads, except the friction incidental to the bearings and seals. All of the pumping or compression load is transmitted through the rotor and the gate merely idles.

I claim:

l. In a uid device of the character described, the combination of a casing having parallel cylindrical chambers which intersect to form a common chamber, a rotor member and a gate member rotatably disposed in said chamber, said members having complementary intermeshing helical threads and grooves of such shape as to form a continuous seal line therebetween which tained as the members rotate. the threads of the rotor member extending through no more than one complete turn, both chambers being open at one end providing a fluid inlet, an end wall clos- .ing a portion o i' both chambers at the other end providing a iiuid outlettherein, the cylindrical walls of the chambers an'd the threads and grooves of the members cooperating to form fluid pockets which advance toward the outlet end when the members rotate, saidy end wall covering substantially one side of the correspondingends of said members and extending between and to the other side of said members to the intersection of said chambers to completely close each pocket until said pockets are closed at the other end by the cooperation of the threads and grooves of the members forming the sealing line across the common chamber at the intersection of the two chambers.

2. In a fluid device of the character described, the combination of a casing having parallel cylindrical chambers which intersect to form a common chamber, a rotor member and a gate member rotatably disposed in said chambers, said members having complementary intermeshing helical threads and grooves of such shape as to form a continuous seal line therebetween which extends from one end to the other and is maintained as the members rotate; the threads of the rotor member extending through approximately one half turn and the threads of the gate extending through approximately one quarter turn, the cylindrical walls of the chambers and the threads and grooves of the members cooperating to form iiuid pockets which form at one .end and advance toward the other end as the members rotate, walls closely adjacent the ends of said members partially closing both ends of said chambers and deiining an' opening in'each wall on opposite sides of the plane passing through the axes of both members, said openings extending from the intersection of said chambers by an amount determined by the twist of the gate threads to posed in' parallelism and having complementary extends from one end to the other and is mainintermeshing helical threadsl and troughs, the crests of the threads of the members being cylindrical and bounded by extending helical edges, the rotor having two threads which extend through not more than one-half turn and the gate having'four threads which extend through .not more than one quarter turn, the sides of the rotor threads being described by the continuous edges of the helical threads of the gate, and the troughs of the gate being described by the edges Aof the crest of the helical threads of the rotor.

4. In a uid device of the character described, the combination of a casing having a pai'r of parallel cylindrical chambers which intersect to form a common chamber, heads closing the ends of the common chamber, a rotor member and a gate member arranged to rotate in the cylindrical chambers with their ends closely adjacent said heads and having complementary intermeshing helical threads and troughs, a port in each head diagonally disposed with respect to each other and positioned on opposite sides of the plane intersecting the axes of said members, each port being open for substantially one-half of the areas of the ends of said cylindrical chambers, rotor and gate sealing plates secured on each end of said members and having the same cross sectional contour as the threads of the respective members but angularly displaced relative thereto `-for closing` the v'void formed between the trailing edges of the rotor threads and the leading edges of the gate troughs as they intermesh before passing beyond said ports.

5. In a fluid device of the character described,

the combination of a casing having a pair of parallel cylindrical chambers which intersect to form a common chamber, heads closing the ends of the lcommon chamber," a rotor member and a' gate member arranged to rotate in the cylindrical chambersr with their ends closely adjacent said each port being open for substantially one-half of the area oi the ends of said cylindrical chambers, rotor and gate sealing plates secured on each end of said members and having the same cross sectional contour as the threads of the respective members. but angularly displaced relative thereto for closing the void formed between the trailing edges of the rotor threads and the leading edges of the gate troughs as they intermesh before passing beyond said ports, and slots extending diagonally across the ends of thread portionsof the rotor plates from the crest of the leading side to a point adjacent the root of the thread but spaced from its trailing edge for ventthe ports up until the time' ing the pockets to each of said pockets runs completely out. 6. In a fluid device of the character described, the combination oi a casing having parallel cylindrical chambers which intersect to form a common chamber, heads closing the ends of the common chamber, fluid connections in said heads opening into the cylindrical chambers, rotor and gate rotatin members arranged to operate in the cylindrical c ambers and' having complementary intermeshing helical threads and troughs of such shape as to form a continuous sealing line therebetween and extending from one end to the other of said members and which coact with each other and the walls of said chambers to form pockets traveling from one end of the casing to the other, the extent and pitch of the intermeshing threads and troughs together with said heads being arranged to seal each pocket from communication with one of said connections before it opens to the other thereof, the axial pitch of the helical threads on said members becoming less as the hreads approach the discharge end to compensate for the unbalancing torque characteristics created in the independent traveling pockets.

7. A pair of rotary elements for use in a uid `device of the character described, comprising a rotor member and a gate member rotatably disposed in parallelism and having complementary intermeshing helical vthreads and troughs, the crests of the threads of the members being cylindrical and bounded b'y extending helical edges, the sides of the rotor threads being described by the continuous edges of .the helical threads of the gate, and the troughs of the gate being described by the edges of the crest of the helical threads of the rotor, the overall diameter of the gate member being smaller than the diameter of the pitch circle thereof and the radius of the troughs of the rotor member being larger than the radius of the pitch circle thereof.

. A pair of rotary elements for use in a fluid ,device of the character described comprising a rotor member and a gate member rotatably disposed in parallelism Vand having complementary intermeshing helical threads and troughs. the overall diameter of the gate' member being smaller than the diameter of the pitch circle thereof, and the radius of the troughs of the rotor member being larger than the radius of thepitch circle thereof.

9. A pair of rotary elements for use in a fluid device of the character described comprising a rotor member and a gate member rotatably disposed in parallelism and having complementary intermeshing helical threads and troughs of dii'- ferent pitch, the overall diameter of the gate member being smaller than the diameterof the pitch circle thereof, and the radius of the troughs of the rotor member being larger than the radius of the pitch circle thereof.

10. A pair of rotary elements for use in a fluid device of the character described comprising a rotor member and a gate member disposed in parallelism and having complementary intermeshing helical threads and troughs, the ratio of '-the threads on said members being one to two .eter of the rotor member respectively, the overall diameter of the gate member being smaller than the diameter of the pitch circle thereof, and the radius of the troughs of the rotor member being larger than the radius of the pitch circle thereof. g,

11. A pair of rotary elements forl use in a iiuid device ofthe character described comprising a rotor member and a gate member rotatably disposed in parallelism intermeshing helical threads and troughs, the ratio of the threads on said members being one to two respectively, the overall 'diameter of the gate member being smaller than the diameter of the pitch circle thereof, the radius of the troughs of the rotor member being larger than the radius of the pitch circle thereof, and the overall diambeing greater than the overall diameter of the gate.

12. A pair of rotary elements for use in a fluid device of the character described, said members being disposed in parallelism and having complementary intermeshing helical threads and grooves, the threads and grooves of each member twisting in the same general direction about the axis of said member, the axial pitch of said complementary threads of each member adjacent the ends thereof being less than the pitch of the intermediate portion of said threads.

13. 4A pair of rotary elements for use in a fluid device of the character described, said members being disposed in parallelism and having complementary interme'shing helical threadsy and grooves, the threads and grooves of each member twisting in the same general directionv about the axis of said member, the axial pitch of said complementary threads of each member changing from a small pitch to a large pitch and back to a small pitch from one end of each rotary member to the other end thereof.

14. A pair of rotary elements, for use in a nuid device of the character described, comprising a rotor member and a gate member rotatably disposed in parallelism and having complementary intermeshing helical threads and troughs, a plate secured to an end of each member having the same contour as the threads of said member but angularly displaced thereto for closing the void formed between the trailing edge of the rotor and and having complementary the leading edge of the gate threads as they in` termesh to substantially their full depth.

15. A pair of rotary elements, for use in a iluid device of the character described, comprising a rotor member and a gate member rotatably disposed in parallelism and having complementaryintermeshing helical threads and troughs, a plate secured to an end of each member, said rotor plate having the same contour as the trailing edge of the rotor threads, said gate plate having the same contour as the leading edges of the gate threads, said plates being angularly displaced relativev to their respective rotor or gate threads to overlie and close the voids formed between the rotor thread and the gate trough as the threads intermesh to substantially their fully depth.

16. A pair of rotary elements, for use in a fluid device of the character described, comprising a rotor and a gate member rotatably disposed in said heads opening into`the cy' drical chambers, a rotor member and a gate member rotatably disposed in the cylindrical chambers and having complementary intermeshing helical threads and grooves which cooperate with the casing walls to form huid-conveying pockets therebetween, shafts supporting said members, bores in said heads axially aligned with said cylindrical chambers, Asleeves rotatably mounted in the bores of one head, bearing assemblies mounted-on each shaft adjacent the ends of said members and arranged to be inserted into the bores in one head and the sleeves in the other parallelism and having complementary intermeshing helical threads and troughs, the crest of the threads of the members being cylindrical and bounded by extending helical edges, a portion of the end of the rotor threads, bounded by the leading side from the edge of the crest, and from a point where the edge of the crest of the gate thread intersects the leading side of the rotor thread when the rotor thread is in the fully meshed position, to a point adjacent the root of the trailing side of the rotor thread, being cut away for venting the space between the leading side of the rotor threads and the gate to one side of the rotary members as the threads approach their full meshing position and thereafter venting said space to the other side of said rotary members.

17. A pair of rotary elements, for use in a fluid device of the character described, comprising a rotor member and a gate member rotatably disposed in parallelism and having complementary intermeshing helical threads and troughs, the crest of the threads of the members being cylindrical and bounded by extending helical edges, a slot extending diagonally across the end face of each rotor thread from theedge of the crest on the leading side to'a point adjacent the root of the thread but spaced from its trailing side for venting the space between the leading side of the rotor threads and the gate until the time this space runs completely out.

18. In a fluid device of the character described, the combination of a casing having a pair of parallel cylindrical chambers which intersect to form a common chamber, a rotor member and a gate member arranged to rotate in the cylindrical chambers and having complementary intermeshing helical threads and grooves which cooperate with the casing walls to form fluidconveying pockets therebetween, heads closing the ends of the common chamber, nuid connections in said heads opening into the cylindrical chambers, arcuate plates rotatable relative to the axes of said members and immediately interposed between the ends of said members and the iluid connection in one of said heads for varying the time at which the pockets become connected to the opening of the iluid connection in said head, and means responsive to the discharge pressure for actuating said arcuate plates.

19. In a fluid device of the character described, the combination of a casing having a pair of parallel cylindrical chambers which intersect to form a common chamber, heads closing the ends o! the common chamber, duid connections in head for rotatably supporting said members, an arcuate plate connected to the inner end of each sleeve and lying between the fluid connection in said one head and the end of its respective member for varying the time at which the pockets become connected to the opening of the iluid connection, intermeshing gear segments iixed to the other ends of said sleeves for moving the arcuate plates in unison, and means responsive to the discharge pressure for actuating said gear segments.

20. In a uid device of the character described, the combination of a casing having a pair of parallel cylindrical chambers which intersect to form a common chamber, a rotor member and a gate member rotatably disposed in said chambers and having complementary intermeshing helical threads and troughs of such shape as to form a continuous sealing line therebetween and extending from one end to the other of said members and which coact with each other and the walls of said chambersl to form and advance pockets along the grooves -of the threads as the members rotate, and walls at both ends of the common chamber closely adjacent the ends o'f said members covering portions of said ends when interengaged and dening inlet and outlet fluid connections to the chambers, the extent and pitch of the intermeshingv threads and grooves together with said last named walls being arranged to seal each pocket from communication with the inlet before it opens to the outlet and to maintain said seal until and while such outlet communication takes place.

21. A pair of rotary elements for use in a fluid device of the character described, comprising a rotor member and a gate member rotatably disposed in parallelism and having complementary intermeshing helical threads and troughs, timing gears operably connecting said members, the crests of the threads of the members being cylindrical and bounded by extending helical edges, the sides of the rotor. threads being described by the respective edges of the helical threads of the gate and the sides of the troughs of the gate being described by the respective edges of the crest of the helical threads of the rotor, said threads being so shaped and dirnensioned to produce a continuous sealing line between the members that is symmetrical on both sides of the plane which includes the axes of the members, said sealing line following the lower edge of the gate crest along the coacting side of the rotor thread from said plane to the point of intersection of the crest edges of the rotor, and gate members at one side of the members at which point the sealing line transfers to the upper edge of the crest of the succeeding rotor thread byY down along the center line of the gate trough across the rotor crest to a point in the same vback up along the lower edge of the crest of the rotor thread to the point at which the crest edges of the members intersect at the other side of the members and-in the same transverse plane as the upper end of the sealing line along the bottom of the gate trough, said sealing line extending thence downwardly along the upper edge of the next adjacent gate crest to said lrst mentioned plane and thence across the face of the gate crest to the lower edge thereof, thus completing a sealing cycle, whereby the extent of the sealing line along the bottom center line of the gate trough is such as to provide equal areas on each side of said center line exposed to the same fluid pressure thereby producing a balanced load condition on the gate member and reducingthe timing gear load.

22. A pair of rotary elements for use in a. iluid device of the character described, comprising a rotor member and a gate member rotatably disposed in parallelism and having com'- plementary intermeshing helical threads and troughs, the crests of the threads of the members being cylindrical and helical edges, the rotor having two threads which extend through less than one complete turn and the gate having four threads which extend` through less than one half turn; the sides of the rotor threads being described by the continuous edges of the helical threads troughs of the gate being described by the edges of the crest of the helical threads of the rotor.

JOSEPH E. Willmann.'

bounded by extendingl of the gate, and the'

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