US1905142A - Boiler water control - Google Patents

Description

April 25, 1933.

B. BURNS ET AL BOILER WATER CONTROL Filed June 17. 1929 2 Sheets-Sheet v 2 Howard 5. ,4ew/11 Patented Apr. 25, 1933 UNITED STATES PATENT OFFICE BRUCE BURNS AND HOWARD B. LEWIS, LOS AN GELES, CALIFORNIA, ASSIGNORS 'IO HUGHES TOOL COMLPANY, 0F HOUSTON, TEXAS, A CORPORATION OF TmAS BOILER WATER CONTROL Application filed June 17, 1929. Serial No. 371,610.

Our invention relates to boilers of the flash or semi-flash type which have the capacity of raising a fluid ordinarily water, to the boiling point, vaporizing this fluid and usually superheating the vapor, these steps taking place continuously and consecutively as the fluid passes throughout the length of the boiler.

One type of flash boiler comprises a long tube in which these operations take place, so that a section near the intake end thereof may be considered a liquid-heating section, while a section near the throttle may be termed-a superheater section, there being an evaporator section therebetween. The water is supplied-to the intake end of this tube by means of a suitable high pressure pump, and the superheated steam is withdrawn from the superheater section thereof.

It is an object of this invention to provide a novel method of boiler control which I may be utilized on such flash or semi-flash boilers, or on certain other types of boilers.

It is very desirable in certain boiler installations, especially those incorporated in self-propelled vehicles where the demand for power'is not a constant, to be able to control the supply of water in such a manner that the pressure and temperature relations of the superheated steam at the throttle remain relatively constant. The temperature of the steam in such a boiler is, of course, a function of the output of this boiler and, upon first thought, it might seem a relatively simple solution of the problem to utilize a thermostat or other heat-responsive element in the boiler for controlling the supply of feedwater thereto.

Experiments have shown, however, that such a system of control is usually impraciical and dangerous when the type of thermo- .-tats commercially available are utilized, especially if the thermostat is not positioned in the superheater sections In fact, steam temperature at the throttle, temperature at the thermostat, and boiler feed-water requirements appear to show no correlation which might be utilized in controlling the supply of feed-water to the boiler.

We have found, however, that Very satisa method of boiler regulation or operation which utilizes a thermostat, or other heatresponsive means, set to operate at a temperature above the temperature of saturated steam in the boiler for controlling the feedwater supplied to this boiler at one or more oints.

A further obiect of our invention is to provide amethod of boiler regulation or operation wherein a plurality of thermostats, or other heat-responsive elements, is utilized for controlling the feed-water of a boiler, whether this feed-water be supplied at a single point, or at a plurality of points relatively spaced in the boiler.

Still a further object of'this invention is to establish an auxiliary superheater section in the boiler, and to place a heat-sensitive element so as to be responsive to boiler temperature in this auxiliary section for controlling the admission of feed-water at one or more points. In this event another heatsensitive element may be positioned in the main superheater section for controlling the admission of feed-water at one or more points, whether or not these latter points are the same as the former points where feedwater is admitted as a function of the boiler temperature in the auxiliary superheater section.

Further objects of this invention lie in the novel combinations of elements for performing the above outlined methods.

In steam-propelled vehicles, it is desirable to have the waterv pumps operated directly from the engine, which requires the use of an auxiliary pumping means receiving its energy from a separate source if the main engine is to be directly connected to the wheels of the vehicle without an intermediate transmission. In our system we provide an auxtion.

'iliary water pump driven by an electric matically ceases to function when the main feed-water pump comes into normal opera- Furthermore, we have found it desirable to connect the auxiliary pump in such a manner that it supplies water to the boiler at one or more primary points and to connect the main pumps so that they supply water to one or more secondary points after steam has been generated.

It is an object of this invention to provide primary and secondary intake points for a boiler at which points feed-water may be supplied at diflerent instants of time.

It is a further object of our invention'to provide two pumping systems for supplying feed water to a boiler, these systems being connected to diflerent portions of the boiler so that the individual operation of these systems will vary the points of entrance of feedwater into the boiler. j v

A further object of our invention is to provide a system of boiler control whereby the factor of safety of tube boilers is greatly increased without sacrificing efiiciency considerations. r

The ordinary flash boiler has its superheater section exposed to the hottest part of the heating gas, while the evaporator and liquid-heating sections are subjected to the action of the heating gas only after this gas has given up a portion of its heat to the superheater section. It thus becomes advisable to shift from the hottest portion of the heating gas, the points atwhich the danger of tube burn-outs is highest. In other words, it is desirable to shift such points away from the superheater section.

It is an object of this invention to provide a boiler control system whereby any possible danger-points in the boiler are" shifted far enough down in the boiler so that the heat at such a point will be enough lower to make the chances of tube burn-outs, even under extremely low water conditions, small.

, The term boiler temperature has been and will be used in its generic sense to include either the temperature of the contents of the boiler (steam or water temperature, for instance), or to include tube temperature alone, oran intermediate temperature between steam and tube temperatures, or a temperature intermediate the fire tempera= ture and, the tube temperature. Thus, a heat-responsive element placed in the center ture, while if at the same time this element can receive heat directly from the tube temperature it may respond to a temperature intermediate the true tube temperature and steam temperature. s

The embedding of the heat-sensitive element in the material forming the tube makes this element responsive only to tube temperatures, while if the element receives heat from the exterior of the tube and at the same time is exposed to the fire or heating gas, the regulation effected by the heat-responsive element will be a function of both the fire and tube temperatures. I

A sensitive heat-responsive element posi tioned so as to be affected only by steam temperature in a tube through which steam is flowing will usually respond quicker than an equally sensitive heat-responsive element affected only by tube temperature. However, the danger of tube burn-outs is increased by such a system, especially when starting with a dry boiler. We have found it desirable to position our heat-sensitive element in such a manner that it is affected by a temperature intermediate the tube and steam temperatures, and this invention has as one of its'objects a construction permitting such results as well as a system of boiler control using one or more heat-sensitive elements thus placed.

A heat-responsive element thus placed in a boiler tube is alfected both by steam and tube temperatures and its action may be considered to vary as a function of either the steam or the tube temperature, or as a function of both. In this latter case it should be clear that in a heating'system suchas present in a flash boiler it is impossible for one variable (the tube temperature, for instance) to increase and the other Variable (the steam temperature, for instance) to decrease at such respective rates that the net' effect on, the

, thereto.

L Fig. 2 is a sectional view taken on the line 22 of Fig. 1, and illustrates the placement of the heat-responsive element in the boiler tube.

Figs. 3 to 7 inclusive graphically illustrate our control system on a coordinate system wherein the peculiar thermodynamical relationships which exist are best il ustrated.

Fig. is a graphical representation on such' a coordinate system of conditions in a boiler during starting-up operations.

As previously mentioned, the ordinary type of flash boiler comprises a relatively long tube indicated by the numeral of Fig. 1, this tube being enclosed in a suitable 10 grammatically illustrated the tube 10 as being in the form of a helix, and have diagrammatically illustrated a burner and blower 13 or other heating device, this device being utilized to force the heating gas downward through the housing 11 and into contact with successive portions of the tube 10. Ordi-' narily, water is supplied exclusively to the intake end 14 of the tube 10 by means of any suitable high pressure pump capable of operating at pressures above the steam pressures generated in the tube 10.

lVhen the water first enters the tube 10 at a temperature of T for example, this'water is heated by heat conducted through the walls of the lower portion of the tube 10 until this water reaches a boiling temperature T corv responding to the pressure existingin the tube 10. This lower section of the tube 10 in which the Water is heated to a boiling temperature has thus been termed a liquidheating section and is designated by the numeral 15 of Fig. 1.

This and succeeding changes in temperature may be best shown graphically on a coordinate system such as illustrated in Figs. 3 to 7 where the temperature of the contents of the boiler, whether in the form of a liquid vapor or gas, is represented by the ordinate scale calibrated in degrees F., the scale of abscissas representing the percentage of total heat transmitted to the water, Vapor or gas in the boiler, the zero percentage point representing the heat at the intake end 14 of the boiler, and the 100% point indicating the heat at the exhaust end or throttle. Inasmuch as we are at present considering a boiler having a continuous tube in which the evaporation and the superheating takes place, it follows that the abscissa scale represents to some complex scale the tube length. It is not to be assumed, however, that this scale is invariable, or even that it is a lineal function. Furthermore, it should be noted that our considerations at present are limited to boiler temperature as measured only by the temperature of the contents of the boiler. This is not true in regard to Fig. 8, as will be hereinafter explained, although the general type of coordinate system shown in Fig. 8 .is similar to that shown in Fig. 7.

Referring now to Fig. 3, the line AE represents the rise in water temperature from T to T the abscissa of. T being H and the horizontal distance between A and E represents roughly the liquid-heating section 15 of the tube 10.

After being raised to the boiling'temperature T evaporation takes place as heat is supplied to the boiler in suflicient quantities to furnish the heat of vaporization necessary to convert all of the water into steam. During this vaporization process, the-mixture of water and steam passes through what has been termed an evaporator section 19 of the tube 10. The tube temperature in this evaporator section 19 is greater toward the throttlev end of the boiler. However, the temperature of the mixture inside. the tube remains substantially constant during the time that the heat of vaporization is being supplied thereto. Thus, this vaporization process can be represented on the coordinates of Fig. 3 by a substantially straight line ED. Variations in pressure will cause a corresponding change in saturation temperature, thus making the line ED a band under ordinary working conditions instead of a'line, as shown. The error introduced through the substitution of a line for a band must be taken into account in considering thermostatic settings. VVe have shown this line to be substantially parallel to the base line of the coordinate system, but this showing neglects any material flow to or from the boiler. Under flow conditions the pressure at the inlet end of the boiler is naturally higher than the outlet end, causing a slight drop in the saturation temperature from E to D. The line ED as shown is thus a line of constant temperature, but represents increasing steam quality with increasing total heat.

At the point D, all of the water has been evaporated and the resulting steam is said to be saturated, any further heat supplied acting to superheat the steam. Such a superheating action is represented by the line DF of Fig. 3, the point F lying on a vertical line 17 representing the point at which the steam is throttled as it passes through a throttle 20 on its way to an engine 21 (see Fig. 1). This superheating action takes place in a main superheater section 22 of the tube 10, this section being subjected to the highest temperature because of its proximity to the burner and blower 13.

Heretofore, feed-water has been invariably supplied to the tube 10 only at the intake I have shown, however, that such a system is to shut off the supply of feed-water at a temperature'below T and to call for more water at temperatures above T Our experiments impractical on boilers which are suitable for use in self-propelled vehicles, due to the inherent time-lag in operation of commercially available thermostats, and due to the fact that over-compensation invariably takes place even with extremely sensitive thermostats, thus making it impossible to maintain any semblance of constant pressure and constant temperature at the throttle.

Furthermore, very definite limitations exist as to the strength of the walls of the tube at high temperatures and internal pressures, and it becomes necessary to limit the temperature in such a way that a safe maximum at any tube section will not be exceeded.

Tube temperature is a function not only of the temperature of the heating gas, but is also a function of the temperature of the steam therein. The higher the steam temperature the lower the heat conduct on through he walls of ,the tube, thus giv ng rise to an increased tube temperature which tends to burn the metal forming the walls of the tube 10, thus decreasing the strength of the tube'and increasing the danger of burnouts. Withv a system of control such as shown in Fig. 4, the tube may be subjected to excessive and dangerous temperatures due to the length of the tube, for if the thermo stat calls for more water, a material length of time elapses before the cooling effect of the water is felt in the main superheater.

thusmaking it possible for the line section,

position as GB, the

DF to assume some such point B lying above the safe limits of steam temperature to prevent tube burn-outs.

WVe have fdund that a safer control may be obtained by utilizing the thermostat for shutting off the supply of-heating gas at a temperature of T as illustrated in Fig; 4.

However, even with such a system over-com ensation invariably exists, and conditions at the throttle are far from satisfactory. L To improve these conditions we have found it desirable to split up the feedwater supply and introdlice feed-water at a plurality of different points in the boiler, so that feedwater is simultaneously introduced at different sections of the boiler instead of entering only the intake end of the boiler tube. So also, we have found it desirable to utilize a plurality of thermostats or other heat-responsive elements so placed as to be influenced by the temperatures existing at different sections of the boiler.

The system of control suggested in Fig. 5 is sometimes desirable, and comprises the use of two thermostats positioned at sections of the boiler indicated respectively by lines 28 and 29. With the thermostats thus positioned, quite satisfactory control is obtained by supplying feed-water in varying amounts to the intake end of the boiler, as indicated by the arrow 30, and at a point in the boiler just ahead of section 29 and indicated by arrow 31. The thermostat at section 28 is responsive to variations in water temperature in the liquid-heating section of the boiler, and is adapted, When subjected to temperatures above T to call for more feed-water at point 30, and to cutoff the feed-water at this point at temperatures below T In addition, we prefer to utilize this thermostat for shutting off the heat at a temperature T somewhat above T The thermostat at section 29 is responsive to variations in boiler temperature existing in the main superheater section and is set to admit feed-water at point 31 when subjected to temperatures above T, and to shut ofl the heat when subjected to temperatures above T A dangerous condition with'such a system might arise if the steam became superheated before it reaches the point 31 at which feedwater is introduced. Such a condition is diagrammatically shown in Fig. 5 by dotted lines HT, it being clear that the temperature of this superheated steamwould be decreased when feed-Water was supplied-thereto at a point indicated by the arrow 31. The only protection for points in the middle of the evaporator section 19 is that afforded by the thermostat atsection 28, since the thermostat at section 29 is beyond the point of water inlet indicated by the arrow 31, and is not responsive to hot points which might exist in the evaporator section. .To minimize this danger we have found it sometimes preferable to divide the feed-water supplied to the point 31 and tosupply a portion of this feed-water at a point indicated by the arrow The temperature of the tube at this point is correspondingly lower due to this section being lower in the boiler and subjected to a heating gas of a lower temperature, so that there is less danger for superheating with its consequent decrease in tube conductivity which might result in burn-outs.

Another system of control which may be advantageously utilized in certain installations is that shown in Fig. 6 wherein a single thermostat or other heat-responsive element is pos tioned at a section 33 lying in the main superheater section of the boiler and positioned a distance from the throttle. This thermostat is used to control feed-water supplied at points indicated by arrows 34, 35, and 36, substantiallv 50% of this water entering as ind cated by the arrow 34. andsubexisting in the evaporator section. With this ably constant.

system we have found it necessary to accurately position the points of feed-water inlet in order to reduce possible hot spots to a minimum. Possible danger points with this system are indicated by dotted lines J K and LM, but danger therefrom may be largely eliminated by proper regulation of the heat, and by proper placement of thepoints of feed-water inlet. In certain instances we have found it desirable to decrease the proportion of feed-water delivered to the boiler at the point 36 so that less than 25% is supplied at this point.

The preferred embodiment of our invention, however, is illustrated in Fig. 7 and also in Fig. 1, and comprises a primary thermostat or heat-responsive element 40 positioned at a section 41 of the boiler, and a secondary thermostat 42 positioned at a'section 43 of the boiler, this latter section lying in the main superheater section 22. Feed-water is supplied to the intake end of the boiler as indicated by arrow 45, and to a section toward the intake end of the boiler from the primary thermostat 40, as indicated by the arrow 46, as well as to a section intermediate the two thermostats, as indicated by the arrow 47 The primary thermostat at section 41 is set to call for more feed-water at temperatures above T this thermostat controlling the feed-water supplied at the intake end of the boiler, as indicated by the arrow 45, and at an intermediate section in the boiler, as indicated by the arrow 46. It should be noticed that the temperature T lies above the saturation temperature and' that this thermostat will not call for more feed-water until the steam thereadj acent is superheated. Thus, in effect we establish an auxiliary superheater section in the boiler tube which lies between the intake end and the main superheater section. The secondary thermostat 42 is set to call for more feed-water at temperatures above T this feed-water being supplied at the inlet point indicated by the arrow 47 and acting to reduce the temperature of the superheated steam in the auxiliary superheater section, just described, to saturation temperature. The thermostat 42 operates on a fairly short cycle and maintains the steam quality at the beginning of the superheater reason- The thermostat 40 operates on a somewhat longer cycle determined by the distance between this thermostat and the water inlet indicated by the arrow 46. r

In such a system the feed-water entering V at the intake end of the boiler is heated to in the event that superheating has already taken place. Superheating may also take place at some point beyond the point indicated by the arrow 46, such as point 0, the steam being then superheated to a point P determined by the feed-water supplied at the point indicated by the arrow 47 This supply of feed-Water decreases the temperature to the saturation temperature, and the steam is not again superheated until reaching some point, such as point Q, the throttle temperature being indicated by T We prefer to utilize either or both of the thermostats 40 or 42 for shutting off the heat at temperatures above T12, So that the maximum temperature rise in the auxiliary superheater section before the heat is shut off may be indicated by BS. The only possibledanger point which might exist in such a system would be due to a superheating action which might take place in the boiler tube toward the intake end from the section indicated by the arrow 46. Due, however, to the fact that such a danger point is quite low downin the boiler and the temperature of the heating gas is relatively low, the chances of tube burn-outs, even under extremely low water conditions, are small.

As mentioned above, Figs. 3 to 7 are based on heat-responsive elements which are responsive directly to variations in steam temperature such as might be obtainable by placing the heat-responsive elements inside the boiler tube and completely surrounded by thermostat or heat-responsive element 40 is placed therein. This element comprises an outer tube 51 through which a rod 52 passes, the tube 51 and rod 52 being of dissimilar materials having different coeflicients of expansion. For most sensitive response we prefer to make the rod 52 of a material of very low coefficient of expansion, such as fused quartz. It thus remains of substantially constant length, with the result that the response of the thermostat will be closely proportional to temperature changes 1n tube 51. The tube 51 is welded to. the wall 53 of the boiler tube 10 as indicated at 54. The thermostats are thus influenced not only by the temperature of the steam passing through the boiler tube 10, but also by the temperature of the boiler tube 10, inasmuch as heat may be conducted directly from this boiler tube to the outer tube of the thermostat.

In Fig. 1 we have diagrammatically illustrated our preferred system of control as applied to one type of boiler such as might be utilized in self-propelled vehicles. In this figure we illustrate main feecF-water pumps 61, 62, and 63 directly connected to.

10 at a point corresponding to that indicated by the arrow 46 of Fig. 7, and the pump 63 communicating with the boiler tube through an inlet means positioned at a point indicated by the arrow 47 and supplying feedwater at this point. The pumps 61 and 62 with their associated inlet means provide a primary feed means for. the boiler, while the pump 63 with its associated inlet means comprises a secondary feed means. The supply of feed-water to theboiler through these feed means is controlled by the thermostats 40 and 42 through primary and secondary thermostatic switches 67 and 68 which are electrically connected, in a manner to be described, to solenoid windings 69, 70, and '71 which, when individually or collectively energized, cause the pumps 61, 62, and 63 to which they are respectively connected to pump feed-water into the boiler.

We prefer to place the solenoid windings 69, "70, and 71 in controlling relationship withthe intake valves of .the pumps 61, 62, and '63, respectively. These intake valves may be of the ordinary poppet type actuated by'a difference in pressure on the two sides thereof. This may be accomplished by a suitable-armature 72 positioned in the field of influence of each of the solenoid windings so that the armature corresponding to any solenoid winding will move into engagement with the intake valve to hold this valve open when that solenoid is de-energized. The energization of this solenoid will withdrawthe armature from contact with the intake valve and allow normal operation to take place. Thus, the pumps 61, 62, and 63 do not force water-into the boiler until the solenoid winding associated with any particular pump 'is energized. a,

The primary and secondary thermostatic switches 67 and 68 are diagrammatically i1 lustrated in Fig. 1. The primary thermostatic switch 67 comprises an arm 7 5'adapted to be held in resilient contact with the rod 52 of the primary thermostat and pivoted to a bracket secured to the outer tube 51 of this thermostatso as to be rotated in a counter-clockwise direction by a relative movement between'the rod 52 and outer tube 51 such as takes place when the thermostat 1s subjected to increasing temperatures. The lower end of the arm is contacted by an ad- ]usting screw 76 passing through a water a contact 82 which normally engages a contact 83 due to the spring of the arm 81,

These latter contacts are separated shortly after the upper end of the arm 75 engages the adjusting screw 80. n l

The secondary thermostat switch 68 comprises a similar pivoted arm 85 which is contacted by the rod of the secondary thermostat 42, this arm being adapted, when moved in a counter-clockwise direction, to first make contact between contacts 86 and 87 corresponding to contacts 78 and 79 of the primary thermostaticswitch, and subsequently to break contactbetween contacts 88 and 89 corresponding to contacts 82 and 83 on the primary thermostatic switch.

The separation of either of the contacts 82 and 83 or 88 and 89 breaks the circuit through a heat-control means 92 which shuts off the supply of heating gas to the boiler. One terminal of this heat-control means is connected by a conductor 93 to the contact 89, the contacts 88 and 83 being connected by a conductor 94. A return circuit to the heatcontrol means 92 is formed by a conduct5r 95 which includes a manually operable switch 96, one terminal of which is connected to a battery 97, the other terminal of which is grounded as is also the remaining terminal of the heat-control means 92.

This return conductor 95 also includes a pressure-operated switch 98, the switches 96 and 98 being in series. The switch 98 may be of anyone of a number of forms known to the art and is responsive to changes in boiler pressure being usually set to automatically break the circuit through the heatcontrol means 92 at pressures above one thousand pounds per square inch, thus preventing a rise in pressure above the critical pressure. The switch 96 is positioned on a dash of the vehicle and is under control of the operator. The closing of this switch when the thermostatic switches are in the position shown in Fig. 1 will start a. flow of heating gas through the boiler, and the opening of the switch 96 or the separation of either" of the contacts 88 and 89or 82 and 83 will stop this flow of heating gas.

The contact 82 is connected to the contact 78 by a conductor 100, there being a conductor 101 which extends therefrom to the contact 86. The contact 87 is connected by a conductor'102 to the winding71, while the r the windings is grounded, so that when the contacts 86 and 87, for instance, come into engagement,- thus indicating that the thermostat 42 is calling for water, current passes from the battery through the switch 96, conductors 100, 101, and 102, through the winding 71, this current returning to the battery through ground. This causes the mainpump 63 to force feed-water into the boiler at a point indicated by the arrow 47.

Similarly, the engagement between the contacts 78 and 79 causes current to flow from the battery through the switch 96, conductors 95, 100, 103, through the windings 69 and 70 and to return to the battery through ground. This causes the main pumps 61 and 62 to force water into the boiler. The amount of water forced into the boiler by any pump may be regulated by iuitable valves 105, 106, and 107, positioned in the inlet means respectively connected to I the pumps 61, 62, and 63, or pumps 61, 62,

and 63 of different capacity may be utilized.

In starting up such a boiler it is necessary to supply feed-water thereto by auxiliary pumping means such as indicated by the. numeral 110, inasmuch as no steam is being\ generated for operating the engine 21. In Fig. 1 we have illustrated this auxiliary pumping means as being connected to a motor 111, one terminal of which is grounded, as indicated at 112, the other terminal being joined to one terminalof a pallet switch 113 by a conductor 114. The other contact of the pallet switch is connected to the ungrounded terminal of the battery by a conductor 115. The pallet 114a is adapted to be moved upward to short-circuit the contacts of the pallet switch when the winding of a :olenoid 115a is energized. One terminal of this winding is grounded as indicated at 116, the other terminal being connected to a speed switch 117 through the conductor 119, and also to one terminal of a solenoid winding 118 which functions to allow the auxiliary pumping means to force water into the boiler when energized and to prevent this flow when de-energized in a manner previously described for windings 69, 70, and 71.

The speed switch 117 may be a centrifugal switch adapted to break contact when the engine 21 is operating the main pumps 61, 62, and 63 in such a manner that these pumps may function normally and supply water :0 the boiler as previously explained.

We have found it desirable to connecttheauxiliary pumping means 110 'so that it supplies feed-water at the points indicated by the arrows 46 and 47, no feed-water being ;upplied to the boiler at the intake end until the main pumps come into operation. A pipe 125 is shown as connecting the auxiliary pumping means with the inlet means at these sections of the boiler, there being valves 126 1nd 127 for controlling the relative am boiler.

of water entering at these two points. A branch pipe 128 extends from the feed-water. supply pipe 64 and conducts feed-water to the auxiliary pumping means.

WVhile we have shown the auxiliary pumping means 110 as communicating with the same inlet means connecting the points 46 and 47 with the pumps 62 and 63 respectively, it should be understood that this particular connection is not a necessary part of the invention. auxiliary pumping means for supplying feed.- water to these sections, this auxiliary pumping means might be utilized for supplying water to one side or the other of these particular sections without deviating materially from the results obtained. The points at which feed-water is supplied from the auxiliary pumping means is not as critical as the points fed by the main pumps.

One of the novel features of this invention lies in the use of one pumping means supplying feed-water to one group of points in the boiler, and another pumping means supplying feed-water to another group of points in the boiler, these pumping means being utilized at different intervals of time and under different conditions of boiler operations. This is true whether or not certain points in one group'are common with points in the other group. An arrangement such asthis allows water to be supplied to a dry boiler during the steaming-up conditions in such a way as to protect the boiler throughout and to make large quantities of steam at normal temperature and pressure in a very short period of time.

The operation of the apparatus shown in Fig. 1 is as follows: 1

Assuming that the boiler is cold, the switch 96 is closed which energizes the-heat-control means 92 and supplies heating gas to the boiler. This quickly heats up the tube 10, especially that portion of the tube 10 in the superheater section 22, due to the fact that no water or steam is present inside the tube. Furthermore, the secondary thermostat 42, receiving heat directly from the'boiler tube, is very quicklyheated so as to close the contacts 86 and 87, thus supplying current through these contacts, as previously mentioned, and through the solenoid windings 69, 70, and 71.

' Due to the fact that the engine is not turning the main pumps are not operated and the energization of these solenoid windings does not affect the feed-water supply to the Current, however, flows from the conductor 102 through the speed switch 117, which is at this time closed, and energizes the solenoid winding 1150;. This closes the pallet switch and energizes the motor 111, current flowing through the conductors 115,

114, and 112. The auxiliary pumping means thm .qunnlies feed-water at points indicated Thus, instead of utilizing the by the arrows 46 and 47, preferably, although not invariably, in equal amounts. The boiler tubeat these points being already hot, this feed-water is almost immediately turned into steam, and when the pressure in the tube 10 builds up sufiicientlythe opening of the throttle 20 will start the engine 21, thus driving the main feed-water pumps61'to 63. In the event that the throttle is not opened, the temperature will continue to build up in the boiler and the contacts 88 and 89 will separate at a temperature corresponding to T in Fig. 7 at which time the supply of heating gas is cut ofl.

As soon as the vehicle starts to move, the main feed-water pumps 61, 62, and 63 start to operate. Thecapacity of these pumps may not be high enough to immediately force adequate quantities of feed-water into the boiler for normal operation until the vehicle has attained more speed. In the meantime, the auxiliary pumping means 110 continues to supply feed-water to the boiler until such a time as the Vehicle is travellin fast enough to open the speed switch 11 As previously mentioned, this switch is not opened until the main feed-water pumps 61 to 63v are functioning normally and the speed of "thevehicle is suflicient to cause these pumps to force adequate quantities of feed-water into the boiler. When the speed switch 117 opens, the motor 111 isde-energized, thus stopping the auxiliary pumping means until such a time. as the velocity of the vehicle is lower than the velocity at which the speed switch 117 is-set to operate.

This sequence of operations may also be illustrated on a coordinate system such as 40 shown in Figs. 3 to 7 inclusive. Thus in Fig.

8', we have diagrammatically illustrated the sequence of events in the boiler during steaming-up operations. In considering Fig. 8, it should be particularly noted that the temperatures plotted thereon are the temperatures to which the thermostats are responsive in the preferred form of 'our invention. In other words, the temperatures illustrated in Fig. 8 correspond to some temperature intermediate the true steam temperature and the true tube temperature. 4

Assuming that the boiler is dry, and that heating gas is being supplied to the boiler, curye U indicates the rise in the intermediate temperature mentioned above which takes place'throughout the length of the boilerv tube 10. Curve V illustrates conditions at a subsequent instant and shows a rise in temdecreases the temperature of both the tube and the steam, thus giving rise to a temperature curve similar to that illustrated by the letter W. Curve X shows a rise in temperature throughout the boiler, and passes through T so that the thermostat 42 calls for more water. The auxiliary pumping means is still operating so that at least a major portion of the feed-water is supplied to the sections indicated by the arrows 46 and 47 Curve Y illustrates the beginning of steam flow when the throttle is cracked, while curve Z illustrates additional flow. By this time the vehicle is moving and the speed switch 117 opens. Feed-water is at this time being supplied to the main feed-water pumps 61, "62, and 63 to. the sections indicated by the arrows 45, 46, and 47 previously described. The full-line curve A shows the 7 beginning of normal operation, both the thermostats 40 and42 calling for water. We have shown the curve A as crossing the section 41 above the temperature T thus shutting OK the supply of heating gas in a manner previously described.

- Another very successfuland slightly dfferent method of control has been found wherein the water inlet at the point indicated by the arrow 46 has been eliminated. In this case'the primary thermostat 40 may be positioned somewhat closer to the inlet end of the boiler, and may be adjusted to call for water at slightly lower temperatures, in order to properly protect the tubes of the evaporator section. As a rule the elimmaton o water inlet at the point indicated by the arrow 46 will cause the primary thermostat 40 to operate on a longer cycle.

It should thus be apparent that by splittin'g up the feed-water supply, and controlling th1s supply by a plurality of thermostats we achieve not only safer boiler operation, but a decrease in the time necessary for generating steam. Furthermore, with such a system of control the temperature and pressure relationships at the throttle may be maintained relatively constant.

While we have illustrated a plurality of main feed-water pumps directly connected to the engine 21 and controlled by solenoid windings operatively connected to the intake valves of these pumps, we are not hmited to this combination. If desired, a single pump of large capacity may be utilized and the solenoid windings 69 to 71 utilized for controlling the opening. of a plurahty of valves positioned in branch lines extending from this pump to the different 3801120118 in the boiler at which it is desired to introduce feedwater. Furthermore, if desired the solenoids 69 to 71 maybe utilized for operatively connecting the engine and the main feed-water pumps without this invention.

While the positionin of each thermostat departing from the sp rit of relative to the walls of the boiler tube is an important detail of this invention inasmuch as it permits very accurate and sensitive control of boiler conditions, nevertheless the utility of our invention is not predicated upon this feature for obviously thermostats responsive only to steam temperature or tube temperature might be used in combination with a plurality of water inlet means or in combination with other of the novel features and steps herein disclosed.

We claim as our invention:

1. In combination: a boiler adapted to produce steam; a steam-operated pumping system actuated by the steam generated by said boiler for supplying feed-water to said boiler at a plurality of sections; and an auxiliary pumping system for supplying feed-water to only a portion of said sections.

2. In combination in a self-propelled vehicle a boiler; an engine adapted to be driven by steam produced by said boiler; a main pumping system operated by said engine and adapted to supply feed-water to. said boiler when said vehicle is in motion; an auxiliary pumping systemfor supplying feed-water to said boiler when said vehicle is stationary; and a speed-controlled device for rendering said auxiliary pumping system inoperative when said vehicle has reached a suflicient speed to cause said main pumping system to adequately supply said boiler with feed- Water. v

3. In combination with a boiler of the flash or semi-flash type having a main and an auxiliary superheater section: a primary heatresponsive element responsive to changes in boiler temperature in said auxiliary superheater section; a secondary heat-responsive element responsive to changes in boiler temperature in said main superheater section; primary feed means adapted to supply feedwater at a section toward the intake end of said boiler from said primary heat-responsive element; secondary feed means adapted to supply feed-water to said boiler at a point intermediate said primary and secondary heatresponsive elements; primary means controlled by said primaryheat-responsive element and adapted to control the flow of feedwater passing through said primary feed means; and secondary means controlled by said secondary heat-responsive element and adapted to control the flow of feed-water passing through said secondary feed means.

4. In combination with a boiler of the flash or semi-flash type having a main and an auxiliary superheater section: a primary heatresponsive element responsive to changes in boiler temperature in said auxiliary super heater section; a secondary heat-responsive element responsive to changes in boiler temperature in said main superheater section; primary feed means adapted to supply feedwater to the intake end of said boiler and to a section between said intake end and said mary heat-responsive element; secon ary feed means adapted to supply feed-water to said boiler at a point intermediate said primary and secondary heat-res ons'ive elements; primary means contro ed by said primary heat-res onsive-element and adapted to control the ow of feed-water passing through said primary feed means; and secondary means controlled b said secondary heat-responsive element an adapted to control the flow of feed-water passmg through said secondary feed means In testimony whereof, we have hereunto set our hands at Los Angeles, California, this 13th day of June, 1929.

' BRUCE BURNS.

HOWARD B. LEWIS.

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