US2215326A - Means for starting free piston motor compressors - Google Patents

Description

p 7, 1940. H. JANIcKE 7 2,215,326

MEANS FOR STARTING FREE PISTON MOTOR COMPRESSORS FiledJuly 26, 1935 4 Sheets-Sheet l 9*- H. JANICKE 2,215,326

MEANS FOR STARTING FREE PISTON MOTOR COMPRESSORS Filed July 26, 1955 4 Sheets-Sheet 2 /n vehtor:

SOPL 17, 1940. JANlCKE 2,215,326

MEANS FOR STARTING FREE PISTON MOTOR COMPRESSORS Filed July 26, 1935 4 Sheets-Sheet 4 pasted Sept-17, I 2,215,326

. UNITED STATES PATENT OFFICE MEANS FOR STARTING PISTON MOTOR COMPRESSORS Hermann Jinicke, Dessau, Germany, asslgnor to Therese Junkers, ne Beunhold, Gauting, near Munich, Germany L Application July 28, 1935, Serial No. 33,253 In Germany August 11, 1934 11 Claims. (01. 230-56) My invention relates to the starting of multiif not impossible, to accommodate, more espestage free piston motor compressors which shall cially in the higher stages.

be started from the side of the compressor with According to the present invention these difthe aid of gas under pressure. Hitherto such ficulties and drawbacks are obviated by using I free piston motor compressors have been started only part of the compressor stages for starting by first arresting the freely moving masses in purposes and introducing into these stages gas the starting position, for instance by means of under a pressure, which is higher than the presa pawl or the like, placing them under pressure sure attained in these stages of the compressor by means of a compressed gas on the side of the under. normal operating conditions. The use of compressor and thereafter releasing them by restarting gas under a higher pressure than the moving the pawl in order to enable compression normal operating pressure in the stage used for to take place and the motor charge to be ignited. starting ofljers the advantage that the storer for It has also been suggested to start single-stage the starting gas and the pipes and valves confree piston motor compressors by first placing nected with it may be of smaller size than in u the freely moving masses in a position which the case where the gas e e Placed u e e substantially corresponds to their position at the sa e pr sure as n a ly attained in the combeginning of the compression of the motor charge pressor stage us d f r r in and thereafter setting them moving by suddenly According to. this invention starting of the comacting on the compressor pistons with compressed pressor can he efi o in s a ner that the gas. starting process is already ended in a single cycle,

In both cases it is intended that th r sur i. c. after a single compression stroke of the moof the compressed gas to be used for starting o charge and a single W g oke of the be reduced after the end of the first starting motor piston have been gone th ough. I may stroke (1. e., the stroke for compressing the mohowever also start the motor compre sor in actor charge which shall hereinafter be termed reeo danoe with this invention by causi the comturn stroke") to the suction pressure of the com.. pressed g pp to p of the Co pressor pressor space used for starting, which means that s ages to expand and to be compress d again in a single-stage compressor it will as a rule be in a plurality of consecutive ycles, and at e reduced to atmospheric pressure. Consequently, end 1' each compression P of this starting the pressure of the gas used for starting pracgas is d schar ed from th mpr s r yl ntically corresponds t th end pressure produced der, so that the final pressures attained in the in the regular operation of t compressor, 11 consecutive compression steps become lower and this mode of starting were applied to multistage, lower until they h finally pped down to compressors, each stage would h v t b acted the end pressures arising under normal operation upon w compressed gas under the end pres in the stages used for starting, while on the other sure arising in this stage during regular opera hand the end pressure in the other stages, which tion and therefore each compressor stage would are used for starting" rises from one cycle have to be provided with a storer for the comto the other until the normal operating Pres 4,0 pressed starting gas, the pressure in which corsure has been reachedresponds to the final pressure arising in that zgg figg g ggg g igg gi gi gfi g c r p gompressor stage Obviously the provision tons of the second stage serving for starting are odies of compressed gas under several diflerent Supplied with gas under a pressure which corre pressures would be very inconvenient and it has sponds substantially to the doubl or treble therefore been suggested to supply all stages of the final pressure arising during normal per a multistage compress with starting gas under ation in the second compressor stage. When a the m pressure, Which Should be $0 chosen starting pressure of such'magnitud'e is used, the that the total efiort exerted by the pistons in starting gas can flow particularly quickly through starting be substantially as high as in the northe ports under control, so that there is imparted mal operation during the beginning 0! the re-. to the freely moving massesa high initial velocity turn stroke. This pressure is however comparafor the compression stroke of the motor charge, tively low and therefore very.large storers and which is particularly advantageous in a. starting pipes and valves of large cross sectional area process in which the freely moving masses are 5 w ld be r quired which it would be dimcult, not locked in their osition by a pawl or the like.

, stages of the compressor, the operating end pressure of which is lower than the highest end pressure arising duringoperation. In that case the starting gas under pressure may be withdrawn from a higher stage ofthe compressor, which is not used for starting. In the case that in this process several compressor stages shall be used for starting, these stages are preferably supplied with starting gas under equal pressure, which is however higher than the highest end pressure arising in the normal operation of these stages, so that the starting gas under pressure may be stored in a single reservoir, which can moreover be filled directly from a higher stage of the compressor. Here also the starting process may already be ended after the first cycle, but it may also extend over a plurality of cycles. In the latter case the pressures in the working spaces of the starting stages near the end of the compression stroke and the amounts of energy accumulated in the bodies of gas in the dead spaces of the compressor drop from one cycle to the other down to the magnitudes" corresponding to normal operation, while in the spaces of the compressor stages, which are not used for starting, these values gradually rise from the magnitudes corresponding to rest up to the magnitude of normal operation.

In the drawings afiixed to this specification and forming part thereof, free piston motor compressors embodying my invention are illustrated diagrammatically by way of example.

In the drawings,

Fig. 1 is an axial section, partly in elevation, of the left-hand half of a two-stage free piston motor compressor with permanently movable, i. e. never locked masses which move in opposite senses.

Fig. 2 is a similar illustration of a compressor in which the starting process is ended within one cycle.

Figs. 3 to 12 are pressure-volume diagrams of a' starting process extending over several cycles, Figs. 3, 5, 7, 9 and 11 being the diagrams of the second compressor stage used for starting, while Figs. 4, 8, 8, 10 and 12 are the diagrams of the ifirst compressor stage, which is not used for start- Fig. 13 is a view, similar to that shown in Fig. 1, of a two-stage free piston motor compressor, in which the freely moving masses are locked in their starting position by means of a pawl.

Fig. 14 is an axial section, drawn to a larger scale, of a pressure-controlled exhaust valve for the compressor stage used for starting.

Throughout the figures of the drawing similar parts are marked with similar reference numerals.

Referring first to Fig. 1, I is the motor cylinder, 2 is the motor piston, which is directly connected with the compressor piston 3 of the first stage and the compressor piston 4 of the second stage, these latter pistons moving in the compressor cylinders Ii and 6, respectively. The rear face I of the compressor piston 3 serves as a scavenging pump, the scavenging air being sucked during operation into the cylinder through the suction valves 8 and forced through the pressure valves 9 into the scavenging air reservoir II, from which it flows through the scavenging ports ll of the motor cylinder I, which are controlled by the piston 2. Fuel is introduced through. a nozzle l2 into the cylinder charge, which is highly heated by compression, and ignited by the heat of compression.

In order to secure synchronism of the two freely moving masses, each mass carries a rack- I 3', which meshes with a toothed wheel [4. By rotating the wheel I 4, for instance by means of a crank to be mounted on its axle, the freely moving masses may be placed by hand into the starting position shown in the drawings, in which they almost touch the stop I! mounted on the cover of the cylinder of the second compressor stage.

During normal operation atmospheric air is sucked through the valves it during the return stroke in the first compressor stage and forced during the working stroke of the motor through valve l1 into the receiver I8. From here the air flows through the intake valves it into the cylinder 8 of the second compressor stage to .be compressed further, whereupon it is forced through the exhaust valves 20, 2 l and pipe 22 into the receiver 23, from which it is conveyed through a spring-acted valve 24 into the reservoir 25. The valve 2| is mounted on a piston 26, the end face of which is larger than that of the valve disc and which is acted upon by a spring 21 tending to close the valve. In the wall of the dead space of the second compressor stage is arranged a starting valve 28, which controls the passage of the compressed starting gas from a storer 3| into the compressor cylinder 6. The disc of this valve is mounted on a piston 29 having a larger end face than the disc and being acted upon by a spring 30, which tends to close the valve.

This compressor is started as follows: first of all the movable pistons 2, 3, 4 (only one of which is shown in the drawings) are moved asunder by means of a crank handle placed on the axis of the toothed wheel 14 (or by other suitable means) until they meet the stops l5. Now the starting gas storer 3| is filled from a source of gas under pressure 34 through the pipe 32 and valve 33 which may also be replaced by a cock or the like. While this is being done, the starter valve 28 is still prevented from opening since the pressure of the starting gas acting on the difierential surface of the piston 29 and the force of the spring 30 keep the valve 28 closed. As soon however as the starting gas in the storer 3| has attained the pressure required for starting, the spring-actuated valve 35 in the conduit 31 leading from the storer 3| to the space 36 adjoining the rear side of piston 29 will open. The valve 35 might also be replaced by a manually operated member such as a cock or the like. The pressures acting from opposite sides on the piston 23 are now balanced and the pressure of the starting air in the storer 3|, which acts on the valve disc 23, causes the valve to open quickly. The starting air now acts on the compressor piston 4 and shifts the freely moving mass with great velocity towards the right, the charge in the motor cylinder being at the same time compressed. This compression in the combustion chamber is followed by combustion and expansion of the combustion gasesfwhich cause the first working stroke of the motor to take place. After the starting gas has left the storer 3|, the valve 28 is closed by the spring 30. A narrow vent opening 38 in the wall of the chamber 36 or some other venting device of a well known kind is provided for allowing air to escape from this chamber.

I am now going to describethe first cycles of operation of a two-stage motor compressor serving to start same, having reference to the diagrams shown in Figs. 3 to 12. In these diagrams the arrows I indicate return strokes serving to compress the motor charge, while the arrows 11 indicate working strokes of the motor.

Fig. 3 illustrates the sequence of pressures in the compressor cylinder of the second stage during the first starting stroke, the starting gas in the sltorer 3| (having the volume vs) being placed under a pressure of 24 atms. As soon now as the starting valve 28 opens, the starting gas flows into the space All (dead space 's) and expands therein, the pressure dropping to about 23 atms. Under this pressure the freely movable mass starts moving and on the way to the uncovering of the exhaust valves 20 by the piston l (the volume or being enclosed between the compressor cover and piston) a further expansion of the starting gas down to about 20 atms. takes place. As soon as the piston 4 has uncovered the ports of the exhaust valves 20, the starting gas expands into the space 4| between the valves 20 and 2|, its pressure dropping to about 16 atms. In the further course of the first compression stroke for the motor charge (return-stroke) the starting gas expands down to about 7 atms. While this occurs, air or gas of atmospheric pressure has been sucked into the first compressor stage (Fig. 4). After ignition of the motor charge the gas in the compressor cylinder 8 (of the second stage) is refrom 7 atms. upwards (Fig. 5).

compressed during the first motor working stroke The curve of compression is somewhat steeper than the curve of expansion in'Fig. 3, since in consequence of valve 28 closing, the storer II is cut off from the compressor cylinder, so that the compression must take place within a smaller total space than the preceding expansion. One thus obtains near the end of the compression a pressure (for instance of 18 atms.) in the cylinder 8 and in the space 4|, which is higher than the highest pressure (16 atms.) prevailing in the space 4| during the return stroke. The tension of the spring 21 acting on the valve 2| is now so adjusted, that this valve opens at this higher pressure (of 18 atms.), so that part of the recompressed starting gas is discharged into the receiver 23, this being illustrated in the diagram of Fig. 5 by the horizontal discharge line. Fig. 6 illustrates the compression of the gas sucked into the first compressor stage toabout 2 atms. during the first working strokeof the motor piston. The freely movable mass is moved back: into its former position by the energy stored in the body of compressed gas stored in the dead spaces of the compressor. During this return stroke (compression stroke for the motor charge) the gas in the cylinder of the second compressor stage expands from 18 atms. to about 5 atms. (Fig. '7), while in the compressor space of the first stage the pressure of the gases drops again to atmospheric pressure (Fig. 8). In consequence of the discharging of part of the starting gas through valve 2| into the conduit 22 and the receiver 23, which already occurs during the first motor working stroke, the pressure in these spaces has also been increased. This increased pressure now acts on the differential surface of the piston 26 counter to the action of the spring 21 and in consequence thereof the valve 2| will, during the-second motor working stroke (Fig. 9),already open at a pressure of 14 atms. in the compressor cylinder 6,

whereupon another portion of the starting gas is exhausted into the receiver 23. While this is going on, the gas in the first compressor stage (Fig. 10) has been compressed to 2.5 atms. This sequence of operations, according to which the pressures prevailing at the end of the motor working stroke (or compression stroke of the compressor) in the working chamber of the second compressor stage serving for starting and the amounts of energy stored in the bodies of compressed gas in the dead spaces of the compressor drop, whilethe same values gradually rise in the first stage of the compressor, which is not utilized for this starting, will now be repeated until the pressure in the receiver 23, which acts on the differential surface of the piston 28, has become so high as to overcome the pressure of spring 21, thus keeping valve 2| permanently open. At this point the normal operating condition illustrated in the diagrams of Figs. 11 and 12 is reached. According to Fig. 11 a compression of the gas from'3.5 atms. to the final operating pressure of 8 atms. is effected in the second stage, according to Fig. 12 a compression of the gas from 1 atm. to the operating and pressure of 3.5 atms. is eflected in the first stage.

Fig. 2 illustrates a modified form of a starting second compressor stage serving for starting, this valve opening towards the outside and being held 1 closed'by a spring 5|. The casing surrounding this valve communicates through pipe 52 with the receiver l8 of the first compressor stage and through pipe 53 enclosing a check valve with the space enclosed between the disc-of valve 2| and itspiston 26.

With this device starting is eflected as follows:

The preparations for the start and the introductory steps for the compression stroke (return.- stroke) for the motor charge occur similarly as described with reference to Fig. 1. However while in the device according to Fig. 1' no starting gas could escape from the cylinder 6 at the end of the first compression stroke for the motor charge, here part of the starting gas escapes near the end of the first compression stroke of the motor charge from the cylinder 6 through valve ill. The spring 5| acting on this valve is so dimensioned as to close the valve as soon as sufllcient gas under pressure has escaped, that the residual gas in the compressor cylinder 6 merely possesses the normal operating pressure (for instance 3.5 atms. according to Fig. 11) at the end of the expansion of the body of gas in the compressor cylinder. The gas, which escapes through valve 5|, now flows partly through check valve 54 into the casing surrounding'valve 2| and acts on the piston 25. The surface of this piston is so dimensioned with-respect to the surface of the valve disc 2|, that the pressure exerted by the gas on this differential surface is able to overcome the resistance of spring 21 and to thus open 6 same time expanding to the pressure prevailing in the receiver l8, which is equal to the normal operating pressure.

Since meanwhile the charge in the motor has u as in-the cylinder i (for instance according to Fig.1l) from 3.5 to 8 atms. and part of this gas is exhausted into the receiver 2! through the valve 24, which is normally held closed by a suitably dimensioned spring. Further, since the receiver ll already contains gas under normal operating pressure (for instance 3.5 atms.) the gas sucked during the first motor charge compression stroke (return-stroke) into cylinder 5 of the first compressorstage is compressed from the beginning to the end operating pressure of this stage (for instance according to Fig. 12 from 1 atm. to 3.5 atms.) as illustrated by Fig. 12. Thus here the starting process has come to an end in a single cycle.

Fig. 13 illustrates the left-hand half of a twostage free piston motor compressor with masses moving in opposite directions, which are shown in the starting position and can be locked in this position by means of a disengageable locking device.

This device here consists of a nose 4! formed on one or the racks l3 and a pawl 45 cooperating with it and hinged to the engine casing. In order that this pawl can be disengaged through the action of the starting gas, its free end is hinged tothe rod 44 of a piston 41 movable in a cylinder 48 against the action of a spring 49, which tends to hold the pawl 45 in looking position. The cylinder 48 communicates by way of a pipe and valve 56 with the starting gas reservoir 34. The pawl 45 can be locked in the position, in which it does not engage the freely movable mass, by a spring-loaded bolt 51, which can be moved into the path of the: piston 41 as soon as this latter is depressed by the gas pressure. This locking of the piston is indispensable in order to prevent the pawl from passing during the operation of the compressor into locking position, whereby the compressor would be stopped. In an engine such as shown in Fig. 13, starting is effected as follows:

The freely movable masses are first of all shifted into starting position by means of a crank lever to be mounted on the axle of the toothed wheel l4 and the bolt 51 is now pulled back by meansof the handle 58 to allow spring 49 to force the piston '41 upwardly and to thus shift the pawl 45 into locking position, wherein it engages the nose 46. Now thestarting gas reservoir I4 is connected through valve 23 with the compressor cylinder 6 of the second stage. While this is going on, the freely movable masses are .not set in motion, being still retained by the locking device 45, 46. Only after the valve 58 has been opened, and the starting gas pressure allowed to act on the piston 41 so as to depress it, the pawl 45 is disengaged from the nose and the freely movable masses are now free to move towards each other, being propelled by thegas pressure acting on the compressor pistons of the second compressor stage. During this movement the motor pistons compress the air for combustion in the motor working chamber for the first time. On fuel being injected near the inner dead centre position of the motor pistons, combustion takes place, followed by an expansion of the gases in the motor working chamber, whereby the first working stroke of the motor is brought about. For the rest the starting process occurs in the manner described with reference to Figs. 1 to 12. As shown in Fig. 14, a narrow passage 80 is provided in the disc of valve 2|, which allows starting gas under pressure to enter the spaces 22, 22 behind valve 2| already during the first compression stroke for the motor charge. By this arrangement the starting process.

extends over a plurality of cycles, can be shortened in a simple manner. For in consequence of the inflow of starting gas under pressure from the beginning of the starting process the pressure acting on the piston 24 in the spaces 22, 22 rises more quickly and thereby forces the valve 2| to remain permanently open at an earlier moment, than if the passage 00 were not'provlded. This narrow passage 00 further has the remain closed, so that in such a case theengine could not be put into normal operation. The passage 60 offers a way for the compressed gas toenter the spaces 22, 22 to the rear of valve,2| in case that, owing to a too short stroke of the movable masses. the end pressure attained in cylinder 6 should not be sufllciently high to overcome the resistance of spring 21 and to open the valve 2|. Owing to the passage of compressed gas through the passage 60 into the spaces -22, 22, the pressure in these spaces gradually rises until it suffices to keep the valve 2| permanently open. The passage might as well be replaced by some other passage from the chamber 4|.

In multistage free piston motor compressors. in which some or all compressor stages are subdivided in a plurality of compressor spaces, for instance in compressors of symmetrical design, my invention may be applied in such manner that only part of the compressor spaces of the same compressor stage is utilized for the starting process.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.

I claim: a

1. Means for starting multi-stage free piston motor compressors comprising a motor cylinder and two free pistons arranged in said motor cylinder for reciprocation in opposite directions, a first compressor cylinder at each end of said motor cylinder and a compressor piston at the outer end of each free piston arranged for reciprocation in the corresponding first compressor cylinder, another compressor cylinder to the rear of each first' compressor cylinder, a piston connected with the corresponding compressor piston and arranged for reciprocation in such other compressor cylinder, a starting air storer-to the rear of said other compressor cylinder, a source of starting air connected with said storer, a valve opening arranged to govern the admission of starting air from said storer to the outer end of said other compressor cylinder, a valve body arranged to cooperate with said opening and to open towards the dead space, an auxiliary piston connected with and having a larger effective end face than said valve body, a spring arranged to act on said auxiliary piston so as to close said valve, a permanently open communication between said storer and the end of said auxiliary piston adjoining said valve body and another-valve arranged to establish communication between said storer and the other face of said auxiliary piston. u

auras" 2. In a free piston motor-compressor, in combination, a motor working chamber. a plurality of compressor working chambers of diflerent size and interconnected so as to form the working chambers oi. a multi-stage compressor; means for starting said motor-compressor, said means comprising a starting gas reservoir, menas for connecting only during the first starting stroke a selected part only of the compressor working chambers with said reservoir,a body of gas provided in said reservoir under a pressure higher than the highest end pressureoccurring, during normal operation, in said selected compressor chambers; exhaust valves, for normal operation arranged on said compressor chambersand means torrendering inoperative, during the first starting stroke, the exhaust valves of said, selected compressor stages; discharge conduits 'i'or the compressed gas associated with each or .said selected-compressor stages,a discharge valve ineach of said conduits and comprising a valve body adapted to open outwardly and loaded for closing,

and a valve piston, said valve piston being connected with, and having a larger active surface than, said valve body, the side of said valve piston facing the valvebody being conected with a receiver through which gas discharged from the compressor fiows; the loading of the said valve body and the area of the'valve piston race being so chosen that the valve, as long as the pressure prevailing in said receiver has not yet reached the amount corresponding to normal operation, opens only, when the pressure prevailing in the discharge conduit of the compressor stage and acting on the valve, exceedsthe end pressure corresponding to normal operation of the compressor stage wherein this valve is provided,'but that it remains constantly open when the pressure in said receiver has reached the amount correspondingly to normal operation.

3. In a free piston motor-compressor, in combination. a motor working chamber, a plurality of compressor working chambers of different size and interconnected so as to form the working chambers of a multi-stage compressor; means for starting said motor-compressor, said means comprising a starting gas reservoir, means for connecting only during the first starting stroke a selected part only of the compressor working chambers with said reservoir, body of gas provided in said reservoir under a pressure higher than the highest end pressure occurring,vduring normal operation, in said selected compressor chambers; exhaust valves for normal operation arranged on said compressor chambers and means for rendering inoperative, during the first starting stroke, the exhaust valves of said selected compressor stages; discharge conduits for the compressed gas associated with each 01' said selected compressor stages, a discharge valve in each of said conduits and comprising a valve body adapted to open outwardly and 1oaded-ior closing,

valve, as long as the pressure prevailing in said receiver has not yet reached the amount corre- 1 spending to normal operation, opens only, when the pressure prevailing in the discharge conduit of the compressor stage and acting on the valve, exceeds the end pressure corresponding to normal operation or the compressor stage wherein the valve is provided, but that it remains constantly openwhen the pressure in said receiver has reached the amount corresponding to normal operation, said conduit being provided, at a point located behind the connection with said discharge valve, with a valve loaded for closing in a manner such that it afiords passage to the gas when the bination, a motor working chamber, a plurality of compressor working chambers of different size and interconnected so as to form the working chambers of a multi-stage compressor; means for starting said motor-compressor, said means comprisinga starting gas reservoir, means for connecting only during the first starting stroke a selectedpart only of the compressor working chambers with said reservoir, a body of gas provided in said reservoir under a pressure higher than the highest end pressure occurring, during normal operation, in said selected compressor chambers; exhaust valves for normal operation arranged on said compressor chambers and means for rendering inoperative, during the first starting stroke, the exhaust valves of said selected compressor stages; discharge conduits for the compressed gas associated with each of said selected compressor stages, a discharge valve in each of said conduits and comprising a valve body adapted to open outwardly and loaded for closing, and a valve piston, said valve piston being connected with, and having a larger-active surface than, said valve body, a second discharge conduit arrangedin the cylinder wall of the compressor stage provided with said discharge valve in a manner such that it is laid open by the piston moving in said'stage when the piston has travelled over at least a large part of'its first starting stroke; a loaded, outwardly opening valve in said second discharge conduit, the load ing being so chosen that after this second discharge conduit is opened by the said piston, this valve permits of the discharge of the starting gas contained in said compressor stage at the end of the first starting stroke, until its pressure has dropped to that prevailing in this compressor stage, and with this position of the piston, during normal operation; this second discharge conduit being connected with a conduit leading from said compressor stage to the one in front ofit, and with that side of said valve piston facing said valve body; the loading of the said valve body and the area of the valve piston face being so chosen that the valve, as long as the pressure prevailing in said receiver has not yet reached the amount corresponding to normal operation,

opens only, when the pressure prevailing in the discharge conduit of the compressor stage and acting on the valve, exceeds the end pressure corresponding to normal operation of the compressor stage wherein this valve is provided, but that it remains constantly open when the pressure in said receiver has reached the amount 8 atlases" closedwhensaid pistonisbroughtintoitsini position for the starting process. I

6. A tree piston motor-compressor according to claim 1, comprising compressor chambers prol vided with a gas storing space, asour'oe or gas under pressure adapted tobe connected to said storing space, a conduit leading from the storing space to the working space oi the compressor stage and an automatically acting gas inlet valve 10 in said conduit, said inlet valve including a valve body opening toward the working space and loaded for closing, and a piston connected with the valve body, the eflective face of the piston being larger. than that oi the valve body, the

1 side of thepiston facing the valve body being constantly exposed to the pressure in the storing space, the other side of the piston beingconnected, through a valve loaded for closing and opening toward the piston, with the storing 20 space; and through a narrow passage, with the atmosphere, the loading of the last-named valve, and the loading oi. the valve body being so chosen, that the inlet valve opens when the pressure in the storing space reaches the amount required 25 for discharge, and closes, when this pressure has dropped on account of pressure gas passing over into the working space of the compressor stage.

'7. A tree piston motor-compressor according to claim 1, comprising means for supplying. to- 80 all compressor stages used for starting purposes,

' used for starting being provided with the starting device.

starting gas under the same pressure which e:- ceedsthehighestendpressureoccurringinthese compressor stages during normal operation.

8. A tree piston motor-compressor according to claiml, wherein compressor stages are used a.

for starting which have a lower end pressure than other stages, comprising means for supplying, for starting purposes, the stages designed for starting with gas from the connecting and dis-; charge-conduits oi the stages of high pressure la which are still iilled with gas from a proceeding operation oi themachine. 9. A tree piston motor-compressor according to claim 1, comprising compressor stages including several compressor working spaces which, 15 in regard to the transportation of gas, are provided in parallel, only part or the compressor working spaces belonaing to a compressor stage so 10. A free piston motor-compressor according to claim 1, comprising means for locking the free piston in the initial position for the starting process, and means for rendering the locking means inoperative. a 11. A free piston motor-compressor according to claim 1 wherein the valve body is provided with a narrow passage.

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