US1997725A - High vacuum pump - Google Patents

Description

April16,1935. W.GAEDE 1,997,725

HIGH VACUUM PUMP Filed Dec. 23, 1933 .3 Sheets-Sheet l INVENTORT I wmyyw Z 4 BY 1 ATTORNEY April 16, 1935. w; GAEDE HIGH VACUUM 'PUMP Fil'ed Dec. 23, 1933 3 Sheets-Sheet 2 HINVENTOR WWW BY hm ATTORNEY April 16,1935. v w. GAEDE 1,997,725

HIGH VACUUM PUMP Filed Dec. 23, 1935 ,3 Sheets-Sheet 3 INVENTOR.

, By W I ATTORNEY- Patented Apr. 16, 1935 Wolfgang Gaede, Karlsruhe, Germany Application December 23, 1933, Serial No. 703,764

Germany December 31, 1932 11 Claims.

My invention relates to improvements in high vacuum pumps and more particularly in pumps comprising a casing having acylindrical chamber, a delivery chamber connected therewith by a valve-controlled passage, a cylindrical piston mounted eccentrically within said cylindrical chamber and adapted to move therein with its wall in line contact with the wall and circumferentially thereof, the said cylindrical chamber and piston providing a crescent-shaped working chamber, and a partition wall shii'table radially of the said cylinder and dividing the working chamber into a suction chamber and a pressure chamber, the suction chamber being adapted to be connected with a container to be evacuated, and the pressure chamber being connected with the said delivery chamber through the valve-controlled passage. In pumps oi this type the delivery chamber is filled with a suitable packing liquid such as oil to prevent leakage of the outer air into the working chamber and .the container to be evacuated, and it has been found that the said packing liquid and air contained therein are liable to leak through the pressure valve into the working chamber and through the same into the container when the operation of the pump is interrupted,.so that in the course of time the vacuum within the container is spoiled. Further, when the working chamber has. been filled with oil, much power is needed at the beginning of the operation of the pump to remove the oil from the working chamber, because the resistance of oil to propulsion from the working chamber to the delivery chamber is considerably higher than the resistance of air to such propulsion.

The object of the improvements is to provide a pumpof the class indicated in which the flow of oil from the delivery chamber to the container is made impossible, and in which in addition only a limited amount of oil has access to the working chamber of the pump. With this object in view my invention consists in dividing the said delivery chamber into two sections-connected with each other by a valve-controlled passage, the section which is directly connected through the pressure valve with the working chamber having a capacity smaller than that of the working chamber of the pump, and the said subsidiary valve being provided with mechanism controlled by the piston for keeping the same continuously open during the operationbf the pump and permitting the same to be closed only when the pump is out of operation. I have found that by thus providing a subsidiary valve which, as distinguished from the pressure valve of the pump, is not continuously seated and unseated during the operationof the pump, the said subsidiary valve is adapted to separate the main body of the oil from the'working chamber and to prevent leakage of the said main body of oil into the working chamber. In carrying out the inventlonthe mechanism controlling the said subsidiary valve is constructed so that it is adapted to be positively connected with the piston moving.

in a direction for opening the said subsidiary valve, braking means being provided for preventing rapid return movement of the said mechanism, and permitting the valve to be gradually closed only after the pump has been arrested.

For the purpose of explaining the invention several examples embodying the same have been shown in the accompanying drawings in which the same reference characters have been used in all the views to indicate corresponding parts. In said drawings,

Fig. l is a sectional elevation showing the pump,

Fig. 2 is a sectional elevation taken on the line 2-2 of Fig. l and showing the bottom part of .the P p,

Fig. 3 is a fragmentary sectional elevation similar to the one illustrated in Fig. 1 and showing a modification oi the delivery chamber and the valve controlling mechanism,

Fig. 4 is a sectional elevation showing a modification oi the pump,

Fig. 5 is a similar sectional elevation showing another modification, and

Fig. 6 is a sectional elevationtaken on the line 9-6 of Fig. 5.

In the construction shown in Figs. 1 andi2, the pump comprises a casing l formed with a cylindrical chamber 2, 3 and a delivery chamber 4, 5 communicating therewiththroughapassage icontrolled by a spring-pressed check valve 7 formed with bores 8 to permit back flow of liquid at a low rate, a cylindrical piston ill mounted eccentrically on a. rotary shaft ii and in line contact with the wall of the cylindrical chamber 2, and a partition I 2 radially shiftable in a slot made in the casing i and in sliding engagement with the piston ill. Between the wall of the cylindrical chamber 2 and the piston iii a. crescentshaped working chamber is provided which is divided by the partition l2 into a pressure chamber 2 and a suction chamber 3, the said pressure chamber being connected by the passage 6 with the delivery chamber 4, 5, and the suction chamber 3 being adapted to be connected through a suction passage I5 with the container to be evacuated. So far the pump is known in the art, and its operation is, briefly stated, as follows: The delivery chamber 4, 5 is filled with a suitable liquid such as oil. By the rotary movement of the piston ill in clockwise direction the capacity of the suction chamber 3 is enlarged, so that air is drawn from the container into the said suction chamber. When the piston has been rotated so far that the point where \it makes contact with the wall of the cylindrical chamber passes the pressure passage 5 the suction chamber is brought into communication with the said pressure passage and the delivery chamber, and after the said point of contact has passed the partition l2 and the suction passage l5 the volume of the said chamber, which now is the pressure chamber, is reduced. Therefore the air within the pressure chamber is compressed and forced through the passage 6 into the delivery chamber 4, 5.

The delivery chamber is divided into the lower section 4 connected with the passage 6 and the upper section 5. An opening is provided, through which the said sections are brought into communication, and a spring-pressed check valve I8 is provided, controlling such opening. The capacity of the lower chamber 4 is smaller than that of the working chamber 2, 3. During the operation of the pump the valve |8 is maintained in open position, and it is only after the pump-has been stopped that the valve is permitted to descend to its seat so as to close the upper section 5 of the delivery chamber as against the lower section 4. Thus the seat of the valve I8 is not spoiled by continuous seating and unseating of the valve II.

For thus controlling the position of the valve l8 the following mechanism is provided: Within the section 4 there is a cylinder l9 which is supported on the wall of the said section by arms 28. The said cylinder is formed at its top with an enlarged portion 2| which is closed above by a flexible diaphragm 22, and upon this diaphragm the valve l8 rests. Within the cylinder |9 there is a piston 23 which is connected with the partition l2 by a rod 24. To the said rod a disk 25 is secured which is acted upon by a coiled spring 28 tending to'force the piston 23 and the partition |2 downwardly and with the said partition in engagement with the piston ll. Within the enlarged portion 2| there is a valve disk 21 formed with a vent 28 and adapted to separate the cylinder I! from the enlarged portion 2|. Near its upper end the cylinder I9 is formed with a vent 29 the area of which is larger than that of the vent 28. The top part of the cylinder including the vent 29 is surrounded by a cup 3|).

In the operationof the pump the cylinder I9, the enlarged portion 2| and the cup 30 are filled with oil. By the rotary movement of the piston III the partition l2 and the piston 23 connected therewith are reciprocated, and by the upward movement of the piston 23 the oil within the cylinder I9 is forced upwardly. Thereby the valve disk 21 is unseated and the diaphragm 22 is forced upwardly, thus unseating the valve l8.-

At the beginning of the downward movement of the partition l2 and the piston 23 the valve disk 21 returns to its seat and thereafter only a slight amount of oil may flow from the enlarged portion 2| through the vent 28, the main portion of the oil being supplied to the cylinder |9 from the cup 30 through the vent 29. The valve l8 acted upon by the spring 3| is retarded in its descent by the relatively slow escape of oil through vent 28 and before it reaches its seat the piston 23 begins another upward stroke and forces a new supply of oil into the enlarged portion 2| and below the diaphragm 22, and causes the valve l8 to rise again. After the pump has been stopped, however, the spring 3| forces the valve l8 downwardly and on its seat, the oil gradually escaping from the enlarged portion 2| and through the vents 28 and 29.

From the foregoing description it appears that the oil confined within the cylinder l9 forms a part of the mechanism intermediate the partition l2 and the valve l8, and this part of the mechanism performs the braking action above referred to because the flow of the oil from the portion 2| into the cylinder |9 is retarded by the vented disk 28.

Since the capacity of the part 4 of the delivery chamber is smaller than that of the working chamber 2, 3 the said working chamber is but partly filled with oil when the pump is out of operation. Internally the section 4 of the delivery chamber 4, 5 must be constructed so that the air delivered into the same from the working chamber is free to escape through the opening l1, and that no air bubbles are deposited therein. Such air bubbles would make it impossible to maintain the vacuum within the container. Further, it is important that a sufficient supply of oil be maintained within the cup 38 for refilling the cylinder l9 and the enlarged portion 2|, and that no air bubbles have access through the vents 29 and 28 to the enlarged portion 2|.

The pump shown in Fig. 3 is similar to the one illustrated in Figs. 1 and 2, and the same reference characters have been used to indicate corresponding parts. As distinguished from the construction shown in Figs. 1 and 2 the stem of valve l8 becomes a piston within a cylinder 36 and the cylinder 35 is the enlarged continuation of cylinder I9.

In theconstructions shown in Figs. 1 to 3 the partition I2 and the piston 23 carried thereby are forced downwardly and into engagement with the piston H] by the spring 25. In the construction shown in Fig. 4 the partition 40 is positively connected with the piston.

The general construction of the pump casing and the other parts is similar to the corresponding parts illustrated in Fig. 3. and the same reference characters have been used to indicate corresponding parts. As distinguished from the construction shown in the said Fig. 3, to the shaft 4| an eccentric cylindrical body 42 is secured, and on the said body an annular piston 43 is rotatably mounted through the intermediary of an anti-friction bearing 44. The piston 43 is made integral with a partition 40, and the said partition is passed through a slot made in a cylindrical roller 45 rockingly mounted in bore 48 made in the wall of the casing The partition 40 passes through the said roller into a chamber 41 connected with a cylindrical chamber 48 and adapted to be partly closed relatively thereto by a valve disk 49 formed with a vent 50. The chamber 4'! communicates with the bottom part 4 of the delivery chamber through a vent 5| the cross-sectional area of which is larger than that of the vent 58. In the cylindrical chamber 48 a piston 52 is movable, and 52 is a stem for the valve disk l8.

While the pump is out of operation the disk I8 is pressed on its seat by the spring 3|, so that the section 5 of the delivery chamber is separated in a tight way from the section 4 of the said chamber. Therefore only a limited amount of oil may leak from the part 4 through the valve 1 or the bores 8 thereof into the working chamber 2, 3,, the capacity of the part 4 being smaller than that of the said working chamber. Thus transmission of oil and air confined therein to the evacuated container is made impossible. If now the pump is operated by turning the piston 42 in clockwise direction the oil confined within the working chamber and thereafter the air drawn'into the suction chamber 3 from the container to be evacuated are forced through the valve 1 into the chamber 4, 5. As the piston 42 moves from the position shown in the figure the partition 40 is forced upwardly and into the chamber 41. Thereby the oil within the said chamber 41 is forced upwardly and into the chamber 48, a part of the said oil escaping through the smallvent 5|, and the valve disk 48 being unseated. Thus the piston 52 and the valve disk 18 are forced upwardly against the action of the spring 3|. When the partition 40 is retracted from the chamber 41 the disk 45 is immediately placed on its seat and only a slight amount of oil flows through the small vent 50 into the chamber 41, the bulk of the said oil being taken into the said chamber through the larger vent 5|. Thus the partition 40 begins its next upward stroke before the excess oil in chamber 48 has made its escape, and the valve disc I8 does not come to its seat.

After the pump has been stopped, the spring 81 forces the valve 18 on its seat and it gradually drives a part of the oil from the chamber 48 and through the vents 50 and 5! into the chamber 4.

The construction shown in Fig. 4 is preferable as compared to the constructions shown in Figs. 1 to 3 in that the spring 26 is dispensed with, so that the capacity of the section 4 of the delivery chamber is considerably reduced.

In Figs. 5 and 6 I have shown a modification in which the casing I of the pump, the piston 43 and associated parts, and the valve 16 are similar in construction to the corresponding parts described with reference to Fig. 4. Thus the said piston is made integral with the partition 40 guided in the roller ,45. Within thesection 4 a cylinder 51 is fixed to the wall of the casing l by means of screws 56, and in the said cylinder at plunger 58 is mounted. To the said plunger a'sleeve 59 is secured in which a tubular extension 60 of the valve disk I8 is guided, the said tubuf lar extension being closed at its bottom and open at its top. By means of the said tubular extension the valve 18 is guided on a rod 6| fixed to a bracket, 62 secured to the top part of the easing I. Between the top of the bracket 62 and the valve disk 18 the spring 8| is located. To the bottom part of the cylinder 51 a flanged sleeve 63 is secured which projects into the plunger 58. At its top the said sleeve is formed with a vent 64, and at its bottom with holes 65, the vent 64 and holes 65 establishing communication between the bottom part 66 of the cylinder 51 and I the bottom side of the plunger 58. The said bottom part is adapted to be connected with the chamber 41 through a passage 61, which passage is adapted to be closed by a valve 68 acted upon by a spring 69 coiled around a stem fixed to the sleeve63 and extending into an axial socket of thevalve 68 for guiding the same. The plunger 58 is formed with a circumferential recess and a with a vent .12, and the cylinder 51 is formed with a vent 13 having an area larger than that of the vent 12.

At one side of the cylinder 51 there is an extension 55 open above and having a plug at its bottom, which plug is formed with an axial bore 16 connecting the chamber 4 with the chamber 41. It will be seen that the extension 55 is analogous in function to the cup 30 of the structures of Figs. 1-3. 4

The operation of the mechanism controlling.

the valve 18 is as follows: By the upward movement of the partition 40 into the position shown 4 3 in Fig. 5 oil is forced from the chamber 41 and through the valve 68 into the bottom part 66 of the cylinder 51, the said oil passing through the large holes 65 below the plunger 58.- Thus the said plunger is forced upwardly and into engagement with the tubular extension 60, so that the valve I 8 is unseated. When the partition 40 is retracted from the chamber 41, the valve 68 is forced on its seat, and thereafter oil is supplied to the chamber 41 only from the chamber 4 through the bore 16. The pressure of the spring 3| acting on the plunger 58 tends to expel the oil from the bottom part of the cylinder 58 and below the said plunger. But as the valve 68 is closed only a slight amount of oil can escape through the vent 12, the circumferential recess of the plunger, and the vent 13, so that the valve l8 does not arrive onits seat before the partition 40 performs another upward stroke. Thus the valve i8 is not placed on its seat during the .operation of the pump, and it is not subject to the wear caused by continuous seating and unseating thereof. When the pump is stopped the spring 31 continues to act on the valve disk I8 and the plunger 58, and the oil gradually escapes through the vent 12, the recess of the plunger 58, and the vent 13, until the valve 18 arrives on its seat and closes the lower section 4 of the delivery chamber from the top part 5 thereof.

Thereafter oil leaks into the working chamber of the pump only from the section 4 of the delivery chamber, and the volume of the said oil is not suflicient to fill the working chamber. Therefore, when the pump is started only a small amount of oil must be delivered from the pump.

I claim:

1. A high vacuum pump, comprising a casing having a cylindrical chamber, a delivery chamber communicating therewith, and a suction passage, a prmsure valve intermediate said cylindrical chamber and delivery chamber,.a piston within said cylindrical chamber providing therein a crescent-shaped working chamber and mounted for moving in contact with the cylindrical wall of said cylindrical chamber and circumferentially thereof, an outwardly movable partition plate dividing said working chamber into a pressure chamber and a suction chamber, said delivery chamber being divided into two sections one connected through said pressure valve with said working chamber and having a capacity smaller than that of the working chamber, a valve intermediate said sections of the delivery chamber, and mechanism intermediate said pis ton and valve intermediate said sections of the delivery chamber adapted to be operated by said piston for opening the said valve intermediate the said sections of the deliveryv chamber and comprising braking means adapted to retard the movement of the said valve on its seat.

2. A high vacuum pump, comprising a casing having a cylindrical chamber, a delivery chamber communicating therewith, and a suction passage, a valve intermediate said cylindrical chamber and delivery chamber, a piston within said cylindrical chamber providing therein a crescent-shaped working chamber and mounted for moving in contact with the cylindrical wall of said cylindrical chamber and circumferentially thereof, an outwardly movable partition plate dividing said working chamber into a pressure chamber and a suction chamber, said delivery chamber being divided into two sections one connected through said pressure valve with said working chamber and having a capacity smaller than that of said working chamber, a valve intermediate said sections of the delivery chamber, and mechanism intermediate said piston and valve intermediate said sections adapted to be operated by said piston for opening the said valve intermediate the said sections and comprising a liquid brake adapted to retard the movement of said valve on its seat.

3. A high vacuum pump, comprisinga casing having a cylindrical chamber, a delivery chamber communicating therewith, and a suction passage, a pressure valve intermediate said cylindrical chamber and delivery chamber, a piston within said cylindrical chamber providing therein a crescent-shaped working chamber and -mounted for moving in contact with the cylindrical wall of said cylindrical chamber and circumferentially thereof, an outwardly movable partition plate dividing said working chamber into a pressure chamber and a suction chamber, said delivery chamber being divided into two sections one connected through said pressure valve with said working chamber and having a capacity smaller than that of said working chamber, a valve intermediate said sections of the delivery chamber, and mechanism intermediate said piston and said valve within the delivery chamber comprising a cylinder, a piston reciprocating therein and adapted to be operated by said partition plate, a closing member for said cylinder acting on said valve within the delivery chamber, and a valve within said cylinder permitting unobstructed action of said piston within the cylinder on said member and adapted to retard the flow of the fluid from said cylinder.

4. A high vacuum pump, comprising a casing having a cylindrical chamber, a delivery chamber communicating therewith, and a suction passage', a pressure valve intermediate said cylindrical chamber and delivery chamber, a piston within said cylindrical chamber providing therein a crescent-shaped working chamber and mounted for moving in contact with the cylindrical wall of said cylindrical chamber and'circumi'erentially thereof, an outwardly movable partition plate dividing said working chamber into a pressure chamber and a suction chamber, said delivery chamber being divided into two sections one connected through said pressure valve with said working chamber and having a capacity smaller than that of said working chamber, a valve intermediate said chambers of the delivery chamber, and mechanism intermediate said piston and said valve within the delivery chamber comprising a liquid-filled cylinder divided by a valve into two compartments, a piston within one of said compartments connected with said partition plate, a member closing the other compartment and in position for engagement with said valve within the delivery chamber, said compartment in which the piston is movable being connected through a vent of larger area with said delivery chamber and through a vent of smaller area with the compartment closed by said member.

5. A high vacuum pump, comprising a casing having a cylindrical chamber, a delivery chamber communicating therewith, and a suction passage, a pressure valve intermediate said cylindrical chamber and delivery chamber, a piston within said cylindrical chamber providing therein a crescent-shaped working chamber and mounted for moving in contact with the cylindrical wall of said cylindrical chamber and circumierentially thereof, an outwardly movable partition plate dividing said working chamber into a pressure chamber and a suction chamber, said delivery chamber being divided into two sections one connected through said pressure valve with said working chamber and having a capacity smaller than that of said working chamber, a valve intermediate said sections of the delivery chamber, and mechanism intermediate said piston and said valve within the delivery chamber and comprising a liquid-filled cylinder divided by a valve into two compartments, a piston within one of said compartments connected with said partition plate, a diaphragm closing the other compartment and in position for engagement with said valve within the delivery chamber, said compartment in which the piston is movable being connected through a vent of larger area with said delivery chamber and through a vent of smaller area with the compartment closed by said diaphragm.

6. A high vacuum pump, comprising a casing having a cylindrical chamber, a delivery chamber communicating therewith, and a suction passage, a pressure valve intermediate said cylindrical chamber and delivery chamber, a piston within said cylindrical chamber providing therein a crescent-shaped working chamber and mounted for moving in contact with the cylindrical wall of said cylindrical chamber and circumferentially thereof, an outwardly movable partition plate dividing said working chamber into a pressure chamber and a suction chamber, said delivery chamber being divided into two sections one connected through said pressure valve with said working chamber and having a capacity smaller than that of said working chamber, a valve intermediate said sections of the delivery chamber, and mechanism intermediate said piston and said valve within the delivery chamber comprising a liquid-filled cylinder divided by a valve into two compartments, a piston within one of said compartments connected with said partition plate, and a piston within the other compartment closing the said other compartment and in position for engagement with said valve within the delivery chamber, said compartment in which the piston is movable being connected through a vent or larger area with said delivery chamber and through a vent of smaller area with the compartment closed by said piston engaging the valve within the delivery chamber.

'7. A high vacuum pump, comprising a casing having a cylindrical chamber, a delivery chamber communicating therewith, and a suction passage, a pressure valve intermediate said cylindrical chamber and delivery chamber, a piston within said cylindrical chamber providing therein a crescent-shaped working chamber and mounted for moving in contact with the cylindrical wall of said cylindrical chamber and circumferentially thereof, an outwardly movable partition plate dividing said working chamber into a pressure chamber and a suction chamber, said delivery chamber being divided into two sections one connected through said pressure valve with said working chamber and having a capacity smaller than that of said working chamber, a valve intermediate said sections of the delivery chamber, said casing being formed with a chamber into which said partion plate projects, and mechanism intermediate said piston and said valve intermediate the sections of the delivery chamber adapted to be operated by said piston for opening the said valve intermediate the said sections and comprising a cylinder within the sections of the delivery chamber connected with said worksage, and a plunger within said cylinder adaptedto unseat said valve within the delivery chamber, the portion of said cylinder connected with said chamber into which said partition plate projects being formed with a vent permitting retarded flow of liquid, and said casing being formed with a vent through which the chamber into which said partition plate projects communicates with the delivery chamber.

8. A high vacuum pump, comprising a casing having a cylindrical chamber, a delivery chamber communicating therewith, and a suction passage, a pressure. valve intermediate said cylindrical chamber and delivery chamber, a piston within said cylindrical chamber providing therein a crescent-shaped working chamber and mounted for moving in contact with the cylindrical wall of said cylindrical chamber and circumi'erentially thereof, an outwardly movable partition plate dividing said working chamber into a pressure chamber and a suction chamber, said delivery chamber being divided into two sections one connected through said pressure valve with said working chamber and having a capacity smaller than-that oi the working chamber, a valve in-' by said piston for opening the said valve intermediate the said sections and comprising a tubular body formed with a cylinder within said section of the delivery chamber connected with said working ,chamber, said cylinder being connected by a passage with said chamber into which the said partition plate projects, a valve controlling said passage, a plunger within said cylinder adapted to unseat said valve within the delivery chamber, the portion of said cylinder connected with said chamber into which said partition plate projects being'iormed with a vent permitting retarded flow oi. liquid, and said casing being formed with a vent throughwhich the chamber into. which said partition plate projects communicates with the delivery chamber. a

" 9. A high vacuum pump, comprising a casing having a cylindrical chamber, a delivery chambercommunicating therewith, and a suction passage, a pressure valve intermediate said cylindrical chamber anddelivery chamber, a piston within said cylindrical chamber providing therein a crescent-shaped working chamber and mounted Y for moving in contact with the cylindrical wall of that of said working chamber, a valve intermediate said sections of the delivery chamber, said casing being formed with a chamber into which said partition plate projects, and mechanismintermediate said piston and said valve intermediate said sections of the delivery chamber adapted to be operated by said piston for opening the said valve intermediate the said sections andcomprising a cylinder within said portion of the delivery chamber connected with said working chamber, said cylinder being connected by a passage with said chamber into which said partition plate projects. a valve controlling said passage, a plunger within said cylinder adapted to unseat said valve within the delivery chamber, said plunger being chamber with a suction passage opening through its wall, a delivery chamber with. which the work ing chamber communicates, a, piston adapted in its operation to draw successive charges of fluid through said suction passage and into said. working. chamber-and to. propel such indrawn charges from the working chamber to. the delivery chamher, a check valve permissive oi back flow of liquid at low rate controlling communication between working chamber and delivery chamber, the delivery chamber including an; inner section with which, subject to such check valve control, the working chamber has immediate communication and an outer section with which, through an opening, the inner section has communication, the inner section of the delivery chamber being of less capacity than thew'orking chamber, a second- 11. A high vacuum-pump, comprising a casing 1 having a cylindrical chamber, a delivery cham-- ber communicating therewith, and a suction passage, a pressure valve intermediate said cylindrical chamber and delivery chamber, a rotary piston (eccentrically arranged) within said cylindrical chamber and forming with the cylinder wall a working chamber, a partition plate dividing said working chamber into a pressure chamber and a suction chamber, said delivery chamber being divided into two sections, one connected tli'rough said pressure valve with said working chamber and having a capacity smaller than that of the working chamber, a second valve intermediate said sections or the delivery chamber, and mechanism intermediate said piston and said second valve adapted to impart an opening traverse to the said valve with each rotation 01 the piston, and braking means adapted to retard the ensuing closing traverse of the said valve, whereby the said second valve closes when and only when normal piston rotation ceases.

WOLFGANG GAEDE.

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