US2608342A

US2608342A - Fluid compressing apparatus

Info

Publication number: US2608342A
Application number: US9688A
Authority: US
Inventors: Burton S Alkman
Original assignee: Westinghouse Air Brake Co
Current assignee: Westinghouse Air Brake Co
Priority date: 1948-02-20
Filing date: 1948-02-20
Publication date: 1952-08-26
Anticipated expiration: 1969-08-26

Description

Patented Aug. 26, 1952 FLUID comnsssmc srrsa'srus p Burton 8. Aikman, 8t. Petersbnrg, Fla, assignor to Westinghouse Air Brake Company, a corporation of Pennsylvania Application mam 20, 1948, Serial No. 9,888

15 Claims. 1

This invention relates to fluid compressing apparatus of the type embodying a storage reservoir and an air compressor for compressing air into said reservoir and one object of the inven- :ion is to provide an improved apparatus of this Another object of the invention is the provision of improved means for cooling the compressed air delivered by the air compressor before it is forced into the storage reservoir.

Another object of the invention is the provision of improved means for cooling the compresforming a part of the specification.

Inthe drawing, the single figure is a diagrammatic view, mainly in section, illustrating the preferred embodiment of the invention.

Description As shown in. the drawing, the fluid compressing apparatus comprises an air compressor I, a cooling coil 2, an unloading and drain valve device I, a small reservoir 4 and a large storage reservoir 5 provided in a casing 6 and separated by ;a partition wall 1, and a cut-oif valve device 8. A pipe 9 extending from a discharge valve chamber iii ofthe compressor I is connected through the cooling coil 2'to the unloading and drain valve device 3. A pipe ii connects the unloading and drain valve device 3 to the large reservoir 5 while a pipe l2 connects said valve device to I the small reservoir 4. r The fluid compressing apparatus further comprises a pipe I 3 connecting the discharge valve chamber In in the air compressor l to the cut-off valve device 9 and a pipe i4 connecting said cut- 5 oil valve device to the reservoir 5.

Considering the parts of the equipment in greater detail, the compressor I, which may be of the reciprocating type and driven in any suit- .ahle manner, comprises a discharge valve I 5 contained in chamber in and arranged for 00" operation with a seat It formed in a cylinder head It which is mounted over the upper end of a cylinder bore i 9, said'bore being encircled by a gasket which prevents leakage of fluid under pressure between the upper end of said bore and the atmosphere. The valve i5 is urged to its seat by a spring 2i disposed between said valve and a cap 22 having screw-threaded engagement with the cylinder head l8. The cap 22 is provided with a recess 23 in constant communication with the discharge valve chamber Iii through one or more notches 22a in the lower end of said cap, and a series of bores 24 in said cap connect said recess with a chamber 25 formed in-the cylinder head i8 and to which the pipe II is connected.

The cooling coil 2 comprises a suiilcient length of pipe disposed between the discharge val'vo chamber ill and the unloading and drain valve device 3 to provide for a certain transfer to atmosphere of heat from compressed air dis charged by the compressor i past the discharge valve I! to said pipe so that by the time the said compressed air reaches said valve device its temperature will be considerably lower than that leaving the discharge valve chamber i0. 3

Theunloading and drain valve device 2 comprises two casing sections 28 and 21 secured to each other and to an end cover 29 common to both of said casing sections. Casing section 22 is provided with a chamber 29 to which the cooling coil 2 is connected, and a smaller chamber having a connection with the atmosphere through a choke 3i. The chambers 29 and ll are connected by a bore 32 in which is disposed a valve stem 33 having at one end a valve 24 disposed in chamber 30 for controlling communication between said chambers by way of a passage 40. The opposite end of stem 83 is connected centrally with a diaphragm 35, clamped around its edge between casing section 28 and cover 28, by means of two diaphragm followers 38 and 31 and a nut 38 having screw-threaded engagement with the stem 33. One side of diaphragm 35 is exposed to pressure of air in chamber' 29 and the opposite side to pressure ofair in a chamber 5|.

The casing 21 is provided with a chamber i which is adapted to be connected to the cham 0 her 29 by a bore 52. The casing 21 is also provided with two spaced apart and coaxially arranged valve seats 43 and I4, and the connection between chamber II and bore 42 is through the valve seat 43. Provided in the chamber ll between the valve seats 43, 44 is a flat disc type valve 45 which is adapted at one time to seat on the seat 43 and at another time to seat on the seat 44., Disposed between the valve 45' and a wall 45 separating chambers 28 and 4i and through which the bore 42 is provided is a spring '41. With the valve 45 resting on the seat 44 the top or the spring 41 and the wall 45 is less however than the distance between valve seats 43 and 44 so that when the valve 45 is moved into engagement with the valve seat 43 the spring 41 will be compressed a certain chosen amount which depends on the free-height or said spring.

The chamber 4| is connected to the reservoir 4 by the pipe i2, which together with bore 42, chamber 28, cooling coil 2 and pipe 9, provides a fluid pressure communication between said reservoir and the discharge valve chamber Iii when the valve 45 rests on seat 44. A chamber 48 formed in the casing section 21 beneath the valve seat 44, is connected to the reservoir 5 by means of a passage 48 and the pipe II. A branch passage 50 connects the passage 43 to chamber 5| formed at the leift hand side or the diaphragm 35 so that the pressure in the reservoir 5 is always present in said chamber.

The cut-oil valve device 8 comprises a casing 52 having a bore 53 and a counterbore 54. Disposed in these bores in a differential type piston 55 comprising a larger piston 55, the diameter of which is slightly less than that of bore 53 to permit a limited flow or fluid under pressure therepast, and a smaller piston 51 on which is provided a valve 58 for cooperation with a seat 58 formed at the upper end oi counterbore 54, to control communication between said bores. The larger piston 55 divides the bore 53 into a lower chamber BI and an upper chamber 55, to which latter chamber the pipe I4 is adapted to be connected at a point Just above the top of said larger piston when said piston occupies a lower position in which it is shown in the drawing.

The differential type piston 55 is provided with a large counterbore 52 open to chamber 55 and a '4 that the valve 34 may be either seated or unseated. Upon starting the compressor I fluid under pressure will be discharged past the valve i5 to the chamber II from whence it will flow through the pipe 8 and cooling coil 2 to the chamber 28, wherein it will act on diaphragm 35 to urge it in the direction of theleit hand'ior seating the valve 34, it not already seated. It the valve 34 is initially open there will be a flow or fluid under pressure from chamber as through passage 45, past the valve 34, and through chamber 35 and choke It to the atmosphere. Since the capacity or the choke 3| is less than the capacity or the compressor i, the fluid under pressure being supplied to the chamber 25 at the right hand side of the diaphragm 35 will promptly provide a pressure on said diaphragm which so exceeds the atmospheric pressure acting on the leit hand side thereof as to deflect said diaphragm in the direction or the left hand carrying with it the. stem" and the valve 34 until said valve engages its seat which will thereby terminate flow oi! fluidiu'nder pressure to the atmosphere through the choke 3i.

With the valve 34 closed, the fluid under pressure supplied to the chamber 29 by the com'presw sor I will flow through the bore 42, chamber 4i and pipe 12 to the reservoir ,4 thereby increasing.

' to the chamber 55 and thence through the. pipe.

small bore 63 connecting said counterbore to chamber 55 below valve 58. The bore 53 is provided near its upper end with a valve seat 64. A ball-type check valve 55 is provided for cooperation with the seat 54 to control a by-pass chamber 56 below the said valve and the chamber 55. Disposed in the bottom of counterbore 52 is a spring seat 51 having a bore 58 to provide a fluid pressure communication between chambers and when the check valve 55 is raised from its seat. Disposed between the spring seat 51 and a cap 59 having screw-threaded engagement with the casing 52 is a spring 10 for urging the differential type piston 55 to its lower positio with the valve 55 seated.

Th reservoir 5 is provided with an outlet pipe Ii for supplying fluid under pressure to any location where it may be desired to use the same.

operation With the various parts 01' the fluid compressing apparatus in the position in which they are shown in the drawing and with no fluid under pressure in the apparatus, atmospheric pressure will be present on both sides 01' the diaphra m 35 or the unloading and drain valve device 3 so communication around the valve 58 between I4 to the large reservoir 5, the major portion or the air compressed by the compressor'being displaced into reservoir 4, as above described, while the cut-oil valve 58 is seated. Therefore the pressure of fluid in chamber 55 will gradually increase along with that in reservoir 4 until such pressure in said chamber acting on the cut-oil valve 58 provides a force so exceeding the opposing force on said valve including spring 15, as to unseat said valve. Upon unseating the cut-off valve 58 fluid under pressure in the chamber 55 will flow past said valve to the chamber 5i where it acts on the lower side of the larger piston 55 outside ofv the smaller piston 51 to provide an increased upwardly acting force on said pistons to snap said pistons-upwardly until said larger piss ton strikes the cap 69 which arrest further upward movement 01' said pistons.

At the time the differential type Piston 55 comes to rest against the cap 58 the bottom or the large piston 55 will be above the connectionoi the pipe I4 to the chamber 55 which permits a rapid flow of fluid under pressure from the chamber 55,, tl'll'Olgh the chamber 5i and pipe l4 to the reservoir The flow of fluid under pressure from the chamber 55 to the reservoir 5 results in a'de'crease in the pressure in said chamber. As the pressure decreases in chamber 55, fluid under-pressure in the reservoir 4, which is at the same pressure as that in the chamber 55 at the time the valve 55 was opened, flows back through pipe l2, chamber 4i, bore 42, chamber 29, cooling coil 2, pipe I, chamber Hi, recess 23, bores 24, chamber 25, pipe l3, chamber 58, past the open valve 58 and through the pipe l4 to the reservoir 5.

aeoasea As the pressure of fluid in reservoir 8 builds up as above described, the pressure of fluid in chamber 88 above the piston 55. which pressure was initially the same as in reservoir 5, may build up past the check valves 55 and by leakage past the piston 58, and hence will equalize substantially with that in pipe l4 and in said reservoir. when the pressure of fluid in chamber 88 and in reservoir 5 is thus increased sufllciently with respect to the pressure of fluid in chamber 85 the spring 18 will start moving the piston 58 downwardly and such movement will continue under the reducing pressure of spring 18 in proportion to the reducing differential between the pressures in chambers 88 and 88 until eventually the cut-oi! valve 58 will reseat which it is desired will occur when said differential is of some chosen value such as flve pounds. When the cut-oil. valve 58 is thus reseated further flow of fluid under pressure from reservoir 4 to reservoir 5 is prevented except for that past the check valve 35.

- When the cut-off valve 58 is closed as just described, the pressure of fluid in chamber 8| surrounding the smaller piston 51 reduces by equalizing past piston 55 to that present in chamber 88 and reservoir 5 whereby only the smaller piston 51, which controls opening of the cut-off valve 58 as previously described, is subject to the increasing pressure of fluid in chamber 88.

By reason of the fact that the area of the piston 58 is lar er than the area of the piston 51, it will be evident that the pressure at which the valve 58 closes will be less than that at which i it opens. this pressure differential being dependent on the relative diameters of the two pistons.

When the pressure of fluid in the reservoir 4 and chamber 88 in the cut-oil. valve device 8 again becomes increased to a degree sufllcient to open the cut-ofl valve 58 against spring 18 and the pressure of fluid in chamber 88, the cut-oi! valve will again open to permit flow of fluid under pressure from resevoir 4 to reservoir 5 until the pressure in the latter reservoir is increased to with perha s five pounds of that in reservoir 4 whereupon the cut-oil valve 58 will a ain close in the manner above described. In this manner the pressure of fluid in reservoir 5 will be increased and maintained by successive charges of fluid under pressure from the reservoir 4.

The time elapsing between the instant at which the cut-off valve 58 closes and that at which it opens again provides for a certain amount of cooling of the fluid under pressure being supplied to the reservoir 4 by radiation from the outside surface of said reservoir, due to the fact that the temperature of the atmosphere surrounding said surface is considerably lower than that of the fluid under pressure being supplied to said reservoir by the compressor l. Therefore, due to the cooling of the fluid under pressure produced by flowing through the cooling coil 2 to the reservoir 4 and subsequently from said reservoir to reservoir 5 and that produced by radiation of heat from the outside surface of the reservoir 4, the fluid under pressure supplied to reservoir 5 from reservoir 4 at the time the valve 58 opens, is considerably cooler than that being delivered by the compressor past the discharge valve I5, and effects a cooling of said discharge valve in flowing over said valve in its passage from the reservoir 4 to the reservoir 5 in the manner which has been previously explained Thus it is seen that the fluid under pressure compressed by the compressor will be cooled to a certain degree before it is discharged into the large reservoir 5 from whence it may be conducted through the pipe II to the point where it is used. At the same time the cooling of the fluid under pressure is utilized to keep the temperature of the discharge valve I5 and discharge valve chamber I8 below 8. dangerous value.

During the time that the compressor i is operating, the fluid under pressure discharged therefrom and present in the chamber 4| maintains the valve 45 seated on its seat 44, since the discharge pressure in said chamber is greater than the pressure in the reservoir 5, tending to unseat said valve, thereby preventing flow to the reservoir 5 through the pipe However, fluid under pressure from the reservoir 5 flows through the pipe I and branch passage 58 to the chamber 5|, but since the higher compressor discharge pressure is present in the chamber 28 the dia.-.' phragm 35 is operated thereby to hold the valve 34 seated.

When the compressor is shut down the fluid under pressure in the reservoir 4 equalizes with that in the reservoir 5 past the ball check valve 55 in the cut-off valve device 8. When the pressures in the two reservoirs become equal the pressures on both sides of the diaphragm 35 will be the same and the fluid under pressure present in the chamber 29, which is compressor discharge pressure, and acting through the passage 48 in bore 32 on one side-of valve 34 will unseat said valve since only atmospheric pressure is present in the chamber 38 acting on the opposite side of said valve. With the valve 34 unseated the fluid under pressure in the chamber 23, cooling coil 2, pipe 9, discharge chamber i8, pipe l3 and chamber 88 in the valve device 8 flows past said valve and through the choke 3| to the atmosphere, the check valve 65 and seated cut-oil valve 58 holding the fluid under pressure in reservoir 5. At the same time fluid under pressure from the reservoir 4 will flow through the pipe l2, chamber 4| and bore 42 to the chamber 29 and thence through the choke 3| also to the atmosphere.

As soon as the pressure in thechamber 4| has fallen slightly below the pressure in. chamber 48, which pressure is the same as that in the reservoir 5, the higher pressure in chamber 48 will unseat the valve 45 from its seat 44 and move it, together with the spring 41 which rests thereon, upward until said spring contacts the wall 45. The spring 41 will then be compressed by the further flow of fluid under pressure from the chamber 4| to the atmosphere until the valve 45 seats on the seat 43. With the valve 45 thus seated on the seat 43, further flow of fluid under pressure from the reservoirs 4 and 5 to the atmosphere is prevented and reservoir 4 is connected to the reservoir 5 through pipe l2, chambers 4| and 48, passage 49 and pipe permitting the fluid under pressure in both reservoirs to be supplied through the pipe H to the point of use.

During the time the valve 45 is unseated fromthe seat 44 and before it is seated on the seat 43 both reservoirs 4 and 5 are connected through the choke 3| to the atmosphere to permit any moisture present in the bottom of either reservoir to be discharged therefrom through the choke 3|. Every time the compressor is shut down any moisture present in either reservoir is thus drained tothe atmosphere.

After the valve 45 seats on the seat 43, the fluid under pressure remaining in the chamber 28, cooling coil 2, discharge valve chamber l8, pipe l3 and chamber 68 in the cut-oil valve 8 will flow to the atmosphere through the choke for relieving the compressor discharge valve of pressure of fluid in chamber It, ,i. e.. for unloading the compressor, for subsequent starting.

The area of the clearance space between the periphery of valve 45 and the wall of chamber M is so related to the venting capacity of choke ll as to ensure the pressure of fluid in chamber 4| at one side of said valve reducing sufflcientiy belowthat in chamber 48 at the opposite side to cause operation of said valve as just described.

When the compressor I is started again it will therefore start against atmospheric pressure in the discharge chamber III. The fluid under pressure discharged from the compressor I will flow from the discharge chamber III through the cooling coil 2 to chamber 29 and past the valve 34, if open, and through choke 3| to the atmosphere. Since fluid under pressure is being supplied to the chamber 29 more rapidly than it can be exhausted'through the choke 3|, the pressure in chamber 29 and on the right hand side or the diaphragm 85 will increase until it exceeds that in chamber II on the left hand side of said dia. phragm. When the pressure on the right hand side of the diaphragm 35 exceeds that on the left hand side, said diaphragm will be deflected toward the left hand until the valve 34 is seated which prevents further flow o1 fluid under pressure from the chamber 29 to the atmosphere through the choke 3 I.

With the valve 34 seated, the pressure in the chamber 29 continues to increase until it slightly exceeds that in chamber 4I and the reservoirs 4 and I, at which time the valve 45 will be forced from its seat 43 and drop by gravity against the seat 44. Fluid under pressure which is being supplied to the chamber 29 by the compressor I can now flow to the reservoir 4.. At the same time that fluid under pressure is being supplied to the chamber 29, it is also supplied to the chamber of the cut-ofl valve]. When the pressure in the chamber 66 is raised sufllciently reservoir and operable at one time to close fluid pressure communication through said discharge valve chamber between said first reservoir and said second reservoir and operable upon the establishment of a chosen diiferential of pressures between said second reservoir and said first reservoir to establish a fluid pressure communication between said reservoirs to equalize the pressures in said reservoirs.

2. In combination, an air compressor comprising a discharge valve disposed in a. discharge valve chamber, a first reservoir for cooling and a second reservoir for storing fluid under pressure,

I valve chamber, a first reservoir and a second to overcome the force of the spring I0, the cutof! valve 58 ,willvbe unseated and the fluid under pressure present in the small reservoir 4 will flow to the large reservoir 5, in the manner which has already been explained.

Summary It will now be seen that I have provided a, fluid compressing apparatus embodying means for precooling the compressed fluid under pressure before it is forced into the main or storage reservoir and for using this precooled fluid under pressure to cool the compressor discharge valve to keep its temperature below a dangerous value.

- a second reservoir for storing fluid under pressure, an unloading and drain valve device disposed between and connected to said discharge valve chamber and said first reservoir and operable upon the shutting down of the compressor to momentarily drain moisture from each of said reservoirs and to unload said compressor, and a cut-0E valve disposed between and connected to said discharge valve chamber and said second reservoir, a fluid pressure communication connecting said valve chamber and said first reservoir, a second fluid pressure communication connecting said valve chamber and the said second reservoir, and a cut-off valve disposed in said second fluid pressure communication comprising a difl'erential area piston subiect to pressure of fluid in said second reservoir opposing pressure of fluid in said first reservoir and operable to open said second fluid pressure communication upon a chosen preponderance in pressure of fluid in said first reservoir over that in said second reservoir and to close said second fluid pressure communication upon a chosen reduction in the degree of said preponderance.

4. In combination, an air compressor comprising a discharge valve disposed in a discharge valve chamber, a first reservoir for cooling and a second reservoir for storing fluid under pressure, a cooling coil, an unloading and drain valve device connected in series with said coil between said discharge valve chamber and said first reservoir and operative in response to substantial equalization of pressures in said reservoir to momentarily open a drain from. said reservoirs and to dissipate fluid under pressure in said discharge valve chamber, and a cut-oi! valve disposed in a connection between. said discharge valve chamber and said second reservoir operative in response to a chosen increase in pressure of fluid in said first reservoir above that in said second reservoir to open a fluid pressure flow communication between said reservoirs for permitting flow of fluid under pressure in 'the direction from said first reservoir to said second reservoir and for permitting cooling of said discharge valve and discharge valve chamber by fluid under pressure passing through said chamber from said first reservoir to said second reservoir. and operative in response to a reduction in the difl'erential in pressures in said reservoir to a chosen degree to close said fluid flow communication.

5. In combination, an air compressor comprising a discharge valve disposed in a discharge valve chamber. a first reservoir, a cut-ofi valve disposed between and connected to said first re sbetween said valve chamber and said second resvice comprising means operative upon shutting down 01 said compressor to unload said compressor, means for momentarily opening a moisture drain from each of said reservoirs upon operation of said valve device, and means for establishing a fluid pressure communication between said reservoirs upon unloading said compressor and terminating said draining.

8. In combination, an air compressor comprising a discharge valve disposed in a discharge valve chamber, a first reservoir open to said chamber for receiving and cooling fluid under pressure compressed by said compressor, a second reservoir for storing fluid under pressure I compressed by said compressor, and a cut-off valve device operative in response to the pressure in said first reservoir exceeding that in said sec-- ond reservoir by a chosen degree to establish a fluid pressure communication between said reservoirs and operative to close said communication upon the pressure in said first reservoir reaching a chosen lower degree.

'7. In combination, an air compressor, a first reservoir for receiving and cooling fluid under pressure compressed by said compressor, a second reservoir for storing fluid under pressure, and a cut-oil valve device comprising a casing, a valve seat in said casing encircling a fluid flow communication from said first reservoir to said second reservoir, a piston means slidably mounted in said casing subject on one side to pressure of fluid in a control chamber, a. valve of smaller area than said piston means projecting from the opposite side thereof for cooperation with said seat to close said communication, a spring urging said valve to said valve seat, a restricted communication connecting said first reservoir to said chamber, and a check valve in said restricted communication for preventing-flow of fluid under pressure therethrough in the direction from said chamber to said first reservoir.

8. In combination, an air compressor, a first reservoir, 9. heat radiating pipe connecting the discharge of said compressor to said first reservoir, a second reservoir, cut-off means operable in response to a chosen differential in pressures in said first and second reservoirs upon an increase in pressure in said second reservoir over that in said first reservoir to establish a fluid flow communication between said reservoirs and operable upon a chosen reduction in said difi'erential to close said communication, an unloading valve device comprising a first means subject opposingly to pressures of fluid in said pipe and atmosphere controlling a vent from said pipe and a second means operable by pressure 01' fluid in said pipe upon exceeding that in said second reservoir to operate said first means to close said vent and operable upon substantial equalization of pressures of fluid in said pipe and second reservoir to render pressure of fluid in said pipe acting on said first means effective to actuate said first means to open said vent, means controlling a communication between said first and second reservoirs and said pipe including a check valve operable by pressure 0! fluid in said pipe when in excess 01 that in said second reservoir to close communication therebetween and to open said first reservoir to said first means and operable upon a reduction in pressure in said pipe below that in said second reservoir to first establish communication between both oi. said reservoirs and said first means and to then disconnect said reservoirs from said first means while-retaining said reservoirs open to each other,

, and a spring acting on said check valve for controlling operation thereof in response to operation or said first means.

9. In combination, an air compressor, a first reservoir connected to said compressor for receiving compressed fluid delivered thereby. a second reservoir, one way flow means connecting said reservoirs for permitting flow oi. fluid under pressure from said first reservoir to said second reservoir, and a drain valve device disposed between said compressor and said first reservoir and having a fluid pressure communication with said second reservoir, said valve device comprising means operable in response to operation of said compressor to establish a fluid pressure communication between said compressor and said first reservoir, means operable in response to the shutting down of said compressor to establish a fluid pressure flow communication from said second reservoir to said first reservoir and from both of said reservoirs to atmosphere to drain moisture from said reservoirs, and time limiting means operable to close the last mentioned communication after a chosen interval of time.

10. In combination, an air compressor having a compressed air discharge chamber, a first reservoir connected to said chamber for receiving and precooling fluid under pressure delivered by said compressor, a fluid pressure storage reservoir, and a pressure limiting cut-oil valve device disposed between and connected to said reservoirs, said valve device comprising a first means controlling a communication between said reservoirs and a second means for rendering said first means operable in response to a chosen diflerential between the pressures in said first reservoir and in said storage reservoir to efiect a flow of fluid under pressure from said first reservoir 60 said storage reservoir, and for actuating said first means for closing said communication upon a reduction in said differential to a degree lower than said chosen diflerential.

11. In combination, an air compressor having a compressed air discharge chamber, a first reservoir connected to said chamber for receiving and precooling fluid under pressure delivered by said compressor, a fluid pressure storage reservoir, a pressure limiting cut-ofi valve device disposed between and connected to said reservoirs, said valve device comprising a first means controlling a communication between said reservoirs and a second means for rendering said first means operable in response to a chosen differ-- ential between the pressures in said first reservoir and in said storage reservoir to effect a fiow of fluid under pressure from said first reservoir to said storage reservoir, and for actuating said first means for closing said communication upon a reduction in said difierential to a degree lower than said chosen difierential, and means operable upon shutting down of said compressor to disconnect said first reservoir from said chamber and open said chamber to atmosphere and to also establish a fiuid flow communication from said first reservoir to said storage reservoir.

12. In combination, an air compressor comprising a discharge valve disposed in a discommunication-between said cooling means and reservoir and responsive to a lower dill'erential to close said-communication.

18. In combination an air'compressor. a flrst reservoir for cooling ,fluid under pressure compressed by said compressor. a second reservoir for storing fluid under pressure, means operable upon shutting down of said compressor to establish a fluid flow communication from said first reservoir to said second reservoir for equalizing pressures in said reservoirs, and means operable in response to substantial equalization oi. pressures in said reservoirs to unload said compressor.

14. In combination, an air compressor. a first reservoir for cooling fluid under pressures compressed by said reservoir. a second reservoir for storing fluid under pressure, means operable upon shutting down of said compressor to equalize pressures oi fluid in said reservoirs. and means operable in response to substantial equalisation of pressures in said reservoirs to drain moisture from said reservoirs.

15. In combination, an air compressor. a first reservoir for cooling fluid under pressure compressed by said reservoir, a second reservoir for storing fluid under pressure, means operable upon shutting down 01' said compressor to equalize the pressures of fluid in said reservoirs. and means operable in response to shutting down of said compressor and the equalization oi pressures in said reservoirs to unload said compressor and momentarily open a liquid drain irom said reservoirs.

BURTON S. AIKMAN.

REFERENCES CITED The following references are of record in th file of this patent:

UNITED STATES PATENTS Dewitt Feb. 22, 1946