US2809596A

US2809596A - Pressurized reservoir for cavitationfree supply to pump

Info

Publication number: US2809596A
Application number: US435569A
Authority: US
Inventors: Richard H Sullwold; Louis E Berthelson
Original assignee: North American Aviation Corp
Current assignee: North American Aviation Corp
Priority date: 1954-06-09
Filing date: 1954-06-09
Publication date: 1957-10-15
Anticipated expiration: 1974-10-15

Description

1957 R. H. SULLWOLD ETAL 2,809,596

PRESSURIZED RESERVOIR FOR CAVITATION-FREE SUPPLY TO PUMP Filed June 9, 1954 f I0 T L.- as 28 1 \\\\\\\\\\\;\l\\\\\\\\\ 5.

Richard H. Sullwold a 7 Louis E. Berfhelson INVENTORS AT TORNE Y.

PRESSURIZED RESERVOIR FOR CAVITATION- FREE SUPPLY TO PUMP Application June 9, 1954, Serial N 0. 435,569

4 Claims. (Cl. 103-223) The present invention relates generally to hydraulic pressure systems and pumping means therefore, and more particularly to improvements in such systems whereby cavitation and similar conditions are prevented and eliminated.

In many hydraulic pressure systems, wherein rotary pump means are used for developing suitable actuating pressures, as in aircraft hydraulic systems, conditions in the suction line to the pump frequently give rise to cavitation and similar problems. As i well known, cavitation is inherently an unstable phenomenon and may arise through the lowering of the fluid pressure and the formation of vapor bubbles in a liquid. When such cavities of air and vapor form, the flow conditions are changed to the detriment of the efficiency of the pumping means and that of the hydraulic system. Cavitation is also undesirable inasmuch as it creates pressure waves which are frequently repeated at high frequencies and produce impacts of such itensities that portions of the pump and the adjacent system components may be seriously damaged.

It is known that numerous prior elforts have been made to prevent or minimize cavitation within fluid systems by increasing the suction head to the pump, pressurizing the liquid reservoir or storage container by various means so as to maintain the suction line to the pump under sufficient pressure. The present invention is an improvement upon such systems in that a pressure fluid line is branched off from the high pressure pump discharge to a relatively small diameter piston and cylinder unit mounted upon the wall of the fluid reservoir in such manner as to apply a continuous force upon a floating piston in the reservoir for maintaining the stored fluid under pressure. The improvement resides essentially in a combined liquid storage reservoir to which the pressurizing piston and cylinder is mounted and suitably linked to the floating piston there is an indicating means for showing the amount of liquid within the reservoir at all times. The present invention also resides in the cavitation-free hydraulic system as well as in the details and general arrangement of the improved storage and pressurizin components.

it is, accordingly, a major objective of the present invention to provide an improved hydraulic pressure system in which cavitation of the pump means and adjacent conduits is substantially eliminated. It is a further object to provide an improved liquid storage reservoir with means for its automatic pressurization by the pump means within the system. It is a further object to provide an improved pressurized liquid reservoir of relatively li ht weight, which is positive-acting and foolproof in its operation. A further object resides in providing such a pressurized reservoir which is automatically pressurized by operation of the pump thereby insuring pressure upon the stored liquid Whenever the pump is operating. A still further object resides in the provision of such a pressurized reservoir of the airless piston type tates Patent 6 "ice with means for indicating the amount of liquid stored within the container.

Other objects and advantages of the present invention will occur to those skilled in the art after the reading of the following description, taken in conjunction with the accompanying drawings, forming a part hereof, in which:

Fig. l is a diagrammatic view of a hydraulic pressure actuating system to which an improved form of the pressurized reservoir has been applied; and

Fig. 2 is an enlarged cross-sectional view of the pressurized reservoir shown in Fig. 1.

Referring to Fig. l, the hydraulic pressure system includes the rotary pump 5 discharging into the high pressure line 6 from which a branch 7 is connected to the pressurizing auxiliary cylinder 8. The main discharge line 6 from the pump 5 extends through the pressure relief valve 9 and continues through to the main pressure line 11, the relief line 12 from the valve 9 being connected to the main return line 13 for return of fluid to the main fluid reservoir 10. An indicator 15, to be more fully described below, shows the quantity of fluid in the reservoir at all times. In addition to the return line connection 13 to the bottom of the reservoir 10 it is provided with an outlet for the suction line 14 to the pump 5 and a further line 16 to the pressure relief valve 17 from whence, in the case of an aircraft installation, for example, the relieved liquid may be discharged into a suitable sump provided for such purposes or otherwise passed overboard.

The main pressure line 11 may continue to the fourway rotary selector valve 18 provided with the operating handle 19 for selective connection of the pressure and return lines 11 and 13, respectively, to either of the

lines

21 and 22 extending to the ends of the cylinder of the fluid actuating motor 20. The latter may be pivotally mounted upon suitable supporting structure, as by the pivot 23, and is provided with an internal piston attached to the piston rod 24 pivotally connected to the member to be actuated, such as indicated at 25. 7

Referring now to Fig. 2, the pressurized reservoir assembly 10, having an internal storage space 19a, has mounted thereon the auxiliary pressurizing cylinder 8 supplied through the pump discharge branch 7. The main body of the reservoir 10 is formed by the cylindrical shell or casing 26 which has fitted thereto at its upper end the top head element 27 suitably apertured for the auxiliary cylinder 8, and the casing 26 also has the bottom head element 28 fitted to the bottom thereof. The casing head element 27 is provided with an orifice or passage 27a which serves to vent the space directly beneath the casing head 27 to the atmosphere. The casing bottom 28 is provided with a suitable seal at 2311 as well as the fill and drain plug 2 b, and both

casing heads

27 and 28 may be of hexagonal or other polygonal shape in plan form, being suitably apertured to receive the plurality of tie rods or bolts 29 by which the

end elements

27 and 28 are drawn together by tensioning the bolts 29 for the retention of the casing head on both ends of the casing shell 26.

A main piston element 30 is reciprocably slidable within the internal bore of the casing wall 26, being sealed thereagainst by the O-ring or other seal means 31 and having a transverse diaphragm wall 32. On the underside of the latter, there is formed, or suitably attached, a centrally disposed pin 33 having a lock collar 33a for the retention on the pin 33 of the pivotal link element 34. The link member 34 extends radially from the centrally disposed pin 33 and carries a pivotal connection 34a at its outer end to the folding linkage 35-36. The

links

35 and 36 are intermediately pivoted at 35a, both being of substantially the same length, and the lower end of thelower link 36 is attached to a furthertransverse .pin 37 suitably journalled in the lower head element 28. The pin 37 extends through the outer wall of the head element 28 through a suitable liquid-tight seal and has the pointer 33 of the indicating means 15 secured thereto. The pointer 38, as the piston moves downwardly within the casing bore 26, folding the linkage 3536, is rotated in the clockwise direction from its substantially horizontal full position to its substantially empty position shown in the construction lines in Fig. 2. Suitable graduations may be provided on the quadrant 39 to provide the scale for the indicator 5 as may be shown by the lever 38 serving as the pointer.

I Within the bore of the auxiliary cylinder 8, there is provided the hollow elongated piston 40 of relatively small diameter as compared with the diameter of the main piston 39. The end of the bore of the auxiliary cylinder 8 is suitably plugged by the threaded plug tting 41 and the outer surface of the piston 40 is suitably sealed and made fluid-tight where it passes through the lower hub portions of the cylinder 3 as by means of the Q-ring seal 42. The adjacent hub portion ofthe cylinder 3 is provided with a transversely extending flange 43 by means of which the casing of the cylinder 8 is secured to the undersurface of the main casing head 27 as by the attachment bolts 44. The lower end of the small auxiliary pistion 40 has secured thereto the enlarged diameter flange or plunger portion 45 which is adapted to bear downwardly against the transverse diaphragm or web 32 of the main piston 39.

When the hydraulic system shown in the drawings, is filled with fluid, care must be taken to insure that the storage space 19a within the receiver is completely filled with liquid and all air has been expelled from beneath the main piston 30. It is also essential that when the system is filled all of the lines and the space within the cylinder of the actuating motor 20 as well as the cylinder 3 are all completely filled with fluid and devoid of air. This may be accomplished in a number of ways familiar to those skilled in the hydraulics art and may be done by venting the highest points of the system as well as any other high points in which air might become trapped. As the pump 5 is started it will be seen that it has ample fluid to insure its being properly primed and immediately as the pump delivers fluid under pressure into the discharge line, this pressure is also transmitted through the branch line 7 and is exerted downwardly upon the exposed cross-sectional area of the auxiliary piston 46. This downward force, due to the pump discharge pressure, is exerted by the plunger 45 upon the main piston 3% which transmits this pressure to the upper surface of the liquid stored within the reservoir storage space 10a. The amount of pressurization is determined by the ratio of exposed piston areas as well as the cut-out pressure of the system and may be varied to suit any individual installation.

Any reduction in volume of the liquid stored within the space 10a, 'as well as any reduced pressure due to the starting of the pump 5 and the withdrawal of fluid through the suction line 14, is immediately taken-up and more than compensated for by the increased pressure developed by the auxiliary piston 40 causing the main piston to be moved downwardly and to thereby maintain a pressurized condition within the reservoir 19. In the event of leakage from the hydraulic system or loss from excess pressures relieved through the pressure relief valve 17 causing reduction in the volume of the fluid stored within the space ltla, the piston 3G is automatically forced down upon the reduced volume of the liquid to maintain the desired back pressure or suction head upon the pump 5 to avoid any possibility of cavitation. As the main piston 3i) moves downwardly within the casing 26 of the reservoir 10, air is permitted to enter through the opening 27a into the space above the piston 39 and below the casing head 27 so as not to create a suction which might oppose the force exerted upon the auxiliary piston for pressurizing the liquid. Also as the main piston 30 moves 4 downwardly within the reservoir the pivotally interconnected

links

35 and 36 tend to fold or flatten out indicating their relative position and that of the piston 30 on the indicating means 15. The selector control valve 18 and the fluid actuator motor 20 have been shown and described by way of example only and it will be obvious that the improved anti-cavitation means is applicable for use with other hydraulic components than those which have been illustrated, and in hydraulic systems other than the gen eral type which has been shown.

It will be understood that the modification which has been shown and described is by way of example only, that it simply represents one form of the invention and should not in any way be considered as a limitation thereto. For example, reservoir units of the type disclosed have also been very satisfactorily employed when disposed in a normally horizontal position, such as would be assumed by the unit by rotating Fig. 2 of the drawings 90 in clockwise direction to the lengthwise position with the pressurizing unit to the right. This permits outlet 16 to be disposed at the top left to provide a vent for any air which may have entered the fluid chamber 10a, for which purpose the small recessed space adjacent the outlet 16 within the end member 28 has been provided. In other modifications of the reservoir units round end heads have been provided in place of the polygonal type which has been shown and described. Other forms and modifications of the present invention which will occur to those skilled in the art after reading the foregoing description, are intended to come within the scope and spirit of this invention, as more particularly set forth in'the appended claims.

We claimi l. A pressurized reservoir unit for receiving hydraulic fluid from and supplying the same to a pump in a cavitanon-free arrangement, comprising a cylindrical casing having an internal bore, a primary piston slidable within said cylindrical bore defining a reservoir chamber on one side thereof, fluid connections for the supply of fluid to and from said pump to said reservoir chamber, a secondary cylinder formed by said casing, a secondary piston of lesser diameter than said primary piston slidably mounted within said secondary cylinder and having a portion in engagement with said primary piston, and conduit means in communication with the discharge of the pump and the interior of said secondary cylinder for transmission of fluid pressure to said secondary piston whereby a force is exerted by engagement with said primary piston for the pressurization of the fluid within said reservoir chamber for the minimization of cavitation in the supply of liquid to the pump from said pressurized reservoir chamber.

2. A cavitation-free pressurized reservoir for hydraulic fluid supply to a pump comprising a cylindrical casing having an internal bore, end fittings for enclosing the ends of said cylindrical casing, a floating piston slidable within said cylindrical bore and defining a reservoir chamber on a first side thereof, fluid connections to said reservoir chamber for the supply of fluid to and from a pump, a secondary cylinder of smaller diameter than said internal bore supported from said casing, a piston slidably mounted within said secondary cylinder having a portion in engagement with said floating piston, conduit means in communication with the interior of said secondary cylinder for transmission of fluid pressure from the pump to said secondary piston for the exertion of a force against said floating piston for the pressurization of the fluid within said reservoir chamber for the cavitation-free supply to the pump.

3. A pressurized reservoir unit for receiving hydraulic fluid from and supplying it to a pump in a cavitation-free arrangement, comprising a cylindrical casing having an internal bore, end fittings for enclosing the ends of said cylindrical casing, a free piston slidable within said cylindrical bore dividing said bore into a chamber open to the atmosphere on a first side of said free piston and a reservoir chamber on the second side of said free picton, fluid connections for the supply of fluid to and from said pump to said reservoir chamber within said cylindrical casing on said second side of said floating piston, a secondary cylinder of smaller diameter than said internal bore supported from said casing, a secondary piston slidably mounted within said secondary cylinder having a portion in engagement with said free piston, and conduit means in communication with the discharge of the pump and the interior of said secondary cylinder for transmission of fluid pressure to said secondary piston whereby a force is exerted by it by direct engagement against said free piston on its atmospheric chamber side for the pres surization of the fluid within said reservoir chamber for the minimization of cavitation in the supply of liquid to the pump from said pressurized reservoir chamber.

4. In a pressurized reservoir system, a fixed casing having a cylindrical chamber therein forming a reservoir for the supply of hydraulic fluid to the suction inlet of a pump, a primary piston reciprocable within said fixed c'as ing dividing the same into an unpressun'zed chamber and a reservoir chamber for fluid under pressure, a secondary cylindrical chamber formed adjacent said unpressurized chamber by an intermediate transverse wall extending across said casing, said transverse wall having a central aperture, said secondary chamber communicating with the discharge outlet of the pump to receive high pressure hydraulic fluid therefrom, a secondary piston reciprocable Within said aperture through said transverse Wall and having a portion disposed within said high pressure secondary chamber subjected to said fluid discharge pressure, said secondary piston being in engagement with said primary piston whereby both said pistons move together under the influence of the respective pressures within said high pressure chamber and said reservoir chamber and a fluid pressure of suflicient magnitude is maintained within said reservoir chamber for preventing cavitation in the fluid supply to the suction inlet of the pump.

References Cited in the file of this patent UNITED STATES PATENTS 2,349,253 Edmond May 23, 1944 2,426,320 Messinger Aug. 26, 1947 2,440,065 Ashton Apr. 20, 1948 2,605,716 Huber Aug. 5, 1952 2,673,527 Ashton et a1 Mar. 30, 1954