US2478213A

US2478213A - Unloading valve for hydraulic pumps

Info

Publication number: US2478213A
Application number: US522843A
Authority: US
Inventors: Towler John Maurice; Towler Frank Hathorn
Original assignee: Electraulic Presses Ltd
Current assignee: Electraulic Presses Ltd
Priority date: 1943-03-15
Filing date: 1944-02-17
Publication date: 1949-08-09
Anticipated expiration: 1966-08-09

Description

1949. J. M. TOWLER ET AL UNLOADING VALVE FOR HYDRAULIC PUMPS Filed Feb. 17, 1944 I WW 1 l Alll tatentecl Aug. 9, 1949 UNLOADING VALVE FOR HYDRAULIC PUMPS John Maurice Towler, Harrogate, and Frank Hathorn Towler, Otley, England, assignors to Electraulic Presses Limited, Rodley, England Application February 17, 1944, Serial No. 522,843 In Great Britain March 15, 1943 6 Claims. 1

This invention relates to an unloading valve for use with either a single reciprocating ram pump having two or more rams or with a plurality of single or multi-ram pumps, said valve being of the kind embodying a valve member in the form of a sliding plunger which is moved against a predetermined load by hydraulic pressure to unload in sequence either the pump chambers of a multi-ram pump or to unload, also in sequence, a group of two or more pumps by bypassing the delivery of each such pump in turn. An unloading valve of this character is described in the specification of our U. S. Patent No. 2,247,261.

One of the principal uses of an unloading valve of the kind with which this invention is concerned is to enable a predetermined pressure to \be maintained in a hydraulic system supplied with pressure liquid by one or more continuously running pumps.

One such system is one which embodies a moulding press in which the work has to be maintained under full pressure for an appreciable period. Theoretically, when the full pressure behind the press ram has been reached, such pressure should be maintained without further pumping, but in practice there is always a cer tain amount of leakage of pressure past the ram so that unless make-up liquid is occasionally supplied, the pressure behind the ram will slowly fall.

The unloading valve of our prior patent will automatically operate to compensate for this leakage but in doing so the valve plunger is free to move sufficiently to load all the pump chambers or pumps in the series whereas it is only required that one of said chambers or pumps shall be momentarily loaded to restore the pressure to the figure required.

As soon as loading occurs the resulting build up in pressure in the system will at once move the plunger in the unloading direction and by reason of the freedom of movement above referred to and the resulting sensitiveness of the plunger to variations in pressure in the operating liquid the tendency will be for the plunger to dither or oscillate rapidly.

The object of the present invention is to provide means in an unloading valve of the type specified which will limit the loading movement of the valve plunger when full pressure has been attained so that only the required number of pump chambers or pumps necessary to supply occasional make-up liquid to compensate for normal leakage will be loaded, the remaining one or more pump chambers or pumps remaining unloaded until fall in pressure has occurred which is substantially greater than could result from normal leakage. y

7 An unloading valve according to the present invention has means which necessitates a substantial rise in the pressure of the operating liquid to effect the last part of the unloading stroke of the valve plunger whereby said valve plunger is rendered capable of moving to load at least one of the pump chambers or pumps against an opposing pressure, afiorded by the operating liquid, which is substantially greater than the pressure which the plunger is capable of moving against to load the remaining one or more pum chambers or pumps so that said first mentioned pump chamber or pump can 'be cut in and out rapidly to supply make-up liquid to a hydraulic system, for example to counteract normal leakage, with the other one or more pump chambers or pumps remaining unloaded.

In the preferred embodiment of the present invention the means above referred to consists of a piston of larger area mounted on and so as to have independent movement relative to a ram of smaller area, the first part of the valve plungers unloading stroke being effected by both the piston and ram acting together and the last part of the same stroke by the ram alone whereby a rise in the pressure of the operating liquid has to take place before the smaller area ram can overcome the pressure opposing the valve plunger so that whereas the opposing pressure can force the valve plunger and ram back against said higher pressure to load the pump chamber or pump that was last to be unloaded, a substantial fall in the pressure of the operating liquid must occur before said load can force the valve plunger and piston back owing to the larger area of said piston.

In a further embodiment of the invention the means specified consists of an additional spring load which comes into action to supplement the opposing efiort of a main spring only during the last part of the unloading movement of the valve plunger, so that again a substantial increase must occur in the pressure of the operating liquid before the plunger can be moved to overcome the additional load. Said additional load will act to move the plunger in the return direction against the increased pressure to load the number of pump chambers or pumps required to supply the make-up liquid, but, as in the first embodiment, the remaining pump chambers or pumps will 3 remain unloaded until a substantial fall in the pressure of the operating liquid takes place.

In the drawings:

Fig. 1 is a vertical longitudinal section through a valve according to the invention.

Fig. 2 is a vertical longitudinal section through a portion of the valve illustrating a. modifiedembodiment of: the invention.

In Fig. 1, the pump illustrated comprises a pump body I which is bored to provide three pump bores 2, 3 and 4.

On opposite sides of each pump bore and at the inner end thereof are situated two: transverse outlet passages, the passages 55-, W and- B being the normal discharge outlet for the pumped liquid to pass the delivery valves atoa commondelivery main b and the opposing passages 8; 9: and ll) being the by-pass passages.

The by-pass passages open into a transverse bore H in the pump body which is machined to receive a packingless piston: valve [:2 Withi a fit which while permitting. the piston: valve: to move freely thereinwill= yet prevent the: leakagesof; the pressure liquid.

The'spindle; which constitutes the piston valve has a passage l3 extending longitudinally through itsv centre, whichpassagei's open at both ends: toexhaust.

In the example: illustrated the valve spindle is provided with three" circumferential reduced portions I' l, l5 and t6;- These reduced. portions are connected by radial passages t1; with the hollow centre passage 13 of. the valve spindle;

The piston'valve is showndn; the drawing. in its partially open. positionbut. is normally held. in the closed position by aspringi l9= which acts against the open or exhaust end of. the valve through a thrust washer 2:05. the load on the: spring, being adjusted by a screwor-other means. not.- shown.

With the construction above: described endwise movement of the: piston valve against the spring l9 brings. the; reduced portions :4, l5 and H5 inturnintoregistration: with the open. ends of the by-pass passages 8 9 and I'll respectively thus placing the corresponding, pump bores in communication with the passage t3- inv the valve and so to exhaust.

The reduced. portions ofthevalve spindle are so arranged that, as the. valve is made to traverse the by-pass passages by the actuating ram the passage 8 is first uncovered tosuch anextentthat the pressure in the associated pump bore is not sufiicient to lift the delivery valvea and therefore that pump ram stops. pumpingt As the. pressure rises in the delivery main 11,, the spindle is moved further over so. as completely to unload the pump bore 2 and the second reduced. portion l5 of the spindle begins to uncover. the intermediate by pass passage 9 connected to the intermediate pump" bore 3 so that the pressure in that pump bore isreleased to such an extent that the inter mediate ramv ceases to pump. Finally, as the pressure in the delivery main increases still further, the valve spindle ismoved' partially to uncover the third by-passage Ill, thereby reducing the delivery of the third ram up to such a point that it ceases pumping. As the pressure drops, the sequence is reversed until the three rams are pumping again.

The endwisemovement of the piston valve I-Z'is eflected intwo stages by two independently mov-- able pistons 2| and 22" of difierent areas. The larger piston 21 is'mounted on the smaller'piston' 22 along which it is free to slide and within a cyl' i'niler 23, the interior of which is open by means of inlet 24 with the delivery main of the pump or pumps to be controlled. The piston 2| acts with the piston 22 to perform the first part of the unloading stroke of the plunger. The position of the valve plunger at the end of this partial unloading stroke is shown in the drawing and in this position; the two near bores 2 and 3 are unloaded whilst the third bore is still loaded-L As the area of the piston 22 is less than the area of the piston 2! a correspondingly greater pressure will be required to move it. When this pressure in the cylinder 23, has, however, been reached the piston 22 will operate independently of the piston 2F to move the valve plunger to unloadthethird pump bore 4.

Asa resultoi. thesmaller area of the piston 22 the: spring; It is capable of moving the plunger back to load the third pump bore 4 against the increased pressure of the, operating liquid but further return movement of the plunger to load the remaining: pump chambers: cannot. take:- place until thepressure of the operating liquid. has fallen to a substantial extent owing to' the: higher resistance oilered by the larger area of the. piston: 2|

Inthe modified embodiment shown inv Fig; 2 the-same efiect can beattain'ed by dispensing. with the piston 21 andiusing asingle piston,- and. providing an additional spring 25 of shorter length than the spring t9 which additional spring. is compressed to supplement the opposing force of the main spring l'9 only during the latter part of the valve plungers stroke. To move the: valve plunger to unload the third pump bore will thus require a rise inpressure inthe cylinder 23 and the return movement of the valve plunger to load the secondv and first pumpbores will not take place until the pressure of the liquid has fallen considerably.

Although in the above description the unloadi'ng valve has been described as being used for unloading the pump chambers of a single multiram pumpit is equally capable of use in' unloading in sequence two or more pumps. The only material alteration in the construction. of the valve is that the valve plunger is mounted in a separate valve block having two or more chambers each connected to the delivery manifold of a pump; Thus when the part communicating with the delivery of the pump is opened the delivery of that pump is by-passed to the pump reservoir or in other words is unloaded.

The supply of pressure liquid to the cylinder which actuates the unloading valve may be effected in various manners, without departing from this invention. Furthermore, a number of unloading valves constructed as described in the previous embodiments may be made tooperate in sequence, when actuated bya' common pressure supply, by making" the actuating pistons of different area or'making; theopposlng springs of different strength.

What we claim is? I. An unloading valve" for a plurality of pressure liquid delivery chambers connected to a de livery main, comprising a bore open' toexhaust, passages communicating with said bore, and con-' nected to said chambers; a valve plunger slid'able in said bore having a passage extending longitudinally therethrough, circumferential reduced portions arranged to register in sequence with said passages in the movement of the plunger said bore and openings connecting said reduced portions with said passage of the plunger, whereby the delivery chambers are sequentially connectable to exhaust to unload the same, said plunger being normally held in a position wherein the reduced portions thereof are isolated from said passages, a plurality of pistons associated with said plunger, at least one of which causes the plunger, upon attainment of a predetermined pressure of the liquid in the delivery main, to move from said normal position thereof through an initial part of its stroke to sequentially cause some of said reduced portions to register with some of the passages aforesaid to unload some of the delivery chambers, and only one of which pistons causes the plunger to effect the final part of its stroke only upon a further and substantial increase in the pressure of the liquid.

2. An unloading valve for a plurality of pressure liquid delivery chambers connected to a delivery main, comprising a bore open to exhaust, passages communicating with said bore and connected to said chambers, a valve plunger slldable in said bore having a passage extending longitudinally thcrethrough, circumferential reduced portions arranged to register in sequence with said passages in the movement of the plunger in said bore and openings connecting said reduced portions with said passage of the plunger, whereby the delivery chambers are sequentially connectable to exhaust to unload the same, means for holding the plunger in a normal position wherein the reduced portions thereof are isolated from said passages, a plurality of pistons respectively of different area, associated with said plunger, at least the piston of larger area, upon attainment of a predetermined pressure of the liquid in the delivery main, causing the plunger to move from said normal position thereof through an initial part of its stroke to sequentially cause some of said reduced portions to register with some of the passages aforesaid to unload some of the delivery chambers, and only the piston of smaller area, upon a further and substantial increase in the pressure of the liquid, causing the plunger to eifect the final part of its stroke, whereby the remaining chamber is caused to be unloaded and loaded while the other chambers remain unloaded.

3. An unloading valve for a plurality of pressure liquid delivery chambers connected to a delivery main, comprising a bore open to exhaust, passages communicating with said bore and connected to said chambers, a valve plunger slldable in said bore having a passage extending longitudinally therethrough, spaced circumferential ree duced portions arranged to register in sequence with said by-pass passages in the movement of the plunger in the bore and openings connecting said reduced portions with said passage of the plunger, whereby the delivery chambers are sequentially connectable to exhaust to unload the same, means for resisting movement of the plunger from a normal position wherein the reduced portions of the plunger are isolated from the passages, means associated with the plunger comprising a plurality of pistons of different crosssectional areas, at least one of which is operable in response to a predetermined increase of the pressure in the delivery main and moves the plunger from said normal position thereof in opposition to said movement resisting means, and means effective at a predetermined point of the unloading stroke of the plunger to increase the resistance to the movement of the plunger whereby a further increase in the pressure of the liquid is required, to further move said plunger, the said piston of smaller area. efiective only upon a fur- '6 ther increase in the pressure of the liquid, moving the plunger to effect the last part of its stroke for unloading the delivery chambers.

4. An unloading valve for a plurality of pros sure liquid delivery chambers connected to a delivery main, comprising a bore open to exhaust, passages communicating with said bore and connected to said chambers, a valve plunger slidable in said bore having a passage extending longitudinally therethrough, circumferential reduced portions arranged to register in sequence with said passages in the movement of the plunger in said bore and openings connecting said reduced portions with said passage of the plunger, whereby the delivery chambers are sequentially connectable to exhaust to unload the same, means for holding the plunger in a normal position wherein the reduced portions thereof are isolated from said passages, a cylinder open to the pressure of the liquid in the delivery main, a piston in said cylinder associated with the plunger for causing this latter to perform part of its unloading stroke upon a predetermined increase in the pressure of the liquid in the delivery main, and a second piston of smaller area in the cylinder independent of the first piston and associated with the plunger for causing this latter to complete its unloading stroke only upon a further and substantial increase in the pressure of the liquid.

5. In combination with a plurality of pressure liquid delivery chambers connected to a delivery main, an unloading valve comprising a plurality of inlets communicating with said delivery chambers, a reciprocable plunger adapted to sequentially connect said inlets to exhaust and normally maintained in a position to close said inlets, a piston for moving said plunger from said normal position thereof through an initial part of its stroke upon attainment of a predetermined pressure of the liquid in the delivery main, to sequentially connect some of the inlets to exhaust to unload some of the delivery chambers, and a second piston independent of said first named piston for moving the plunger to effect the final part of its stroke only upon a further and substantial increase in the pressure of the liquids, whereby to cause at least one of the delivery chambers to be unloaded and loaded while the other chambers remain unloaded.

6. In combination with a plurality of pressure liquid delivery chambers connected to a delivery main, an unloading valve comprising a plurality of inlets communicating with said delivery chambers, a reciprocable plunger adapted to sequentially connect said inlets to exhaust to unload said delivery chambers and normally maintained in a position to close said inlets to load said chambers, and means responsive to the pressure of the liquid in the delivery main and loading means associated with the plunger cooperating to cause the plunger to effect its stroke in two distinct stages as substantially diiferent pressures of the liquid, whereby to cause the plunger to unload and load at least one of the chambers while the other chambers remain unloaded, said means comprising two pistons, associated with said plunger and mounted for conjoint and relative movement, said pistons being actuable together to effect the stroke of the plunger in its first stage, and only one of which is actuable to effect the stroke of such plunger in its second stage.

JOHN MAURICE TOWLER. FRANK HATHORN TOWLER.

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