US2834295A

US2834295A - Pneumatic liquid pressure pump

Info

Publication number: US2834295A
Application number: US481443A
Authority: US
Inventors: Hjarpe Eric Georg
Original assignee: Svenska Kullagerfabriken AB
Current assignee: SKF AB
Priority date: 1954-01-20
Filing date: 1955-01-12
Publication date: 1958-05-13
Anticipated expiration: 1975-05-13

Description

May 13, 1958 E. G. HJARPE, 2,834,295

PNEUMATIC LIQUID PRESSURE PUMP Filed Jan. 12, 1955 TOATMOSPHERE United States Patent 2,834,295 PNEUMATIC LIQUID PRESSURE PUMP Eric Georg Hji irpe, Goteborg, Sweden, assignor toAktiebolaget Svenska 'Kullagerfabriken, Goteborg, Sweden, a corporation of Sweden Application January 12, 1955, Serial No. 481,443

Claims priority, application Sweden January 20, 1954 Claims. (Cl. 103-49) The present invention relates to a liquid pressure pump in which liquid pressure is obtained by permitting air pressure to act alternately on two-pistons which each actuate a pump piston in such a manner that pressure liquid is obtained at a constant pressure and temperature and in which the capacity will always adjust itself automatically at each moment in accordance with the consumption of pressure fluid for the time being.

The device according to the invention is provided with a plurality of differential pistons arranged to operate mechanically independent of each other in separate cylinders, the said pistons being subjected at one outer end surface to pressure from a gaseous pressure medium and acting with their other outer end surfaces upon a liquid. The purpose of the invention is to provide a device of this kind which operates satisfactorily even when such great quantities of liquid'are consumed that the working stroke of the pump takes place during a shorter period than the return stroke and is characterized mainly thereby that the pistons are governed by a distributing valve or valve system common to all of the pistons, the said valve system being in communication with the cylinder chamhers in such a manner that at least one of the. pistons always carries out complete working strokes of constant length while the other pistons carry out only such part of a complete working stroke as is required to maintain the pressure or pumping action during the period required for the first-mentioned piston to carry out its return stroke and begin a new working stroke;

The accompanying drawing shows diagrammatically and in partial section, a form of a device according to the invention. a

The device comprises a cylinder and valve casing or pump body 1 submerged in a liquid container 2 containing liquid 3 which by way of valves 4 and 5 canflow into two lower chambers 6 and 7 in the valve casing or pump body 1. From the chambers 6 and 7 the liquid can flow to an upper chamber 8 through valves 9 and 10 respectively. The chamber 8 is, for example, connected through one or more pipes to the manoeuvre members i which control the movements of a machine (not shown) which is to be actuated by hydraulic pressure.

The smaller pistons of two differential reciprocating pistons 1112 and 1314 are, respectively, in direct ber thus operates the piston valve, in a manner to be explained. a

Two end chambers 21 and 22 of the piston valve 19 are in communication with the air pressure line 20 through narrow channels 24 and 23, respectively. An

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adjustable needle valve 24 restricts flow of air from air pressure line 20 to end chamber 21, and a like adjustable needle valve 23 regulates the volume of air passing to and from end chamber 22' by way of channel 23. A by-pass valve 34 is so adjusted relative to needle valves 23 and 24 that a reduced pressure only is available in the chamber 21. The piston valve 19 is of magnetic material, hence is subjected to the influence of two permanent magnets 25 and 26 located in end chambers 21 and 22, respectively, and can thus be retained in either of its end positions until the air pressure on the piston valve overcomes the magnetic pull. The air pressure line 20 to both valve chambers 27 and 28 of the piston valve divides into two branches 29 and 30 which open into the piston valve at a greater distance from each other than the length of the central piston 31 .of the piston valve. For this reason, both cylinder chambers 15 and 16 can never be cut off simultaneously from the air pressure line 20.

The differential pistons 1112 and 1314 are lifted by air pressure admitted through

chambers

43 and 46 to small auxiliary pistons 32-33 (of which several, for example 3, are provided for each differential piston) as soon as the respective cylinder chambers 15 or 16 are put into communication with the atmosphere through the piston valve 19. When the piston 14 approaches its lower position, the valve chamber 22 is put into communication with the atmosphere through channels 35-40, the cylinder chamber 37 and a channel 39, of which the latter leads to the atmosphere. The

cylinder chambers

36 and 37 are continuously in communication with the atmosphere through the

channels

38 and 39. These chambers are therefore always pressureless, whereby all risk that air can leak between the pistons 11 and 13 and their cylinder walls is eliminated.

The device functions as follows.

In the position in which the piston valve 19 is shown in the drawing, air pressure is communicated from the line 20 through the channel 30, valve chamber 28 and channel 18 to the cylinder chamber 16 and forces the piston 14 downwards.

The liquid under the piston 13 is thus subjected to a pressure, the magnitude of which depends upon the pressure of the air in line 20 and the ratio of the areas of the pistons 14 and 13. As pressure liquid is withdrawn from the pipes (not shown) connected to the chamber 8, other liquid flows from the chamber 7 through the valve 10 to the chamber 8. When the diflFerential piston 1314 has been forced down so far that the upper reduced end of the auxiliary piston 33 opens a channel 40 from the valve chamber 22, the latter will be put into communication with the atmosphere through the cylinder chamber 37 and the opening 39-and will thus become practically pressureless by reason of the needle valve 23 which limits flow of air to chamber 22 from compressed air line 20. The piston valve 19 will then be moved to its right hand end position against the permanent magnet 26 by the air pressure in the valve chamber 21, whereby the cylinder chamber 16 will be put into communication with the atmosphere through the channel 18, valve chamber 28 and a port 41 in the walls of the piston valve chamber.

Under the influence of the pressure of the air in the cylinder chambers 42, the differential piston 13-14 will now be moved upwards by the auxiliary pistons 33 and the valve 10 will close of its own weight. Hereby the valve 5 will be opened partly by the static pressure of the liquid 3 in the container 2 and partly by the suction created in the chamber 7 as the piston 13 moves upwards.

During the above described movement towards the right of the piston valve 19, the cylinder chamber 15 Was put into communication with the air-'pressuruiie 26 through the channel 29, valve chamber 27 and the channel 17. Before the channel 30 was closed by the central portion 31 of the piston valve 19, both cylinder chambers and 16 were momentarilyiu' cc riruniea tion with the air pressure line 20. Thus a'dr'op inpre'si sure of the liquid in the chamber 8 upon movement of the piston valve 19 from one end position to the'ot her is prevented, even if liquid is simultaneously beingwithdrawn. Through the action of air pressure "in thecyl irider chamber 15 the piston 11-12 is forced downwards. The liquid under the piston 11 is then subjected to the same pressure already existing in the chamber 8 and as long as liquid is being withdrawn therefrom to the ma chine cylinders, the differential piston 11-12 will sink, thereby forcing liquid from the valve chamber 6 through the valve 9 to the chamber 8.

. The downward movement of the ditfer'ential piston 11-12, or if no liquid is being withdrawn from the chamber 8, static pressure on the liquid in the chamber 6, is maintained only for the length of time required'fo'r the differential piston 13-14 to reach its upper end position and begin its new work stroke. This'will occur when the auxiliary pistons 33 have attained a position in which a longitudinal groove 47 in each piston 33 opens a channel 40 and the pressure air from the cylinder 42 passes through the groove 47 'and the channels 40 and 35 to the valve chamber 22, where it forces the piston valve 19 towards the left to its other end position. This is possible because of the reduced pressure in the end chamber 21, governed by the relief or by-pass valve 34, and the restricting action of needle valve 23 which limits flow of air from end chamber 22 by way of passage 23. The'differential piston 13-14 thus always makes a complete stroke no matter whether small or large quantities of liquid are being withdrawn from the chamber 8. The differential piston 11-12 on the other hand serves mainly to maintain the pressure in the chamber 8 during the time required for thereturn stroke of the differential piston 13-14.

If no liquid is being withdrawn during the return" stroke of the diiferenti'al piston 13-14, the differential piston 11-12 will be practically immovable duringthis time. The only movement required will be to compensate for leakage.

The piston valve'19 has now assumed the position above described and the differential piston 13-14 is again moving downwards or is maintaining the pressure in the chambers 7 and 8. I

In this position of the piston valve 19, the cylinder chamber 15 is in communication with the atmosphere through the channel '17, the valve chamber 27 and the port 44. The air-driven auxiliary pistons 32 force the differential piston 11-12 upwards to its upper end position where it will remain until the'differ'ential piston 13-14 has completed its working stroke and the piston valve 19 is thereby moved in the manner described. As long as liquid is being withdrawn from thechamber 8 the device will continue to function at thespeed required to maintain a pr essure'in the chamber 8 which corresponds to the pressure of the compressedair source and the ratio of the areas of the dilter'ential pistons. As soon as liquid is no longer being withdrawn from the chamber 8 the device will-stop with at le'ast one iston acting upon the contained liquid to mai'ntainthe constant pressure for which the device has been "adjusted. At each withdrawal from the chamber 8 one of'the'pi stc ns 13-14 or 11-12 will carryout'the corresponding'movement. By adjusting a reducing valve-45in the 'air'*p'ressure line 20 to a pressure corresponding "to a certain pressure on the liquid this latter can beadjusted' as required.

I claim:

1. A- pneumatically operated liquid pressurei puinp including, in combination, a'connection to a source of compressed air; a valve body carrying said connection;

a pair of cylinders;. a pair of differential pistons reciprocable in said cylinders, each difierential piston consisting of a large piston and a small piston united together; a pressure-responsive piston valve reciprocable in a valve chamber provided in said valve body; means connecting said valve chamber with said source of compressed air; said valve body having air channels leading-from saidva'lve chamber to said cylinders at such points that the compressed air flowing through said channels acts only on the large piston of each differential piston; the piston valve being so shaped, positioned and proportioned relative to said air channels and said means connecting the valve chamber with 'said source that both cylinders can never be cut off simultaneously from said source; said cylinders and said valve chamber all having exhaust ports to the atmosphere; a plurality of reciproca'bleauxiliary pistons movable in chambers adiacerit said cylinders and connected to said source, said auxiliary pistons being operatively associated with said differential pistons to move'the same in their suction strokes rneans providing channels for flow of air from the auxiliary piston-chambers associated with one differential piston to one end of the piston'valve chamber; a pair of separate liquid chambers, one connected with each of said cylinders and into each of which liquid chambers the small 'piston 'offone o f'the differential pistons moves as the differential piston makes its working or liquid-displaciiig stroke; automatic inlet valves controlling inflow of liquid to said liquid chambers; automatic outlet valves controlling egress of liquid from said liquid chambers to afdi'scharge' outlet; the parts being so constructed and arranged that one of said differential pistons always makes complete working strokes of constant length while the other difierential piston moves through only such part of a complete working stroke as is required to maintain the pressure on the liquid being pumped during the period of thereturn or suction strokeand the initiation of the working stroke of the'first-mentioned differential piston.

2. The'inv ention defined in'claim 1, wherein the piston valve chamber has a permanent magnet fixed in each end, and the piston valve is made of magnetic material, so that when 'the'piston valve approaches close to either end of its chamber it will be magnetically attracted and will move into contact with the magnet-at that end and will remain in that position until pulled away by a superior force exerted by air pressure.

3. "The invention defined in claim 1, wherein the ends of the piston valve chamber have narrow channels communicating with said source, an adjustable needle valve restricting fiow through each such channel, and an adjustable relief valve being provided in a channel connecting s'aidi'ieedle valves.

4. The invention defined in claim 1, wherein the connection to the source of compressed air has a reducing va'lve'which is adjustable so that the pressure on the liquid delivered by'the pump canbe'controlled.

5. 'A pneumatic liquid pressure pump comprising a plurality of separate cylinders; a plurality of diflerential pistons working mechanically independent of each other in said cylinders, each of saidp'istons acting at an outer end'sur face upon a body ofliquid "to withdraw liquid from said body'iof liquid'by'suction on one stroke and to displace'the withdrawnliquid under pressure on the other s;troke;'a'sourceof pneumatic pressure;'mcans connected to "said source and exerting continuous pressure separately on both differential pistons tending to move said pistons in their suction strokes; a distributing valve and pneumatic channels for connecting the cylinders alternately to said source so as to move the pistonsin their working strokes against said continuous pressure and to evacuate the cylinder notso connectedlpreparatory'to-and during the suction .str'okeof 'its pistonf-andmeansresponsive to the movements of one of said pistons for actuating the distributing valve so that the pneumatic pressure reciprocates the last named piston continuously through a full working stroke and the other of said pistons through only such part of a complete working stroke as is required to maintain pressure displacement of the first one of said pistons and initiation of the succeeding pressure displacement stroke of the last named piston.

References Cited in the file of this patent UNITED STATES PATENTS