US2895423A

US2895423A - Variable capacity pump

Info

Publication number: US2895423A
Application number: US606771A
Authority: US
Inventors: Guy T Shoosmith
Original assignee: Plenty and Son Ltd
Current assignee: Plenty and Son Ltd
Priority date: 1955-08-31
Filing date: 1956-08-28
Publication date: 1959-07-21
Anticipated expiration: 1976-07-21

Description

July 21, 1959 G. T. sHoosMl'rH 2,895,423

' VARIABLE 'CAPACITY'PUMP Filed Aug. 2s. 1956 A ttarne United States Patent C) VARIABLE CAPACITY PUMP Guy T. Shoosmith,` St. Mary Bourne, England, assigner to Plenty and Son Limited, Newbury, England Application August 28, 1956, Serial No. 606,771 Claims priority, application Great Britain August 31, 1955 3 Claims. (Cl. 10S-120) This invention relates to variable capacity pumps of the sliding vane type.

Because of the alternating pressure and suction in the pumping spaces or chambers of such pumps, the sliding block which bounds those chambers and the eccentricity of which relatively to the rotor governs the stroke of the vanes and consequently the capacity of the pump is subjected to cyclic pulsations. These are transmitted to the screw control gear through which the sliding block is adjusted. In pumps of small capacity operating at low pressure, the pulsations are of small magnitude and of no great consequence. In pumps of large capacity operating at high pressure, however, they are large. For example, in a pump designed to deliver 400 tons an hour at 300 lb. per sq. in., they can be of the order of 40 tons and the screw control gear has to be designed to enable it to be operated when subjected to an alternating force of 40 tons having a periodicity of four times the shaft revolu` tions.

It is therefore an object of the invention to -relieve the screw control gear of all or a substantial part of the loading resulting from the cyclic pulsations so that it does not have to be made cumbersome, expensive and heavy to operate.

Another object is to provide a variable-capacity pump wherein the cyclic pulsations of the sliding block are liquid-damped.

A further object of the invention is to provide an hydraulic damping system for the sliding block of a variable capacity pump which is simple and comparatively inexpensive.

Yet another object is to prove an hydraulic damping system for the sliding block of a variable capacity pump which does not hinder variation of the capacity of the pump when such variation is desired by the pump operator.

According to the invention, the sliding block is made a good sliding fit in the body of the pump so that on either side of it there are sealed chambers. These chambers are lled with a liquid (generally oil), and are interconnected by a passage containing an adjustable throttle valve. The liquid thereby serves to damp out the cyclic pulsations of the sliding block.

In order that the invention may be thoroughly understood, a variable-capacity pump in accordance with it will now be described with reference to the accompanying drawing which shows the pump in partial cross-section with parts broken away for the sake of clarity.

It will be seen that the pump comprises a pump body or housing 8 having a suction passage or inlet 9 and a delivery passage or outlet 11. Within the housing 8 there is mounted for rotation a rotor shaft 10 having a pair of slots 12 lying on ydiameters of the shaft in which are mounted to slide a pair of vanes 14. The ends of the vanes 14 bear on plane surfaces 16 formed on the interior of the rotor proper shown at 18.

The rotor 18 is mounted Within a bearing sleeve 20 carried by a. cage or sliding block 22 mounted for rec- 2,895,423 Patented July 21, 1959 lice tilinear, vertical movement along the slides 23 formed on the inside of the pump housing 8. The sliding block 22 has straight outer surfaces which bear on the slides 23 and is a good sliding fit. As will be seen, vertical displacement of the sliding block 22 varies the extent of the sliding movement of the vanes 14 and, therefore, the capacity of the pump. This displacement of the cage is effected through a capacity-adjusting control spindle 24 which extends up through the pump housing and which can be rotated by means of the screw-wheel 25.

Above and below the sliding block 22 there are formed two sealed

chambers

26, 28 each of which is bounded on one of its sides by the sliding block. These

chambers

26, 28 are inter-connected by a pipe 30 which is provided with an adjustable throttle valve 32 and, at its highest point, with an air cock 34. The two

chambers

26, 28 and the interconnecting pipe 30 are filled with a liquid, usually oil. As will be seen the

chambers

26, 28 are entirely separated from the suction and delivery passages 9, 11 by

mating portions

27, 29 of the sliding block 22 and the pump housing 8.

Thus, by adjustment of the valve 32, the pulsations transmitted through the sliding block 22 to the liquid can be damped out either entirely or to any desired extent, and the

screw control gear

24, 25 can thereby be relieved of any undesirable loading.

By closing the valve 32 altogether, a complete hydraulic lock can be produced and the pump will normally be operated in that condition when working on a fixed stroke. When the stroke of the pump is to be altered, the valve 32 is opened to some extent so that liquid can be transferred from one chamber to the other but so that the cyclic vibrations are damped out or reduced so as not to interfere with the operation of the screw control gear.

It is of importance that the hydraulic circuit comprising the two

chambers

26, 28 and the passage 30 connecting them should be free from air and this is the reason why an air cock 34 is provided at the highest point in the circuit. As the liquid may contain entrained air, the air cock 34 may have to be left open for a considerable period before all the air is expelled.

I claim:

1. A variable capacity pump comprising a hollow pfump body, a suction passage and a delivery passage in said pump body, a sliding block slidably mounted within said pump body, a rotor shaft rotatable within said pump body, means mechanically connected to said sliding block and arranged externally of said pump body on an upper portion thereof for slidably moving said sliding block whereby to alter the relative positions of said sliding block and said rotor shaft, sealed chambers on either side of said sliding block Within said pump body, each of said sealed chambers being bounded on one side by said sliding block, portions of 'said pump body and said sliding block sealingly preventing at all times communication between said sealed chambers and said suction passage and said delivery passage, a passage inter-connecting said sealed chambers, a throttle valve in said inter-connecting passage, valve adjusting means independent of said means rnechanically connected to said sliding block for adjustably moving said throttle valve into a plurality of throttling positions and into one position wherein said valve closes said interconnecting passage, said valve adjusting means being adapted to maintain said throttle valve fixed in any position to which said valve is moved irrespective of variations in the fluid pressures in said pump body, said sealed chambers and said inter-connecting passage being lilled with liquid whereby cyclic pulsations of said sliding block are damped out.

2. A variable capacity pump comprising a hollow pump body, a suction passage and a delivery passage in said 3 pump body, 'a rotor shaft within said pump body, slots in `said rotor shaft, sliding vanes ,slidably mounted within said slots, a sliding block slidably mounted within said pump body, a rotor body rotatably mounted within said sliding body, bearing surfaces internallyfdisposed on 'sai'd rotor body, bearing :surfaces fon the 'ends lof "said 'sliding vanes :in sliding lengagement with said bearing surfaces of said rotor body, 4means mechanicallyconnected to said sliding block and arranged externally of 'said pump body on an upper portion thereof for slidably movingsaid sliding :block whereby to alter fthe relative positions of said sliding block-and said irotor shaft, a^sealed chamber immediately above said rsliding block and bounded on-one side by said sliding block Awhereby movement of Asaidblock varies the capacity of said chamber, a second sealed chamber immediately below said ysliding block and bounded'on one side by said sliding block whereby movement of Vsaid lblock varies the :capacity of said second chamberrinversely-as the capacity of said Erst-mentioned sealed chamber is varied, Aportions of said pump body vand said sliding block'matingwith each other whereby to separate at all .times said sealedl chambers from said suction passage and said delivery passage, .a tubeconnecting said sealed chambers together, a throttle valve in said rtube, valve adjusting means independent of said means mechanically connected to said sliding block 'for adjustably moving said throttle valve into a plurality of throttling positions and into one position wherein said valve closes said tube, said valve-adjusting means being adapted .to maintain said throttle valve xed in any position to which said valve is moved irrespective of variations in the fluid pressures in said pump body, an air-cock in said tube and located at the highest point thereof, 'said sealed chambers and said connecting tube being filled with oil whereby cyclic pulsations of said sliding block are damped out.

3. A variable capacity pump as -claimed in claim 2 wherein said valve-adjusting means are operable solely through a manually-actuated :member :located lexternally of said pump body.

References Cited in the file of this Apatent UNITED STATES PATENTS 1,370,810 Hansen Mar. 8, 1921 1,467,837 Colebrook Sept. 11, 1923 2,296,876 Samiranet al Sept. 29, 1942 2,330,558 -Curtis Sept. '28, 1943 2,678,607 Huferd et al. May `l8, 1954 2,684,636 Heldenbrand J uly 27, l1954 2,724,339 'OConnoret al Nov. 22, 1955 2,823,614 Lapsley Feb. 18, 1958 FOREIGN yPATENTS 414,752 "Great :Britain Aug. 9, 1934 609,906 AGreatBritain Oct. l8, 1948