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IDisptaeameni of pump ond hydrouUc motor ol this voriobla. t% Porollel-pbton variable-displacement pump in which Spaed drive Is chonged by adjusting the wobbler plate W 4 cylinder, barrel with Us pistons rotates with drive \ u'*i. aumo the cylinder barrel with It. pistons swings ,0 rt, drivc th0h ,0 dilJ`' dllchar8 r0'* 4Vorloble-dlptocement wobbler-ploto pump in which the wobblor plots morked W does not rotots with the drive shaft Variable-Displacement Pumps Control Hero'* how to apply variable-delivery pump* to thoie When the pump wobble plate makt (obt where fluid flow mutt be held within close limits. vne-half. revolution its top piston efl have completed Its suction stroke ia Read on--these solid facts will be a big help to you the bottom piston its discharge unit During this period, if pump cod natei By F A ANNSTT, Ctfilnhiliny Editor wobblers have the same angle, tha.'aw tor shaft makes half a revolution, li doing this the motor's top piston atbfn Dlscharc* of centrifugal pumps can be adjusted by throttling, if thoy run et constant speed, but output of con* slant-delivery pumps cannot be ihroi* tied. If their discharge has to be adjusted, pump must provide some means for doing this. About every type of constant-delivery pump has been de veloped in variable-displacement de signs. These include rotary-piston, plunger, rotary, diaphragm and pulsat ing types. Rotary-piston pumps are made in several designs for variable-displace ment service. They are used as part of voriable-speed power transmissions for stokers, paper machines, machine toola, and many other units, and to supply pressure fluid to hydraulic cylinders in presses, ship-steering gears, steel-fur nace chargers, bulldozers and other ap plications. These pumps are of two gen eral designs: parollel-pision and radialpiston. Parallel-Piston Typos. Fig. 1 Is a cross-section of a hydrautio variablespeed transmission and torque converter. It has a variable-displacement multipis- ton pump, which delivers oil to a var iable-displacement fluid motor of the tame design. The piston barrels do not rotate, nor are the pistons connected to wobble plates IP. Free ends of the pis tons ore spherical and ride against rtag R that rests against a ball-thrust bear ing on the wobble plate. A small makeup pump, driven by the input shall, supplies oil from a reser voir for charging pump's pistons to hold them on their return stroke agtinst wob ble-plate face. It also supplies oil lost by piston leakage or slippage in the closed circuit between pump and mo tor. Oil not required to replace the leakage is bypassed through a relief valve and used to lubricate the wobbler end bearings of pump and motor. Eccentric on* pump and motor shafts actuates circular valves V to control oil flow from pump to motor. These valves do not rotate but ore given a gyrating motion as the shafts turn, to open ond close ports leading to pump and motor cylinders. How It Works. In Fig. 1 the pump's bottom piston has completed its suction stroke, and the top one its discharge stroke. The path of this discharge is Indicated by arrows to the top piston, which has completed its driving stroke. to full discharge and its bottom pistoe to full driving position. If pump's wobbler is set at so stifle to give its piston one-half tbe stroke length of the motor, the motor shell rotates at one-half pump speed, but out put torque is double input torque. Bui' if pump's wobbler it set for full stroke and that of motor for half stroke, motet speed will be double pump speed, snd motor will develop oae-haU the torque of the pump. Hydraulic-control tneeb anlam regulates angle of wobbler pistes.' Tilting Plate. In the pump, Fig V the cylinder barrel with its pistons ro-' tales with drive shaft. It consists ol s 1 lihing-boi T in which socket ring ff j ' revolves. Box T is held stationary by sj connection to control worm C. Socket 1 ring R connect# to input shaft through s J universal joint U and rests on roller i thrust bearing D In tilting box f, oe ; which it revolves. Socket ring has seven or nine bronze sockets for on equal number of plsionconnecting rods 0 with spherical en4Pistons P and cylinders C *t* ground to a good fit, which keeps leakage l* without use of piston rings. Spiral spring S, between cylinder rel B and a collar on input shaft, hold* PUNT OPERATION AND MAINTENANCE SECTION POWfl vid Delivery to Meet load Needs (ifoinsi valve plots V when they not under pressure. When pump is , .ning, the barrel it held against valve is by pressure resuiting Irom the erence in the valve-plate and cylin- port areas. Two semicircular porta valve plate connect to auction and lychtrge pom in the cylinder-barrel ate.- elsch valve-plate port extendi Soul 12U deg on lue cylinder side, srrel B has ss many equally spaced micircultr ports as it has cylinders. I barrel revolves with input shaft, its rts pass in succession over the valve- i ports. Una of these aeu as a sueand the other as a discharge port < the pump cylinders. Piston Olsdtorgo. Tilting Bo* T ond ket ring R are in the vertical (neuI) position In Fig. 2. If Input shaft Jims socket ring R, cylinder barrel B with it, but the pistons have no ft in their cylinders. Turning cooC until socket ring R takes position 'XX pulls the top pistons farther out o( ths cylinders and pushea bottom ones in. .With socket plate tilled to XX when tteket ring and cylinder barrel turn hall a revolution, pistons that were on ,0P will be at the bottom and thoVe at bottom will be on top. During this cb*DJC' pistons that were on top ore pushed in oa they move to the bottom. :^*se at the bottom are pulled out as they move to (he top. So by rotating the socket plate and cylinder barrel, . when the former it tilted, the pistons re moved in and out of the cylinders to produce a pumping action. Assume you are looking at the driveshaft end ol the unit wheo shaft turns clockwise. As cylinder barrel ond socket ring turn, pistons end cylinders' move up on the left and down on the right. This causes the left-hand pistons to pull out of their cylinders and draw fluid into them*'from valve plate. On the right, the pistons move into the cyl inders and force fluid out through valve-plate port into the discharge. Socket-Ring Adjustment. Amount of pump-piston motion and quantity ol -fluid pumped depends on socket-plate angle. When socket plate is at an angle of 20 deg with the vertical, pump out put is maximum. As socket plate is moved toward the vertical or neutral position, pump discharge decreases, un til it becomes cero. By adjusting posi tion of socket-ring li, pump discharge can be varied from maximum to zero in infinite changes. Fluid motor similar to pump can be combined with it to form variable-speed transmission, Fig. 1. High Speed. Pump in Fig. 3 operates similarly to the unit in Fig. 2, but in stead of having a tilting plate its socketring cylinder block B with its pistons, swings at an angle with the drive shaft and piston connecting-rod socket pfate P. Until pump is running, a spring holds the cylinder-block ported face against valve-plate F in which li is sup ported by a stub shall in a bearing. Sockel-plote P is pari of drive shaft 5 snd is supported in two radial roller hearings and a ball-thrust bearing. A floating universal-joint shaft U connects ilia cylinder block with the drive shaft ana socket-plate flange so they all revolve at drive-shaft speed. Valve plate V, against which cylinderblock d rides, is fixed in pump yoke, not shows. Two semicircular porta in valve plate male with passages in pump yoke, which conducts fluid to swivel connections that serve os yoke pintles. Wltlt the cylinder barrel at an angle with drive shaft as shown, the lop pis ton is in /uil-discharge position and the bottom one on suction. When pump makes half a revolution, bottom piston will be at the top on full discharge and top piston at bottom on suction. Each piston thus functions to create suction during one-half revolution to fill the cylinders with fluid. This is followed by a pressure stroke. Zero OUchorge. |f cylinder barrel end valve plate are swung to where face is parallel with the socket flange on drive shaft, the uiiembly revolves without causing any piston motion. Dincharge is zero. Length of piston stroke then depends on angle formed between cylinder block and drive-shaft axis. An infinite range of fluid delivery up tu maximum rated capacity eon be had by varying angular position of cylinder barrel relative to drive-shaft axis. Control of pump discharge can be manual by using handwheel IP, ao in Fig. 3, or by mechanical, hydraulic or electric means. Reverse pumping ac tion is obtained by swinging the cylin der block to the other tide of the center {Continued on page 210) UFTtMtlR 1*53 PtANT OPEIATION ANO MAINTENANCE SECTION