【正文】 causes the vanes to move outward in their slots and bear against the inner bore of the pump casing or against a cam ring. As the rotor revolves, fluid flows in between the vanes when they pass the suction port. This fluid is carried around the pump casing until the discharge port is reached. Here the fluid is forced out of the casing and into the discharge pipe. In the slidingvane pump in Figure the vanes in an ovalshaped bore. Centrifugal force starts the vanes out of their slots when the rotor begins turning. The vanes are held out by pressure which is bled into the cavities behind the vanes from a distributing ring at the end of the vane slots. Suction is through two ports A and A1, placed diametrically opposite each other. Two discharge ports are similarly placed. This arrangement of ports keeps the rotor in hydraulic balance, reliving the bearing of heavy loads. When the rotor turns counterclockwise, fluid from the suction pipe es into ports A and A1 is trapped between the vanes, and is carried around and discharged through ports Band B1． Pumps of this design are built for pressures up to 2500psi. Earlier models required staging to attain pressures approximating those currently available in one stage. Valving, used to equalize flow and pressure loads as roter sets are operated in series to attain high pressures. Speed of rotation is usually limited to less than 2500rpm because of centrifugal forces and subsequent wear at the contact point of vanes against the camring surface. Figure shown that the characteristic curves of the pump when operating at 1200rpm and handing oil having a viscosity of 150SSU at 100F. Two vanes may be used in each slot to control the force against the interior of the casing or the cam ring. Dual vanes also provide a tighter seal, reducing the leakage from the discharge side to the suction side of the pump. The opposed inlet and discharge port in this design provide hydraulic balance in the same way as the pump. Both these pumps are constantdisplacement units. The delivery or capacity of a vanetype pump in gallons per minute cannot be changed without changing the speed of rotation unless a special design id used. Figure shoes a variablecapacity slidingvane pump. It does not use dual suction and discharge ports. The rotor runs in the pressurechamber ring, which can be adjusted so that it is offcenter to the rotor. As the degree of offcenter or eccentricity is changed, a variable volume of fluid is discharged. Figure shows that the vanes create a vacuum so that oil enters through 180 of shaft rotation. Discharge also takes place through 180 of rotation . There is a slight overlapping of the beginning of the fluid intake function and the beginning of the fluid discharge. Figure shows how maximum flow is available at minimum working pressure. As the flow decreases to aminimum valve, the pressure increases to the maximum. The pump delivers only that fluid neended to replace clearance floes resulting from the usual slide fit in circuit ponents. A relief valve is not essential with a variabledisplacementtype pump of this design to protect pumping mechanism. Other conditions within the circuit may dictate the use of a safety or relief valve to prevent localized pressure build up beyond the usual working levels. For automatic control of the discharge, an adjustable springloaded governor is design to protect pumping mechanism. Other conditions within the circuit may dictate the use of a safety or relief valve to prevent localized pressure build up beyond the usual working levels. For automatic control of the discharge, an adjustable springloaded governor is used. This governor is arranged so that the pump discharge acts on a piston or inner s