【文章內(nèi)容簡介】 ns 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 surface of the ring whose movement is opposed by the spring. If the pump discharge pressure rises above that for which the by governor spring is set, the spring is pressed. This allows the pressurechamber ring to move and take a position that is less off center with respect to the roter. The pump then delivers less fluid, and the pressure is established at the desired leval. The discharge pressure for units of this design varies between 100 and 2500psi. The characteristics of a variabledisplacementpump pensator are shown in Figure. Horsepower input values also shown so that the power input requirements can be accurately puted. Variablevolume vane pumps are capacity of multiplepressure levels in apredetermined pattern. Twopressure pump controls can provide an efficient method of unloading a circuit and still hold sufficient pressure available for pilot circuits. The black area of the graph of Figure shoes a variablevolume pump maintaining a pressure of 100psi against a closed circuit. Wasted power is the result of pumping oil at 100psi through an unloading or relief valve to maintain a source of positive pilot pressure. Twopressuretype controls include hydraulic, pilotoperated types and solenoidcontrolled, pilotoperated types. The minus of Figure shoes the solenoid energized so that the pilot oil is diverted to the tank. Thus, the pilot oil obtained from the pump discharge cannot assist the governor spring. Minimum pressure will result. The plus Figure shows the solenoid energized so that oil assists pensator spring. The amount of assistance is determined by the small ball and spring, acting as a simple relief valve. This provides the predetermined maximum operating pressure. Another type of twopressure system employs what is termed a differential unloading governor. It is applied in a highlow or twopump to a minimum deadhead pressure setting. Deadhead pressure refers to a specific pressure level established ad a resulting action and the resulting flow at deadhead condition are equal to the leakage in the system and pilotcontrol f