Radial Piston PumpsFigure 4-11 illustrates the operation of theradial piston pump. The pump consists of a pintle,which remains stationary and acts as a valve; aFigure 4-11.—Principles of operation of the radial pistonpump.cylinder block, which revolves around the pintleand contains the cylinders in which the pistonsoperate; a rotor, which houses the reaction ringof hardened steel against which the piston headspress; and a slide block, which is used to controlthe length of the piston strokes. The slide blockdoes not revolve but houses and supports therotor, which does revolve due to the friction setup by the sliding action between the piston headsand the reaction ring. The cylinder block isattached to the drive shaft.Referring to view A of figure 4-11, assume thatspace X in one of the cylinders of the cylinderblock contains liquid and that the respective pistonof this cylinder is at position 1. When the cylinderblock and piston are rotated in a clockwisedirection, the piston is forced into its cylinder asit approaches position 2. This action reduces thevolumetric size of the cylinder and forces aquantity of liquid out of the cylinder and into theoutlet port above the pintle. This pumping actionis due to the rotor being off-center in relation tothe center of the cylinder block.In figure 4-11 view B, the piston has reachedposition 2 and has forced the liquid out of theopen end of the cylinder through the outlet abovethe pintle and into the system. While the pistonmoves from position 2 to position 3, the open endof the cylinder passes over the solid part of thepintle; therefore, there is no intake or dischargeof liquid during this time. As the piston andcylinder move from position 3 to position 4,centrifugal force causes the piston to moveoutward against the reaction ring of the rotor.During this time the open end of the cylinder isopen to the intake side of the pintle and, therefore,fills with liquid. As the piston moves fromposition 4 to position 1, the open end of thecylinder is against the solid side of the pintle andno intake or discharge of liquid takes place. Afterthe piston has passed the pintle and starts towardposition 2, another discharge of liquid takes place.Alternate intake and discharge continues as therotor revolves about its axis-intake on one sideof the pintle and discharge on the other, as thepiston slides in and out.Notice in views A and B of figure 4-11 thatthe center point of the rotor is different from thecenter point of the cylinder block. The differenceof these centers produces the pumping action. Ifthe rotor is moved so that its center point is thesame as that of the cylinder block, as shown infigure 4-11, view C, there is no pumping action,since the piston does not move back and forth inthe cylinder as it rotates with the cylinder block.4-10
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