N2 Fitting and Machining Theory|Hands-On! 113


Te squeesing and opening of the impeller blades creates vacuum at the suction side to induce fluid, and pressure at the delivery side to expel the fluid.


Reciprocating pumps


Reciprocating pumps have a forward and backward (to and fro) motion that is different to the rotating (circulating) motion of centrifugal pumps. It is important to know that the moving parts inside the reciprocating pump may consist of a piston, plunger or bucket. Te reciprocating pumps (piston or plunger type pumps) can be seen in Figure 9.10. Tis type of pump is a positive displacement pump, which implies that with every stroke of the pump the same amount of fluid is displaced (pumped). One way valves (also known as non-return valve) allow the fluid to flow in only one direction. Te fluid pump’s main function is to liſt fluid or liquid from a low level to a higher level and also to transfer (displace) fluid over a level surface from one point to another.


Piston pump


Te piston type pump works best at medium pressures. Tis pump is nearly always double-acting as the inlet (suction) valve and outlet (delivery) valves are connected at the end of the cylinder.


As the piston moves to the leſt, liquid is sucked through the right inlet valve and discharged through the leſt outlet (delivery) valve. On moving to the right, liquid is sucked through the leſt inlet valve and discharged through the outlet valve situated on the right side.


delivery valve


delivery (outlet) port


non-return valves


stuffing box in stroke


piston delivery valve


inlet valve out stroke


inlet valve


suction (inlet) port


Figure 9.10 Double-acting piston pump


Plunger pumps Te plunger functions in two separate fluid boxes which are only connected by inlet and outlet pipes. Every fluid box has two valves (inlet and outlet valve) for the fluid. In the sketch below it can be seen that when the plunger moves from the right-hand side to the


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