Construction of Reciprocating Pumps
Reciprocating Positive Displacement Pumps or simply Reciprocating Pumps has fluid displacing arrangement which runs by reciprocation of certain parts. The motion of the reciprocating part is mating with a cavity or chamber and the contact is leak proof. There is relative motion between the reciprocating part and the chamber body but with perfect mating the cavity is a closed volume. The volume of the cavity increases or decreases with the motion of the reciprocating part. The chamber has one inlet valve, which can allow liquid to enter the chamber but does not allow it to exit the chamber, and one outlet valve which only allows liquid to exit the chamber.
Working of Reciprocating Pumps
When the piston or diaphragm moves backward the volume of cavity increases and pressure inside it drops, this opens the inlet valve and liquid is taken in until the differential pressure between the supply side and the chamber is zero. Then the piston or diaphragm moves forward decreasing the volume of the chamber and pressure inside the chamber increase, this opens the outlet valve and the liquid from inside the chamber is pushed outside in the discharge line until the differential pressure is zero. This cycle repeats and an intermittent discharge of fluid is obtained.
Specifications of Reciprocating Pump
One backward movement, taking in the liquid plus one forward movement discharging the liquid is counted as one stroke. The distance between the two ends of the movement of piston or diaphragm is called as the stroke length. Volume displaced in one stroke equal to the stroke length multiplied by the cross sectional area of the chamber or cylinder. The volume discharge per stroke is an important parameter of any reciprocating pump to consider while deciding to use it for a particular application. The flow rate through a pump is the product of volume discharge per stroke and the frequency of strokes.
Applications of Reciprocating Pump
Reciprocating pumps has low discharge rate and high pressure ratios. For moderate pressures of the range 10 bar rotary pumps can be used but for sustained high pressure work of the range 500 bar reciprocating pumps are used. As the volume of fluid displaced per stroke is accurate the reciprocating pumps are used in metering application where a certain calculated amount of liquid has to be supplied.
Types of Reciprocating Pumps
The reciprocating part in pumps is mainly of two types, a piston or a diaphragm. Based on this, reciprocating pumps can be divided in two types, piston pump and diaphragm pump. In the following articles each type will be presented in detail.