What is a reciprocating pump?

Short Answer:

A reciprocating pump is a type of positive displacement pump that uses a piston or plunger to move liquid through a cylinder. The pump works by suction and discharge strokes of the piston, which draw in and push out fluid alternately. It is mostly used where high pressure and small discharge are required.

In this pump, liquid enters during the suction stroke when the piston moves backward and is forced out during the discharge stroke when the piston moves forward. Reciprocating pumps are used in hydraulic systems, oil industries, and irrigation where precise fluid flow is needed.

Detailed Explanation :

Reciprocating Pump

A reciprocating pump is a type of positive displacement pump in which a piston or plunger moves back and forth (reciprocates) inside a cylinder to move liquid. It operates by alternating suction and discharge strokes, which draw liquid into the cylinder and then push it out. Unlike centrifugal pumps, reciprocating pumps deliver a fixed quantity of fluid in each cycle, making them ideal for high-pressure and low-flow rate applications.

Working Principle

The working of a reciprocating pump is based on the to-and-fro motion of a piston or plunger inside a cylinder. It consists of a piston, cylinder, suction valve, discharge valve, crank, and connecting rod. The piston is connected to a crankshaft, which converts rotary motion into reciprocating motion. The pump has two main strokes:

  1. Suction Stroke:
    During this stroke, the piston moves backward in the cylinder, creating a vacuum. Because of this vacuum, the suction valve opens, and the liquid from the sump enters the cylinder.
  2. Delivery or Discharge Stroke:
    When the piston moves forward, the suction valve closes and the delivery valve opens due to pressure. The liquid inside the cylinder is forced out through the delivery pipe.

This continuous process of suction and delivery strokes helps the pump maintain a constant flow of liquid, though in pulses.

Main Components

  1. Cylinder:
    It houses the piston or plunger and is designed to withstand the pressure developed inside.
  2. Piston or Plunger:
    It moves back and forth inside the cylinder, creating suction and discharge.
  3. Suction and Delivery Valves:
    These are non-return valves that ensure liquid flows only in one direction — into the cylinder during suction and out during discharge.
  4. Crank and Connecting Rod:
    They connect the piston to the rotating shaft, converting rotary motion into reciprocating motion.
  5. Suction and Delivery Pipes:
    The suction pipe draws liquid from the source, and the delivery pipe sends it to the required location.

Types of Reciprocating Pumps

  1. Single Acting Pump:
    The liquid is pumped only during one stroke (usually the forward stroke). Suction occurs during the backward stroke.
  2. Double Acting Pump:
    The liquid is pumped during both strokes. While one side of the piston is on suction, the other side performs discharge, giving more uniform flow.

Working Cycle Explanation

When the crank starts rotating, it moves the piston inside the cylinder. During the backward movement of the piston, a vacuum is formed in the cylinder, and the liquid enters through the suction valve. During the forward movement, the liquid is pushed out through the delivery valve.

In the double acting type, both sides of the piston are used. This reduces pulsations and increases efficiency. The flow rate depends on the speed of the crank and the size of the piston.

Advantages

  • It can handle high pressures easily.
  • Gives accurate and controlled discharge.
  • Can be used for viscous liquids.
  • Self-priming in nature — does not need priming before starting.

Disadvantages

  • The flow is not continuous; it is pulsating.
  • Requires more maintenance because of moving parts.
  • Initial cost and space requirements are higher.
  • Speed is limited to avoid vibration and wear.

Applications

  • Used in hydraulic systems and oil refineries.
  • For boiler feed water where high pressure is required.
  • Chemical and pharmaceutical industries for accurate dosing.
  • Irrigation systems and water supply in rural areas.
Conclusion

A reciprocating pump is a reliable and precise positive displacement pump that operates on the reciprocating motion of a piston. It is suitable for small quantities of fluid at high pressure and is widely used in industries requiring accuracy and reliability. Though it requires higher maintenance and has pulsating flow, its ability to handle high pressure makes it essential in various mechanical and industrial operations.