What is a reciprocating pump?

Short Answer:

A reciprocating pump is a type of positive displacement pump that uses a piston or plunger moving back and forth (reciprocating motion) inside a cylinder to move liquid. During the suction stroke, the piston draws fluid into the cylinder, and during the delivery stroke, it pushes the fluid out under pressure.

Reciprocating pumps are mainly used for high-pressure and low discharge applications. They are ideal for situations where an accurate amount of liquid must be delivered, such as in hydraulic systems, oil refineries, and chemical industries.

Detailed Explanation :

Reciprocating Pump

A reciprocating pump is one of the oldest and most reliable types of positive displacement pumps used in engineering applications. It operates by converting the mechanical energy supplied by a motor or engine into hydraulic energy through the back-and-forth motion of a piston or plunger. Unlike centrifugal pumps, which work on kinetic energy conversion, reciprocating pumps deliver a fixed volume of fluid with every stroke, making them suitable for high-pressure, low-flow operations.

Principle of Operation

The reciprocating pump works on the principle of positive displacement. In this type of pump, a certain volume of liquid is trapped inside the cylinder during the suction stroke and is then pushed out during the delivery stroke. The liquid is displaced by the mechanical movement of a piston or plunger, hence the name “positive displacement pump.” The quantity of liquid discharged per cycle remains constant, making the pump highly accurate and efficient for precision applications.

Main Components of a Reciprocating Pump

  1. Cylinder: It is a hollow body in which the piston or plunger moves back and forth.
  2. Piston or Plunger: It is the main moving part that creates suction and delivery pressure inside the cylinder.
  3. Suction Valve: It allows the fluid to enter the cylinder during the suction stroke and closes during the delivery stroke.
  4. Delivery Valve: It opens to allow the fluid to leave the cylinder during the delivery stroke and closes during suction.
  5. Crank and Connecting Rod Mechanism: It converts rotary motion from the motor or engine into the reciprocating motion of the piston.
  6. Suction Pipe: It connects the fluid source to the pump cylinder.
  7. Delivery Pipe: It carries the pressurized fluid from the pump to the required destination.
  8. Air Vessel (optional): It is fitted on both suction and delivery sides to smoothen the flow and reduce pressure fluctuations.

Working of a Reciprocating Pump

The operation of a reciprocating pump consists of two main strokes:

  1. Suction Stroke:
    • The piston moves outward (away from the cylinder head).
    • This movement creates a partial vacuum in the cylinder, causing the suction valve to open.
    • The liquid from the sump or reservoir flows into the cylinder due to the pressure difference.
  2. Delivery Stroke:
    • The piston now moves inward (towards the cylinder head).
    • The suction valve closes, and the delivery valve opens.
    • The trapped liquid inside the cylinder is pushed out through the delivery pipe under pressure.

This cycle of suction and delivery continues as long as the pump operates. The discharge is intermittent, but it can be made smoother by adding air vessels.

Types of Reciprocating Pumps

Reciprocating pumps can be classified based on the type of cylinder and action:

  1. Based on Cylinder Type:
    • Single-acting pump: The liquid is pumped during one stroke only (generally during the forward stroke).
    • Double-acting pump: The liquid is pumped during both forward and backward strokes.
  2. Based on Drive Mechanism:
    • Power-driven pumps: Operated by an electric motor or engine.
    • Hand-operated pumps: Used for small-scale or manual operations.

Advantages of Reciprocating Pumps

  1. Capable of developing very high pressure.
  2. Suitable for small discharge and precise flow applications.
  3. Efficiency is high even at low speeds.
  4. Can handle viscous liquids effectively.
  5. Discharge is independent of the head or pressure conditions.

Disadvantages of Reciprocating Pumps

  1. Flow is not continuous (pulsating nature).
  2. Maintenance cost is high due to many moving parts.
  3. Complex construction compared to centrifugal pumps.
  4. Requires more space for installation.
  5. Not suitable for large discharge applications.

Applications of Reciprocating Pumps

  • Used in hydraulic presses and elevators.
  • Used in oil drilling and refineries.
  • Employed in chemical dosing and metering systems.
  • Used in irrigation and high-pressure cleaning systems.
  • Suitable for boiler feed water systems and pressure testing equipment.
Conclusion:

A reciprocating pump is a positive displacement type of pump that transfers liquid by the reciprocating motion of a piston or plunger within a cylinder. It provides high-pressure output with a precise and consistent flow rate. Although its discharge is not continuous, it is highly reliable for applications requiring accurate delivery and high pressure. Due to its durability and precision, it remains an essential component in hydraulic and industrial systems.