Short Answer:

A reciprocating pump is a type of positive displacement pump that uses the back-and-forth (reciprocating) motion of a piston or plunger to move a fixed amount of liquid during each stroke. It works on the principle of suction and delivery strokes, where the piston draws liquid into the cylinder and then forces it out under pressure.

Reciprocating pumps are commonly used for applications requiring high pressure and low flow rate. They are widely used in hydraulic systems, water supply for boilers, and oil industries because they deliver precise quantities of fluid with each stroke and can handle high-pressure operations efficiently.

Detailed Explanation :

Reciprocating Pump

A reciprocating pump is one of the most common positive displacement pumps used in engineering and industrial applications. It works by the to-and-fro motion of a piston or plunger inside a cylinder to draw in and discharge fluid. The movement of the piston creates pressure differences that allow the liquid to move through suction and delivery valves.

This pump is known for delivering accurate and constant volumes of liquid, making it suitable for high-pressure, low-discharge applications. The fundamental working principle is that during one stroke, the liquid is drawn into the cylinder (suction stroke), and during the next stroke, the liquid is pushed out (delivery stroke).

Working Principle

The working of a reciprocating pump is based on the principle of positive displacement. This means the pump traps a fixed amount of fluid and forces it from the suction side to the discharge side with each stroke.

The pump consists of a piston or plunger that moves inside a close-fitting cylinder. The motion of the piston is provided by a crank mechanism connected to an electric motor. When the piston moves backward, it creates a partial vacuum in the cylinder, causing liquid to enter through the suction valve. When the piston moves forward, it closes the suction valve and opens the delivery valve, forcing the fluid out under pressure.

This process continues repeatedly, resulting in an intermittent but high-pressure discharge of liquid.

Main Components of a Reciprocating Pump

Cylinder:
The cylinder is the main body in which the piston moves. It is made of metal and designed to withstand high pressure.
Piston or Plunger:
The piston or plunger is the moving part that performs suction and delivery actions. It is connected to the crankshaft through a connecting rod.
Crank and Connecting Rod Mechanism:
This mechanism converts the rotary motion of the motor into the reciprocating motion of the piston.
Suction Pipe and Valve:
The suction pipe carries liquid from the source to the pump cylinder. The suction valve opens during the suction stroke and closes during the delivery stroke.
Delivery Pipe and Valve:
The delivery pipe carries liquid from the pump to the required point. The delivery valve opens during the delivery stroke and closes during the suction stroke.
Air Vessel (Optional):
Air vessels are sometimes fitted on suction and delivery pipes to reduce flow fluctuations and ensure a more uniform discharge.

Types of Reciprocating Pumps

Based on Cylinder Arrangement:
- Single-acting Pump: The liquid is discharged only on one side of the piston during each revolution.
- Double-acting Pump: The liquid is discharged on both sides of the piston, resulting in smoother flow and higher efficiency.
Based on Number of Cylinders:
- Single-cylinder Pump
- Double-cylinder Pump
- Triple-cylinder Pump

The use of multiple cylinders helps balance the flow and reduce pulsations in discharge.

Working of a Single-Acting Reciprocating Pump

The operation can be divided into two strokes:

Suction Stroke:
When the crank rotates, the piston moves backward, creating a vacuum inside the cylinder. Due to atmospheric pressure, liquid from the sump enters the cylinder through the suction pipe and suction valve.
Delivery Stroke:
As the piston moves forward, the suction valve closes, and the pressure inside the cylinder increases. This pressure opens the delivery valve, and liquid is forced out through the delivery pipe.

This cycle repeats continuously, leading to intermittent discharge of the liquid.

Advantages of Reciprocating Pump

Can generate very high pressures.
Suitable for accurate and fixed discharge.
Capable of handling viscous liquids.
Works efficiently for small flow rates.
Can be used in metering and dosing operations.

Disadvantages of Reciprocating Pump

Discharge is not uniform; it is pulsating.
Requires high maintenance due to moving parts.
Not suitable for large volume flow rates.
More complex and costly than centrifugal pumps.
Produces more noise and vibration during operation.

Applications of Reciprocating Pump

Reciprocating pumps are used in:

Hydraulic systems and oil refineries.
Feeding water to boilers.
Fuel injection in engines.
Chemical dosing and laboratory applications.
High-pressure cleaning and testing systems.

Conclusion:

A reciprocating pump is a positive displacement pump that delivers a fixed amount of fluid by using the back-and-forth motion of a piston or plunger. It is ideal for applications requiring high pressure and precise discharge, although it produces pulsating flow and requires more maintenance. Despite its limitations, the reciprocating pump remains a crucial device in industries where accurate and reliable delivery of liquids is essential.