Short Answer:

A reciprocating pump is a type of positive displacement pump used to move fluid by the back-and-forth motion of a piston or plunger inside a cylinder. It draws fluid in during the suction stroke and pushes it out during the delivery stroke. These pumps deliver a fixed amount of liquid in each cycle.

It works by creating a vacuum during the backward movement of the piston, which allows fluid to enter the chamber. As the piston moves forward, it pushes the fluid out through a discharge valve. Reciprocating pumps are used where high pressure and accurate flow control are required, such as in water supply, oil industries, and chemical plants.

Detailed Explanation

Reciprocating Pump

A reciprocating pump is a mechanical device used to transport fluids by using the repeated linear motion of a piston, plunger, or diaphragm within a cylinder. It is classified under positive displacement pumps because it displaces a fixed volume of fluid with each stroke. These pumps are widely used in civil engineering applications where precision, high pressure, and small flow rates are important.

Construction and Components

A typical reciprocating pump consists of:

A cylinder with a piston or plunger that moves back and forth.
An inlet valve that allows fluid to enter during suction.
An outlet valve that allows fluid to exit during discharge.
A crankshaft and connecting rod mechanism to convert rotary motion into reciprocating motion.

The cylinder is partially filled with fluid. The piston is connected to a crankshaft which is rotated by an external motor. As the crankshaft turns, the piston moves forward and backward inside the cylinder.

Working Principle

The pump works in two main strokes:

Suction Stroke:
As the piston moves backward inside the cylinder, it creates a vacuum. This vacuum opens the inlet valve and fluid enters the cylinder from the source (such as a tank or reservoir).
Delivery Stroke:
When the piston moves forward, it compresses the fluid in the cylinder, causing the inlet valve to close and the outlet valve to open. The fluid is then pushed out through the discharge pipe.

This cycle repeats continuously, pumping fluid in a steady, pulse-like flow. Some pumps have double-acting pistons, meaning both strokes (forward and backward) are used for suction and delivery, which increases efficiency.

Types of Reciprocating Pumps

Single-Acting Pump: Only one side of the piston is used for pumping.
Double-Acting Pump: Both sides of the piston are used for suction and discharge.
Diaphragm Pump: Uses a flexible diaphragm instead of a piston to move the fluid.

Applications in Civil Engineering

Reciprocating pumps are used in various fields where precision and high pressure are necessary:

Water supply systems for high-rise buildings.
Hydraulic systems and pressure testing.
Oil and gas refineries.
Chemical dosing in treatment plants.
Irrigation systems for controlled water flow.

Advantages

High pressure output even at low flow rates.
Suitable for handling viscous and abrasive fluids.
Accurate and controlled flow.
Can pump fluids to high elevations.

Limitations

Low discharge compared to centrifugal pumps.
Complex design with more moving parts.
Pulsating flow needs dampers for smooth operation.
Higher maintenance due to wear and tear.

Conclusion

A reciprocating pump is a positive displacement pump that moves fluid using the back-and-forth motion of a piston or plunger. It works by drawing fluid during the suction stroke and discharging it during the delivery stroke. These pumps are best suited for applications that require high pressure and accurate flow control, making them important in civil engineering systems such as water supply and industrial processes.