How a Self-Priming Pump Works (Complete Guide for Chemical Plastic Self-Priming Pumps)

Technical Guide | Easy-to-Understand Blog Version

Introduction

A self-priming pump is an improved type of centrifugal pump. Unlike a standard centrifugal pump, which must be completely filled with liquid before starting, a self-priming pump has a built-in liquid storage chamber that keeps a certain amount of liquid inside the pump.

After the first filling, the pump can automatically remove air from the suction pipe and lift liquid from a lower-level tank without using a foot valve or manual priming.

This design makes self-priming pumps ideal for applications where the liquid level is below the pump installation position, such as chemical transfer, wastewater handling, plating systems, and industrial liquid circulation.


1. Basic Working Principle

A normal centrifugal pump can only move liquid when the pump chamber and suction line are already filled with liquid.

A self-priming pump solves this problem by using:

When the pump starts, it mixes the stored liquid with the air inside the suction pipe. The pump separates the air and liquid automatically:

After the air is completely removed, the pump works like a normal centrifugal pump and continuously transfers liquid.


2. Key Components That Make Self-Priming Possible

1) Liquid Storage Chamber (Priming Chamber)

The enlarged pump body contains a small amount of liquid after shutdown.

Its main functions:

This is the most important part of the self-priming function.


2) Gas-Liquid Separation Chamber

Located above the pump chamber, this area separates air from liquid.

During operation:

This continuous separation allows the pump to remove air from the suction pipe.


3) Check Valve (One-Way Valve)

The check valve is installed at the suction side.

Its functions:

Without this function, the pump would lose its stored liquid and need to be manually filled again.


4) Impeller and Volute Casing

The impeller and volute work similarly to a standard centrifugal pump.

Their functions:


5) Air Discharge Passage

During self-priming:

This process repeats until the suction pipe is fully filled with liquid.


3. Step-by-Step Self-Priming Process

Step 1: Initial Liquid Filling

Before the first operation:

  1. Add liquid into the pump through the filling port.
  2. Close the filling cover.
  3. The check valve keeps the liquid inside the pump chamber.

The pump now has enough stored liquid for self-priming.


Step 2: Air and Liquid Mixing Process

When the motor starts:

Inside the pump:


Step 3: Automatic Air Separation

The gas-liquid mixture enters the separation chamber.

Because air and liquid have different densities:

The liquid then returns to the impeller and repeats the cycle.


Step 4: Complete Priming and Normal Pumping

After several cycles:

At this stage:


Step 5: Shutdown and Liquid Retention

After stopping:

During the next startup:



4. Special Features of Plastic Chemical Self-Priming Pumps

For chemical applications, many self-priming pumps use PP or PVDF plastic materials.

Common applications include:

Main Advantages

Corrosion Resistance

The wetted parts are made from chemical-resistant plastics:



Typical Self-Priming Height

Most industrial plastic self-priming pumps can achieve:

4–6 meters self-priming height

However, actual performance depends on:

Higher temperature or higher viscosity liquids will reduce self-priming ability.



Avoid Long-Time Dry Running

Although self-priming pumps can run briefly during the air-removal process, they should not operate without liquid for a long time.

Long-term dry running may cause:

The pump should always have enough liquid inside before operation.



5. Simple Explanation

A self-priming pump works like this:

Keep some liquid inside → Start the pump → Mix liquid with air → Separate and remove air → Fill the suction pipe with liquid → Pump normally

The built-in storage chamber and gas-liquid separation design allow the pump to remove air automatically and start pumping without repeated manual filling.

Because of this advantage, self-priming pumps are widely used for:

A self-priming pump is the ideal solution when the liquid source is lower than the pump installation position and reliable automatic suction is required.