How Pneumatic Diaphragm Pump Part 1: Fundamentals & Components

Part One: Fundamentals & Components

Author: Stella Chan | Reading Time: 4 minutes

1. What Is a Pneumatic Diaphragm Pump?

A pneumatic diaphragm pump, also known as an AODD pump (Air-Operated Double Diaphragm Pump), is a type of positive displacement pump powered entirely by compressed air.

Unlike electric pumps, AODD pumps do not require motors, which means they avoid electrical sparks and reduce overheating risks. This makes them widely used in chemical plants, paint production, wastewater treatment, and other hazardous environments.

So, what fluids can they handle? A wide range of media, including:

2. Main Components and Their Functions

2.1 Air Distribution Valve (Air Switching Valve)

The air valve is the "control center" of an AODD pump. Its main functions are:

• Direct compressed air to the left or right air chamber
• Automatically switch airflow direction
• Maintain continuous diaphragm movement

By repeatedly changing the airflow path, the valve creates the pump's suction and discharge cycle.

2.2 Double Diaphragms

An AODD pump uses two flexible diaphragms connected by a common shaft.

Their main roles are:

• Separating the air side from the liquid side to prevent contamination
• Moving back and forth to change chamber volume and transfer fluid

Common diaphragm materials include:

Choosing the correct diaphragm material is essential for pump performance and service life.

2.3 Check Ball Valves

Check ball valves control one-way fluid movement through the pump.

• During suction: the inlet ball opens and allows liquid to enter.
• During discharge: the outlet ball opens and allows liquid to leave.

This prevents backflow and ensures stable pumping.

Common ball materials include stainless steel, ceramic, PTFE, and EPDM. Selection depends on the fluid's corrosion level and operating temperature.

2.4 Liquid Chambers

The liquid chambers are the areas between the diaphragms and ball valves.

As the diaphragms expand and contract, these chambers create pressure changes that complete the pumping process.

3. How an AODD Pump Works: Two-Step Cycle

An AODD pump works through two alternating diaphragm movements.

Step 1: Left Side Suction, Right Side Discharge

• Compressed air pushes the left diaphragm outward.
• The left chamber expands, creating a vacuum.
• The inlet valve opens, allowing liquid to enter.

At the same time:

• The right diaphragm moves inward.
• The right chamber compresses and pushes liquid out through the outlet valve.

Result:
   Left side = suction
   Right side = discharge

Step 2: Automatic Switching — Right Side Suction, Left Side Discharge

When the diaphragm reaches its stroke limit, the air valve switches automatically.

• Compressed air moves to the right diaphragm.
• The right chamber expands and draws liquid in.
• The left diaphragm compresses and pushes liquid out.

Result:
   Right side = suction
   Left side = discharge

The Continuous Pumping Cycle

The process repeats automatically:

Suction → Discharge → Suction → Discharge → ...

Because the pump relies on diaphragm movement instead of a rotating impeller, the flow has a slight pulsation. This is a normal characteristic of AODD pumps and can be managed through proper system design.