What is a Diaphragm Pump?

- It is a type of reciprocating pump involving flexible membranes made of fabric-reinforced elastomers (usually synthetic rubber) with flap, ball, or poppet type check valves that transfer fluids into and out of the pumping chamber.

- Used for transfer of fluids up to 300 GPM.

- Different kinds of diaphragm pumps are used to transfer a wide variety of fluids including chemicals, powders, slurries, wastewater, etc.

- Seals and packs are absent making the Diaphragm pump applicable for zero leakage processes.

How does it work?

- Firstly, the diaphragm expands causing a net suction area inside the cavity.

- The vacuum formed inside the cavity opens the check valve in the suction site; therefore, allowing the flowing in of the fluid.

- In some pumps, air regulators are used to control the sudden pressure peaks of the discharge site.

- Afterwards, the diaphragm collapses pushing the check valve; thereby,

pushing the liquid out of the chamber.

- This reciprocating motion creates an intake and discharge of pumped liquid in and out of each chamber.

Three Categories of Diaphragm Pumps

1. Mechanically-driven Diaphragm Pumps- Used commonly on industrial,

chemical, and wastewater treatment applications.

- Works by reciprocating plungers.- Normally limited to 50ft of

differential head and suction lifts up to 25ft for construction industry applications.

- Motor-driven pumps and electromagnetic pumps are usually used for chemical and wastewater treatment industries.

- Other mechanically-driven pumps involve automotive fuel pumps and hand-operated diaphragm used commonly on sailboats.

2. Hydraulically-driven Diaphragm Pumps- Used to transfer or inject

chemicals into process streams at high pressures.

- In this pump, the diaphragm is pressure-balanced, the stresses are low thereby requiring minimum maintenance.

- Handles a wider range of chemicals than the mechanically-driven pump.

- Three types of liquid ends are used: disc diaphragm, tubular diaphragm, and high performance diaphragm.

ChE 134 Diaphragm Pumps (Cruz, Ochiai)

Diaphragm Pump

- Disc diaphragm involves a suction-side and process-side restraining plates to prevent displacement of the diaphragm.

- Tubular diaphragm configuration involves a disc diaphragm configuration with a tubular chamber placed in front of the disc reducing viscous losses and wear especially if a slurry is being processed.

- High performance diaphragm configuration removes the process-side restraining plate in a tubular configuration.

3. Air-Operated Diaphragm Pumps- In this diaphragm pump, air is

used to ensure continuous operation of the pump.

- There are two common types of air-operated diaphragm pumps: single, and double diaphragm pumps.

- The air is supplied by the air compressor at the air motor containing an air distribution valve that shifts position at the end of each stroke of the pump.

- During this process, the diaphragm collapses pushing the fluid out of the chamber.

- After the collapsing process, the air in the air motor is released through the exhaust thus enabling the pump to expand again.

- This expansion creates a vacuum inside the chamber allowing the fluid to enter the chamber and the cycle is repeated.

- Diaphragm pumps are usually used for handling abrasive slurries since they provide laminar steady flow of fluids at a low velocity.

- Can be used for dry pumping with air as the fluid medium.

Advantages of the Diaphragm Pump

- Simple field repairability- High pressure- Suitable for suction lift- Moderate shear rate- Low cost- Can meter flow- Handles viscous liquids, sandy,

and muddy waters- Ease of repair- Used for low flows- Used for dewatering excavations- Used for slurry pumping- Used for high grit loads

Disadvantages of the Diaphragm Pump

- Instant shutdown on component failure

- Solids handling ability is limited by ball check

- Poor for rags, sticks, and string

References[1]

ChE 134 Diaphragm Pumps (Cruz, Ochiai)

Karassik, Igor J. Pump Handbook 4th Edition. McGraw Hill Companies Inc, 2008.

[2] McAllister, E.W. Pipe Line Rules of Thumb Handbook 3rd Edition. n.d.

ChE 134 Diaphragm Pumps (Cruz, Ochiai)