How an EODD Pump Works?
An electric diaphragm pump works by using an electric motor to move two flexible diaphragms back and forth. Each movement either draws liquid into a chamber or pushes it out, and two check valves per chamber make sure the liquid only travels in one direction. The motor sets the speed, the diaphragms set how much liquid moves with each stroke, and the system around the pump decides how much of that volume actually arrives.
Quick answer. In an electric operated double diaphragm pump the motor, usually through a gearbox and a crank or eccentric, turns rotation into a back and forth push. When a diaphragm pulls back, its chamber grows, the pressure drops and liquid enters through the inlet check valve. When it pushes forward, the chamber shrinks, the inlet valve closes and the liquid leaves through the outlet check valve. The two chambers work in opposite phase, so one fills while the other empties.
What happens inside an electric diaphragm pump during one cycle?
A full cycle has five parts. Open each one to see what the diaphragms, valves and motor are doing at that moment.
1. The motor turns rotation into diaphragm movement
The electric motor spins at a steady rate. A gearbox and a crank or eccentric mechanism convert that spinning into a back and forth motion. This is the part that replaces the compressed air of an air operated pump, and it is why the pump can be controlled through the motor.
The two diaphragms are linked so they move in opposite directions. When one moves out, the other moves in.
2. The suction stroke fills the chamber
When a diaphragm pulls back, the volume of its chamber increases and the pressure inside falls. The pressure outside the pump is now higher than the pressure in the chamber, so the inlet check valve opens and liquid flows in. The outlet check valve stays shut because the pressure on the discharge side is higher than the pressure in the chamber.
3. The discharge stroke pushes the liquid out
When the diaphragm moves forward, the chamber volume shrinks and the pressure rises. That pressure closes the inlet check valve and opens the outlet check valve, and the liquid is forced into the discharge line.
4. The two chambers alternate
While one chamber is filling, the other is discharging. This alternating action keeps the transfer steady and positive, and the liquid never touches a mechanical seal because it only contacts the diaphragm, the chamber and the check valves.
5. The next cycle starts as the motor keeps turning
Nothing needs to reset. The motor keeps turning, the strokes keep alternating, and the flow continues for as long as the suction side supplies liquid and the discharge side can accept it.
How do the parts fit together?
This is a simplified picture. Real pumps differ in layout, but the chain from motor to diaphragm to check valve is the same.
What decides how much liquid an electric diaphragm pump delivers?
The flow depends on how much liquid each stroke displaces and how many strokes the motor makes per minute. The motor speed sets the strokes, the pump size sets the displacement, and everything around the pump decides how much of that volume really reaches the discharge. Open the table to see which factor does what.
| Factor | What it changes | What to check |
|---|---|---|
| Pump size | The volume each stroke can displace | Connection size, from 1/2 inch to 3 inch in the EODD range |
| Motor speed | How many strokes happen each minute | Motor rating and the control system that sets the speed |
| Liquid viscosity | How easily the chamber fills and empties | Viscosity at the real operating temperature |
| Suction condition | How completely the chamber fills on the suction stroke | Suction line size, length, lift or flooded head |
| Discharge pressure and piping losses | How much pressure the pump must work against | Total discharge pressure, pipe size and fittings |
Worked illustration with assumed numbers, not a pump rating. Suppose each chamber displaces 0.2 L on its discharge stroke and the drive completes 50 cycles per minute. Both chambers discharge once per cycle, so the ideal output is 2 x 0.2 L x 50 = 20 L per minute. A thick liquid, a long suction line or a high discharge pressure will push the real figure below that, which is why the ideal number is a starting point and never a guarantee.
This is also why the flow of an electric pump can be adjusted through the motor, while pump size and chamber displacement stay fixed. The final figure for a given duty comes from the pump data and the system, which is what the pump selector is built to work through.
Why do the check valves matter so much?
The diaphragm moves liquid, but the check valves decide which way it goes. Each chamber has an inlet valve that lets liquid in and stops it leaving the same way, and an outlet valve that lets liquid out and stops it flowing back. If a valve cannot seal because of debris, wear or a swollen part, the diaphragm still moves and the motor still runs, but part of the liquid slips backwards and the delivered flow drops.
The same ball and seat logic applies to air operated pumps, which is why a worn or blocked valve is one of the first things to check when a diaphragm pump moves but does not deliver.
Pick a question about how it works
Why does an electric diaphragm pump need no mechanical seal?
The liquid only touches the diaphragm, the chamber walls and the check valves. The motor and its drive sit on the other side of the diaphragm, so no rotating shaft passes through the liquid. That is what sealless means here, and it is why this design suits leakage-sensitive liquids.
Why does the flow pulse, and does the second chamber help?
Each stroke delivers liquid in a push, so the discharge naturally rises and falls with the stroke. Two chambers working in opposite phase fill the gap, because one is discharging while the other is filling. Long discharge lines or a pulsation damper can smooth it further where a steadier flow matters.
How do I change the flow rate?
Through the motor speed and the control system, within the limits of the pump size you chose. That is why electric diaphragm pumps are often used where flow needs to be repeatable, such as batching and metered transfer.
Where to go next. The EODD pump range lists the sizes and the applications where controlled flow matters.
What happens if the discharge line is blocked?
A diaphragm pump is a positive displacement pump, so it keeps pushing a fixed volume per stroke. With a closed line the pressure keeps rising until something gives way, which is why discharge pressure protection and a clear line matter more than they do for a centrifugal pump. Check the pump's pressure limit before you choose a discharge arrangement.
Which materials touch the liquid?
The chamber, the diaphragm and the check valves. The range is offered in PP, PVDF, SS316, SS316L, aluminium, conductive PP, conductive PVDF and super duplex, and the right choice depends on the liquid, its concentration and temperature, abrasion risk and any hygiene or conductivity requirement.
Where to go next. Match your liquid to a material in the chemical compatibility guide before you settle on a build.
How does the working principle differ from an AODD pump or a centrifugal pump?
All three move liquid, but they get the energy to the liquid in different ways. That difference is what decides where each one fits.
| Parameter | Electric diaphragm (EODD) | Air operated diaphragm (AODD) | Centrifugal |
|---|---|---|---|
| What drives the movement | Electric motor moves the diaphragms | Compressed air moves the diaphragms | Electric motor spins an impeller |
| How liquid is moved | Positive displacement by diaphragm strokes | Positive displacement by diaphragm strokes | Velocity from a rotating impeller |
| How flow is controlled | Pump size, motor speed and the control system | Air pressure and air volume | Valve throttling, a VFD or impeller choice |
| Energy profile | Lower compressed air dependency | Depends on the compressed air system | Efficient for clean fluids at a stable duty point |
| Best suited to | Controlled transfer, batching and frequent process duty | Portable transfer, hazardous areas and plants with available air | Continuous high flow of clean, low viscosity liquid |
If compressed air is available and portability matters, the AODD pump may suit better, and how an AODD pump works explains the air side of the story. For clean liquid at continuous high flow, the centrifugal pump range is the usual starting point. Sando's own product page states that an EODD pump can cut energy cost by up to 80 percent compared with an AODD pump, and the real saving depends on how efficient your compressed air system is, so check it against your own plant.
What should you check before choosing an electric diaphragm pump?
Tick these off as you collect the data. They come straight from how the pump works, because each one changes a part of the cycle above.
Once you have those values, the pump selection manual helps match the liquid and industry to a pump type, and the EODD pump specifications show the build options. If you would like a second pair of eyes on the duty, the enquiry form reaches the technical team.
Frequently asked questions
What is an EODD pump?
An EODD pump is an electric operated double diaphragm pump. An electric drive moves two diaphragms, and the pump transfers liquid with a sealless positive displacement action.
How does an electric diaphragm pump work?
An electric motor, usually through a gearbox and a crank or eccentric, moves two diaphragms back and forth. On the suction stroke a chamber grows and fills through the inlet check valve, and on the discharge stroke it shrinks and pushes the liquid out through the outlet check valve. The two chambers alternate.
What controls the flow rate of an electric diaphragm pump?
The pump size, the volume each diaphragm displaces, the motor speed, the liquid viscosity, the suction condition, the discharge pressure and the piping losses. The motor speed is the part you can adjust during operation.
Why does an electric diaphragm pump have no mechanical seal?
The liquid only contacts the diaphragm, the chamber and the check valves, and the drive sits on the other side of the diaphragm. No rotating shaft passes through the liquid, so a mechanical seal in contact with the liquid is not needed.
Is an electric diaphragm pump the same as an AODD pump?
Both are double diaphragm pumps that move liquid by positive displacement. The difference is the drive. An EODD pump uses an electric motor to move the diaphragms and an AODD pump uses compressed air.
What size and materials are available for electric diaphragm pumps?
The EODD range runs from 1/2 inch to 3 inch connections, with PP, PVDF, SS316, SS316L, aluminium, conductive PP, conductive PVDF and super duplex construction. The right size comes from the flow, pressure, viscosity and duty cycle, and the right material from the liquid, its concentration and temperature.
Where to go next
Industry pages for chemical transfer, pharmaceutical, food and beverage and water and wastewater show how the same working principle is applied in each setting.
Sando Editorial Team
The Sando Editorial Team consists of pump technology experts and engineers at Sando Rotary Equipments, dedicated to sharing insights and innovations in the fluid handling industry.
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