Diaphragm Pump

A diaphragm pump is the most famous type of pump from the category of positive displacement pump. It is also called a Membrane pump. For pumping a fluid, a diaphragm pump uses a combination of the reciprocating action of the diaphragm made of  Teflon, thermoplastic, or rubber with the corresponding valves (globe valves, flap valves, butterfly valves, check valves or any other type of valves) on both sides of the diaphragm.

The diaphragm pump

The diaphragm pump has the following types:

• In the 1^st type, one side of the diaphragm seal consists of pumped fluid and the other consists of hydraulic oil or air. The curved diaphragm increases or decreases the volume of the pump chamber. In this type, a pair of one-way check valves prevent the liquid’s backflow.
• Those with positive volume displacement, in which the diaphragm prime mover is electromechanical, is driven by a geared motor or a crank or is purely mechanical, e.g., with a handle or a lever. This technique uses a simple mechanical movement to flex the diaphragm and open one side of the diaphragm to the air.
• In the third type of diaphragm vacuum pump, one or more opened membranes require for pumping fluid on both sides. The membrane bends again, and the volume changes.

These types of pumps are widely used in numerous factories because they can handle an extensive collection of fluids. The diaphragm pumps are very famous because they can move liquids with high, medium, or low viscosity and liquids with high solids contents. This pump can also be made from various body materials and membranes to handle a variety of harsh chemicals such as acids.

Working Principle of Diaphragm Pump

A diaphragm or membrane pump is a positive displacement pump that uses two flexible diaphragms that move forward and backward to form a temporary Vacuum. This Vacuum can either draw or drain the liquid from the diaphragm pump. The membrane acts as a partition wall between liquid and air. The working principle of the diaphragm pump is given below:

First Stroke:

The two diaphragms connect by a shaft through the central part in which the air valve is placed. The air valve uses to force compressed air behind the first diaphragm and moves it away from the middle section.

The 1^st diaphragm creates a pressure stroke that removes fluid from the pump. Simultaneously, the second diaphragm performs the suction stroke. The air behind the 2^nd diaphragm is released to the atmosphere, and atmospheric pressure forces the fluid to the suction side.

The suction valve pushes out of the seat, and fluid flows through the ball valve into the pump’s fluid chamber.

Second Stroke:

As the 1^st pressurized diaphragm reaches the end of its stroke, air transfers from the 1^st diaphragm to the back of the 2^nd diaphragm through the air valve. The pressurized air pushes the 2^nd diaphragm away from the central block, and the 1^st diaphragm is pulled into the central block.

In the second chamber of the pump, the outlet ball valve is pushed out from its seat, while the first chamber has the opposite situation. When the second stroke completes, the air valve pumps air behind the 1^st diaphragm, and the whole cycle repeats.

Types of Diaphragm Pumps

The diaphragm pumps have the following major types:

1. Air-Operated Pump
2. Motor-Driven Pump
3. Small Motor Driven Pump
4. Small Air-Operated Pump
5. Wanner Hydra-Cell Pump

1) Air-Operated Diaphragm Pump

It is the most common type of diaphragm pump. The operation of the air-operated pump may be carried out with compressed air. It has 2 assembly chambers with a diaphragm.

This pump has a discharge check valve and a suction check valve for each assembly chamber. The air supply moves from one assembly chamber to the second assembly chamber through an air spool regulator unit that may install inside the pump.

The systematic operation of air transfer from one assembly chamber to another chamber causes liquid from one assembly chamber to flow down the drainpipe by filling the other assembly chamber with liquid. As a result, the pump has a pulsation in the discharge flow, which the pulsation damper can reduce in the delivery pipe.

2) Small Pneumatic Pumps

A small pneumatic pump can handle normal fluid viscosities, and there is no phenomenon that the slurry tends to concentrate.

Therefore, these pumps use for low volume fluids distribution accounts. The suction and discharge ports of this pump have 3/8, 1/2, otherwise 3/4 with flow rates ranging from 2 GPM to -10 GPM.

3) Small Electric or Motor Driven Pumps

Small motor-driven pumps produce a force up to 60 PSI and sometimes 100 PSI. There are two different types of this type of pump-style:

• The first is the demanding style with fixed force switches that regularly stop and start the pump with accurate force settings. This style is very popular all over the world.
• The second style is a bypass style. Regardless of how much force is applied to the system, the pump of this style will continue to work everywhere. Whenever the outlet valve is closed, it stops the internal flow. However, closing the outlet valve for a few minutes may overheat the fluid and damage the internal part of the pump.

4) Wanner Hydra-Cell Pumps

This is a larger shaft-operated pump that can deliver up to 1500 PSI of pressure, and in some cases, 2500 PSI, and the flow rate is 36 GPM. These pumps design by using various metals and elastomers for acid solutions, hot fluids, wettable powders, violent chemicals, abrasives, and mud.

Characteristics of Diaphragm Pump

• This positive displacement pump can pump flammable, toxic, abrasive, and corrosive fluids.
• It can handle very viscous fluids. The viscosity correction table can use as a tool to prevent the AOD pump from being reduced in size.
• It has excellent self-priming ability.
• The design of this pump differentiates the pump fluid from potentially sensitive internal pump components.
• The maximum efficiency of this pump can reach 97%.
• It uses the production of air pumps for small aquarium filters.
• Internal pump components are often suspended in oil and insulated to extend the life of the pump.
• These pumps are best suitable for corrosive and abrasives solutions
• A diaphragm or membrane pump may use to create an artificial heart.
• It has good idling properties.
• Appropriate for exhaust pressures up to 1200bar
• These pumps have good suction lift features, some of which are low flow rate and low-pressure pumps. Other models can provide higher flow rates depending on the diaphragm’s stroke length and effective working diameter. You can handle slurries and sludge with relatively large solids and particle sizes.

How to Choose a Diaphragm or Membrane Pump

Diaphragm pumps include in the famous types of pumps that are oil-free. Nowadays, these are used in numerous products to prevent the oil vapor impurity problems that plague many of today’s rigorous processes.

The diaphragm pumps available in the market that does not contain seal oil or lubricant in the pump head. That is, a vacuum can be created where the exhaust gases are completely free of oil vapors.

All oil-free or not oil-free diaphragm vacuum pumps have distinct operating properties due to that they are perfectly suited for one application but not for another.A diaphragm pump is no exception.

In the pump choice, it isn’t easy to match the type of pump to your application. But the best way to choose a diaphragm vacuum pump is to compare the pump modes of working in terms of strength, characteristics, and weaknesses with your application that can alleviate some issues.

A diaphragm pump is ideal for pumping large volumes of materials at relatively low pressure. These pumps generally resist wear because they don’t move the piston in the cylinder, but one or more simple rubber diaphragms move left and right to transfer material.

You should follow the below steps for choosing a diaphragm pump:

1) Pump Volume Requirements

When choosing a diaphragm pump, it is essential to make sure that the pump that you are trying to choose operates at 50 percent of its highest potential during normal use.

If the pump is operated at half of its highest capacity, it should run for an extended period without extensive maintenance. Diaphragm pumps should indicate their operating capacity (gallons/minute) on the sales sheet or in the deal manual.

2) Type of displacement pump drive

A diaphragm pump has many ways to move the diaphragm backward and forward to allow material to be pumped. The most popular drive options for diaphragm pumps are pneumatic or electrical drive pumps. This drive is important for the safe use of the diaphragm pump, and also it affects the operating position of the pump.

3) Pump material

These positive displacement pumps are available in different materials. In general, the most suitable material choices for available diaphragm pumps include the pump seat and ball materials and the material of the pump body.

There are many things to consider, but common coating options include stainless steel seats and balls and PTFE membrane materials. Stainless steel is high wear-resistant, but it has a high price. PTFE, on the other hand, has low price than stainless steel but may not tolerate abrasives. In addition, stainless steel tends to be more elastic when it is hot.

4) Pump performance curve for air operated Diaphragm Pumps

Each diaphragm pump has a performance curve that contains many more details about the pump. The general information covered by the performance curve of the diaphragm pump includes the amount of air (CFM) the pump needs at different levels of operation and the amount of material that can be supplied and transported at different levels of operation.

It is vital for a specific diaphragm pump to know that there should have enough air to operate the pump and that the pump can move the material at the required speed and delivery distance.

It is essential to check that the diaphragm pump under consideration can deliver the required amount of material (the curves will show higher operating speeds, but it should be noted that it is generally desirable to operate the pump at a capacity of up to about 50% to reduce wear). You should have sufficient air to operate the pump within the required distance.

Which fluids a Diaphragm Pump can Pump?

The diaphragm vacuum pump can pump the following fluids

• Powders
• Titanium Dioxide
• Latex
• Adhesives
• Lacquers
• Greases
• Paints
• Varnishes

Applications of Diaphragm Pump

• Mixing Tanks
• Filling Machines
• Paint Filtration
• Pigment Milling
• Filter Press
• 55 Gallon Drum Transfer
• Air Spray – Supply or Transfer
• General Unloading/Transfer
• Powder Coating
• The elastomeric diaphragm can use as a general-purpose dynamic seal, removing numerous restrictions found with other sealing techniques. They can be built leak-free, friction-free, and sensitive to low pressure. With proper material considerations, the diaphragm can be sealed over wide pressure and temperature range without maintenance or lubrication.

Advantages and disadvantages of Diaphragm Pump

Advantages	Disadvantages
This is an oil-free pump and has less seal	It has low speed
It can be used for food design	Not very energy efficient
Excellent wear resistance	Pulse flow: dampers are required for the decline
It has self-priming until six meters	These pumps do not deliver high pressure when pumping
It has a large displacement volume
Easy maintenance/cleaning
It can work without oil for a short time
It has a multifunctional design and functions (suitable for most media types)
The lifting capacity of a diaphragm pump refers to the vertical height at which the pump effectively picks up material. The capacity to pump material up makes diaphragm pumps an excellent choice for moving material out of the area like well or similar conditions.

Difference between the Diaphragm Pump and Peristaltic Pump

The main difference between the peristaltic pump and diaphragm pump is given below:

Diaphragm Pump	Peristaltic Pump
A diaphragm pump moves fluid by creating suction by a vibrating diaphragm.	A peristaltic pump moves the fluid by squeezing a liquid-filled hose.
These have a complex design.	These have a simple design.
The diaphragm pumps have more valves than the peristaltic pump.	These have a low number of valves.
These have a complex operation.	These pumps have an easy operation.
This pump has a check valve.	It doesn’t have any check valve.

Ultimately diaphragm pumps are a great way to move large volumes of materials efficiently and quickly. When choosing a diaphragm vacuum pump, consider the four features (given above) to ensure that your diaphragm or membrane pump produces excellent results.

If you follow this simple tip, you can choose between a long-lasting, high-performance diaphragm pump. If you have any further suggestions for diaphragm pumps, please contact Thai Khuong immediately.