What’s The Working Principle Of Gas Diaphragm Pumps And Compressors?

Diaphragm pumps, also frequently called membrane pumps, are reciprocating pumps. They are a type of positive displacement pump. 

A flexible diaphragm in the pump head is moved up and down via the conrod and through the action of an eccentric on the motor shaft.

On the downstroke, the medium is drawn into the pump chamber and expelled on the upstroke. Internal valves mounted within the pump head act as check valves and control the direction of flow.

Diaphragm Gas Pump - working principle

This is how the diaphragm pump works.
Thanks to the membrane connected to the conrod the air is pumped in or out.

What Are The Main Features Of Diaphragm Pumps And Compressors?


The main features of diaphragm pumps are:


  • low sound level, 
  • high efficiency and gas tightness
  • operational water vapor tolerance
  • working point controllability
  • very good size to performance ratio

Thomas membrane pump models are available with AC or DC drive. They are available in single and multiple head models, which can be configured in series or parallel.

Our range of diaphragm pumps proudly provides a wide range of flow rates from 0.01 cfm (0.3 l/min) to 3.2 cfm (91 l/min), along with end vacuum 29.2 in.Hg (990 mbar), and pressure up 44 psi (3.0 bar).

Most of Thomas diaphragm pump product lines feature several motor options ranging from AC, to low-cost DC up to brushless DC solutions. The sealed air path is inherent to the design itself. We address your required chemical resistance with a variety of pump head and elastomer materials such as PPS (Ryton) or FKM (Viton).


Can Diaphragm Pumps Run Dry?


Diaphragm pumps are oil-less pumps and can run dry. Thanks to that they are often used for the transfer of contaminated air or liquids or air with liquid particles.


Where Are Diaphragm Pumps Used?


Membrane pumps are equally suitable for use as a vacuum pump or an air compressor. Typical applications that use miniature diaphragm air pumps or miniature diaphragm vacuum pumps are handheld or portable gas detectors and analyzers used for environmental applications. Here, leak tightness and chemical resistance come into play. Dental autoclaves or Negative Pressure Wound Therapy (NPWT) devices rely on pump controllability, a low sound level, or pump lifetime and efficiency due to brushless DC configurations. Other equipment that uses diaphragm pumps are various medical devices or laboratory and life-science instruments, food and beverage, or round off-target applications, that require efficient, compact miniature vacuum pumps or miniature air compressors.


What Are The Benefits Of Selecting Gas Diaphragm Pumps?


  • They are suitable for pressure, vacuum, or a combination of the two
  • Provide gas tightness to the outside
  • Are made from durable plastic or corrosion-resistant coated aluminum
  • Can be customized, including a wide variety of elastomers and pump component materials
  • Use long-life diaphragms
  • Are balanced for low vibration
  • Oil-less operation and low noise level
  • Permanently lubricated bearings
  • Thomas diaphragm pumps provide flow rates up to 3.2 cfm (91 l/min), end vacuum levels up to 29.2 in.Hg to (990 mbar), pressure up to 44 psi (3.0 bar)

How Do Liquid Diaphragm Pumps Work?

Diaphragm pumps for gases and liquids might look very similar on the outside. However, due to the contrary nature of gases and liquids, you can see significant differences in the construction of pumps for both types of media. 

The main impact on pump design is that liquids cannot be compressed. Therefore they create higher forces on the pump components and induce pulsation. This leads to diaphragm pump designs with smaller diaphragm strokes, stiffer diaphragm materials, and more robust bearings.

Iiquid diaphragm pump - working principle

This is how the liquid diaphragm pump works.
Notice the difference in the construction of the pumps, necessary to pump fluids efficiently.

What Characterizes Liquid Diaphragm Pumps From Thomas?

Thomas is one of the few manufacturers dedicated to liquid diaphragm pumps. Our pumps provide flow rates ranging from 0.006 cfm (0.18 l/min)  to more than 0.064 cfm (1.8 l/min) along with operating pressures up to 6 bar, maximum suction height up to 10 m H2O ,and max pressure height up to 40 m H2O.

Similar to our gas diaphragm pump portfolio, we offer single or multiple head configurations, as well as an extensive range of brushed and brushless DC motors depending on your flow requirements. Thomas manufactures pumps in all sizes, from mini, through miniature diaphragm pumps up to small units.


What Makes Thomas Liquid Diaphragm Pumps Stand Out?


Pressure pulses are a common problem in positive displacement pumps for liquids. In order to reduce those pulses, we implemented an additional resonating diaphragm to allow more gentle pumping. This also reduces the effect of cavitation and air bubble formation and provides gentle fluid transfers.


What Liquid Diaphragm Pumps Are Used For?


Many applications benefit from liquid diaphragm pumps. For example, digital inkjet printers use liquid diaphragm pumps for ink handling. Digital inkjet printer manufacturers rely on the resistance against aggressive inks as well as the ability to gently move inks for up to 2 years without maintenance.

In-vitro Diagnostic equipment (IVD) such as hematology analyzers require pumps for cleaning the fluid handling system. In these applications, pumps need to operate with high-pressure levels or need to aspire to residue liquids in a fast and thorough way.


What Are The Main Benefits Of Liquid Diaphragm Pumps


Thomas liquid diaphragm pumps are remarkably robust and made for heavy-duty applications. That’s characterized by

  • Long-term suitability with high media temperatures, 
  • Superior resistance to chemical or mechanical damage by fluids. 
  • The highest pressure capacities and highest chemical compatibility among all pump technologies
  • Provides smooth flow and minimized pulses
  • Deliver bubble-free transfer of media
  • Self-priming pumps
  • Oil-less operation
  • Thomas liquid diaphragm pumps provide flow rates up to 0.064 cfm (1.8 l/min), maximum suction height up to 10 m H2O, and max pressure height up to 40 m H2O,

Our small and miniature pumps provide excellent performance regardless of their size. Depending on the type of liquid, you can choose pump components in the most suitable material, such as EPDM, FKM, PTFE, or FFKM.

Among liquid pumps, the diaphragm technology stands out due to its excellent ratio between cost and pump lifetime. This makes it the prime solution for applications requiring continuous operation without the need for maintenance. With the range of brushless DC motors (BLDC) lifetimes of over 10,000 hours can be achieved with Thomas liquid diaphragm pumps.

Select Max. Pressure Level

Up to 1 bar/14.5 psi
1-2 bar/14.5-29 psi
2-5 bar/29-72.52 psi
5-7 bar/72.52-101.53 psi
7-10 bar/101.53-145 psi
above 10 bar/145 psi

Select Flow Rate (cfm)

up to 0.035 cfm
0.035-0.176 cfm
1-2 cfm
2-3 cfm
3-4 cfm
4-5 cfm
above 5 cfm

Select Max. Vacuum

Up to 300mbar / 9 in.Hg
300-500 mbar / 9-14.75 in.Hg
500-800 mbar / 14.75-23.6 in.Hg
800-900 mbar / 23.6-26.6 in.Hg
Above 900 mbar / 26.6 in.Hg

Select Flow Rate (l/min

up to 1 LPM
1-5 LPM
5-10 LPM
10-20 LPM
20-30 LPM
30-50 LPM
50-100 LPM
above 150 LPM

Select Max. Suction Height

0-3 mH2O
3-6 mH2O
6-10 mH2O

Select Primary Medium Type


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