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Specialist diaphragm seals for hygienic and ATEX applications

This article illustrates how LABOM’s patented diaphragm types, and customer-specific designs for diaphragm seals were ideally suited for measuring the difficult media involved in Eisenmann’s painting systems.

What are diaphragm seals?

Diaphragm seals are partitions in pressure measuring instruments, which prevent the measured medium from entering the measuring system.

This allows them to protect the gauges from aggressive, highly viscous or solidifying measurement media as well as from high media temperatures, vapours, measurement pressure fluctuations and pressure spikes as well as increasing the overload capacity.

They also provide relief in case of an unfavourable location of the pressure measurement device. Diaphragm seals also enable the use of pressure gauges in potentially explosive areas as well as a measurement arrangement free of dead space.

Diaphragm seals for paint applications

For the painting systems in operation at Eisenmann, a leading supplier of surface finishing technology, LABOM designed a ‘piggable’ inline diaphragm seal, whereby its specially designed shape ensures self-draining.

These cleaning options are important for quality assurance, as they prevent undesired mixing of different paint colours. They are also important for economic operation, as even minor residue of the pasty paint in the process pipes can lead to considerable loss of material in the long run.

Eisenmann used the inline diaphragm seals, together with pressure gauges and pressure transducers, for the colour supply of the painting systems. Here the paint containers are pumped, together with solvents, into the circulation and distributed through the pipes to the application.

Diaphragm seals

The measurement equipment monitors the process pressure of approx. 12 to 16 bar and regulates the circulation process using this variable. The paint is processed at a temperature of 22 °C.

LABOM developed a diaphragm seal that was particularly suited to the transmission fluid at Eisenmann - a diaphragm seal system filling that is absolutely free of silicone and prevents paint wetting. The fill fluid can easily withstand temperatures from -20 to +120 °C and the aseptic screw fitting ensures a dead-space free measurement in which the paint is not compromised in any way.

The device combination is in an intrinsically safe ATEX design in Eisenmann painting systems for automotive manufacturers around the world.

The advantages of LABOM’s diaphragm seals

For applications in which sinusoidal diaphragms are not the optimal solution, LABOM has developed two patented alternatives. One of them is the compensation diaphragm made of Hastelloy or tantalum. With a material thickness of 0.1 millimetres, it is suitable for low-pressure applications.

The temperature-dependent volume expansion of the transmission fluid, which would also affect the pressure recorded by the measurement element, is compensated by the compensation diaphragm automatically. This is possible due to the diaphragm contour and the different materials of the body and the diaphragm that are used here.

LABOM diaphragm seal

The volumes under the individual circular rings of the diaphragm and the expansion behaviour of the diaphragm seal materials caused by the temperature ensure that the increasing volumes of the transmission volume are compensated for.

The LTC (Low Temperature Coefficient) diaphragm, also developed by Labom, compensates the temperature-dependent volume expansion of the pressure transmission fluid with a stainless-steel diaphragm. The mechanically robust stainless-steel diaphragm with a thickness of at least 0.1 millimetres is spanned radially to the centre using a special manufacturing process. Thus, it has at least two zero positions that it wants to assume.

Inline diaphragm seal

Using a special manufacturing process, the diaphragm is put into a position between the two zero positions and operates in this range with almost no deflection. This allows the diaphragm to absorb volume changes to the fluid due to the influence of temperature so that these fluctuations have practically no effect.

Compared to conventional sinusoidal diaphragms, an LTC diaphragm can deliver up to 70 per cent greater measurement accuracy.

Diaphragm seals for specialist applications

LABOM have positioned themselves as experts in diaphragm seals and instrumentation for specialist applications. They are most comfortable dealing with the extra-ordinary and pride themselves in adding value to applications that engineers didn’t know could even be improved.

If you are currently using diaphragm seals in your application, why not explore what LABOM has to offer you?

To contact LABOM, visit their PIF Profile. Or visit our Solution Centre to ask a technical question, LABOM experts will be on-hand to answer your questions.

Company Profile


For over 40 years LABOM has been one of the leaders in quality for industrial pressure and temperature measurement technology.

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