FAQ

Diaphragm Seals

What is a diaphragm seal?

A diaphragm seal is an additional component which protects a pressure measuring instrument or process transmitter. It transfers the medium to the measuring instrument without it coming into contact with the measuring instrument.

How does a diaphragm seal work?

A diaphragm made of the appropriate material separates the medium to be measured from the measuring instrument. The internal space between the diaphragm and the pressure measuring instrument is completely filled with a system fill fluid. The process pressure is transmitted by the elastic diaphragm into the fluid and from there to the measuring instrument.

When should a diaphragm seal be fitted?

Diaphragm seals are used for pressure measurements when the process medium should not come into contact with the pressurised parts of the measuring instrument or if adjustment to the harsh conditions of a process is needed.

How are diaphragm seals integrated into processes?

Diaphragm seals are mounted to existing connecting flanges or welding sockets, which are welded to a pipeline, a process reactor or a tank.

What are the advantages of diaphragm seals?

Diaphragm seals offer the advantage that the “contact surface” between pressure medium and diaphragm is relatively large, thus ensuring accurate pressure measurement, especially for very low pressures (< 600 mbar). Furthermore, they can be easily dismounted, e.g. for cleaning or calibration purposes.

What are the characteristics of an in-line diaphragm seal?

The in-line diaphragm seal is perfectly suited for use with flowing media. With the seal being completely integrated into the process line, measurements do not cause any turbulence, corners, dead spaces or other obstructions in the flow direction.

What are the advantages of an in-line diaphragm seal?

With in-line diaphragm seals, with their perfectly circular cylindrical form, the medium flows through unhindered and effects the self-cleaning of the measuring chamber. Different nominal widths allow the in-line diaphragm seals to be adapted to any pipeline cross-section.

What is a capsule-type diaphragm seal?

This type is especially suitable for heterogeneous media, since it is inserted directly into the medium. It has a particularly small space requirement in comparison to other diaphragm seals. The pressure is captured 'at a point'. The seal consists of an oval tube, closed at one end, as a pressure sensor and a connector part welded to it.  To stabilise it, the sensor is mounted to a fitting.  The adaptation to the measuring point is made using female or male threads.

With which instruments can a diaphragm seal be combined?

A diaphragm seal can be combined with almost all pressure gauges, process transmitters, pressure switches or pressure sensors.

What are the mounting options for a diaphragm seal?

A diaphragm seal can be mounted via a direct connection, a cooling element or a capillary.

How flexibly can a diaphragm seal be assembled?

The optimal diaphragm seal designs, materials, filling media and accessories are available for each application. Certificates can be supplied depending on the requirement.

What is a diaphragm seal characteristic curve?

The diaphragm seal characteristic curve shows a graphical representation of the elasticity of the diaphragm. In this representation, the volume change is related to the pressure change and illustrated.

When are flange connections used with diaphragm seals?

The combinations of diaphragm seals with flange connections can be used for processes with extreme temperatures and with aggressive, adhesive, corrosive, highly viscous, environmentally hazardous or toxic media. With its connection dimensions, the flange-type diaphragm seal is suitable for all currently used standard flanges and is mounted in lieu of a blind flange.

How are the diaphragm seals connected?

The diaphragm seals are available with female or male thread in their basic design. Due to the wide variety of available process connections they can be mounted to many different connections without any problems. Generally these connections are T-pieces which are integrated into a pipeline or welded to a pipeline by means of a welding socket.

When are sterile connections used with diaphragm seals?

The combination of diaphragm seals with pressure measuring instruments in hygienic design can be used for processes with gases, compressed air or vapour and also with liquid, paste-like, powdery and hot media. The diaphragm seals resist the temperatures that occur and meet the requirements for sterile connections.

SIP and CIP criteria, which are an essential requirement for sanitary applications, are met by using diaphragm seals. These acronyms stand for the sterilisation and cleaning of the wetted parts in the process. The combination of pressure measuring instruments with flush diaphragm seals or in-line diaphragm seals meets the stringent demands made on hygienic instrumentation and is suitable for even the most difficult measuring requirements.

Why are there different materials or coatings with diaphragm seals?

Various materials or coatings are available for diaphragm seals to allow accurate measurement of difficult media (aggressive, corrosive, abrasive, highly viscous, heterogeneous, toxic, hot or aseptic). Suitable materials or coatings are available for almost all processes.

Why are there different system fill fluids with diaphragm seals?

In selecting the system fill fluid for diaphragm seals, factors such as compatibility (physiologically harmless) and also temperature and pressure conditions at the measurement location are of crucial importance. Depending on the system fill fluid, the appropriate minimum and maximum operating temperature range must be observed.

What influence does the diameter of the diaphragm have on the display?

Diaphragms with small diameters can only measure small volume changes. The larger the diameter of a diaphragm, the better the deviations that occur can be compensated for.

What is a diaphragm seal with an extended diaphragm and when are these used?

A diaphragm seal with extended diaphragm is used for thick and/or insulated product pipelines or vessel walls. The cell-type design is a sub-category, which is used with a blind flange at the tapping flange. Special designs can be manufactured to customer's specific requests.

When are threaded connections used with diaphragm seals?

The combinations of diaphragm seals with threaded connection can be used for processes with extreme temperatures and with aggressive, adhesive, corrosive, environmentally hazardous or toxic media.