The diaphragm seal – overview

General

Diaphragm seals separate the pressure gauge from the actual medium. They prevent the ingress of media into the measuring system. This is particularly necessary for aggressive substances and for processes with special hygienic requirements. In addition, diaphragm seals solve measurement problems, such as shocks, vibrations and high temperatures, which would otherwise falsify the measurement result.

What are the functions of diaphragm seals?

  • Measuring pressure fluctuations and pressure peaks are dampened
  • Measuring point arrangement without dead space
  • Measuring devices are protected against vibrations when connected via long-distance lines
  • Provide protection against high temperatures and temperature fluctuations
  • Protection against aggressive, solidifying, highly viscous and crystallizing media
  • For special applications, you can use special materials, possibly coatings at the points in contact with the medium
  • It is possible to spatially separate the measuring device and measuring point through remote maintenance

How does a diaphragm seal system work?

The process pressure acts as homogeneously as possible via a membrane on a liquid, which in turn affects the measuring element of the pressure gauge via a line.
With this basic principle, pressure gauges can generally be connected to any process via diaphragm seal systems.

What designs are there?

There is a large variety of different designs for diaphragm seals. A distinction can essentially be made between two basic designs - pipe diaphragm seal and flat diaphragm seal.

In-line diaphragm seal

In-line diaphragm seals are cylindrical diaphragms welded into a tube. Since this design is easy to clean and is self-draining, and also avoids various hygienic risks such as flow obstructions and turbulence, it is ideally suited for dead space-free applications, constant measurement material changes and viscous media.

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Flat diaphragm seal

Flat diaphragm seals are simple in design. The membrane lies on a plane and is mostly circular. This design provides minimal sensitivity to temperature changes due to the resilience of the diaphragm. This makes it suitable for processes that require high accuracy or have to measure small pressures.

flat pressure transmitter

What is the diaphragm seal?

The diaphragm dictates the basic properties of the diaphragm seal. The rigidity is the most important parameter when considering errors. It depends on the material, the material thickness, as well as the shape of the bead and the nominal diameter.
A very important task of the diaphragm is to compensate for temperature-related volume fluctuations in the pressure transmission fluid. In order to obtain accurate measurement results, the temperature error must be compensated. The sinus membrane is the standard and can therefore be used universally. It can be recognized by the sinusoidal waves. This shape allows for minimal temperature error. Additional coatings are possible, as is the manufacture of the sinus membrane from different materials.

What materials is the diaphragm seal made of?

Unless there are special process requirements, 316L stainless steel diaphragms are standard. 316L stainless steel is very resistant, even to weak acids and alkalis. Diaphragms made of stainless steel 316L are used as standard in the pharmaceutical industry.

Duplex steel is resistant to stress corrosion cracking in media containing chlorine and also to pitting. Because it is resistant to seawater, it is used in the chemical and petrochemical industries.

Tantalum has the highest corrosion resistance, making it resistant to almost all pure acids.

Due to the formation of titanium dioxide as a protective layer, titanium has very good corrosion resistance. It can be used with strongly oxidizing and chlorine-rich solutions and suspensions.

Hastelloy is a nickel-based alloy. It has a high resistance to pitting, crevice and stress crack corrosion, as well as to medium-concentrated sulfuric acid, acetic acid, phosphoric acid and to chlorides.

Monel is a nickel-copper alloy. It is resistant to strong alkalis, most salt solutions, diluted and medium-concentrated inorganic acids and sea water.

Nickel is resistant to strong alkalis, such as sodium hydroxide and potassium hydroxide.

What are diaphragm seals coated with?

Gold is suitable for hydrogen applications because it has a low tendency to react.

PFA is used with adhesive media and is resistant to almost all chemicals. It is suitable for temperature ranges from -40° C … +260° C.

PTFE has a very good non-stick effect. It is resistant to strong alkalis and acids.

Rubbing is often used in the cement industry as it protects the membrane from sharp objects.

ECTFE (Halar) has a layer thickness of 200 ÎĽm - 300 ÎĽm, which means that non-porous layers are possible. In addition, this thermoplastic has the highest resistance to most chemicals and solvents.

What transmission fluids are there?

The choice of transmission fluid depends entirely on the application. There are many different substances with individual properties. For example, silicone-free synthetic oil is well suited for the food industry, halocarbon oil is suitable for oxygen applications and alcohol-water mixtures are used in the paint industry.

What process connection variants are there?

Flange connections are a good connection, so they are also suitable for high pressures. They are often used in the chemical and petrochemical industries.

Clamp connections are easy to disassemble and clean. That is why they are used almost exclusively in hygienic processes.

Screw connections are available for aseptic applications.

  • Dead-space free, direct installation in pipes
  • Easy to open, self-draining in all mounting positions
  • Quick cleaning, without residue
  • Suitable for COP, SIP and CIP
  • Autoclavable version

 

Datasheet
User Manual

  • For cleaning easy to open
  • Quick cleaning of measuring point, without residue
  • Suitable for SIP and CIP
  • 3-A certified
  • Flush, welded diaphragm

 

Datasheet
User Manual

  • Pressure and temperature measurement in one measuring location
  • Completely round diaphragm (European Patent No. 0609846) to avoid dead spaces
  • Self-draining in all mounting positions
  • Quick measuring point cleaning without residues
  • Suitable for SIP and CIP

 

Datasheet
User Manual

  • Dead-space free installation in pipes
  • Self-draining in all mounting positions
  • Quick cleaning, without residue
  • Suitable for SIP and CIP
  • EHEDG-certified and 3-A-compliant

 

Datasheet
User Manual

  • For direct, quickly removable installation in pipelines
  • Self-draining in all mounting positions
  • Quick cleaning, without residue
  • Suitable for COP, SIP and CIP
  • Dead-space free installation in pipes

 

Datasheet
User Manual

  • High pressures up to PN 400 / class 2.500
  • Flange with internal welded diaphragm
  • Small process connections
  • Flushing connections optionally available

 

Datasheet
User Manual

  • Quick cleaning, without residue
  • Suitable for SIP and CIP
  • EHEDG certified and 3-A compliant
  • Certified hygienic design

 

Datasheet
User Manual

  • For cleaning easy to remove
  • Quick cleaning of measuring point, without residue
  • Suitable for cleaning out of place (COP)
  • 3-A compliant
Datasheet
User Manual

  • Flush diaphragm
  • Process connection to provide for direct threaded connection with block flange or saddle flange
Datasheet
User Manual

  • Rotatable retainer flange
  • Versions with 90° pipe elbow and vibration damper
Datasheet
User Manual

  • Completely round, no corners and edges
  • For direct installation between two flanges
  • Wide choice of special materials
Datasheet
User Manual

  • Completely round, no corners and edges
  • For direct installation between two flanges
  • Wide choice of special materials
Datasheet
User Manual

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