Pressure -MD28-38 Diaphragm SealsIndonesia Industrial Parts

MD28-38 Diaphragm Seals

Pressure – MD28-38 Diaphragm Seals are auxiliary components for pressure gauges, designed to protect pressure transmitters, pressure gauges, or other measuring devices from aggressive, dirty, or high-viscosity media.

Using a sensitive yet durable membrane, they transfer pressure from the media to the gauge without direct contact, ensuring accuracy and longevity of the gauge.

General Description

Diaphragm seals are used to isolate pressure/differential pressure measuring instruments such as gauges, transmitters, or sensors, from the media to be measured. This becomes necessary in unfavourable operating conditions such as

High media temperature
Corrosive media
Difficult measuring locations

Important Features

Corrosion resistant materials
Easy installation
Maintenance free

Principles of Operation

Diaphragm seals are added to pressure/ differential pressure measuring devices to protect these from corrosive media, high media temperatures, and other difficult measuring conditions. A diaphragm seal provides a fluid-filled isolation stage between the pressure medium (5) and sensitive parts of the measuring device (4). A flexible diaphragm (1) of suitable material (generally stainless steel) is the primary barrier between the pressure media and the measuring device. The space between the isolating diaphragm and the sensing surface of the measuring device is filled with special liquid (3), e.g., silicone oil. Media pressure (P) is transferred to the measuring device through the flexible diaphragm and filling liquid.

As a rule, pressure seals and pressure gauge are assembled together, precharged with filling fluid, and supplied as one unit. The pressure measuring device is directly fastened to the diaphragm seal assembly, or connected to a remote diaphragm seal assembly by means of a
capillary tube. The capillary tube versions are used to isolate high media temperatures from pressure measuring devices.

Selection criteria

To select a suitable diaphragm seal for a particular application, several factors need to be considered:

Chemical and physical properties of the pressure medium
Pressure displacement volume
Media temperature
Pressure measuring range

The manufacturer’s recommendations on this subject should be considered. Regarding diaphragm seal size, the following guideline should be generally followed. Small displacement volume seals (Model MD 38) should be used for higher pressure and differential pressure ranges, particularly with electronic sensors/transmitters. Large displacement volume seals (Model MD 28) should be used for low pressure and differential pressure applications, particularly when mechanical gauges are used.

Lined system

For particularly aggressive media, all components coming into contact with the medium can be given a protective lining of pure PTFE. The lining is about 0.5 mm thick for the diaphragm, and about 2 mm thick for other media contact parts of the seal. O-rings used in such applications are FEP coated.

An economical alternative to PTFE is ECTFE lining, which has the same chemical resistance properties. The chemical resistance however, must be tested for each application before use.

A note regarding connections: For diaphragm seals with PTFE/ECTFE lining, suitable sealingmaterial (PTFE) must also be used for the process connections.