Chemical Seals

Dale Foster Sales offers a broad range of chemical seals from Ashcroft, WIKA and Trerice. For use in isolating pressure instruments from clogging or corrosive fluid media, chemical seals are available in a wide choice of models to meet your specific application need.

Please note Chemical Seals are Special Order Items.

For Immediate Price and Availability, Contact Customer Service at: Live Chat Online, Customer Service Line 1-800-326-6518, or e-mail

Principles of Operation

A Diaphragm (or Chemical) Seal is a device consisting of a diaphragm clamped between two suitable housings that are properly gasketed to prevent leakage of liquid or gas. The diaphragm (a dividing membrane or thin partition) acts as a barrier to isolate and protect the sensing element of a pressure instrument from potentially destructive process media. Without such a barrier, the process media might clog or corrode the pressure instrument, causing failure or inaccurate response. The sensing element of the pressure instrument, as well as the space above the diaphragm of the seal, is evacuated and then filled with an incompressible liquid. When force (process media) is applied to the diaphragm seal, the internal diaphragm will flex and the displaced liquid fill will then transmit the force to the sensing element of the pressure instrument, resulting in a pressure measurement.


Diaphragm seals will meet a wide variety of application or installation requirements. Over 30,000 variations are possible with the types, connections and materials available. Ashcroft diaphragm seals are normally mounted directly to the socket of an instru­ment. A flexible stainless steel armored line assembly is available for mounting the gauge at some point away from the seal location to provide easy reading or to limit the temperature at the gauge to 150°F maxi­mum. Diaphragm seals (isolators) with filled, capillary line assemblies are another good solution to the problem of hot liquid and gas lines. Due to the small diameter of the flex­ible line (capillary) a five foot line length will usually assure that the temperature of the gauge connection does not exceed 150°F. This solution is also superior to a siphon on steam service where the water filled siphon might freeze.


Diaphragm Seals are available in a variety of diaphragm sizes: Mini (Series 2), Compact (Series 3), Sanitary (Series 4), Standard (Series 5) and Large (Series 6). Mini and Compact diaphragm sizes are designed to provide economical protection for pressure gauges (Contractor/Commercial/Utility) with a dial face size of 41/2" or smaller. Sanitary Diaphragm Seals are designed for use with Tri-Clamp process connections. Standard and Large diaphragm sizes are the most versatile, with a variety of available materials and connections. The Large diaphragm size has twice the diaphragm surface area of the Standard diaphragm size and is therefore more sensitive and better suited for low pressure applications.


Diaphragm seals are available to fit a wide variety of applications. WIKA has long manufactured diaphragm seals for the following applications: Assembled systems, Threaded, Flanged, Inline, Sanitary, Plastic and Capsule.

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Special Order Products

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