Type 25/25H Standard & Elevated Pressure, Non-Replaceable Diaphragm Seals

A: Utilizing diaphragm seals with instruments is recommended when instrumentation is to be used in corrosive process media or extreme temperature media environments. Important factors to consider when selecting the correct diaphragm seal for a specific application include the instrument's location, the instrument's process connection size and type, process pressure and temperature limits, and any nontechnical fill fluid limitations such as nontoxic fill fluids for sanitary applications.

A: Process media compatibility is a key factor to consider when selecting a diaphragm seal fill fluid. Process media temperature should also be taken into account as all fill fluids expand or contract with temperature variations. The fill fluid viscosity and density are directly related to the measurement response time; the more viscous the fill fluid, the longer the response time, and a higher density fill fluid may affect mounting as well. Common diaphragm seal fill fluids include glycerin, silicone oils and halocarbon, but NOSHOK offers many more options including Neobee M20, mineral oil and propylene glycol for specialized applications. Glycerin should not be used for vacuum and compound gauges, or where a capillary is used between the instrument and diaphragm seal.

A: A diaphragm seal is designed to provide protection from corrosive, viscous, contaminated or very high temperature process media to valuable instrumentation. The pressure measuring element of the measuring device and the instrument connection port are filled with a suitable liquid using vacuum filling technology, making pressure measurement a direct and simple process. Pressure, when applied to the surface of the diaphragm, causes a pressure increase in the fill fluid which is then transferred to the attached pressure gauge, transducer, switch or other pressure measuring instrument.

A: Diaphragm seals can be used with pressure gauges, pressure transducers and transmitters, and electronic pressure switches.

A: Cooling elements work in combination with diaphragm seals to isolate the instrument from high media temperatures and are recommended for process temperatures above 212 ∞F. They provide effective temperature reductions of up to 200 ∞F depending upon ambient conditions and require a direct mounted system. Stainless steel capillaries with or without stainless steel armor can be used to protect the instrument from high or low process temperatures and allow remote mounting of pressure instruments; the shortest practical capillary length should be selected, as changes in ambient temperature conditions may significantly affect accuracy and response time. Sanitary clamps and gaskets for the NOSHOK Type 12 seal are available in NBR, EPDM, PTFE and FKM and meet FDA and 3A sanitary standards.

A: In general, the diaphragm adds approximately one-half percent to the instrument error at room temperature. There are also additional thermal errors that need to be calculated depending on the application. NOSHOK provides a thermal error calculation document to support these calculations, such as the Diaphragm Seal Thermal Error Calculations PDF available on the NOSHOK website.

A: The fill fluid pressure is equal to the application pressure. If a diaphragm bursts, the fill fluid will be dispersed into the process media and the instrument will be subjected directly to the pressure of the process media.