Where do you need to install chemical seals with pressure gauges or transmitters?
- Where the process medium would corrode the instrument
connection and pressure sensing element. Chemical "attacks"
cause costly instrument failures and unscheduled downtime.
- Where the process medium contains suspended solids or is
viscous enough to clog the instrument connection and the
pressure sensing element. Blocked pressure ports prevent
- Where the process medium might freeze or solidify in the
instrument connection and sensing element due to temperature
changes. Solid media can block pressure ports, preventing
accurate measurement, or distort the diaphragm of your measuring
- Where changing process medium requires flushing the system
to prevent contamination.
- Where the process application requires sanitary connections.
Most measuring instruments cannot meet 3A sanitary standards due
to crevices inherent to their design. Or they can’t withstand
the temperature requirements of steam cleaning. A diaphragm seal
provides a sanitary connection and allows easy cleaning between
- Where your measuring instrument has to be remote mounted to
protect it from high ambient temperatures, vibration, harsh
environments, or accessibility problems. A diaphragm seal
ensures reliable and accurate pressure measurements.
What Do You Need to Know to Pick the Right Chemical Seal?
- Mounting Type
Your options include threaded (NPT), flange attached, pancake
mounting between two flanges, weld attached and sanitary clamp
- Material Compatibility
The proper selection of wetted parts ensures the application
compatibility of your diaphragm seal. Consider all chemicals the
seal will be exposed to during service. You’ll pick the seal
material that will best stand up to corrosion, pitting, stress
cracking, embrittlement, and hydrogen permeation. If you have an
extremely caustic media, look at an all-Teflon insert, flange
attached seal or a pancake-style ring seal. By using elastomers,
you can drastically reduce seal cost and maintenance.
- Process Working Pressures
This is important for extremely low or high pressures. Between
100 and 1000 PSI, almost any seal will suit. It is best to use
elastomer seals for low pressure so the diaphragm will flex
enough to transmit the pressure to your instrument. For high
pressures, it is best to use a metal diaphragm. In most
applications, they will last longer.
- Process Temperatures
In order to transmit the process pressure through the seal to
the sensing instrument, you must fill the sensor with a fill
fluid. All fill fluids have different stable operating
temperature ranges. If you exceed the fluids’ temperature
limits, they can boil and destroy the seal, the instrument, or
Most Common Fill Fluids
- Silicone DC-704 70° to 600°F
- Silicone DC-550 -40° to 500°F
- Silicone DC-200 -60° to 300°F
- Fluorolube FS5 -50° to 400°F
- Halocarbon 4.2 -80° to 400°F
Food-Grade Fills for Sanitary Seals
- Silicone DC-360 -50° to 450°F
- Mineral Oil -30° to 200°F
- Vegetable Oil -30° to 250°F
Each type of fill has a specific use and can dramatically
change the cost to fill the instrument and seal. If your
application is not compatible with our general DC-200 silicone,
please call 1 (800) 9-LESMAN for assistance.
- Attachment to Compatible Instruments
Each seal has a different volumetric displacement or
sensitivity. If the displacement of the seal is less than that
of the sensing instrument, they will not work. Seal displacement
MUST be greater than that of the instrument.
Trained factory technicians use special equipment to avoid
damaging gauge and seal components during assembly and testing. Call
Lesman for assistance in selecting the right combination of gauge,
seal, and fill fluid to suit your application.