Why you Should Use a Diaphragm Seal
Diaphragm seals are protective devices designed to
isolate
pressure gauges,
pressure transmitters, and
pressure switches from potentially damaging process
media. Typical applications where a diaphragm seal
provides a cost effective solution to protecting the
pressure instrument are:
In applications where the process fluid is corrosive
In applications where the process fluid has a high
viscosity, is comprised of slurries, sludge or other
material that can actually coat or damage a traditional
pressure measuring device
In applications where the process fluid can freeze or
polymerize, thus causing a condition that might lead
to the instrument becoming immobilized or incapable
of transmitting an accurate pressure measurement or
signal
Operational Theory:
Mansfield & Green brand
diaphragm seals typically comprise
a metal, TEFLON or elastomer diaphragm mounted
between two housings and sealed to prevent leakage of
process gases or fluids. The space on the instrument
side of the diaphragm, the connections and the instrument-
sensing element, are all completely filled with instrument
oil, silicon or other suitable fluid.
When the process line pressure is applied, the diaphragm
exerts equal pressure on the instrument side of
the seal producing a reading on the gauge or process
instrument. Instruments may be attached directly to the
diaphragm seal or connected remotely by means of a
filled system – typically a length of armored capillary tubing.
Mansfield & Green diaphragm seals may be used
with pressure or vacuum instruments including gauges,
transmitters, and switches that utilize C-type, helical or
spiral bourdons, bellows elements, diaphragms or electronic
strain gauge sensing elements.
Pressure:
Seal pressure limitations vary according to seal design
and their materials of construction. Thread attached,
non-flow thru seals having a metal process bottom
have a maximum working pressure rating from 2500 up
to 5000 psig at 100°F (172 to 690 bar at 38°C). Type T
TEFLON diaphragm seals have a maximum working
pressure of 2500 psig at 100°F (172 bar at 38°C).
In-Line Flow Thru seal
Types R, S, and T are rated
at 1500 psi at 100°F (105 bar at 38°C).
Type L seals are
rated at 1250 psi at 100°F (88 bar at 38°C).
All flange attached seals are sized according to ANSI
B16.5. ANSI standard flange attached and In-line Flow
Thru seals are available with a maximum working pressure
rating equal to the flange class pressure rating.
Seals having a lower housing made of nonmetallic
materials should not be used for working pressures in
excess of 100 psig at 140°F (7 bar at 60°C). TEFLON
threaded connections are limited to pressures of 50 psig
at 100°F (3.5 bar at 38ºC).
AMETEK offers special diaphragm seal designs with
a maximum working pressure rating of up to 5000 psig
(690 bar). Please consult your AMETEK representative
for more information.
Vacuum:
L Series elastomer diaphragm seals (except for Types LB
and LG) are ideal for most vacuum instrument applications
in ranges from 0 to 29" Hg (0 to 736mm Hg at 0°C).
Type ST Series seals are suitable for vacuum applications
from 0 to 29" Hg (0 to 736mm Hg at 0°C).