DIAPHRAGMS
also called
chemical seals,
instrument isolators
and gauge protectors
are isolation
devices used
to separate
pressure instruments
from the process
media, while
allowing the
instruments
to sense the
process pressure.
A diaphragm,
or bladder,
together with
a fill fluid,
transmits pressure
from the process
medium to the
pressure element
assembly of
the instrument.
Diaphragms may
be attached
directly to
the instrument,
or remotely,
using a capillary
line. These
devices are
intended to
keep the process
medium out of
the pressure
element assembly
and to prevent
damage from
corrosion or
clogging. Diaphragms
are also used
to maintain
the sanitary
requirements
of the process
medium and to
reduce the process
temperature
to which the
pressure element
is exposed.
Diaphragms function
using a flexible
diaphragm that
is attached
between the
upper and lower
housing of the
seal. The upper
housing is filled
with a fluid
and attached
to the pressure
instrument.
The lower housing
is in contact
with the process
medium and has
the connection
to the process
system. The
process media
pressure is
transmitted
via the diaphragm
to the fill
fluid in the
upper housing
and subsequently
to the pressure
instrument.
When
specifying diaphragms,
there are a
number of important
points to consider.
These include
the type of
process fluid
and how it will
react with the
material, the
vapor pressure
point of the
fill, the flexibility
of the diaphragm,
and that the
fill fluid is
chemically compatible
with the process
fluid. Common
materials of
construction
for Diaphragms
include Aflas®,
VITON,
SILICON,
HYPALON,
EPDM,
TPR,
NBR,
NEOPRENE,
PTFE, PU,
SBR
& NATURAL.
The hardness
rating on a
Shore A scale
for Diaphragms
can be 30 ~
80 Durometer.
Exact specifications
should be clarified
by our engineers,
as chemical
and physical
properties of
Diaphragms can
differ based
on manufacturing
technique.
