Diaphragm
operated devices are essentially pistons operating within a
cylinder. They transfer pressure from one sealed area to another.
In the case of hydraulic and pneumatic cylinders, the moving
piston is sealed off by a sealing device such as an o'ring,
cup, vee packing, or a similar device. A diaphragm merely limits
the stroke and provides a frictionless seal. Diaphragms generally
cost less, have more tolerance range, and do not require hardened
super finishes or lubrication.
The function
of a diaphragm is the most important factor in its design and
manufacture. Simple diaphragms move from one position to another,
such as pressure switches and solenoid valves. There are only
two positions. In the case of modulating devices, such as regulators,
the diaphragm must respond to small changes in differential
pressure and the diaphragm must return to the same corresponding
position. Here, the concern is with flexibility, uniform spring
rate, and a minimum change in effective area.
Diaphragms
can also be used as shock absorbers as in a dash pot or as dampening
devices in pulsating systems. In the latter the diaphragm reduces
the high pressure spikes and smooths out the flow of fluid or
gas to produce a more uniform flow. Diaphragms can also be used
as barriers between fluids and gasses, such as in a pressure
drop on the fluid side, the compressed gas expands against the
diaphragm to maintain the fluid pressure.
Diaphragms
are also used in pumps, such as automobile fuel pumps, hand
pumps, and diaphragm air compressors. In these cases an outside
mechanical force is actuating the diaphragm. This functions
to displace a volume of media. In the case of a pump the diaphragm
creates a low pressure area causing the fluid or gas to move
into this area. In all the above cases the function of the diaphragm
will generally be the determining factor when considering the
type of construction, the material composition, fabric design
(weave/knit), and the type of polymer.
Supported
diaphragms are produced from a wide variety of fabric, varying
strength, weights, and weaves. The fabrics themselves range
from natural fibers, such as silk and cotton to the man-made
fibers and high strength arimids. The elastomeric coatings can
be put on both sides of the fabric in equal thickness or an
unbalanced coating. Many applications require elastomeric coatings
on only one side such as applications where the pressure differential
is in one direction. When knit fabrics are employed, the coating
is usually on one side and the same side as the pressure. This
allows the fabric to support the coating on both sides for flat
diaphragms.
This construction
suggests possibilities for obtaining a good deal more stroke
with a flat diaphragm. The selection of the fabric substrate,
in terms of strength, weight and flex life will greatly depend
on the application.
Fabric
supported diaphragms have a distinct advantage over homogeneous
diaphragms. Supported diaphragms have less tendency to stretch
under pressure conditions. Because the rubber is continually
under stress conditions it tends to degrade physical properties
quicker. Most importantly, fabric substrate takes all of the
stress from the rubber leaving the rubber to work in the least
stress conditions.
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RMA
TABLE 3.pdf
RMA
TABLE 13.pdf
RMA
TABLE 16.pdf
RMA
TABLE 35.pdf
RMA
TABLE 36.pdf
RMA
TABLE 38.pdf
RMA
Tolerances.pdf