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Pulsation
dampeners (accumulators, surge suppressors) are used to control and
minimize the pulsations that result from a pressurized system’s stroking
action. They increase system efficiency, performance, and pump life;
decrease maintenance costs and down-time; and protect pipes, meters,
valves and instrumentation from pulsation, vibration, and hydraulic
shock. Most pulsation dampeners use a bladder or bellows to separate the
process fluid from a compressible gas. During the pump’s discharge
stroke, fluid pressure displaces the bladder or bellows and compresses
the trapped gas. During the following cycle, the momentary interruption
of fluid flow causes the compressed gas to expand, forcing the bladder
or bellows to push the accumulated fluid back into the discharge line.
There are many types of pulsation dampeners. Adjustable dampeners can be
set or tuned to accommodate different pressure ranges and response
rates. Automatic dampeners use a valve in the device’s non-wetted
section to allow increases in air pressure to balance increases in
liquid pressure. Chargeable dampeners fill a chamber with compressed air
or nitrogen gas to create a cushion that absorbs pressure pulses within
the system. By contrast, liquid-filled pulsation dampeners use a
fluid-filled cavity to smooth the system. Suction-lift dampeners provide
a stabilizer on the inlet side of the pump to reduce acceleration and
ensure even pump feeding. Pressure snubbers are positioned before a
pressure gauge to provide protection against pulsations in the measured
media.
Specifications for pulsation dampeners include maximum pressure,
capacity, inlet size, and inlet type. Many suppliers specify maximum
pressure in pounds per square inch (psi) and capacity in cubic inches
(in3). Inlet size is usually expressed in inches (in). There are several
inlet types for pulsation dampeners. Flanged inlets have multiple bolt
holes for mounting to a mating flange. Threaded inlets have a threaded
connection, usually a pipe thread. Tri-clamp dampeners have a specially
configured flange that fits a clamp.
Pulsation dampeners use bladders or bellows made from a variety of
materials. Buna-N provides good resistance to petroleum hydrocarbons and
fuels. Ethylene propylene (EPDM) offers good resistance to sunlight,
weather and ozone. Chlorosulfonated polyethylene (CSM) provides
excellent resistance to ozone, oxidation, sunlight, and weathering.
Neoprene is used over a wide temperature range and displays outstanding
physical toughness. Polyvinyl chloride (PVC) has good flexibility, a
smooth surface, and nontoxic qualities. Because of its inert nature,
some PVC grades are used in food and chemical handling applications.
Polytetrafluoroethylene (PTFE) is an insoluble compound that exhibits a
high degree of chemical resistance and a low coefficient of friction.
Silicones are polymers that provide heat, cold, and weather resistance;
electrical insulation; good release; and water repellency. Many
proprietary products are available.
Selecting pulsation dampeners requires an analysis of housing materials.
Acetal polymers offer excellent lubricity, fatigue resistance, and
chemical resistance. Polyvinylidene fluoride (PVDF) is a melt-processable
fluoropolymer with better strength and lower creep than other
fluoropolymers. Polypropylene is a thermoplastic material that exhibits
excellent cold flow, bi-axial strength, and yield elongation properties.
It is similar to PVC but can be used in exposed applications because of
its resistance to UV, weathering, and ozone. Other housing materials for
pulsation dampeners include aluminum, brass, cast iron, carbon steel,
and stainless steel.
Summary -
Available in a variety designs, Contains a porous filter disc at the
inlet to the restriction; rate of response is delayed by a fixed time of
about 10 seconds [A], Contains a piston that absorbs shock and surge by
rising and falling with pressure impulses [B], Design provide a means
for adjusting the amount of restriction to obtain the best damped
response [C&D]
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