Pulsation Dampers
Selecting the right Pulsation Dampers - "A Road Map"
1. Pulsation Dampers selection by material.
I Pulsation Dampers selection, preliminary - by external materials,
a). Pulsation Dampers that are for an externally
corrosive environment, whether or not the pulsation damper is for use
with a corrosive liquid. PipeGuard pulsation dampers in standard with a
stainless housing. For Example the PipeGuard Pulsation Damper is therefore a norm for saline environment use; EG on oil and gas production platforms. The WAVEGUARD no moving parts Pulsation Damper,
is also standard in stainless steel - these Pulsation Dampers are for
high frequency pressure wave resonance prevention, by interception.
b). Where the associated pumping equipment with the
Pulsation Dampers are not made of stainless steel, EG the drive end of
pump; then the Nitrogen cushion housing drive end of Pulsation Dampers
may be of Epoxy painted carbon alloy steel. An example of one such Pulsation Damper is the PIPEHUGGER, another example is the PUMPGUARD Pulsation Damper.
II Pulsation Dampers selection, secondarily - by liquid contact parts compatibility.
a). The PIPEHUGGER Pulsation Damper where liquid goes inside a rolling diaphragm bladder made of a suitable
elastomer, and the gas cushion is outside these Pulsation Dampers
membranes, inside the pressure shell. "PIPEHUGGER" Pulsation Damper means to "HUG" - or look after – your pipe system!
b). The PUMPGUARD Pulsation Damper where the liquid goes through a straight "Flex Tube" of an elastomer -
this configuration being an ideal Pulsation Damper for sludges and
slurries.
c). The FLEXORBER Pulsation Damper for system liquids that require PTFE, FLEXFLON or Dupont "Teflon",
where the Pulsation Dampers can not have an elastomer gas bag nor
bladder nor Flex Tube.
2) Pulsation Dampers application definition, decide whether you need:
a). Pulsation Dampers for accumulating FLOW
FLUCTUATION alone, for example: pulsation dampers where you only use
one connection and add it to a "T" piece. A single connection PIPEGUARD Pulsation Damper, or a single integral flange face PIPEHUGGER Pulsation Damper will fill this need perfectly.
--- or ----
b). Pulsation Dampers that "dampen pulsation", -
meaning "dissipates pressure waves" - AND ALSO is a "Pulsation Damper",
or more correctly a Pulsation Damper PREVENTOR, - which works by
accumulating the flow fluctuations, which would otherwise cause
acceleration head change without a Pulsation Damper . The Pulsation Damper called PIPEHUGGER TW, and the PUMPGUARD, also the FLEXORBER Pulsation Damper are all in this DUAL PURPOSE category, because they are all of the FLOW
THROUGH interceptors AND flow fluctuation accumulating Pulsation Damper
category.
--- or ----
c). Pulsation Dampers only for system response
PRESSURE pulsation, Generally known as an "Acoustic Pulsation Dampers".
Examples the WAVERGUARD/cer dispersal type Pulsation Damper, and the WAVEGUARD/rj explosive dissipation Pulsation Damper - neither have any moving parts.
3) Pulsation Dampers type selection, from the above the choice will be from:
a). A corrosion resistant outer shell Pulsation Dampers, example the PIPEGUARD by PulseGuard.
b). A dual-purpose Accumulator and pressure Pulsation Damper, Example the PIPEHUGGER by PulseGuard.
c). A sludge and slurry Pulsation Dampers, example the PUMPGUARD by PulseGuard.
d). A Pulsation Dampers with PTFE diaphragm, example the FLEXORBER by PulseGuard.
e). A no moving parts acoustic Pulsation Dampers, example one of the WAVEGUARD units by PulseGuard.
4) Pulsation damper volume selection. Pulsation
Damper volume required for flow fluctuation reduction by accumulation,
is a volume of Pulsation Damper dependent on the level of tolerable
residual pulsation, and dependent on the level of flow fluctuation that
would otherwise occur.
NOTE
a). Pulsation Dampers for addressing a given volume
of an individual flow fluctuation, will depend on the characteristics
of the source of the fluctuation to be smoothed by the pulsation damper.
b). Relative to the volume necessary for a simplex single acting reciprocating pump, the Pulsation Dampers volume will be :-
c). Pulsation Dampers for duplex pump as little as 25%
Pulsation Dampers for a 2 lobe pump, down to 20%
Pulsation Dampers for a hose pump as low as 15%
Pulsation Dampers for a triplex machine as little as 10%
Pulsation Dampers for quintuplex plunger type as small as 6%
Pulsation Dampers for the displacement per vane of a vane type 2%
Pulsation Dampers centrifugal as small as 0.5%
5. Pulsation dampers pressure selection. Pulsation
Dampers pressure selection depends on whether the design pressure "Pd"
is to be the same as the MAWP, or whether 10% is to be added for a
higher than MAWP safety valve setting. For the safety of a Pulsation
Damper an additional + 15% may be added to the safety valve set
pressure to produce a Pulsation Dampers "Pressure for design" of MAWP x
1.27.
Also Pulsation Dampers may be rated with a Euronorm
"P Max", that is some 40% less safe, than for example an ASME VIII 1995
rating Pulsation Damper where the allowable working stresses were more
conservative.
As a general rule it is wise to choose Pulsation
Dampers with a design pressure rating not less than 50% above any
published Euro "P Max" figure.
Pulsation Dampers are not for a "static pressure
application", Pulsation Damping is a cyclic duty, therefore to avoid
fatigue failure low working stress levels should be used for any
Pulsation Damper application. Current European practice based on the
Pressure Equipment Directive "the PED" and new high stress issues of
ASME VIII part 2D, are both unproven and potentially dangerous for
pulsation dampers.
The responsibility for stating to the Pulsation
Damper fabricator, what pressure for design, should be used, and
whether to use an unsafe static pressure / non-cyclic pressure vessel
code or not, is the responsibility of the Pulsation Damper user, not
the liability of the Pulsation Damper builder.
Pulsation dampers installation mode selection.
a). Pulsation Dampers installed for suction
acceleration head reduction should be placed with the liquid side
uppermost. Doing this with Pulsation Dampers ensures that gravity
enables all the little bubbles that would otherwise collect in the
Pulsation Damper to continue on to the pump. This Pulsation Damper
installation method prevents the bubbles becoming one large bubble,
which will suddenly come out of the Pulsation Damper and cause the pump
to "loose its prime".
b). Pulsation Dampers piping method for discharge
acceleration head generation prevention - by flow fluctuation
accumulation - also requires the use of in-line flow-through Pulsation
Damper connection. Flow through configuration ensures that the
Pulsation Damper does not cause pressure pulsation by the need for
pressure change, i.e. pulsation, simply to cause the mass flow to go
up, stop, then come back down, a single pulsation damper connection in
a split fraction of a second. Single connection Pulsation Damper flow
reversal causes them to be, in many cases only one third as efficient a
damper, as a genuine flow through multi-port, zero direction change
Pulsation Dampers.
c). Pulsation Dampers that are being installed to
intercept the high frequency pressure pulsation, typically traveling at
3500 mph, emanating from short pipe length reflection times, must be an
in-line flow-through connected Pulsation Damper.
Pulsation Dampers performance monitoring.
a). Determining Pulsation Dampers performance is almost impossible to do with a "Pressure Gauge".
b). Pulsation Dampers becomes partially irrelevant
because a pressure gauge has its own response characteristics, it is
after all a weight of mechanism on a spring.
c). It will "wag" at a rate, and over a width of "swing", dependent on its characteristics. A pulse is purely the exciter.
d). Pulsation Dampers will modify the form of the
excitation, but there is a difficult correlation between a Pulsation
Damper characteristics and those of a gauge.
e). It is also misleading to monitor by a gauge
connected to the cushion gas side of a Pulsation Damper, because the
response characteristics of the Pulsation Damper gas/liquid/separator
membrane may be phase lagging.
f). It is advisable to deploy a pressure transducer
with very high response characteristics after the Pulsation Damper
outlet, and to have data capture at least 4 times faster than any
frequency, at which the Pulsation Damper is required to work, and that
is to be detected.
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