PulseGuard Pulsation Dampeners

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PulseGuard Pulsation Dampeners
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REACTIVE PRESSURE PULSATION DAMPER ZERO MAINTENANCE STATIC PARTS

Reavtive Pressure Pulsation Damper



How the damper functions with no moving parts :-

It works by the compressibility of liquids, and the Pressure wave velocity, and the pulsation damper pressure reaction to these essential characteristics. In the design and selection of a "fit and forget" pressure pulsation damper, that is to be "bladderless" or to be of the "no moving parts type", "or static parts type" and so needing zero maintenance, compressibility of the liquid and it pressure wave velocity are the key.

For example an Acetone system, is say 2.5 times more compressible than a water system , and water is twice as compressible as for example a glycerin system. So that to the extent that a damper relies on the volume of compressible liquid for its volumetric smaller than a zero maintenance type designed for use on Glycerine and having static parts.

The comparative figures below will vary with the amount of dissolved and entrained gasses and solids (see:- sea water - dissolved salt - compare to fresh water), and of course the figures will change with temperature, but as a general guide to the relationship between liquid compressibility figures in the table, they are useful in gauging the predicted pulsation damper performance.

"Pressure wave velocity" is also useful to the damper designer of a reactive pressure damper's pulsation, because it enables the distance between chokes and baffles to be optimized. For the applications engineers uses, it can help determine whether a pulsation frequency detected in a system, is a response characteristic from pipe or tube length, or whether the frequency is from some moving component. In this case called a forcing or excitation frequency; typical example of which are valve oscillation or pump part movement.

 

 

HOW DISTANCE and velocity CAN DETERMINE FREQUENCY

Common sense thought:- as the pressure wave velocity of "typical water" is 1465 meters per second, ( a mile being within 200m of 1465 meters), a pressure change at the end of a pipe, will be detected approx. a mile away 1 sec later. This may be called a 1 Hz. system response frequency (Hertz means - "per second")

As it is normal to have one detection point only, a pressure change at that point would be seen again one second later if the pipe were a distance of half a mile long. (Distance traveled there, and then reflected back, being the one mile traveled total). Elsewhere "Pressure wave velocity" may be called "Acoustic velocity" if one wants to sound important. It does not mean that you can hear it. Please see the velocity on the right.

  Bulk Modulus E Compressibility k Pressure Wave Velocity
Liquid Name Imperial
10 e5 psi,
lbf/in2
Metric
10 e9 Pa,
@20°C
Vol, Metric %
per1bar Delta
@20°C
meters per sec
Acetone 1.34 0.92 0.0001087 1175
Benzene 1.5 1.05 0.0000952 1300
Ethyl Alcohol 1.54 1.06 0.0000943 1145
Carbon Tetrachloride 1.91 1.32 0.0000758 925
Gasoline 1.9 1.3 0.0000769 1350
Kerosene 1.9 1.3 0.0000769 1325
Petrol 1.55 - 2.16 1.07-1.49 0.0000935 - 0.0000671 1225 - 1425
SAE 30 Lube Oil 2. 1.5 0.0000667 1290
Paraffin Oil 2.41 1.66 0.0000602 1440
Water 3.12 2.15 0.0000465 1465
Seawater 3.39 2.34 0.0000427 1520
Sulfuric Acid 4.3 3 0.0000333 1275
Glycerin 6.31 4.35 0.0000230 1905

So we can think roughly that Glycerin is 5 times harder than Acetone and water is 2 1/2 times harder than Acetone - so a pressure damper with no moving parts for water will be approx half the size of one for Glycerin other system parameters being the same.

Note: Compressibility is expressed as the fractional or percentage change in volume per unit increase in pressure. For each Bar (approx) increase in pressure, the volume of water would decrease 46.4 parts per million. The compressibility k is the reciprocal of the Bulk modulus, B. (Data Basic Approximations from Sears, Zemansky, Young and Freedman, Georgia Institute of Technology, University Physics, 10th Ed., Section 11-6. )

From the above table we can deduce that a "cubic meter" damper of 1000 liters or one million cm3 (263 gallons) would absorb only a 95.2ml (cm3) pulse of 1 bar in Benzene service. We learn that to purely use the compressibility of a liquid for damping purposes results in a physically huge damper relative to a pump or valve. A reactive 1000 liters damper will normally be, id spherical, 1.4 meters diameter - say 55 inches including an average wall thick-ness.

 

 

DETAILS THAT HELP TO REDUCE TO AN AFFORDABLE SIZE.

But as all dampers deflect within their elastic limit, dilation of the housing will provide some extra volume. Using the modulus for steels of say 2e+11 . and wall thickness "t". The extra elastic volume can reduce the overall size. PulseGuard therefore deploys additional techniques to reach a manageable size.

For low pressure applications, pressure drop across a sharp edged orifice is used to generate bubbles which then rise out of the main flow path to provide a continuously replenished compressible "cap". This compressible volume of bubbles provides elasticity so again reducing overall size required. See the PulseGuard "CAVGUARD" product line.

For higher pressure systems PulseGuard inc. uses both dispersal and dissipative techniques.
Dispersal and dissipation techniques also reduce the overall size of the required pulse damper.

The result of these methods is to reduce pulse damper size by a factor of between 5 and 30, dependent on various system detail, particularly how much pressure drop is tolerable. The more information is provided to us, generally the more efficient the design and selection can be, so reducing the cost.

 

 

THE TEAM WITH THE MOST EXPERIENCE

PulseGuard Pulsation Dampeners
The PulseGuard people have produced dissipative
WAVEGUARD pulse dampers for services up to 100,000 psi ( 6,900 bar) and dampers in general since 1963, please see customer list at :- Customers Americas and Overseas.

30 years experience studying plots of "pressure over time" is an advantage.
Whether Liquid Dynamic's PulseDoctor, on site services, you, or a local oscillograph user captures the shock and pulsation "signatures", it is essential that readable suction side plots be taken first and interpreted. [Read More] [See also: CAVGUARD]

 



 

 


"PULSE" DAMPENER PERFORMANCE PRINCIPLES
WaveGuard pulsation dampers will address pulse frequencies from 20Hz through 2000Hz, and are a broad frequency band approach.
WaveGuard ARE NOT designed on the basis of Helmholtz resonators. RESONATORS GENERALLY ONLY WORK OVER A NARROW FREQUENCY BAND.
Please see FREQUENCY below

1. The WAG-RJ is the simplest WaveGuard by PulseGuard Ltd, having acceleration tube "snorkes" which explode any pulses
at above 8 mis far from points of reflection, dissipating pressure energy as heat. Used from 20hz to 250 Hz.

2. The WAG - OC is as 1 above with thr addition of orifice chokes, thelenths and position of these "chokes" can improve pulsation
dissipation and thus reduce the necessary size of a WaveGuard to save space through not cost. These are more frequency dependent.

3. The WAG-CER (designated because theheball pack is notmally CERAMIC), is disperser. A pressure wave entering a WAG-CER
trvels hundreds of different lengthed paths, each path is of different length, the time to travel is different so that a
pressure wave is converted to a spectrum of waves having reduced amplitude. Best applied 200Hz t0 2000Hz

4. The WAG-COMBO combines the dissipation of WAG-RJ with the dispersion og WAG-CER, making the most effesient high
frequancy damper; through high cost.

5. PulseGuard creates many specials - give us your problems.

 

FREQUENCY
Frequency can not be predetermined without all system dimensions frequency changes with temperature, viscosity, density, and any pipe
additions, removals, and changes of direction to the system. The position for installation of a resonator is also critical according to wave
length from an analysis. resonators are not offered.

Application of liquid filled volume bottles for the purpose of reducing pressure pulsation from positive displacement pumps.

Using cold water as an example, with a modulus of 50e-6, (10 to the minus 6) the same as saying 5 to the e-5 (exponent minus 5)
which means 0.00005 volume change per bar pressure change, which is like saying 0.005% (per sent being two zeros) compressibility
per 15 psi change in pressure - which with a viscosity of 1cP results in an "acoustic" velocity (meaning wave speed) of 1440 meters per second.
To have a"minds eye handle on this" call it, say, "a mile per second", velocity of pressure. ("Acoustic velocity")

 

The WAVEGUARD APPROACH TO DAMPENING
Relative costs: With Solid state, no moving parts, "acoustic" "reactive" - pulsation dampers
PULSATION DAMPER DEVELOPMENT a little more of the "Science".

If you make a pressure by for example striking a pipe with a hammer. If you isolate the pipe its self from transmitting the shock,
you will be able to measure thet pressure spike a mile away one second later (always assuming you have a transducer of
sufficiently fast response characteristics, and data capture at khz)

From the first paragraph, it follows that the compressability figures for each liquid at pumping temperature and pumping
pressure, must be known - otherwise it will not be possible to properly select the volume of a "Damper" to produce a
required level of pressure smoothness relative to the volumetric performance of a positive displacement pump.

 

 

No Maintenance Pulsation Dampener

 

 

 

We can try to simlify the selection of suitable volume bottles by saying - 1 divided by 0.00005 = 20,000, So we find that we
can absorbe a ml or (1cm3) or centimeter cubic - or "cc" of cold water in 20,000 ml (or 20 Litres) by 1 bar pressure increase.

 

NOTE:
Unfotunately the higher the pressure at which the water is, the more dense the water has become, so the volume necessary
for the "volume bottle" pulse absorber will have to be increased still further.
BUT conversely the higher the temperature of the liquid the lower its density - usually given in grams per cc. SO the
compessibility rises with temperature. Making the huge volume otherwise necessary SMALLER.

 

THEREFORE
The rise and cost of a "volume bottle" to supress VOLUME TRIC PULSATION coming from a positive displacement pump is
absolutely dependent on the liquid compressibility AT TEMPERATURE AND PUMPING PRESSURE.


So THREE EXAMPLES:
A 1 ml pulse would need 20,000 ml to compress to reduce to a 1bar pulse 20 Liters.
A 15 ml pulse would need 300,000 ml to compress to reduce to a 1 bar pulse 300 Liters
A 50 ml pulse needs 1 million ml to compress to reduce to 1 bar pulse 1000 Liters

 

Applications:

  • When no moving parts is required.
  • For use as an acoustic filter.
  • Dampers for diffusion.
  • As an acoustic silencer.
  • Helmholtz resonators.
  • As dissipative dampeners.
  • As an orifice damper.
  • For pressure wave dispersion.
  • Used as a resonator.
  • When solid state is required.
  • As reactive dampners.
  • As a pulse absorber.
  • For high frequency and low amplitude.
  • When maintenance free is preferred.
  • When bladderless is specified.
  • When no elastomers or plastomers are needed.
  • If no foam is specified.
  • When flow through is preferred.
  • For hydraulic noise reduction.
  • To hold pulsations constant over broad pressure range.