REACTIVE PRESSURE PULSATION DAMPER ZERO MAINTENANCE STATIC PARTS
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
||Pressure Wave Velocity
10 e5 psi,
10 e9 Pa,
|Vol, Metric %
|meters per sec
||1.55 - 2.16
||0.0000935 - 0.0000671
||1225 - 1425
|SAE 30 Lube Oil
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
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]