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Flow Fluctuation / Suction Systems - Negative Pressure Pulsation / Supply Lines

How suction pulsation dampeners with a gas cushion, separated from the liquid by a membrane, work:
The resistance to a suction demand by a pump to increase supply flow rate, caused by a mass of liquid in a pipe system, causes a pressure fall. That is why it is called suction. This fall is often referred to as "suction acceleration head". The amount of pressure fall, is limited by the volume of compressible gas in the pulsation dampener that can expand and thereby deliver the volume of liquid momentarily required.
Simplistically, where the volume of the compressible gas is a multiple of the volume of liquid required momentarily for the increased in suction flow rate, the pressure will not fall by more than the reciprocal of that multiple.
This is because the flow will come from the path of least resistance. Least resistance will be the expansion of the gas, because that will require less pressure decrease than to accelerate the mass of liquid in the supply line. Which for example is to say that if the gas volume is 10 times the volume of the momentarily increased suction flow, then the pressure will not fall by more than 1/10th or 10% . Similarly, if the flow rate to a pump momentarily decreases, the volume of from continuing to flow down the supply line at the same rate will be stored by the compression of the gas, replenishing the "dampener" with the difference between decreased pump suction requirement and average flow rate.
This process, of ironing out suction flow fluctuations, is a low velocity activity, at normally less than 5 mph and therefore there is generally plenty of time for the flow fluctuations to communicate with the gas loaded membrane.

However:
1. As large as the volume of gas cushion in the accumulator may be, it can not be infinitely large. Therefore there will always be some pressure fall variation even form a huge accumulator cushion device.
2. Further more, the process of accelerating a volume up into an accumulator stopping it, and accelerating it back out again, requires force / pressure to achieve that mass acceleration direction change.
3 Additionally the membrane, which is separating the gas from being lost in the liquid, has stiffness and weight; these also require force to cause the membrane to response.
4. The danger from negative pressure pulsation, is that the low peaks will cause "gassing". Gassing is more likely to be from the de-solution of absorbed gasses than from reaching vapor pressure in most cases. It will cause the supply column to be broken into slugs of liquid inter spaced with voids or gas pockets.

The addition of 1, 2, & 3, above, mean that in the real world, there will always be residual negative pressure pulsation left over form the flow fluctuations, smoothing or "accumulation" process.
This residual negative pressure pulsation however, will then travel back up the supply line at an acoustic velocity of say 3200 mph, depending on liquid compressibility. Negative pressure pulsation will then return from points of impingement in the supply line. The distance to those points of reflection, will determine the frequency of this suction system response negative pulsation.
A short system may for example have a frequency of 1000 Hz., a longer system may cause a 100 Hz. frequency. Not only will a single connection accumulator not intercept this acoustic activity, but he membrane will probably have response characteristics, that make the accumulator incapable of addressing the negative pressure pulsation reflected from the system at these frequencies.
For these reasons, an accumulator is rarely a negative pressure pulsation dampener at all. To address this problem of single connection accumulators - purveyed as "Dampeners" - a multi port, in and separate out connection are used.
Irrespective of the acoustic velocity, all pressure pulsation must now try to go through the "suction pulsation suppression device" aka supply side snubber. The pass through multi port versions of accumulators, address negative pressure pulsation in several ways, and being multi-ported are rightly called SUCTION DAMPENERS.

The ways that a multi-port dampener addresses suction pressure pulsation:
1. The ratio of inlet hole diameter to the distance to any surface from which the pressure wave may reflect, may be called the "discharge Coefficient". "Discharge" in this context being the discharge from the supply line into the suction dampener. The discharge coefficient may express the extent of pressure pulsation reduction. Pressure transient amplitude, decreasing by a cube law to distance; similar to light or magnetism to distance.
2. The mass of liquid inside the dampeners chamber will have a deadening effect on the now reduced pressure pulsation.
3. This pressure wave dissipation turns into a minimal amount of heat which is then radiated from the dampener shell. Dampeners therefore dampen, the accumulation function of flow fluctuation reduction, is not dampening - energy loss, it is acceleration head change prevention to some extent.
SUCTION DAMPENERS THEREFORE HAVE AS STANDARD AT LEAST AN INLET AND AN OUTLET, AS THIS IS STANDARD PRACTICE, THEY COST NO MORE THAN SPECIAL SINGLE CONNECTION VERSIONS. Suction pressure pulsation dampening, costs nothing more than flow fluctuation removal.

Pulsation Dampeners Guard Against Pressure Pulsation

The difference between flow fluctuation on discharge systems and positive pressure pulsation in pump discharge pipe lines

How suction pulsation dampeners with a gas cushion, separated from the liquid by a membrane, work:
The resistance to an increase in flow rate, caused by a mass of liquid in a pipe system, causes a pressure rise. This rise is often referred to as "acceleration head". The amount of pressure rise, in limited by the volume of compressible gas in the pulsation dampener.
Simplistically, where the volume of the compressible gas is a multiple of the volume of liquid in the momentarily increased flow rate, then the pressure can not rise by more than the reciprocal of that multiple. This is because the flow will take the line of least resistance. Least resistance will be compressing the gas, because that will require less force than to accelerate the mass of liquid in the system. Which for example is to say that if the gas volume is 10 times the volume of the momentarily increased flow, then the pressure will not increase by more than 1/10th or 10%. Similarly, if the flow rate from a pump momentarily decreases, the volume of liquid that has been stored by the compression of the gas, will come out of the accumulator aka dampener, making up the difference between decreased flow and average flow rate.
This process, of ironing out flow fluctuations, is a low velocity activity, at normally less than 15 mph and therefore there is generally plenty of time for the flow fluctuations to communicate with the gas loaded membrane.

However:
1. As large as the volume of gas cushion in the accumulator may be, it can not be infinitely large. Therefore there will always be some pressure force variation even form a huge accumulator cushion device.
2. Further more, the process of accelerating a volume up into an accumulator stopping it, and accelerating it back out again, requires force / pressure to achieve that mass acceleration direction change.
3 Additionally the membrane, which is separating the gas from being lost in the liquid, has stiffness and weight; these also require force to cause the membrane to response.

The addition of 1, 2, & 3, above, mean that in the real world, there will always be residual pressure pulsation left over form the flow fluctuations. smoothing or "accumulation" process.
This residual pressure pulsation however, will then travel through out the system at an acoustic velocity of say 3500 mph, depending on liquid compressibility. Pressure pulsation will then return from points of impingement. The distance to those points of reflection, will determine the frequency of this system response pulsation. A short system may for example have a frequency of 1000 Hz., a longer system may cause a 100 Hz. frequency. Not only will a single connection accumulator not intercept this acoustic activity, but he membrane will probably have response characteristics, that make the accumulator incapable of addressing the pressure pulsation reflected from the system at these frequencies.
For these reasons, an accumulator is rarely a pressure pulsation dampener at all. To address this problem of single connection accumulators - purveyed as "Dampeners" - a multi port, in and separate out connection are used.
Irrespective of the acoustic velocity, all pressure pulsation must now try to go through the "pulsation suppression device" aka snubber. The pass through multi port versions of accumulators, address pressure pulsation in several ways, and being multi ported are rightly called DAMPENERS.

The ways that a multi-port pulsation dampeners address pulsation:
1. The ratio of inlet hole diameter to the distance to any surface from which the pressure wave may reflect, may be called the "discharge Coefficient". The discharge coefficient may express the extent of pressure pulsation reduction. Pressure transient amplitude, decreasing by a cube law to distance; similar to light or magnetism.
2. The mass of liquid inside the dampeners chamber will have a deadening effect on the now reduced pressure pulsation.
3. This pressure wave dissipation turns into heat which is then radiated from the dampener shell. Dampeners therefore dampen, the accumulation function of flow fluctuation reduction, is not dampening - energy loss, it is acceleration head change prevention to some extent.

PULSATION DAMPENERS THEREFORE HAVE AS STANDARD AT LEAST AN INLET AND AN OUTLET, AS THIS IS STANDARD PRACTICE, THEY COST NO MORE THAN SPECIAL SINGLE CONNECTION VERSIONS. Pressure pulsation dampening, costs nothing more than flow fluctuation removal.

Pulsation Dampeners - Snubbing, Surge Suppression and Shock Absorbing
Hydropneumatic Device for Acceleration Head Pulsation Prevention
No Moving Parts and Hydropneumatic Pulsation Filters
Flow Fluctuation / Suction Systems - Negative Pressure Pulsation / Supply Lines
Pressure Pulsation Pulse Signatures
Pressure Pulsation Dampeners for Transients and their Interception
Pulsation Dampeners for Amplitude of Pressure Wave Spikes
Pulsation Dampeners and Pump Vendor Responsibilities
Acceleration Head / Pressure that a System Could Create
Pulsation Dampening - Flow Smoothness Requirements
Pulsation Dampener Quick Release Manifolds / Flow Divider Manifolds



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