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How can pulsation be reduced in a sanitary positive-displacement pump system?
Positive-displacement pumps are widely used on sanitary and biopharmaceutical skids because they can provide predictable flow and handle a broad range of process duties. The trade-off is that many positive-displacement pump designs create a pulsating flow rather than a perfectly continuous discharge. A small pressure ripple in a simple transfer line may have little practical impact, but the same fluctuation upstream of a sensitive flow meter, filtration stage or chromatography column can become a genuine process problem.
Why do positive-displacement pumps create pulsation?
A positive-displacement pump moves a fixed volume of fluid during each revolution or stroke. Depending on the pump principle, those volumes may be created by rollers compressing tubing, diaphragms cycling, pistons reciprocating, or lobes or gears rotating. The result can be a repeating change in instantaneous flow and pressure, even when the average flow rate is correct.
The amplitude and frequency of the pulsation will depend on the pump design, speed, number of pumping elements, fluid properties, wetted-part characteristics and surrounding pipework. For more detail on the mechanisms involved, see PCT's guide to pulsation in peristaltic and other positive-displacement pumps.
What problems can pulsation cause on a sanitary or pharmaceutical skid?
Pulsation becomes important when the changing pressure or flow starts to affect the process or the equipment around it. Typical symptoms can include:
Unstable flow or pressure readings
Nuisance trips from pressure switches or process alarms
Vibration and movement in pipework or flexible hoses
Reduced repeatability in dosing or filling processes
Additional loading on filters, chromatography columns or other sensitive downstream equipment
Difficulty maintaining a stable process pressure around the pump
Start with the pump and system design
A dampener should not automatically be the first answer. Pulsation can sometimes be reduced at the source by changing pump speed, selecting a pump head that inherently produces less pulsation, reviewing hose or tubing arrangements, or changing the pipework volume and flexibility around the pump.
One of the first things PCT normally establishes when reviewing a pulsation issue is what the pulsation is actually affecting. A pressure switch tripping, an unstable flow-meter signal and a sensitive downstream process may all require different solutions, even when the pump is the same.
Identify the effect
Establish whether the issue is measurement instability, vibration, alarms, repeatability or process protection.
Review the source
Consider the pump type, speed, head design, tubing, fluid properties and surrounding pipework.
Define the target
Set a measurable objective for the acceptable pressure ripple, signal stability or process response.
Where the pump is already correctly selected and the remaining pulsation is still too high, a dedicated dampening device can be added to the system.
Active pulsation dampening for hygienic applications
The Equilibar PD Series is a sanitary pulsation dampener developed for positive-displacement pump systems where pressure pulsation needs to be reduced without introducing a conventional, non-drainable accumulator into the process line.
The PD uses an air-loaded, double-sided diaphragm arrangement. As the process pressure rises and falls with each pump pulse, the diaphragms respond to absorb the pressure peaks and support the pressure troughs, reducing the amplitude experienced by downstream equipment.
For skid designers, the key point is that the dampener is part of the process design rather than an afterthought. It should be positioned where the pulsation is causing the problem and selected around the actual line size, pressure, temperature and cleanability requirements.
Responding to each pressure pulse
A reference-gas supply acts on the non-wetted side of the diaphragms. When a pump pulse causes the process pressure to rise, the diaphragms deflect and help absorb the pressure peak. As the pressure falls between pulses, the gas pressure supports the diaphragms as they return, helping to reduce the depth of the trough.
This response reduces the pulsation amplitude passed to flow instruments, filters, chromatography columns and other sensitive downstream equipment. The selected configuration and reference pressure must be appropriate for the actual process conditions.
Where is the PD Series particularly relevant?
Typical applications include sanitary dosing skids, buffer and media transfer, filtration systems, chromatography feed systems and other bioprocess duties using peristaltic, diaphragm or other positive-displacement pumps.
The appropriate size, materials, connections, orientation and operating limits must be checked for each application.
Define what “good” will look like
Before choosing a dampener, define the objective. Is it to stop a pressure switch tripping, improve a flow-meter signal, protect a downstream filter, reduce mechanical vibration or create a smoother dosing profile?
Once the acceptable pulsation level is understood, the pump and dampening strategy can be selected around a measurable target rather than simply adding hardware to the skid.
Information that helps PCT assess a pulsation problem
When contacting PCT, it is useful to provide:
- Pump type, model and operating speed
- Minimum, normal and maximum flow
- Line size and operating pressure
- Fluid and operating temperature
- Pipework, hose or tubing arrangement
- Frequency and size of the pressure variation, if measured
- The equipment or process being affected
- The improvement the system needs to achieve
Discuss a pulsation problem with PCT
If you are seeing pulsation from a positive-displacement pump, send PCT the pump type, line size, flow range, operating pressure, fluid and a description of what the pulsation is affecting. We can review whether the issue is better addressed at the pump itself, through system changes or with a dedicated sanitary pulsation dampener.
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