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Pulsation in peristaltic pumps and in other type of positive displacement pumps

Tuesday, April 25, 2023

Why is there pulsation associated with a peristaltic pump?

Peristaltic pumps generate pulsation as a consequence of their operational design. Peristaltic pumps utilize rollers or "shoes" to compress a flexible tube or hose, which results in the movement of discrete volumes of fluid through the tube in “pockets "created. When the rollers or shoes move away from the discharge side track after each volume of fluid is moved forward, the tube behind it expands to its initial shape, causing a temporary void that creates flow fluctuations or pulsation. The same phenomenon occurs on the suction side of the pump just in reverse. An example of this pulsation is shown below to demonstrate its potential magnitude:

Potential magnitude
Potential magnitude of pulsation

In the following screen shot, the peristaltic pump is depicted operating in conjunction with a c, specifically the Equilibar, which reduces the pulsation's intensity by approximately 10 times in this case:

Pulsation dampener
Peristaltic pump is depicted operating in conjunction with a c

What influences pulsation in peristaltic pumps?

Various factors influence the pulsation in peristaltic pumps, such as the speed of the pump, the elasticity and diameter of the tubing, the design of the track, the properties of the fluid being pumped, the number of rollers, and the rotor design.

Is a pulsation a problem in peristaltic pumps?

Yes it can be, but in most applications it is not problem and in a few applications it it even a desired effect.

Pulsations associated with peristaltic pumps have the potential to compromise the integrity of the pumped product and can also place undue strain on the installed equipment. Depending on their severity, these pulsations can cause vibrating pipes and hoses, generate noise, and adversely affect downstream sensors, such as pressure or flow sensors, thereby hindering the accuracy of dosing and filling processes. In addition, pulsations can cause safety pressure switches to trip unnecessarily. Frequent exposure to vibrations resulting from pulsation can lead to the degradation of system components over time. Therefore, proper reduction of pulsation is necessary to increase the lifespan of the equipment.

What is the difference between a pulsation dampener and an “inlet” dampener?

The distinction between a pulsation dampener and an inlet dampener or stabilizer is solely based on their location within the system. When installed on the inlet or suction side of the pump, the device is referred to as an "inlet stabilizer," whereas installation on the discharge or outlet side of the pump would make it a "pulsation dampener." It's worth noting that peristaltic pumps can be bidirectional, and this reverses the naming depending on the flow path direction.

How to reduce pulsation in positive displacement pumps?

  1. The installation of pulsation dampeners
  2. The installation of Equilibar, a type of pulsation dampener that provides exceptional pulsation dampening and is ideal for ultra-sensitive applications

How to reduce pulsation in peristaltic pumps?

  1. Increasing the number of rollers within the pump head results in less pulsation but also reduces the flow rate.
  2. A specially designed peristaltic pump with offset tracks will minimize pulsation.
  3. Installing pulsation dampener(s)
  4. Using longer flexible tubing can also help reduce pulsation.
  5. Use Equilibar, it is recommended for ultra-sensitive applications.

How do more rollers decrease pulsation in peristaltic pumps?

Using more rollers in a peristaltic pump head reduces pulsation. This is because the increased number of rollers results in smaller discrete volumes of fluid, thus reducing the size of the empty voids or "cushions/pockets" in between. This delivers more stable and consistent flow of the fluid. However, the frequency of pulsation will increase but will have smaller amplitude.

Video: Peristaltic pump head pulsation exploring 4 rollers VS 8 rollers

How offset track reduces pulsation in peristaltic pumps?

Although peristaltic pumps are generally less pulsatile than most positive displacement pumps, they still exhibit some level of pulsation. The special low pulsation offset peristaltic pump head design involves compressing twin tubes using offset tracks to split the inlet flow, generating two sets of pulses that are out of phase with one another. These channels are then combined at the discharge, resulting in the cancellation of one pulse by the flow of the other, which leads to a uniform and smooth outlet flow.

Phase compensation structure diagram
Phase compensation structure diagram

How pulsation dampeners reduce pulsation in peristaltic pumps?

A pulsation dampener can absorb pulsation in a manner similar to how a car suspension system works. The dampener often consists of a rubber diaphragm that adjusts to the fluid and pressure levels in the system. When installed and calibrated correctly, a pulsation dampener can result in a steady fluid flow.

How Equilibar reduces pulsation in peristaltic pumps?

Video: Single-Use Pulsation Dampener for Pump Pulsations

Equilibar BPR (back pressure regulators) uses thin diaphragms “loaded” with compressible gas, making the device more sensitive to small changes in pressure compared to traditional BPRs. Equilibar BPRs can react to changes as small as 0.01% of overall set-point.

Pulsation dampening is a natural quality of the Equilibar like traditional pulsation dampeners consist of a flexible membrane (typically rubber) with a pre-loaded air charge on the non-wetted side.

The ultra-wide Cv range of the Equilibar valve allows it to keep up with positive displacement pumps and diaphragm pumps to maintain consistent pressure during operation.

Equilibar valve with positive displacement pump
Equilibar valve with positive displacement pump

The product described in the diagram above is from our Equilibar Biopharmaceutical SD range.

How Equilibar reduces pulsation for sanitary applications?

Equilibar Saintary FD series valves and regulators are designed for use in sanitary applications where pulsations and shear stresses can have adverse effects on downstream processing and may even cause costly damage to the processed substance.

In bioprocessing, challenges often include the need to deliver fluids at precise flow rates across a wide range of flow rates, including very low flow rates. Additionally, positive displacement pumps used in bioprocessing can create pulsations that must be eliminated, and consistent back pressure is needed to prevent bubble formation.

Equilibar BPR is equipped with both passive and active pulsation dampening features for downstream applications. Passive dampening inserts are used to minimize pressure pulsations downstream, and the BPR's active pulsation dampening feature further ensures a steady flow.

Buffer feed pulsation control
Buffer feed pulsation control
Flow and pressure measurements using back pressure regulator
Flow and pressure measurements using back pressure regulator
Flow and pressure measurements using equilibar dampening
Flow and pressure measurements using equilibar dampening

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If you have any questions or would like to discuss you specific application please feel free to contact the team.

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