Peristaltic Pump 1

[alwayslearn]

Hi guys,
Recently I got case study about peristaltic pump.

Does anyone can explain that relationship between of number of rollers and pressure ripple in mathematically?

For my understanding is increasing rollers does tend to decrease the amplitude of the fluid pulsing at the outlet by increasing the frequency of the pulsed flow. But how is link to the pressure?

Thanks

 

[3DDave]

Pressure is resistance to flow, so it depends on how that resistance is generated. If there is no resistance there won't be any ripple in pressure. As to mathematically? Sure, create a transient model FEA. I cannot imagine the number of rollers being a fundamental characteristic anyway - more likely what is important is the volume of fluid trapped and the rate. An infinite number of rollers at an infinite radius will trap an infinite amount of fluid between each pair.

 

[Compositepro]

Flow caused by the pinch roller rolling over the tube is constant. The flow pulsation is caused the pinch roller unpinching the tube, causing the tube volume to increase. This increase in volume has to be filled, thus reducing the volume of flow delivered by the pump, momentarily. This is a geometry problem. Pressure pulsation is a function of how the system downstream from the pump reacts to flow variation.

 

[bimr]

The pump delivers a rate of flow. The single function of the pump is to take fluid from one place and put it somewhere else. Pressure is the result of resistance to flow downstream from the pump.

 

[TenPenny]

It would be somewhat akin to a multistage piston pump; for the same volume of flow delivered, the magnitude of the pulsations would be reduced with more rollers, the same way that a multiplex pump has lower magnitude of pulsations than a single piston pump.

Is there a mathematical relationship? I expect there is at least some approximation; where you would find it, that's the hard part.

Of course, the specifics would be somewhat different because the hose is elastomeric, but the concept is similar: a fixed volume of fluid being delivered in pulses, by either a single or multiple motivators.

 

[LittleInch]

I don't think this is feasible as it all depends on what the pump is connected to.

A simple tube into a tank or bag then virtually no pressure pulse.

Into a hard high strength metal pipe with considerable back pressure - possibly much higher.

Same into a more flexible tubing / plastic pipe - much lower pulsations.

There are people who make a living from analysing piping networks which have pulsations coming from pumps to identify the highest pressures in the system due to vibration and resonance.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Compositepro]

A peristaltic pump does not behave like a multi-piston pump, where the pistons are in parallel and out of phase with each other. In a peristaltic pump the rollers are all in series and they act as pistons and valves. It is the valve action that causes the flow variation as I described above. Read it again:

"Flow caused by the pinch roller rolling over the tube is constant. The flow pulsation is caused the pinch roller unpinching the tube, causing the tube volume to increase. This increase in volume has to be filled, thus reducing the volume of flow delivered by the pump, momentarily. This is a geometry problem. Pressure pulsation is a function of how the system downstream from the pump reacts to flow variation."

It is not a sinusoidal variation. Flow is constant until one roller starts to unpinch the tube. At this time the "valve" starts to open, allowing flow from the next roller to continue. But the tube under the roller is inflating, which absorbs some of this flow volume. So, with a peristaltic pump the flow is constant with periodic small dips in the flow when the roller unpinches the tubing. A similar process occurs at the suction of the pump where a roller starts to pinch the tubing, which reduces the tubing volume and causes a reduction in suction flow due to this volume being squeezed back up-stream, counter to the flow in the tubing. The flow variation at the suction and discharge of the pumps are not related except by timing due to mechanical design of the pump.

A peristaltic pump can have any number of rollers, but at least one roller must have the tubing completely pinched at all times.

 

[MartinLe]

From what compositpro writes, it follows that it is better (in terms of pulsation) to have as little rollers as one can get away with - which depends on the geometry of the pump. The magnitude of the pulsation depends on the size of the tube and to a lesser extent on the roller size.

With quick googling, 3 rollers is common and some pumps where the tubes are closer get away with only two. Don't know if pumps with more rollers exist, if so that would show that my reasoning is wrong.

 

[TiCl4]

The link below may be helpful for evaluation. In general, the more rollers the pump has, the lesser its variation in flow/pressure. I have seen pumps with 8 rollers that are intended to minimize pulsation. So, the more rollers, the lesser the amplitude of pulsations (though they happen more frequently). Pumps with dual cartridges can be set with offset pinch points to even out the flow between pumps.

https://www.coleparmer.com/tech-article/reducing-pulsation-peristaltic-pumping

To answer the OP's questions, you need to evaluate the volume of each "pillow" - the trapped section of liquid between rollers. The opening of a pillow into the discharge section is set by the pump rotational speed only - it is a function of the tube/roller geometry and rpms. Increasing the number of rollers does not change how quickly the tube opens up into the discharge section. By lessening the pillow volume (by increasing rollers), each opening of a pillow discharges proportionally less volume than a larger pillow, but still within the same timeframe. The transient flowrate variation is lower, and thus the pressure amplitude spikes are also lower.