Peristaltic Pump pulsation issues

[mrnatural]

Pulsation is breaking the PVC tubing. We are using a 1/2 HP single lobe peristaltic operating at 1,700 RPM that is moving 10 GPM up 2' to a tube that is at atmospheric pressure. The flow is thru the tube and returns to the pump at the other end. There is only about 10" clearance above the pump so dampeners are out. Replacing the pump with a sine or progressive cavity is too expensive. Currently the discharge of the pump has a stainless connector that feeds a 5' length of 1" flexible PVC tubing that is routed through a 360 degree bend. Then it transitions to 1" Schedule 40. This seems to be working at present but I'm not confident that it will last. The pump is in continuous operation and the tubing has a tendency to kink which increases the pressure.

 

[MikeHalloran]

Is there some unstated reason why you're using a peristaltic pump and not a centrifugal?

What fluid are you pumping?



Mike Halloran
Pembroke Pines, FL, USA

 

[GaTechTheron]

These pumps should not exhibit much of a pulsation at all (compared to a reciprocating pump).

It sounds to me like this "kink" is building too much back pressure on the pump. Eliminate that issue, and you should be ok.

Thoughts?

 

[mrnatural]

Mike the reason for the peristaltic is a need for a low shear pump. The fluid is mostly water with some bugs in it and we don't want to hurt the bugs.

 

[mrnatural]

GaTechTheron as I told Mike, we are interested in low shear and the peristaltic fits the bill in that area. And you are correct they don't pulsate like a recip but they have lots more pulsation than the sine or progressive cavity pumps. The kinking doesn't appear to be an issue because the PVC tubing doesn't start out kinked and the pulsation is the same before and after. I'm inclined to believe that the soft PVC flexible tubing is absorbing most of the energy thereby acting as a dampener but I don't trust that it will last. The stuff I'm using is the clear PVC with a woven braid imbedded in it. It likes to discolor and it likes to kink but it is soft enough to absorb energy. We started off with the flexible white SCH 40 PVC and that just transferred the energy down stream to the first rigid connector.

Steve

 

[MikeHalloran]

How about a bucket wheel, or an Archimedes screw pump?

Mike Halloran
Pembroke Pines, FL, USA

 

[micalbrch]

If there is some pressure a peristaltic pump will create pulsations. It is a rotating positive displacement pump but with only one show it has a very high pulsating flow. Every peristaltic pump manufacturer offers pulsation dampeners but most of them do not include them to keep the pump price down.

If there is no chance for you to install a pulsation dampener and if an expansion joint right after the pump does not help. you'll have to install another pump.

Is the pump really working at 1700 rpm or is that only the motor speed? Isn't there a gear between motor and pump?

 

[mrnatural]

Mike, there just isn't enough room to install a bucket wheel of a screw pump. The screw pump would have been an excellent choice when the design was initially done some years ago but I'm stuck with what is and not what it should be.

micalbrch The pump does indeed operate at 1,700 RPM but I like your comments regarding pressure. I could replace the 1" plumbing with 1.25" or even larger within our existing framework. You mentioned an expansion joint as an option. Currently I'm using the 1" clear PVC and I'm not confident that it will last. Do you have any suggestions for a manufacturer of such an item?

Steve

 

[micalbrch]

Steve,

I can't recommend a certain manufacturer for an expansion joint but there should be plenty of them. I do not even know whether "expansion joint" is the correct word as English isn't my native language. "Flexible connector" and "compensator" are other words for me. These devices are not designed to act as pulsation dampeners but they will at least not worsen the situation but probably help.

How high is the pressure the pump is working at?

 

[mrnatural]

Micalbrch, the pressure is unknown. We have assumed that since the distance from pump output to the tube, which is at atmosphere, is only about 10' and the required lift is only 2' that the pressure is low. That may be incorrect however. The next time one of the systems is down I'm going to upsize it and see what happens. In the interim I'll see if I can find a better suited "flexible connector".

Thanks for your help.