No-leak pump types. 2

[salukikev]

Hi,
I have a system that I want to move fluid into and out at exactly the same rate. In the middle of the system is a reservoir that will be subjected to a maintained high vacuum. Even when the system is not operating, I would like this vacuum maintained indefinitely, consequently I'm left with a very limited choice of pump types. Actually so far the only type I've come up with is a peristaltic, but the flexible and pulsing nature of that type presents other challenges within my system. So I'm here soliciting ideas for other pump types that might work more effectively. Thanks for any suggestions!

 

[moltenmetal]

A hydraulic diaphragm pump will be leak tight to the exterior, but it has check valves, so your high vacuum might draw in liquid through those check valves- you haven't specified your problem properly for us to understand what kind of leakage bothers you. All check valves leak, and aside from peristaltic and progressive cavity pumps, all PD pumps have check valves. But the HDD pump can have a high sealing integrity to the exterior, if you choose a good one. Flow out of those pumps, and out of all continuous positive displacement pumps, is pulsile. Pulses can be minimized by means of pulsation dampeners or by using triplex heads- three pumpheads out of phase with respect to each other.

A magnetically driven pump of any design will also have a high seal integrity to the exterior, but none of those are positive displacement type pumps- they cannot be used for metering. The best you can get would be a gear pump, which really generates a lot of little pulses and isn't really PD- it is best described as semi- PD. Don't use gear pumps with non-lubricious fluids, especially if they are corrosive or you are operating at high temperature or low flows.

 

[Compositepro]

You will have to have some level controls on the reservoir because no open-loop metering pumps will be able to keep the level constant forever by simply pumping in and out at the same rate. Peristaltic pumps generally are not suited to pumping under high vacuum because the tubing will collapse. And if it does spring back, there has to be fluid head or pressure to fill the tube. Under vacuum any type of pump will require some fluid head (gravity) at the pump suction to fill the pump.
I agree that a diaphragm pump will probably be your best choice. An air-operated double diaphragm (AODD) is one possibility.

 

[salukikev]

MM: Thanks! Sorry if I was a little vague but I have all I need from your thorough answer. The check valves are certainly a concern and reason to avoid most. I've literally never even heard of a progressive cavity pump until now- very neat operation! Not likely a fit for this, but I'm going to save that in my "cool stuff" folder. I may have overstated my pulsing concern- I think that will be manageable but its only conceptual for now.

CP: I suspected I might need level controls though I was hoping to avoid it. I share the concern with Peristaltic collapse, though I don't think the pressure will be a problem. I checked into AODD's, but it looks like we'd have the same issue with check valves- thanks so much!

 

[Compositepro]

All valves can potentially leak, though some designs may be more robust than others. And since gravity flow is all that can be used for fluid to drain out of the reservoir into the outlet pump, there probably is not much reason to use a pump on the inlet. All you need is a valve to let the vacuum suck the fluid in.