Diaphragm Compressors

[Thealanator]

Has anyone had experience with diaphragm compressors? I understand one can get large compression ratios because the diaphragm has a large surface area in relation to the gas flow rate. Is there a limit on the low end of suction pressure (can they go down to atmosphere)? Do they last?

 

[iainuts]

Yes, we use quite a lot of diaphragm compressors. They can provide a fairly high compression ratio, primarily because there is so much surface area and given the slow speed, there is quite a bit of heat transfer out of the gas during compression so the discharge temperature is generally well below adiabatic temperature.

There is no real limit to them regarding low pressure. I've seen them used in vacuum applications though that is not a typical application. There are a lot of different types also, including ones made with metal diaphragms and ones made with elastomer and thermoplastic diaphragms. They can last for thousands of hours or even tens of thousands of hours if the gas is absolutely clean. So they can last a long time compared to conventional reciprocating machines. The market niche for diaphragm machines is low flow, high compression ratios and very clean service or service where purity is a prime consideration.

 

[Thealanator]

Iainuts, thanks for the response.

I have the impression that the swept volume is not that large since one does not want to flex the diaphragm too much. You say that the speed is low, so I gather that a flow rate based on 15 psia suction is quite low compared to a rate based on 200 psia suction. I'm thinking that the ratio of pressures could give a rough flow reduction factor, e.g., 15/200=0.075. Ouch!!!!!

I see that many multistage machines are horizontal. Do you see much wear on the pistons/cylinders/rings as opposed to vertical orientation?

 

[iainuts]

Yes, the flow rate is typically very low and the swept volume small. I've seen both horizontal and vertical machines, but I don't think there's much of an issue with wear on the pistons (ie: crosshead). The crankcase and hydraulic system should be good forever. The part that will wear out or fail is going to be the diaphragms, seals around the diaphragms (O-rings) and valves.