Piston Pump and VFD

[Davebones]

Have a new test stand being set . It will have 480v 150 hp motor on it . My boss wants to install a VFD to drive this . The manager of the department says its not a good idea to VARY THE RPM's OF A PISTON PUMP . I'm not a pump person just wondering if that is true !

 

[Jraef]

Have a new test stand being set . It will have 480v 150 hp motor on it . My boss wants to install a VFD to drive this . The manager of the department says its not a good idea to VARY THE RPM's OF A PISTON PUMP . I'm not a pump person just wondering if that is true !

Possibly, some piston driven equipment uses mechanical oiling and if you vary the speed, the oil pump stops moving enough oil, followed shortly thereafter by seizing. The people to ask are the pump mfrs though.

Also, what's his reasoning for wanting VF control on a piston pump? If it's because he thinks it will save energy, he's wrong.

 

[don_resqcapt19]

Why wouldn't save energy? If you reduce the speed there will be less volume pumped.

 

[CONTROL FREQ]

Have a new test stand being set . It will have 480v 150 hp motor on it . My boss wants to install a VFD to drive this . The manager of the department says its not a good idea to VARY THE RPM's OF A PISTON PUMP . I'm not a pump person just wondering if that is true !

I read a thread awhile back titled 'VFD on hydraulic pump' it was posted by twoskinsoneman it changed my views on this general subject. As for the "bad idea" part, it WOULD depend on the pump. I've seen self-lubricating pumps that lube at ANY rpm, because of the specific design (they ARE pumping oil afterall), other pump designs might not fare so well at low rpm's, if they 'sling' oil for example. There was some enlightening info on this subject in that tread though, you might check it out, I don't know if I can hyperlink it or not, never tried that on here. Some smart guys though.

 

[GeorgeB]

Have a new test stand being set . It will have 480v 150 hp motor on it . My boss wants to install a VFD to drive this . The manager of the department says its not a good idea to VARY THE RPM's OF A PISTON PUMP . I'm not a pump person just wondering if that is true !

If you look at the literature on a HYDRAULIC piston pump, you will find minimum and maximum recommended speeds. We've never had problems varying, via VFDs, speeds between these.

But ... unlike centrifugal pumps, at a given displacement a piston pump shaft torque is dependent on pressure, that is, the torque at 600 rpm and 3000 psi is the same as at 1800 rpm and 3000 psi. Be certain your drive is capable of providing the appropriate currents.

Having said that, I've operated fixed displacement piston pumps over a 10:1 range with no trouble. When I asked the manufacturer why he used 600 rpm as his minimum, the response is that no one uses motors of more than 12 poles ... and that their efficiency ratings would not look good at lower speeds, but there would be no damage of any type to worry about.

Positive pressure on the inlet is smart to ensure "priming" is not necessary. The air performance is not good <g> at 30 rpm, so the 30 inches above oil level we use at 1200 and 1800 may be a problem.