3-phase motor drawing high current

[iXod]

there was recently a thread on the practical machinist forum about those types of pumps. not something you can just throw together, or repair. more like trade secret voodoo involving edm, polishing/lapping, running the pump for a certain number of hours, perhaps with very, very fine grit in the oil before you ship it.

Would you please provide a link to that discussion? I searched but couldn't see any relevant discussion in that forum. Thanks.

[ez24]

Watching for the solution 

[iXod]

New pump ordered. The seller (a supplier well experienced in pumps -- no, not from e-Bay) says that this is a known failure mode of this type of pump. Having exhausted every kind of electrical diagnosis I can think of, it's time for a little trust. 

Will report results.

Cheers.

[iXod]

Watching for the solution 

That makes 2 of us! 

[eKretz]

Got to be mechanical then, IMO. You might have tried pulling the end plate off the pump first and checking for wear. Many times with these lobe type pumps the wear mechanism is mostly in side clearance of the lobes, which is pretty straightforward to fix. All you need to do is regrind the sides of the lobed gears and the end plate, leaving a small amount of clearance - usually on the order of .0005" to .001" clearance is good. Ideally you'd want as smooth a surface as you can get for longevity, so it might be advisable to "lap" the lobed gears with fine emery cloth on a surface plate after grinding. Your shop has a bandsaw - does it have a surface grinder?

I was a machinist, toolmaker and weldor for nearly the last 20 years before I hurt my back and started fiddling with electronic stuff, BTW. I've been a member at PM nearly since they started.

[iXod]

Yes there's 3 or 4 surface grinders and more than that in experienced operators. But zero with knowledge of rebuilding this type of pump.

So, re. rebuilding (grinding) the pump, I've got one anonymous source of info: you. With respect, it would be trial and error to do this. More downtime for the saw.

I think they would be best off just buying a $500 pump and paying me to swap it in. No unknowns.

Cheers.

[eKretz]

Hey I hear you - time is money in a machine shop. It really isn't difficult though, no pump rebuilding experience necessary. It's just flat grinding, you don't need to regrind the lobes. If you order the new pump, they should give the job to an apprentice or something so that you have a spare on hand.

[Seekonk]

I have serious doubts that it will be the pump.  That is their solution for everything.  A friend had a large metal shear and the motor just hummed.  I was out of town for a month. Motor rebuilder assured him it was a bad motor. $800 later after a motor rewind it still didn't work.  Got back and 5 minutes later it was fixed. A wire had just come off a motor contactor.

I'm still betting on low voltage.

[eKretz]

He already brought the voltage up with boost XFMRs, didn't solve the issue - though I would have tried to get a bit closer to 240V. The pump could very easily be causing the problem. Gerotor (lobed) pumps rely on minimal side clearance to avoid recirculating the pumped fluid back through the pump (think blowby like with piston rings). Once this side gap wears to a larger clearance, the regulator has to be turned up to maintain the required pressure, causing a higher amperage draw on the motor.

BTW OP, how many years has the pump been in use?