by Doug Coulter » Sat Jun 28, 2014 6:30 pm
Well, I can't see an overheat problem unless you've got a major leak or deliberate flow. Once an hour isn't going to do it. I did it, after all, to save power on the off-grid solar system, and heat == power.
The big problem with the VFD on the one I've got - the ramp up time is so slow, and the other time constants so long, that the thing runs around 30 sec-1 minute when the first revolutionor two gets the job done. That's certainly peculiar to my setup here, but hey - they knew (or should have) when they designed the pump it was going to be the case. It's a positive displacement piston pump in two stages, after all. Zero clearance - the piston top (rubber...) touches the cylinder head. It's kinda cool machining the lets it all be that "tight". No oil anywhere, either.
I thought it was going to need a rebuild after around a few K hours of running. Well, it did start to act wrong, and I was glad I'd bought a rebuild kit along with it. Well, when I pulled the heads off, it turned out that just a tiny amount of dust that had somehow made it through the turbo-drag was affecting the piston/head clearance just enough to make it crummy. Just wiping that off and putting it back together - like new.
It takes an hour of hard work to get that massive motor hot, in my case. That would be moving a lot of gas across a big differential pressure. That's not the norm here - we sometimes pump down from atmosphere, and the first few minutes it's working really hard. But after that? Nah. I do keep the system as clean as I can, and most often it's left at base pressure, not wet shop "STP", which means that after some internal mod, it comes back down to "turbo is pumping but not much and not needing a forepump running" really quick - as in, once the turbo gets to speed and it drops the forepump, it runs a little more often than usual that first day. Then, back to a few times a day. It's really cool in all senses of the word.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.