> Can unloaders be added to any compressor pump or must the compressor pump
> have been designed to accept them?
My only experience is with compressors designed that way. Given that the
valves aren/ as externally accessible on most of the more throw-away (ie
Sears, etc.) compressors I've seen, I don't know how they'd do it.
> Internet searches for air compressor unloaders also get a ton of hits for
> valves that discharge the pressure in the pump to tank line. I assume
> this is just the same name being used for different things?
Sounds to me lots like the pop valve (ie relief valve) alternative I'd
described below
> > Your alternative would be to use a second pop valve on the tank, set a
> > bit below the pressure of the safety valve (assuming you have one
> > already), and just relieve any excess pressure that way. Less
> > efficient, since you're compressing all the time, but for quick and
> > dirty, it'll work.
>
> Yeah, I guess I could go that route, but it does seem pretty klugey.
> Do you know of any good sources for a smaller (say 5 cfm at 90 psi?)
> single stage pump that has unloaders? I found this on ebay:
>
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2372509647&category=22662
>
> That's similar to what I'd want, correct?
It says "head unloaders", but it's impossible to tell whether that's
something that really limits the power used by the compressor while
operating unloaded or just a pressure-relief valve to blow off excess after
it's been compressed. The idea of an unloader is to let the compressor spin
free. with no load on the motor or the bearings, etc. Just pistons sliding
up and down against a nearly-zero load, lower power requirement from the
motor while essentially idling, etc.
I worked for Binks for 10 of the years between 1971 and 1984, and at that
time we used Quincy exclusively. They were actual industrial-quality,
American-made, cast-iron compressors that were designed to serve for
decades. We bought several 25-HP ones for my Dad's company (I got a good
discount ;-) and aside from a valve job or two, they ran from 1 to 3
shifts per day, 10 to 15 years apiece before he sold the company, with them
included. I know that they were all still in service when the oldest one
was over 20 years old.
I have no idea what that unit on eBay is. but Ugly American that I am, I
really don't think it's in the same category. I don't have lots of luck
with cheap Far East stuff... Then again, it may work just fine for hobby or
LIGHT commercial use. Heck, I have a cheap Grainger compressor in the
garage that's worked well since 1970, but it mostly just sits there.
You don't necessarily get what you pay for, you just don't get more !!!
Karl
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