oddball compressor question

[SgtRauksauff]

So, I've got my shop compressor, a nice Quincy with a 5hp single-phase, working great (but I need to change the oil soon). No worries there, this is about another one:

Along with some other stuff, I acquired a vacuum pump and a compressor, both driven by the same motor (3/4hp). Both units are made by Gast. The compressor is the 1550-P195. Vane type, oilless, and puts out a good flow of air (14.5cfm on a 60Hz motor, according to the specs.).

So I thought to myself, this would be a great pump to run an airbrush on, for miniatures modeling (mostly just figures for tabletop wargames).

Problem is, it will fill the tank up to just under 30psi before the motor cuts out on thermal overload. The max pressure according to the specs is only 15psi, and I would really not ruin this compressor by running it at high pressures like that. the problem is, I can't use the air fast enough to keep it from filling a tank and cutting out the motor.

I probably don't even need the tank, but it's a good buffer to collect any moisture. I just need to regulate the pressure to 25psi or so at the airbrush.

Most pressure switches that I've run across are all well above 30psi cut-out, and I'm trying to keep this whole thing on the extra-cheap-to-nothing budget, using stuff that I've got lying around.

Since I don't have an extra-low-cutOut switch, my thought is to, instead of having the regulator/airbrush at the end of the line, put in a tee, and have the end of the line be an open valve, that I can use to keep enough pressure to feed the airbrush at 30psi, but bleed the rest off so the compressor stays in the safe operating zone.

Does this sound like a suitable compromise?

Or, should I dig harder for a low-pressure switch?

Sorry for the long-ish post, but it's better to have too much information than not enough when being asked a question.

Thanks for your time!

 

[zkling]

You say the max pressure on the pump is rated to only 15psi, yet you want to run it up to 25psi

Surplus center and like places have low pressure, pressure switchs for ~$20+ shipping. Is that too much? If so you might be able to do a crude blow off system. Order a spring of proper resistance and built your own bypass to open at a certain pressure, then below that pressure it will be closed. P=F/A, use a small ball bearing or the like and determine how much F then K value for the spring you would need to open at a specific pressure, say 20psi. If you put a scew on the end, you could fine tune the preload on the spring to really dial it in.

 

[SgtRauksauff]

max ~25 psi to the Airbrush, which uses a 1/8" line and is really freakin' small. We're talking 0.5 CFM through that 1/8" line to the brush, not the 14.5CFM that the compressor produces. So there is 14cfm leftover that needs to just go away.

I could just fill a tire with 40psi and have 15-20 minutes of working pressure to the airbrush, but I've got this sweet vane compressor, so why not use it? Any parts I do buy will take a few days to get here, so working with what I have in the short term, while I plan the final details of a "nice" system, is sort of a fun exercise in redneckery, plus it re-familiarizes me with the contents of my parts bins!

 

[larry_g]

Assuming that this is a belt drive setup, you can change the pulley ratio to slow down the pump and relieve some of the load on the motor. What HP motor are you running? I couldn't find your exact model on the Gast site but it looks like this should turn about 1725 rpm and require a 3/4 hp motor.

lg
no neat sig line

 

[SgtRauksauff]

Yep, it's a 3/4 HP 1725rpm Doerr motor. I hadn't thought about changing the pulley, that's a good thought!

I've got an email into Gast to see if they can give me the documentation on these pieces (the vacuum pump is '0740-V177' and doesn't match their listings exactly either.) the compressor serial number is 0986 and the motor is

Zkling, that contraption sounds very similar to a 'manual boost controller' that I stuck on my '85 Volvo 744tic years ago (and boy, was it fun!)