Suped up my compressor

[hotdogstand]

About a year ago a bought a used 60 gallon Husky brand compressor off craigslist. It's in good shape, tank is solid, and the last owner even swapped the pump out for a Quincy QTS-3. Not a bad deal for $400, one would think.

I have always thought that it was a little slow to fill, though, and was curious about the actual CFM (since the stickers on the tank were referring to the pump that was long since replaced). I finally got around to clocking it, and it came out to a measly 6.5 cfm, embarrassingly low for a setup that size IMO.

Formula for approximate cfm (sourced from the web somewhere):

(tank size * .536 * PSIG)/(time to fill in seconds)

I downloaded the manual for the QTS pumps and they claim a maximum output of 16-something, and they list the HP, RPM, and the other little details, too. I already had a 5 hp motor, so I used the following calculation (sourced from the web somewhere) to determine the largest drive pulley I could run to increase my output.

(compressor rpm * flywheel)/motor rpm = drive pulley diameter
Subbing in the max rpm from the manual (1200) and the 12" flywheel I already have, I determined that a drive pulley of 4" would give me the best output without overrunning the pump.

After 3 belt changes (wrong size, thanks to yet another free internet formula), I finally got it going. This time it came in at 11.8 cfm, an impressive improvement for $20.

I'm sure all of this information is on here somewhere, but I figured I would share my experience in case anyone else is trying to get a little more out of their current setup.

 

[jason74]

Great thinking!

 

[hotdogstand]

Thanks! It sure beats dropping the cash on a new pump

 

[guy48065]

OEM pulley was 2"?

 

[larry_g]

The final thing you should do is check the current draw of the motor and confirm that you are not pulling more amps than it is rated for.

lg
no neat sig line

 

[shoot summ]

As indicated, watch your motor, the current draw, and heat.

I went the other way, replaced my pump, thought I was driving the pump at the right speed for the motor I have. Had issues with the motor overheating during high usage. Posted about it on GJ and got a lot of great advice, including slowing it down. So I went from a 4" to a 3" pulley, it fixed my problem....

 

[All]

hotdogstand... can you confirm what the size of your original pulley (that you replaced) was please?

I was trying to backwards calculate it, but without knowing your electrical motor rpm, and without knowing what pressure you are maintaining at either cfm you have measured, and, without my knowing basic math... I'm having trouble coming up with your original pulley diameter.

 

[K-Dog]

The title of this thread made me think of Tim "The Tool Man" Taylor.

 

[hotdogstand]

The OEM pulley was 2.5" OD, the replacement is 4" OD. The RPM is 3450, and the sticker in the motor says 5 hp, which is right in range for the specs offered by Quincy for the pump.

The Quincy is offered with 12" and 10" flywheels, for any given motor size, the larger flywheel allows the pump to run more slowly. Their whole pitch relies on continuous air at a lower RPM. I had the 12" flywheel though, and it basically came down to three solutions: replacing the pump (always an option), replacing the flywheel, and replacing the drive pulley. The drive pulley just happens to be both the most cost effective and ready available solution. I rarely run my compressor continuously and it is on a dedicated 240V/20A breaker. After replacing the pressure switch with a more appropriate unit, (the previous owner had a max of 145 psi, the pump is spec'd to only 125!!!) my confidence is renewed in the longevity of the setup.

 

[hotdogstand]

Regarding temperature: with the new pressure switch, the motor runs for only 60-90 seconds at a time under intermittent use (impact, blow gun), and from empty to full in under 6 minutes. It previously would take 12 full minutes to fill, and would run continuously under even moderate use.
Whatever increase in work the motor may experience will likely be offset by the reduced duty cycle.

 

[benny42]

Whatever increase in work the motor may experience will likely be offset by the reduced duty cycle.

Sure, maybe so. But you NEED to put an amp meter on your set up or you risk
burning up the motor, really. Nice work by the way.

 

[On-Wheel]

I just picked up a 60 gal tank,took 20 minutes to 115psi.Using TWO Quincy QR 106's ! That was max psi due to relief valve on one pump.It sure is quiet but dang it's a slow single stage pumps. A 4" pulley on ( 1/2 hp ) motor and 14" on pumps.There a 450-900 rpm pump at about 525 rpm.Thanks and it's cool you made your faster and do check what your amps.