Quincy Air Compressor Question

[MountaineerMiner]

What size is the sheave on your motor? You could also be pushing the motor a little beyond it’s rated capacity, (but within its practical capacity) which is completely feasible. The cfm can be easily calculated by motor/pump sheave, pump displacement, and motor speed plus some loss due to age.


Sent from my iPad using Tapatalk

[Louie1961]

Yeah, but even if it is off by 10% its still making 8 CFM, which blows my mind. I am more than happy with this unit, especially for $300.

[Louie1961]

What size is the sheave on your motor?

I am in Charlotte on business for a couple of days, I will measure it when I get home

[MountaineerMiner]

Its a bigger pump at a lower speed, it wouldn’t surprise me. That spreadsheet has me close to rated capacity on 2 different compressors. Its not perfect, but I bet you got a little better unit than many others speculated. HP is only a close approximation to CFM (what really matters), pump speed and displacement are everything. You can push a motor, it just won’t last as long. Within reason I would rather change motors that pumps...


Sent from my iPad using Tapatalk

[John T]

Time to trade up Louie.

I’ll give you $150 for the baby Quincy ...

.



https://newhaven.craigslist.org/tls/...730616616.html


Sent from my iPhone using Tapatalk Pro

[jpump5]

What does that have for an air
filter? Can’t see in pic.My used CH came
with a reusable foam element. Fine wood
sanding dust had gotten past the
element. I installed an air cleaner
assembly salvaged from a
scrap Quincy compressor.


Sent from my iPhone using Tapatalk

[Louie1961]

it looks like some sort of felt in the air filter

[Louie1961]

OK, the large pulley is 11 13/16ths in diameter. The small pulley is 2 1/4 in diameter, the motor RPM is rated at 3450, so I get a compressor RPM of 657. The bore and stroke of this compressor is 2.75 bore x 2 inch stroke x 2 cylinders. Using the formula Pi*radius squared*height, each stroke of each cylinder produces 11.88 cu inches. At 657 RPM, that comes out to 9 CFM, which is what I measured. I am guessing the motor is not over amped, since its rated draw is 15 amps and it is not tripping any breakers. I could be wrong however. The really tempting experiment would be to put a slightly larger drive pulley on this beast.

[John T]

Seems silly to me.

Just plug it in and use it....

Don’t try to turn it into something it will never be.


Sent from my iPhone using Tapatalk Pro

[Louie1961]

John, didn't you mother teach you the old adage about if you have nothing good to say STFU? sheesh man. Its an intellectual exercise, it hurts nothing, and I am learning some stuff about compressors that I never knew before. Seems silly? then don't read it.

[John T]

That’s the beautiful thing about message boards Louie...

People write messages on them.

LoL!

You are so precious when you’re frustrated.

Don’t screw up that beautiful compressor Louie.

If you want to exercise your intellect
Page 3 of the newspaper Has a crossword puzzle.


Sent from my iPhone using Tapatalk Pro

[John T]

PS:
I never had a mother.

I was hatched from an egg.


Sent from my iPhone using Tapatalk Pro

[Louie1961]

PS:
I never had a mother.

I was hatched from an egg.

Hahahaha....well I don't know about never had a mother...but you are a mother...if you catch my drift. Why are you so bored today??

[Louie1961]

or is this a case of message boarding while you drive?

[MountaineerMiner]

Don’t try to turn it into something it will never be.

Sent from my iPhone using Tapatalk Pro

That pump is rated to 1200rpm and is only turning at 650rpm. With a larger motor it absolutely “could be”. 650 is about as slow as it gets for a compressor in this class.

The QT-54 from Northern everyone seems to rave about is running at 1310. I bet more than 75% of the compressors folks on this board have are running over 1000 rpm.

That being said, I would encourage keeping it stock. I bought a bigger pump for the intended purpose of running it around 600rpm simply for noise consideration. That unit should last forever running at 650 and would make a great portable rig/backup to a larger stationary compressor.

[Willie B]

OK, the large pulley is 11 13/16ths in diameter. The small pulley is 2 1/4 in diameter, the motor RPM is rated at 3450, so I get a compressor RPM of 657. The bore and stroke of this compressor is 2.75 bore x 2 inch stroke x 2 cylinders. Using the formula Pi*radius squared*height, each stroke of each cylinder produces 11.88 cu inches. At 657 RPM, that comes out to 9 CFM, which is what I measured. I am guessing the motor is not over amped, since its rated draw is 15 amps and it is not tripping any breakers. I could be wrong however. The really tempting experiment would be to put a slightly larger drive pulley on this beast.

Louie, I don't believe you can calculate displacement at barometric pressure for a compressible commodity like air.

[Chad86tsi]

Keep in mind the mass of air is not uniform at all pressures, temperatures, and cubic volumes. A pump drawing in air is creating a vacuum to get that air to enter the cylinder. If you take a cubic foot of air at atmospheric pressure (14.7 PSI) and subject it to a vacuum force to move it, you aren't going to have the mass of that original cubic foot of air at 14.7 PSI at the other end just by moving one cubic foot of volume in the pump. A cubic foot of air at one atmosphere at standard temperatures is 0.0807 lbs. Vacuum/pressure and temperature both alter the mass of that cubic foot of air. Heating it decreases it mass. So does subjecting it to a vacuum. After you have filled your tank with hot air that was induced with a vacuum, you probably have about 2/3 of what the pumps actual displacement is. If temperatures were identical, the pressure change to mass ratio is approximately linear. Sucking a cubic foot of air at 1/2 atmosphere vacuum nets about 1/2 cubic feet of mass.

This is all basics of turbocharging/supercharging and using intercoolers are designed to address on internal combustion engines, which are basically air compressor pumps as well. This is why your numbers don't match rating, and why poorly designed pumps move less CFM per horsepower = different efficiency rates (excess heat, exces vacuum).

[Willie B]

Yeah! What he said...maybe??

[12V71]

OK, the large pulley is 11 13/16ths in diameter. The small pulley is 2 1/4 in diameter, the motor RPM is rated at 3450, so I get a compressor RPM of 657. The bore and stroke of this compressor is 2.75 bore x 2 inch stroke x 2 cylinders. Using the formula Pi*radius squared*height, each stroke of each cylinder produces 11.88 cu inches. At 657 RPM, that comes out to 9 CFM, which is what I measured. I am guessing the motor is not over amped, since its rated draw is 15 amps and it is not tripping any breakers. I could be wrong however. The really tempting experiment would be to put a slightly larger drive pulley on this beast.

Check your amp draw just before it kicks off at the pressure limit. You may have a little "wiggle room" to speed up the pump. More than likely it has been engineered to work at the max of 15 amps. I tried that with a 5hp Gas twin tank years ago and it killed the engine before the unloader popped using a pulley 1/2" larger.

[Louie1961]

Keep in mind the mass of air is not uniform at all pressures, temperatures, and cubic volumes.

Mass matters in combustion because of the stoichiometric ratios of oxygen to fuel in the chemistry of combustion. I would argue that mass has no bearing on the CFM rating of a pump used to power an air tool. Volume is volume, and I think that is all that matters when you are spinning an air powered tool.

Louie, I don't believe you can calculate displacement at barometric pressure for a compressible commodity like air.

Of course you can Bill. Compressor manufacturers do it all the time. How else would you rate a compressor? Its true that that changes in temperature, pressure and humidity can skew the results, but that's why SCFM exists. SCFM is just CFM at STP (standard temperature and pressure). STP is defined at 68 degrees F, 36% relative humidity, at sea level (14.696 psi)

I look at it this way, based on displacement, the math says it should produce ~9 CFM at the RPMs I am running. Based on actual measured output at 90 to 115 PSI, it gets a result that agrees with that 9 CFM. Kind of hard to argue with the data.

[Chad86tsi]

Mass matters in combustion because of the stoichiometric ratios of oxygen to fuel in the chemistry of combustion. I would argue that mass has no bearing on the CFM rating of a pump used to power an air tool. Volume is volume, and I think that is all that matters when you are spinning an air powered tool.



Of course you can Bill. Compressor manufacturers do it all the time. How else would you rate a compressor? Its true that that changes in temperature, pressure and humidity can skew the results, but that's why SCFM exists. SCFM is just CFM at STP (standard temperature and pressure). STP is defined at 68 degrees F, 36% relative humidity, at sea level (14.696 psi)

I look at it this way, based on displacement, the math says it should produce ~9 CFM at the RPMs I am running. Based on actual measured output at 90 to 115 PSI, it gets a result that agrees with that 9 CFM. Kind of hard to argue with the data.

1 bar = 1 atmosphere, or 14.7 PSI. A cubic foot of air at 0 Bar has zero air in it. none. It would be a complete true vacuum.

A cubic foot at one Bar has 0.0807 lbs. of air molecules in it at standard temperatures. We''ll call this a "standard cubic foot". Pressurize 10 cubic feet of it to 10 bar and one cubic foot now holds .807 pounds of air in it at 147 PSI. It's 10 "standard square feet" crammed in to one square foot of space.

Now draw a cubic foot drawn into a pump under a vacuum of 1/2 bar of suction, you have 0.0807 / 2 , or 0.04035 pounds of air molecules per cubic foot of volume. You have 1/2 of a standard square foot. Pressurize that air air to the same 10 bar and you need to move 20 cubic feet of air at 0.4035 pounds per cubic foot to reach 0.807 pounds of air at 147 PSI in one cubic foot (0.04035 x 20 = 0.807) . This should be simple to visualize, if it's 1/2 an atmosphere under suction, you need twice as much of it to equal the same net result. It takes 20 half gallons of gasoline to fill a 10 gallon gasoline tank. Drawing air under vacuum requires displacing more volume to reach the same mass on the other side. unlike gasoline, air is very compressible, and very de-compressible. Mass and volume are not the same thing. Calculating volume and disregarding the mass (due to pressure change) says tells you nothing about what is in the tank when you are done.

The different CFM ratings at different rated pressures on the compressor specs should be your first clue that pressure matters in the CFM's. the motor RPM never changes, but throughput is different. Volume of the pump never changes, the cylinder and bore don't change shape, but the mass of the air that gets through the system is very different.

I looked at the "data" you used, it's an excel spreadsheet. I opened it and the formula has no offset for vacuum losses. It's using the same simplified calculations you are using of volume over time = CFM, so of course the calculations tell you the same thing.

Haven't you ever run an engine with a vacuum gage, or a turbo/supercharged motor and seen the power differences with different inlet pressures? The internal volume of the entine never changes, a 350 CI motor cisplaces 350 CI of volume no matter the pressure, but with more pressure in that air it makes a lot more power, and needs a lot more fuel. It needs more fuel because there is more air molecules in those 350 CI of volume.

I didn't want to start a debate, I only hope to point to the science of "why". It looks like a great compressor for a great price. I"m sure you will enjoy it.

[John T]

Here you go Louie...

.


https://newhaven.craigslist.org/mat/...734240759.html


Sent from my iPhone using Tapatalk Pro