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Maximum fridge - a/c compressor output

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Maximum fridge - a/c compressor output

Unread postAuthor: MRR » Sun Jun 28, 2009 11:29 am

Hi guys,
How the title may say, I'd like to know the maximum output of a fridge compressor (or air conditioner).

I know that you can go past 300 psi but did someone really pushed a fridgy to the limit?

What pressures are safe and at what pressure would you say "damn my insurance is not going to pay for this" ? :wink:
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Unread postAuthor: Technician1002 » Sun Jun 28, 2009 11:39 am

You won't like my answer, but here it is.

It depends

Told you, you won't like it. :)

Piston compressors tend to have a top where they reach a point where the compressed air is small enough it stores in the valve area and re-expands with little getting through the valve.

Vane type do better with less nooks to contain space for gas that doesn't make it through the valve.

A scroll compressor is best, with multiple pockets of air in a linear compression cycle in the spiral.

Vanes and scrolls, you need to worry about proper lube as there is no oil in a crankcase to hit the bottom of a piston. Some oil needs to go through the compressor to lube it. The total ability is limited by leakage and wear and the point where the motor stalls.

At what point the pipe blows out is anybody's guess.
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Unread postAuthor: MRR » Sun Jun 28, 2009 11:46 am

Thanks for your response tech but the question still stands.

Many people here on spudfiles have fridge compressors and I'd like to know what the physical / mechanical limit of it is (in psi).
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Unread postAuthor: Technician1002 » Sun Jun 28, 2009 12:01 pm

I don't know the maximum of each type, or what is unsafe. Most fridge and A/C compressors are designed to have a head pressure of about 250 PSI. Hot conditions my reach pressures of nearly 350-375 PSI, but this is rare.

Those with compressors, feel free to post your pressures. Has anyone had a compressor valve, pipe, or safety plug blow out under abuse? Any motors stall and relay out on overload? MRR and others would like your info.

Freon pressure chart is here;
http://refrigerants.dupont.com/Suva/en_ ... k10911.pdf

Most refrigerators and air conditioners use refrigerants along the range of R12. Deep freezers and large commercial air conditioners use freon along the pressure lines of R22. Pressure chart is here;
http://refrigerants.dupont.com/Suva/en_US/pdf/k10911.pdf
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Last edited by Technician1002 on Sun Jun 28, 2009 12:04 pm, edited 1 time in total.
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Re: Maximum fridge - a/c compressor output

Unread postAuthor: boyntonstu » Sun Jun 28, 2009 12:03 pm

MRR wrote:Hi guys,
How the title may say, I'd like to know the maximum output of a fridge compressor (or air conditioner).

I know that you can go past 300 psi but did someone really pushed a fridgy to the limit?

What pressures are safe and at what pressure would you say "damn my insurance is not going to pay for this" ? :wink:



My idea for >1,000 PSI is to use a 110 VAC pressure washer.

Pump high pressure water into a vertical cylinder and you should have 1,200-2,000 PSI of compressed air at the top.

BoyntonStu
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Unread postAuthor: Dave_424 » Sun Jun 28, 2009 12:08 pm

A member called maggotman tested his to the limit

Just the pump alone wouldn't pump over 1000 psi but when he fed the inlet with regulated 50psi air, he reached 1800 psi and then the "Head gasket" popped

Dave
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Unread postAuthor: POLAND_SPUD » Sun Jun 28, 2009 4:54 pm

yeah dave is right... maggtoman was brave/stupid enough to do it

my answer is simple - there are different compressors... each model can have different specs.... I've reached 700 psi with the one I use now... but that's pushing the limits

I normally use 300 - 400 psi as that's already quite a lot power... past ~550 psi different things can happen - I had several metal BV that started leaking becasue of that, as well as my solenoid 5/2 spool valve (as its manual overide is made from plastic)
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Unread postAuthor: Brian the brain » Sun Jun 28, 2009 5:09 pm

I've had it at 50 bar a couple of times
Than I chicken out and cutt off the power.

It still runs nicely at that point.
50 bar is still over 700 psi.
( it might have done 60 bar or 850 once but I'm not 100% sure :roll: can't really recall)

I'm quite confident my model would reach it's limit at around 1000 psi as well.
I just don't feel comfortable around it...
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Unread postAuthor: Pilgrimman » Sun Jun 28, 2009 6:22 pm

I seem to remember a topic a LONG time ago where the poster ran his fridge compressor up to 1800 psi :shock: before he shut it off (meaning higher pressures were theoretically possible). I have no idea whether this is realistic for all fridge compressors, but I know I would never take it to that pressure.
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Unread postAuthor: THUNDERLORD » Sun Jun 28, 2009 6:49 pm

My idea for >1,000 PSI is to use a 110 VAC pressure washer.

Pump high pressure water into a vertical cylinder and you should have 1,200-2,000 PSI of compressed air at the top.

BoyntonStu


Seems very interesting.
Maybe two paintball tanks could be used,
a small "T" fitting could go onto the top of a carbon fiber or other paintball tank, with a cut off valve between other tank,
fill one with water, and open the valve connected to the other, drain the water and repeat until full pressure is reached...
I've had access to an 8hp 3200psi pressure washer all along too! 8)
Thanks for the idea BoyntonStu! I may try it soon.
I had a similar much smaller scale idea recently involving a hydraulic grease gun, or maybe a hydraulic floor jack version.

Back on topic: So theoretically, a "hermetically sealed" (non-serviceable), fridge compressor casing could hold un-regged CO2???
I'd be worried without more overview/ testing.
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Unread postAuthor: daberno123 » Sun Jun 28, 2009 9:07 pm

I've taken my AC compressor to 800 psi a couple of times, and once 1,000 psi when I wasn't paying attention.

It might go higher but I was scared as hell when I realized the gauge was reading 1,000 psi. I have to admit that bleeding the air hose was quite impressive. :D
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Unread postAuthor: POLAND_SPUD » Sun Jun 28, 2009 9:26 pm

well maggotman has proved (I think we can consider that as true) that you can increase pressure by supplying pressurised air to the air-inlet pipe...

I don't know what the point is in using unregged CO2 as air is readily available (you could use a shop compressor or almost anything else)... besides casings are rated/pressure tested to much lower pressures... again the exact pressure varies - normally there is some info written on them - like 'pressure tested to 150 psi' or something like that

well it's a cool concept but I bet that some would try to achieve dangerous pressures.. even 700 psi is a lot more than should be used with most readily available materials (including QEVs and iron fittings)

so... what's the point in getting more ? to use the extra pressure you would have to build a gun from machined parts... if anyone has access to them he might as well build pressure booster/amplifier
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Unread postAuthor: Technician1002 » Sun Jun 28, 2009 9:31 pm

[quote="THUNDERLORD]

Back on topic: So theoretically, a "hermetically sealed" (non-serviceable), fridge compressor casing could hold un-regged CO2???
I'd be worried without more overview/ testing. [/quote]

Danger :angel7: It's a quick way to fly with the angels. The case on a compressor is on the inlet side and will not hold the same pressure as the outlet pipe. Keep the inlet under 200 PSI.

I found the following online while hunting up shell test pressure.
Tecumseh manufactured and sold to Marquette a sealed compressor refrigeration unit which Marquette incorporated in a refrigerator which it manufactured. The compressor unit was enclosed in a steel casing or shell, whose two halves were welded by Tecumseh. The refrigerator manufactured by Marquette carried a plate which stated that the factory test pressure of the refrigeration unit was 195 pounds.


I found it in a court document where one blew apart at 170 PSI.
http://bulk.resource.org/courts.gov/c/F2/378/378.F2d.601.15958.html

Plaintiff's expert witness, Dr. Guy M. Pound, testified that the cause of the explosion was a defect in the weld of the casing. Tecumseh's expert witness, James R. Elliott, testified that it was the usual practice in the industry for an assembler (such as Marquette), to submit the refrigeration system to an air pressure test of 235 to 250 pounds after connecting the compressor unit to the system. Elliott also testified that Underwriters Laboratory Specifications required that the compressor casing or shell should be able to 'withstand or have a bursting strength * * * of 350 pounds.'


Further in the article, it was noted the case burst from excessive pressure, that the test was done with dry nitrogen and it may have not shut off properly after the test was completed. This was determined by the distortion of the metal (yeld before break) that overpressure does.

For safety, keep the shell away from the 350 LB mark.
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Unread postAuthor: psycix » Mon Jun 29, 2009 3:52 am

Technician1002 wrote:Piston compressors tend to have a top where they reach a point where the compressed air is small enough it stores in the valve area and re-expands with little getting through the valve.

The dead space in piston fridge compressors is minimal. The dead space is not even 1% of the cillinder volume, so those theoretical pressures should be hundreds of bar.
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Unread postAuthor: Technician1002 » Mon Jun 29, 2009 4:13 am

psycix wrote:
Technician1002 wrote:Piston compressors tend to have a top where they reach a point where the compressed air is small enough it stores in the valve area and re-expands with little getting through the valve.

The dead space in piston fridge compressors is minimal. The dead space is not even 1% of the cillinder volume, so those theoretical pressures should be hundreds of bar.


So just how do they port the valve so the valve closes right to the surface of the piston? Last time a checked, the reed valve is on top of a port, which has space between the reed and top of the piston. True the space is small for effeciency, but it does exist and is on the piston (clylinder) side of the reed valve.

The piston is designed to come very close to the end of the cylinder, but it is designed not to hit it. This space is larger than the space left in a vane or scroll compressor, hence, a lower peak pressure. How much lower... I don't know. I never tested it.
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