Fridge compressors?

[rtbcomp]

Just to clarify - I fastened the Jubilee clip round the unit top to bottom. There's no pressure in the casing, it just needs to be oil tight.

 

[Maker]

What pressure is a refrigeration compressor rated at?

 

[oddbob]

What pressure is a refrigeration compressor rated at?

I'd imagine it would vary like mad from model to model. Mine's from a bog standard fridge freezer and it'll push over 100psi without labouring ...as for cfm ...not a lot!

 

[monkeymark]

It's quite common (if you look at Youtube) for people to cut the top off at the seam with a grinder/slitting disk to get at the inside, but I didn't fancy that ...thought there was too much risk of badly contaminating everything, plus you've then got the hassle of fixing the top back on in a watertight way (the compressor sprays the oil around the inside whilst running). What I ended up doing was drilling a hole with a small diamond core drill (the type you'd use for glass), so as not to create any swarf and avoid breaking through in a savage way, also drilling upwards, without draining the oil first, so that when I broke through the oil gushed out taking any crap with it. I then gingerly tapped the hole (M8 if I remember correctly) from underneath again and flushed it, without moving it, by pouring white spirit into the air intake pipe (which just goes into the casing). I then screwed and soldered in a cobbled together brass fitting to take a length of clear hose.

edit... looks like I've repeated some of what rtbcomp has said there!

Good way of doing it, nicely done

 

[monkeymark]

.

I considered removing all my pumps from their cases and installing them in a common sump.

Hmm, that could be interesting!

 

[lotus 30]

Fridge compressors rely on the return gas to cool them they have a stall start metallic strip which will drop out if it does not start it may take 10 mins
to reset if the compressor is hot. they are also lubed by the gas which carries oil in and around the system. when a fridge comp fails 9 times out of ten it is due to the fridge running short of gas and it burns out. most commercial comp's have run and start capacitors to aid start and run. andy b
fridge fixer for 35years.

 

[rtbcomp]

I used mine as a compressor with cheap motor oil as the lubricant. It took about 6 goes before they would run. The oil being thicker than the proper stuff meant it wouldn't start so the Klixon (as above) cut the power for a few minutes. The oil was gradually warmed during the starting process. I used a washing machine valve to release the pressure on the outlet to aid starting.

 

[oddbob]

I've got commercial sewing machine oil in mine. Used it because it's about the same viscosity as that that came out (which I was told not to reuse as it absorbs moisture apparently). I like the washing machine valve idea ...there's not enough pressure from the pump for the purge thing to work on the pressure switch.

edit... probably not pressure, more likely volume.

 

[rtbcomp]

It's pressure & volume. The unloading valve releases the air faster than the compressor can produce it, so pressure doesn't build fast enough to close the valve.

You can get unloading valves that close immediately the switch goes to "on", but most are the delayed type.

 

[oddbob]

You can get unloading valves that close immediately the switch goes to "on", but most are the delayed type.

Yep ...I just used the one I had. It will start without a problem under load anyway, but I did fit a 10bar safety release valve where the purge pipe should be so that I can release the pressure should it be standing unused with a tank full for any length of time.

 

[rtbcomp]

Safety valve is a good idea; a person I know, we'll call him "Luke", left his fridge compressor running overnight and the pressure gauge went right round the clock and bent the needle.

 

[monkeymark]

I used a washing machine valve to release the pressure on the outlet to aid starting.

Which valve did you use?
I would guess at a normally open solenoid placed between output and check valve operated via pressure switch?
I was looking at a mac valve but this could be much cheaper.

 

[eil]

For who wanted to know how much pressure a fridge compressor can get up to,I put an old Hotpoint compressor on a pressure gauge quite a while back, I was trying to find out at what pressure the klixon would cut out, I chickened out when it got up to 500psi.

 

[rtbcomp]

Which valve did you use?
I would guess at a normally open solenoid placed between output and check valve operated via pressure switch?
I was looking at a mac valve but this could be much cheaper.

Again, if you have a look at that link I posted in post #11 it's all there, you just need to wade through it.

I used a bog-standard mains operated washing machine valve.

Basically I wired a relay across the start coil so that when the motor was trying to start the relay opened the washing machine valve. The circuit is on Flickr, but it's playing silly beggars at the moment and I can't download it.

I dare say you could wire the solenoid valve directly across the start coil, but I had several compressors each with its own relay exhausting through the same valve.

 

[normspanners]

For who wanted to know how much pressure a fridge compressor can get up to,I put an old Hotpoint compressor on a pressure gauge quite a while back, I was trying to find out at what pressure the klixon would cut out, I chickened out when it got up to 500psi.

Yeah I did the same got mine to right round the gauge ?, when I was testing, to make up the high pressure unit, I fed the running pump with air at 10 bar to increase the flow, then it is not having to wait for the air to flow in at atmospheric pressure, I was turbo'ing it!.
and the motor did'nt even sound to change note.

 

[normspanners]

What pressure is a refrigeration compressor rated at?

40 bar

60 bar

 

[Bill Edwards]

870 psi...

I think that would make some air tools quite powerful - for short bursts anyway!

 

[rtbcomp]

You may get some interesting popping noises from the airline too!