fridge powered compressor

[rtbcomp]

Excellent stuff Eil - thanks!

 

[eil]

Just one little thing, before you use them do you test them to see if the reeds arent worn, if they are you will be wasting a lot of energy for no pressure you`l only be generating excess heat. after all fridges that have been given the chuck have been for a reason!

 

[rtbcomp]

I've got a little test rig - an old CO2 cartridge from a fire extinguisher fitted with a pressure gauge, I can get some idea of the condition of the pump by how quickly the pressure rises and how long it holds for when I switch off.

I really knackered some reeds up by lubricating it with cooking oil! bad idea.

 

[eil]

The way to test them is to have a vacuum gauge connected to the suction the other suction blanked off then run the comp for a min os so it should give you a vac of about 20 to 28 inHG. then swich off power and observe how long the vac comes up to 0 psi, if ur reeds are knackerd it will rise slowly. if its good it should hold that vac for about 5 to 10 mins. that proves the reeds are good. the other problem that you said that youve had is oil emulsifying you might have a comp that was on an old cfc comp mixed with a comp that had the ester oil in. the two oils dont mix and create a foam like gunge.

 

[aametalmaster]

Hi all!

Does anyone know anything about turning fridge compressors into useful compressors for powering tools from?
I managed to salvage a compressor from an old fridge and got it to run all right now (after spraying freon and nasty fluorescent blue oil all over myself ). Does anyone know what sort of pressure they can pump to, what sort and where to find a reservoir tank, if they would be suitable anyway, if they need any maintenance, or any information at all really
Thanks in advance!

I made one 24 years ago from a freezer pump. I just used an air tank off of a semi truck trailer, a limit switch plus an unloader valve so when the comp shuts off the air in the tank line bleeds off between the pump and the tank. Mine will pump to 150+ psi but i shut it off at 125 psi. My tank is rated at 200 psi. Some AC units have the same pump as my freezer pump so i do have a spare. Mine is prob 45 years old and i found parts online to rebuild it cheap...Bob

 

[rtbcomp]

........ the other problem that you said that youve had is oil emulsifying you might have a comp that was on an old cfc comp mixed with a comp that had the ester oil in. the two oils dont mix and create a foam like gunge.

This emulsion is caused by water mixing with the oil because the pump takes in hot oil vapour & droplets. The original oil is long gone, I'm using the thinnest cheapest engine oil I can get my hands on.

I like the vacuum gauge idea, bit easier than my method.

 

[Gas mark 5]

Thank you all!
I think that I have it sorted now, I have a pressure gauge that goes up to 200 psi, off a big yellow thing I found in a bin So I can test the pressure, which I will do any minute now, and an air tank from a lorry sounds like a great idea! (I have an aversion to buying anything new!) But what are the reeds?
I'll get back to you as soon as I have tested the pressure
Thanks all!

 

[rtbcomp]

....... But what are the reeds?
I'll get back to you as soon as I have tested the pressure
Thanks all!

They are the valves in the compressor, thin strips of spring steel.

Make sure the tank is upto the pressure!

 

[eil]

Gas mark be sure to check that you have oil in the comp before ur test or it wont last long.
Eil

 

[Gas mark 5]

Erm...how do I go about checking that?
When taking it out of the fridge, I tilted at an angle and lots of yellow goo which I asume to be the old spilled out of the intake tube (and all over me...) How do I know if there is enough in it
thanks.

P.S. oh yes, I will have to wait for the araldite to dry before testing it, sorry.

 

[eil]

rtbcomp Ive been having a look at your set up with the bank of three and was thinking that perhaps you should make yourself a homemade oil separator out of say a 12"x 3" pipe tack a piece of plate down the inside so you have two chambers leave the 3/16 discharge pipes of the comps and run them through a flange or similar to one side put a drain at the bottom and on the other side semi circle a larger dia pipe to run into your reciver i would also lag/insulate the separator to keep it warm . you would then be able to firstly remove the bulk of your oil and the hot discharge air would still hold on to the water vapour that would then condense in your reciver for you to drain as usual but with less oil in it ,this way i recon you could re-use the oil as it would be less contaminated with water. just a thought.
Eil

 

[rtbcomp]

Empty the original oil and put about 300-500 cc of thin engine oil back in. It may have difficulty in starting though.

Eil - I've been thinking quite a bit about the oil/emulsion thing. I want to keep it simple and I've used plenty of copper pipe to get the heat out as soon as possible so I can recover the heat into the room. Also I want a large volume between the comps and the non-return valve feeding the receiver so when the dump valve closes pressure builds up slowly to give the motor a sporting chance of starting.

I'm happy to let the emulsion collect in the receiver and collect it in a bucket when I drain down at the end of each day. If I let it stand in a tall bottle I get water at the bottom, emulsion in the middle and a bit of oil on top.

The emulsion makes great chrome cleaner!

 

[eil]

rtbcomp What in your opinion is the cause of your emulsifying oil ?.
I understand you want to keep it simple but youve been buzy on your system and a separator would not be complicated. you would have a large vol in fitting the 22mm pipe youve installed to run from separator to reciver. by lagging the oil separator it would hold the heat and when it leaves through the 22mm un insulated it will give up its heat then just the same as it does now.

 

[rtbcomp]

The emulsion is caused by moisture in the air condensing under pressure and mixing with hot oil particles or vapour. When I extended the inlet pipe to the comp. there was slightly less emulsion although I guess some oil was getting past the piston.

Some emulsion forms in the trap a few metres away, so it obviously travels as a vapour, the black receiver fastened to the wall collects all the air from the system and most of the gunge settles out in that.

I'll certainly bear your suggestions in mind when (if!) I build a MkII system. Another reason for cooling the output is that I carry the air away in Nylon hose, I've actually had some burst by letting it get too hot!

 

[eil]

That is what im trying to get at, by separating the oil first from your high discharge air there would be less moisture in that oil youve traped allowing you recover more of the actual oil and re use it the water vapour would be carried on in the hot air until it reaches your reciver where it is colder and would condense to liquid there.
build a mk2?? im sure you will you just cant leave it alone can you.

 

[rtbcomp]

This would mean a drain on each compressor - the big picture is to have 50 pumps in pairs to replace my 3 hp compressor, so there would be extra maintenance required and if it added a quid to the cost of each unit that's £25 less for me to buy food with! I'd sooner just drain one tank at the end of the day.

The VERY big picture was to have it computer controlled, but I don't think I'm really that bothered anymore.

 

[shenion]

50 pumps, you will spend more on fittings than it would cost to get a decent compressor.

Fridge compressors are good for airbrush setups as theya re small and quiet. Otherwise, I don't see the point. Sure they are quiet, but you can get quiet compressors. My next pump looks to be 68DB and that is 18CFM.

Even if you don't get a quiet compressor, you can spend less building an enclosure to quiet one down rather than messing with all the pieces and hassle.

If I was going to build a compressor, I'd get an old 3HP B&S engine, remove the valves and head and use a plate with check valves. Then add a 3HP motor.

 

[rtbcomp]

My workshop is in a built-up area and I run the compressors between 01:00 and 08:00 to take advantage of half-price electricity. To get what I want "properly" I would have to spend about £2000 (new kit). An enclosure won't stop the vibrations travelling through the walls to my neighbours. Also two of my neighbours work shifts.

If I have 50 pumps and a set of 2 breaks down I lose 4% of my air, if I have one big pump and it breaks down I lose 100%.

If I don't need all the air I don't run all the pumps.

As for fittings I'd need 25 solenoid valves and 25 non-return valves. These can be got from 25 scrap washing machines for free. At the moment a scrap washing machine is worth about £8.00 in scrap that represents a profit of £200. Mains leads, supressors and connecting wire come free with the washing machines.

The compressors would be distributed about the building to provide heat. In some circumstances if I just wanted one room heating I would only use the compressor(s) in that room.

I had considered building one out of a car engine. Remove the rockers, T cylinders 1 & 4 together and 2 & 3 together via the plug-holes and use check valves like you suggest. A 1500cc engine should give a decent output at a failrly low speed too. It would even be water cooled so heat could be recovered.

 

[eil]

Keep your eye out for the commercial type refrigerators more cc`s and just as quiet less mtrs to get ur cfm then !

 

[rtbcomp]

Keep your eye out for the commercial type refrigerators more cc`s and just as quiet less mtrs to get ur cfm then !

Definitely. I wouldn't consider anything less than 100 watts from a fridge either.

The chances are with a larger freezer motor it will start under pressure so you may not need the dump valve. The Machine Mart Ssssshhhhhhhhh compressors use freezer motors and the little dump valve in the pressure switch isn't used. I think they switch off at 8 bar whereas I run my system at 10 bar.