Use of fridge compressors as vacuum/pressure air pumps - I'm new to all this!

Hi there chilled folks ',;~}~

As my hobby and (hopefully!) future 'job', I use a fridge compressor as a vacuum pump for vacuum impregnation of softened woods with resisn and/or plastic solutions to harden and stabilise them.

Well, just after getting my first 'pump' up and running with a small dehumidifier unit and having sucess with the tech, well, I jammed it up when foaming styrene solution passed into the system - guess I should have fitted a bottle trap! - D'oh!

So, I've been out and sourced another compressor, and have a second on its way to me via the E-Bay (will use one as vacuum, the other as compressor, and if either should fail I can swap the units over).

I have made and fitted an inlet bottle trap and filter now, but NOT being a ref. eng, there are things I still don't know - I'm hoping you kind people can help educate me!

Firstly - can I use ordinary compressor oil in the system? How much oil does one of these units normally hold? - The unit I ordered is a TLS6F Danfoss unit, the one I have already been given has most details obscured, but looks to be about the same size (think it was from a small commercial shelf chiller, but not sure)...

Secondly - what's the small copper 'bottle' for that's in one of the pipe lines? Is this an oil recouperator perhaps?... Do I need this with how I'm using these units, and if so, will a home made piece do the job?

Lastly (for now, heheheh... ) - I hear of capacitor start, induction run, or induction start, capacitor run (or similar?) - the old unit I destroyed had just the current/heat trip unit and start relay attached to the side, but the ex-commercial unit has a seperate box besides, with a large capacitor and what looks to be a large silicon controlled recitifier block, with mains leads going in, feeds to compressor also to cooling fan coming out - looking inside, it *appears* that this is only to do with the fan as mains-to-compressor connections, whilst fastened to the SCR block terminals, connect directly through to the unit - do you think I need this little box of tricks just to run the comp. as a vacuum unit?

I REALLY don't want to destroy another one as I have been long term unemployed due to illnesses and we are worse than broke, and this is my chance at an income again, providing it doesn't keep costing me money to keep going!

TIA for any help/advice you have for this non-professional, non-refrigeration engineer - MUCH appreciated!

Be well,

FlowolF (Shaun).

How large is your vacuum chamber and how deep you need your vacuum?
This info will help you to choose the kind of vacuum pump you need.

I don't think that a small refrigerant compressor is what you need.

Thanks for the reply!

Chamber size is small - about 6 x 8 inches at the moment, but will be using a 2 foot by 3 foot chamber soon - other folks doing similar things are using these pumps, and in fact even smaller ones than I have - cost is a huge issue - basically, if it costs me more than a few quid I can't do it right now!

Thanks again bud,

FW/Shaun.

In that case, until you will be rich and famous, it will do, just make the vacuum chamber air tight.

Heheh, Thanks again!

Rich I could cope with, but famous though, I could well do without LOL!

Any advice on the oil or little copper bottle for me though buddy? I'd hate to have this thing bleed out on me and sieze-up...

Cheers, and as ever - be well ',;~}~

FW/Shaun.

What oil and little bottle?

Can you post a picture and elaborate?

Regarding the electrics 'pack' that came with the compressor, yes compressor motors do need to have the correct starting devices or you will burn out the motor very quickly.

If you search the net with your compressor model number you will often find details of the start method needed.

The small bottle is probably a small filter/drier which in your mode of operation if surplus to requirements and will do nothing at all towards drying the air. If it has been open to atmosphere then it is already useless.

Thanks for that Brian.

As for searching the net for the details - I always work-the-web hard on my own before tackling any forum folks - thing is, can't really read any detail from the unit I have currently - the label is badly damaged mate.

Cheers again! Be well ',;~}~

Shaun/FW.

I've found this document from Bristol Compressors quite useful in the past, the models won't be like yours but the basic wiring is much the same for single phase motors and it may prove helpful...

http://www.bristolcompressors.com/Docs/200022.pdf

Bristols website has other docs available as well.

~I would think one of your major problems would be overheating the windings as if the compressor is used as anything other than its intended purpose you will be denying it of any cooling via the suction line - a vacume pump would be the thing, that said I have seen them used as air compressors in the past so as long as its not left on running for hours maybe that wont be a problem!?

You could use a slow speed steel recip air compressor as a vac pump. You`ll have to block off the crankcase breather and maybe reverse the crankshaft oil seals otherwise the oil will be drawn up the cylinders. Fit a vacuum filter before the inlet to prevent any solvents etc entering the pump. if you do get the business off the ground invest in a liquid ring vac pump, they can deal with all sorts of contaminates and are able top run constantly with very little attention.

.

Could I suggest you by a proper vacuum pump?

I have just done an ebay scan and there are 100's new and second hand from £10 to £300.

Then you can replace the oil as and when you see fit and it is designed for the job.

Ps using a normal compressor will work as you have proven and they might be cheap to
obtain, but a one off investment of between £50 and £250 will see you sorted for the next
ten years..

All the best

taz

.

Excellent link - thanks v. much again Brian - have some more rep. mate! ',;~}~

This has given me a clue as to how these things work - the compressor I was given, it seems came with all that was needed for it to start and run a treat, and with the addition of a homemade bottle trap with particle filter on the inlet, is safe from 'ickyness-ingress', and the long copper tube on the outlet serves well as an oil catcher and oil return, so it all runs perfectly and hopefully, should do for some time ',;~}~

As for the unit I just acquired via E-bay (for a tenner plus postage - 16 quid total) - well it's a small Danfoss unit (TLS6F), and it turns out that DIDN'T come with all that was needed - it had the PTC (positive temperature coefficient) switch/'relay' device, but not the start capacitor (it doesn't use a run-cap) - thanks to the pages you posted a link to, however, I've been able to see how and why it is used and get it to start without one this morning which was very handy as we had no working pumps in the house, and our central heating expansion tank needed recharging, and well, it's been bloomin' cold LOL!

Thanks again bud - great help indeed ',;~}~

Be well!

Shaun/FW

Thanks Paulo - I appreciate your cautions mate - the unit I was given is quite large and so far, doesn't even get warm during use, and I've lashed up a vacuum switch (large plastic syringe, small metal leaf spring, micro-switch etc.), so it only runs until it's pulled enough vac. then it rests until the vac. drops a bit - I set it on a timer too, so it only runs for a maximum of 15 mins time before a 15 min. rest. It also came with a nice fan for cooling the refrigerant, which I can use to cool the compressor should I need to in warmer months.

As for these being used as compressors - aye, several companies even use the same basic scroll compressor designs for their silent compressors, such as 'Bambi' for instance, and I believe many dental compressors are also basically the same things, with just a few internal construction differences?..

Anyhow, cheers again bud - be well!

Shaun/FW

Cheers Glen - if/when I get this off the ground I will indeed invest in something a little ' mo' proper ', but it seems a lot of folk doing similar things to this start out the same route - old fridge compressors, and ya can't beat prices like 'free' or the 16 quid I paid for the back-up Danfoss unit, and right now, that's about all we can afford LOL

Thanks again, and be well ',;~}~

Shaun/FW

Taz - Cheers bud - I'll be keeping my eye out for such bargains that's for certain. Guess there's a huge aspect of my self that just loves to 'bodge' and make things work for me in ways outside of their original design parameters, and I can get kinda stuck in all that business a bit 'rut-styled' LOL!

Anyways, as I posted above - it all (based on the freebie unit) seems to be working above my needs and expectations so far and I've already vac. impreg./stabilised a couple of neat knife handles and several ring blanks from softened/weakened spalted woods using this set-up and they came out excellent, and now we have the CH working again, I can turn my hands back to my own work and get some more of my own stuff done!

Cheers again bud, and be well!

Shaun/FW

Thanks for the update, and good luck with your ventures.