Jump to content

Fridge Compressors


rtbarton

Recommended Posts

  • 2 weeks later...

Just de-gunged the last of my seized up compressors - definitely don't use veggie oil as a lubricant!

After freeing it off cleaning out with meths & white spirit didn't help much so I had to strip it down. The valves weren't too bad but the small 1mm hole in the exhaust was blocked, drilling out to 3mm is very beneficial.

Making them oiltight is a bit of a beggar, when hot the oil finds its way out through almost any joint.

I'm also working on a means of detecting whether or not a motor is running by monitoring the vacuum on the inlet.

Link to comment
Share on other sites

  • 2 weeks later...

I think I've got the oil leak sorted. After faffing about with welding, soldering and general gunging what seems to work is the original O-Ring and sealant, but using Silicone RTV instead of Blue Hylomar. The Hylomar tended to harden, shrink and crack if used in any thickness.

Following the instructions on the RTV tube both surfaces were degreased and roughed up slightly. The O-ring put in place and RTV spread over both flanges. After about 30 mins the top was placed on the pot and squeezed down slightly with a hose clip until it oozed out of the sides, it was then smoothed down and left for 24 hours. The top wasn't squeezed down more than necessary to leave a thick layer of RTV.

This worked fine on the Zanussi compressors, but the Sterne's flanges weren't parallel so this was welded up instead.

The position of the breather is important. The best position is dead centre above the rotor. Oil is thrown out from the centre and a 4 inch tall breather placed at one end still allowed oil to splash out.

I had a problem with the silicon tube. The freezer pump inlet pipe was 4mm diameter and tube 3mm, but it was possible to force the tube onto the pipe but as the Silicon tube tears easily it split - after I sealed it all up!!

The other problem I hit was with the leak valve. This is the thing that opens when the compressor switches off. It tended to get gunged up with emulsion from the pumps and didn't close. All the more reason for some electrical method of control.

To be continued..............

Link to comment
Share on other sites

I've been doing some measurements, to fill approx 220 litres of receiver, it took 2 freezer motors and 5 fridge motors 49 minutes to go from 20 to 150 psi (2.65 psi/min). It took my Clarke 14cfm compressor to fill the same volume from 0 to 100 psi 6 minutes (16.67 psi/min) ie 6.3 times as fast, so perhaps 6.3 x 7 = 44 fridge motors would be required to give the same output as the Clarke compressor?

I arrived at a figure of 30 fridge compressors being required on the basis of power consumption, which would be on the low side given that a lot of motors will be less efficient than one big one.

If you used decent sized freezer motors the figure of 44 would be less.

The biggest Clarke Shhhhhhh compressor is 6.5 cfm and has 3 very large fridge motors on it, so you would need two of these (13 cfm) at a cost £939 (inc VAT) each and this will only attain 80psi.

If you can get freezer motors for £1 each at your local tip you'd be quids in, but you'd have to build quite a serious machine!

Link to comment
Share on other sites

  • 4 weeks later...
I'm also working on a means of detecting whether or not a motor is running by monitoring the vacuum on the inlet.

Following on, I threw this together :

330924316_00a75f672a_o.jpg

A 20ml syringe worked best, as the pump starts up the resevoir (100g coffee jar) is evacuated and the plunger in the syringe is drawn towards the end against the spring. If the pump stops air leaks in and the spring pushes the plunger back out. With the correct choice of syringe, size of jar and brand of coffee the plunger will not go all the way unless the pump is up and running properly.

The plunger could be made to activate a switch which could tell the controller that the pump is running.

This all fine, but in reality the whole thing would be a bit cumbersome if a full complement of 50 pumps were to be used!

I think I'll try an electronic method after all.

Link to comment
Share on other sites

  • 2 weeks later...

I've come up with this electrical control circuit:

416683414_eb936a814a_o.jpg

In a nutshell when all three compressors are running the relays A,B & C are all called, the green and brown wires are open circuit which causes the dump valve to close and so air is fed into the receiver via a non-return valve (NRV).

Unit A is the slowest to start, so RLA/2 inhibits Unit C (the 2nd slowest) until A is running, similarly unit B is controlled by RLC/2.

The dump valve was taken from a washing machine, I used a washing machine hose connector with nylon airline fixed to it, seems to work fine. Don't use the washing machine hose as it is only rated at 1.5 bar.

When power is first applied all the motors attempt to start, but the slowest one labours and causes the cut-out to open, this stops the next unit(s) in the chain until the cut-out resets. This repeats several times, depending on the temperature of the oil and for how long the pump has been stopped, but after a lot of clicking, whirring and hissing the whole thing settles down nicely.

When a pump cuts out its external relay opens the dump valve so the pipe between the NRV and pump is at zero pressure which makes it easier for the pump to start.

Link to comment
Share on other sites

A couple more pics.

This is a general view of the unit, note the extra relays just below the start relays. The slightly brown plastic pipe connecting the three compressors maintains the oil level, the three open pipes are the air inlets. The compressors are sloping up at the far end so that the air intake is above the oil level.

418058627_d5d2173866_o.jpg

This shows the washing machine valve plumbed in as the dump valve. This is just a jury-rig at the moment, the valve will be incorporated in a control unit, yet to be built.

418058822_ad526b1fee_o.jpg

Since these photos were taken I've added a fan tray underneath the compressors, thermostatically controlled with a central heating tank stat.

Link to comment
Share on other sites

  • 4 weeks later...

This is how it fits together:

450404178_019b9e1a5a_o.jpg

Basically the bulk of the air is supplied by the 3hp compressor, with the fridge motors adding their bit if the time switch is set to "constant". When the big compressor cuts out (100 psi) the fridge compressors carry on upto 145 psi. If the electric valve is enabled it opens at 130 psi to top up the reserve gas bottles. This operates above the cut-off pressure of the big compressor so it doesn't fill the reserve.

The time switch can be used to set the fridge compressors to fill the reserve during off-peak periods.

The solenoid is a washing machine valve. This has a quirk in that it will allow air to flow from outlet to inlet even though the valve is closed, hence the non-return valve in series with it. Also the pressure switch opens on high pressure, but the valve requires a supply to open it, one way to achieve this would be to use a relay - details to follow.

Link to comment
Share on other sites

Two ways of controlling the transfer valve

454427111_2dd083e56f_o.jpg

In the top pic. when the pressure switch is closed (not up to pressure), the relay is called and the valve is de-energised ie closed. The relay contacts are "Normally Closed" (NC) i.e. closed with no power to the relay coil, open otherwise.

When the set pressure is attained the switch opens, relay drops, NC contacts close, valve solenoid energised and valve opens, sending air to the reserve receivers. Air will flow until pressure in the main receiver drops to the low pressure switching point of the pressure switch.

The bulb in Series (Landrover content ;) ) drops the current through the solenoid to reduce heating in the latter - it gets quite hot otherwise.

The lower pic shows an alternative way, the pressure switch contacts are connected accross the solenoid, high pressure NOT attained, contacts closed, solenoid shorted out, valve closed, bulb glows brightly. When high pressure is attained the switch opens and the valve opens transferring air to the reserve.

The latter method wastes power and will ultimately destroy the planet (unless Iran gets there first) but you will have a good visible indication of the state of the solenoid valve!

Link to comment
Share on other sites

As a matter of interest, interconnecting pneumatic components with copper pipe and conventional plumbing items can be made easier if you bear in mind

8mm microbore unions have 1/4 BSPP (British Standard Pipe Parallel) thread

10mm ditto 3/8 BSPP

15mm Cu pipe ditto 1/2 BSPP

22mm ditto 3/4 BSPP

Use a sealant such as Loctite Threadlock to seal parallel threads, more effective than PTFE tape.

Link to comment
Share on other sites

This is the circuit of the control unit. It includes 2 compressors and will control an external pack of three. Five or six is really the maximum you want to run off one circuit.

460466679_fff3eeff79_o.jpg

This combines the circuits for controlling the compressors and the dump valve. The unit is switched by the relays RLC and RLD, a 12v supply provided by the pressure and time switches calls these relays (each has a 6v coil) RLD calls about 1/2 second after RLC, this reduces the surge on the ring main. (Actual power is taken from the ring main to reduce the load on the pressure switch &c)

Pictures to follow

Link to comment
Share on other sites

i love this thread, i have no idea what the hells going on, but it's great to see people doing things fun like this.

When you have finished the project can you do an abbreviated version for those of us (ie me) that didn't understand the techy stuff!

Link to comment
Share on other sites

i love this thread, i have no idea what the hells going on, but it's great to see people doing things fun like this.

When you have finished the project can you do an abbreviated version for those of us (ie me) that didn't understand the techy stuff!

Basically it's a means of getting quiet compressed air without spending a couple of grand! at the same time using off-peak half-price electricity and recovering the waste heat where possible.

I expect to be integrating microwave cookers and washing machines in the near future.

Link to comment
Share on other sites

An old microwave oven provides an ideal housing for the control unit:-

461597020_be6c30d495_o.jpg

461596836_d47d910f0f_o.jpg

461596656_5359db50f9_o.jpg

A bit of modification was done to provide a decent airflow through the case. I reckon there would be enough room to house three compressors without the control gear (slave unit).

The microwave provides wire, mains lead & supressor, fan as well as the housing.

Remove the turntable otherwise all the pipes and wires get tangled up :o

Link to comment
Share on other sites

  • 2 weeks later...

Been giving this system a bit of welly over the last ten days or so. Two problems developed:

1) One of the motors wouldn't start - relay had worked loose from its three pins. Cure: tighten up the female pins and hold in place with a cable tie.

2) A bit more serious. The dump valve became constricted which meant the pressure in the pipes upto the non-return valve didn't drop sufficiently for a couple of the weaker pumps to start. I changed the valve (typical! it was fine until I enclosed it in a case) and that cured it.

I'm a bit concerned that the emulsion in the air attacked the valve seal - I had this happen to a cheapo non-return valve. I now use proper ones for compressed air rather than central heating ones!

Link to comment
Share on other sites

I expect to be integrating microwave cookers and washing machines in the near future.

so, if you use an old washing machine and strip the inside, you'll have space to house more compressors? or will they always need to be in "open air" (due to heating issues)? if that's not the case and they can be inside the machine, the fridge from where some compressor was taken from, would be a good place to fill with compressors :D

i doubt i could make one of those, but i really like to see these low-cost "hacking" projects. make some videos and upload them to youtube!!

Link to comment
Share on other sites

Never thought of using the washing machine as a case, it would be a bit awkward though from an access point of view. Washing machines are a good source of bits, wire, motor, valves, screws and there is a pressure switch which could be made to operate on a vacuum which would be a means of ascertaining whether or not a pump is running. The door would make an interesting roof hatch on a Landrover :lol:

I had considered mounting them in a fridge, running the fridge to keep them cool but it would probably overheat the motor. My biggest fear was fire, fridges have a lot of plastic in them and the insulation is flammable.

I don't think a video of a fridge motor would be that exciting, although with sound it may get into the charts!

Link to comment
Share on other sites

  • 1 month later...

More emulsion problems. This time with the valve that fills the reserve tanks. Flow through this valve has now slowed down quite a bit. The problem is that the pressure in the main receiver could reach maximum and stop the compressors before the reserve tanks have filled up.

The emulsion won't go away so the problem has to be managed. In this case I have connected two valves in parallel. This is easy using the cold-fill valves from a washing machine because they are mounted as a pair with a common inlet.

They work fine with the lamp wired in series with both coils in parallel - it glows brighter though, but the coils should run cooler.

As for the problem with the dump valve I think the solution here is to limit the number of compressors connect to it. Two or three should be OK, depends on the size of the microwave used!

I had a look at a tumble drier, it would make an excellent housing, the blower looks like a 1/3 horse motor so it should keep a whole load of compressors cool!

Link to comment
Share on other sites

  • 4 months later...

I've come up with a much simplified circuit, not tested it yet.

1917493036_e27ee3722a_o.jpg

This should work with two compressor in a unit. The dump valve is wired to the cold sides of both cutouts in the compressors. The valve should open when only one of the motors is running, thus allowing the other to start under low pressure when its cutout closes.

The valve is also closed when both cutouts are open (motor not running), this reduces the ontime for the valve solenoid so I guess the bulb in series is not required either.

The existing setup continues to run reliably, I'm using it on an almost daily basis.

The valve that fills the reserve tanks is pretty much gunged up so I'll come up with a means of stopping emulsion getting into it.

Link to comment
Share on other sites

  • 1 month later...

First failure today. After about three weeks of daily use for several hours at a time. The left hand compressor in the microwave cabinet (Post 92) siezed up. There has been an oily burning smell for a few days and I guess I let the oil level drop too much. It freed off after cooling down, but failed again after about 90 minutes. I reckon most of the oil leaked out as it is almost impossible to re-seal the lid after removing it.

I disabled the unit by disconnecting the neutral feed, see diagram in post 89 - this fools the relay into thinking the unit is running OK

When I build the next unit I'll alter the position of the fan and improve lubrication.

There is a definte advantage in having units like this indoors, after a day's work the office is nice and warm and I haven't needed to use the fan heater in this cold weather.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy