New compressor required

[michael howarth 1Participant @michaelhowarth1]

My small and infernally noisy compressor is on its last legs and needs replacing. I only have a small workshop and would like a "silent"(ish) runner. The capacity of the machine does not have to be great as the most demanding task that it will be required to perform is blowing up the odd tyre, testing small steam engines and testing safety valves…..so 8 Bar is plenty."Bambi" seems to be the leader in small silent types…….any other ideas would be most welcome.

Mick

[michael howarth 1Participant @michaelhowarth1]

[mechman48Participant @mechman48]

Hi Mick

​Build one using compressor from a defunct fridge & pipe it into your existing compressor's receiver…

George.

[Clive FosterParticipant @clivefoster55965]

Several makes of the lab / dental quiet compressors similar to Bambi. Jun-Air seems to be the other common one. Both do what they say on the tin. In my experience pretty much of a muchness. The ones I used were still going strong after 5 years or so of lab use.

A friend picked up an old, maybe 30 + years, Bambi with thousands of hours on the counter still running OK ish but certainly due for a service. Bambi still had the parts then but did say that particular model was long obsolete and parts would no longer be restocked so anything dubious should be fixed then.

Main downside to Bambi, Jun-Air and similar is the limited duty cycle. Anything over 20% will seriously cut the lifetime. Basically anything much more than 10 minutes per hour is pushing it. Ideally no more than 5 minutes running at a time. Something difficult to evaluate when buying used.

Clarke sssh range look to be same but cheaper. No experience. Panther is a "label brand" of similar lab units.

Many of the oil-free compressors are quiet. This Aflateck on E-Bay **LINK**. shows the typical squat "cylinder" style of the quiet ones. Versions with a proper cylinder and longer stroke piston tend to be louder.

I have a Fiac Compact 106 suitcase style compressor which is decently quiet. Again found in several label varieties. More air than a Bambi and better duty cycle. But still not continuous rated. Just because it looks like a suitcase and has a handle on top doesn't mean you can swing it around like a suitcase. 'kin heavy. The sack barrow comes out every time I need to move mine.

Hydrovane rotaries, and the similar but less well known Mattie, are the quiet endurance kings. Relatively expensive, proper industrial quality and very long lived if serviced at the proper intervals and allowed to warm up every time they are used. My Hydrovane 502 does me just fine for workshop air! £500 well spent.

Clive.

Edited By Clive Foster on 10/12/2017 16:10:31

[Phil WhitleyParticipant @philwhitley94135]

Note also that a great deal of compressor noise is intake noise and can be eliminated by fitting better air filters/ My old BEN patents 22cu ft min unit was fitted with an oil bath air cleaner from a Hillman minx, and it cut the noise by at least 30%. You could use a tractor air filter too, with either a paper element, or oil bath. Makes a huge difference.

[michael howarth 1Participant @michaelhowarth1]

Thank you for those useful suggestions gents.

Clive……I have got one of those compact compressors, bought originally for air brushing but subsequently abused by running it continuously for too long so I take your advice regarding the limited duty cycles of these small ones. If I had more room I might consider splashing out on a bigger more "industrial" model.

George……it did flash through my mind that a fridge compressor might do but the thought did not stay there very long because I know nothing about 'fridge compressors. Have you made one? What sort of pressure and litres per minute could I expect from such a thing? Where is best place to source a fridge compressor…..fridge repair man maybe?

Phil……I will fit my knackered one with a filter to judge the effect, then if all other avenues come to nothing at least I will know how to make a noisy one less noisy.

Has anyone written up a fridge compressor system in MEW by any chance?

Mick

[michael howarth 1Participant @michaelhowarth1]

Just had a look on YouTube George and it looks too simple to be true. I shall be trying to source a compressor in the morning.

Mick

[mechman48Participant @mechman48]

Mick

​Beat me too it, I was going to suggest there are loads of vids of guys making these.

George.

[Brian Sweeting 2Participant @briansweeting2]

The silent compressors are generally hermetic refrigeration compressors.

The reason for the reduced duty cycle is that the motor does not have cooling refrigerant running through it only air.

In normal "fridge" usage the compressors often have a maximum start regime of six ( sometimes 10 ), starts per hour. When the motor starts there is an inrush of energy which generates heat in the windings, the motor then needs to run for a reasonable period the get rid of the heat. When running on air only the motor cooling is minimal.

Also, as an air compressor any oil carry over in the discharge pipework needs to be mechanically caught and returned to the compressor or at least the level monitored so that it can be topped up. In a fridge the oil circulates with the refrigerant and finds its own way back.

[not done it yetParticipant @notdoneityet]

Fidge compressors are usually rated in tens of Watts, sometimes into the hundreds – hence the quietness of them.

Maybe OK for the occasional blow down, but not for using power tools. A decent sized receiver will take ages to fill.

If using power air tools I would suggest a good two stage cast iron compressor pump, fitted to your receiver, might be a better option. I bought a second hand compressor about thirty years ago and it is still going strong. Not used much, but it will likely outlast me. A two horse motor powers it. Certainly not silent but nowhere near as noisy as these 2800rpm buzz boxes.

Putting the pump and motor ouside is a good plan, but I would prefer the air tank was safely remote from my work space… even though I tested it hydraulically, to well above its working pressure.

[michael howarth 1Participant @michaelhowarth1]

Thank you for those further comments. I have done a bit more research into the subject and as mentioned it is not quite as simple as just bolting the bits together if you want a decent result. Research continues.

Mick

[michael howarth 1Participant @michaelhowarth1]

One interesting thing I discovered was that the piston displacement in fridge compressors varies between 2 and 20 cc.

Mick

[Andrew EntwistleParticipant @andrewentwistle]

Hi Mick,

I have had good success adding a Danfoss SC21F 21cc compressor (available new on eBay) beside an existing 2HP compressor. Two valves and IEC mains connectors allow easy switching between the original noisy but high throughput compressor or the silent one. With the fridge compressor the 50 litre receiver fills to 100 PSI in < 5 minutes. For my use with a blowgun and for occasionally clearing swarf at low flow rates it has worked fine for four years, with no obvious signs of oil in the output. There are a couple of photos in my album.

Andrew.

Edited By Andrew Entwistle on 12/12/2017 09:17:53

[Clive FosterParticipant @clivefoster55965]

The Bambi, Jun-Air and, presumably, other refrigerator style compressors supplied for air duties are a little differently to refrigeration units to cope with ambient air cooling rather than refrigerant.

Just realised I had a Bambi manual on file and find that in fact they made re rated for 50% duty cycle rather than the 20% I recalled. Pretty sure that short burst rather than long runs is the best way tho'. The Bambi has a thermal cut out to turn it off if it gets too hot and takes approaching an hour to cool down enough for restart which certainly suggests that cooling isn't wonderful.

Bambi runs either 50 litres per minute or 75 litres per minute nominal depending on whether its the economy or full fat model. Both have 1/2 hp motors. Actual air delivery is around 40 to 30 or 55 to 40 litres per minute depending on pressure. Range is 1 bar to 8. Jun-Air are similar.

Lorry or other commercial vehicle air brake compressors are another effective DIY solution. Need to find your own motor. Maybe 1 or 1 1/2 hp if run at around 1,000 rpm. I've had one under the bench, too good to bin, for years. I'll never use it now so if anyone within striking distance of East Sussex wants it just PM me and arrange pick up.

Clive.

[Gordon TarlingParticipant @gordontarling37126]

When I made my own airbrush compressor unit, I found that the compressor from a freezer had a higher output than one from a fridge. As has already been said, you do need to be able to check or top up the oil level if you want it to have a long life. Mine worked well for may years.

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