What makes a good air compressor?

I'm looking at getting one that can be used for sprayng and tools

what are the basic requirements for a good compessor?

thanks in advance

Mark

If you're running it from a domestic supply you'll need a single phase motor, the biggest commonly available single phase motor is 3 hp and for this you will need a decent supply ie. not an extension lead.

This would power a professional quality spraygun and most air tools, smaller versions 2hp/1 hp would struggle with a professional spray gun but you could compensate by getting a different gun, some of which are pretty good.

Belt drive is better than direct drive, as with direct drive the unit has a smaller pump spinning at higher revs and is less reliable.

Don't get too hung up on it's maximum pressure as 100 PSI is more than enough for most jobs. Pay more attemtion to displacement, a 3Hp compressor will usually produce 14/15 CFM (Cubic feet per Minute)

If you're buying secondhand good luck but be careful, if buying new Machuine Mart is a good place to start looking. A friend who used to deal in compressors always said that they are all "much of a muchness" ie all built in Italy/India/China and then badged as whatever Clarke/Sealey/Sip. Mine is a 3 HP belt drive 15CFM unit that is badged as an Airmark, i bought it secondhand 10 years ago and give Airmark their due I can still order spares for it although it is identical to the clarke ones sold by Machine Mart.

All of the above relates to piston compressors, I'm afraid i don't know anything about Vane compressors apart from they're supposed to be better and cost a bit more.

I have an ancient Chicago Pneumatics 3hp 160 litre 15cfm compressor. Its great advantages (2) are that it has a massive cylinder capacity, so it is VERY slow running and consequently VERY quiet, it sounds more like a V8 on tickover rather than a 125cc 2 stroke at 16,000rpm. The tank size is really important. I used to have a small compressor with a small tank and it would get out of breath in about 20 seconds, I fitted an old calor gas tank in series and increased the work time between charges to about 5 minutes (the 160 never runs out!)

I built one ages ago from a lorry brake tank and a second hand pump and used it for several years. The shop where I got my parts, cutout switch and safety valve, warned me not to use a calor bottle with the pump I had (first idea) as they are only rated to 90psi and it was a 150psi pump. I have had a 3hp SIP V twin direct drive for a few years now and apart from the noise it's fine. If you can get one with cast iron barrel liners it should last longer than the coated aluminium used in the cheaper end of the market.

I had an old Ingersol Rand compressor circa 1962, and it worked fine. However it was not really man enough being about 5cfm.
So I got a Clarke industrial range 14CFM 3HP electric one with Cast Iron Cylinder (better than the sleeved cylinders) from Machine Mart. Cost me £475:00, but are a bit cheaper now.
The 3HP ones need to be wired directl into the 30Amp Ringmain, and CANNOT be used from a plugtop, as the startup current will blow a 13 Amp plugtop fuse. Gess how I found out.
I put a 30Amp switch on the back of a socket, and ran that into the starter box on the compressor.
Its overkill for home use, but runs everything I have or will ever need.
It runs my home made sandblasting cabinet (cost me £50 to make) without stopping to take a breath!.

Get the best you can afford, its a long term investment. I would not want to be without it now. The tools come along, as and when you need / can afford them.

Not quite the best thing I bought, which is the welder, which has more than earned its keep, and heavily into profit on the jobs it has saved me paying out for.

Regards

Geoff

Also have a look at World of Power

They sold me a hefty twin-cylinder compressor, and replaced it without a quibble when I said it was faulty (not their fault!). The prices are competitive, and they often don't charge for delivery (a big factor when the item's as heavy as a compressor).

BTW: Get a conventional 'oily' compressor and fit a filter, not an 'oil-free' one. The oil-free ones are very noisy and tend to wear out rapidly. The conventional ones will go on for ever if you remember to check the oil level in the sump, and also to drain the air tank at regular intervals.

David

[Edited on 4/8/04 by David Jenkins]