Compressor oil.

An oil grade commonly recommended for compressors is SAE 30. Machine Mart sell it, and on some of their packs in small print it also states it is suitable for petrol engines. Aldi also sell stacks of it from time to time.

The small direct drive piston compressors of around 8CFM with a 25 - 50 litre tank are pretty good for the small home workshop, but they are noisy and can't power most air tools very well as they require a lot of air. But they can be used for most other tasks and easily inflate tyres and can be used for paint spraying.

A few years ago I bought a Clarke Air twin cylinder 14CFM belt drive compressor with 50 litre tank from Machine Mart, a very good quality Italian made machine at a reasonable price that can fit under a bench. They are also slightly quieter and more durable than direct drive types.

For several years I have also been using one of Machine Marts rotary compressors with a 25 litre tank, I think it is called Shsss Air or something like that. It is extremely quiet, so is great for constant use in the home workshop, but they are now quite expensive and their air output is feeble when compared to piston type machines.

Last year I really pushed the boat out as I wanted to do my own blasting, so yet again off I went to Machine Mart and bought one of their Industrial Air compressors. This is 3 HP with a 14CFM belt drive pump and 150 litre tank, and this has a relatively soft and quiet exhaust note. These are built in the UK but appear to use mainly Italian components. A bit big for under the bench though, unless you have a big bench.

Apparently, it's the FAD ( Free Air Delivery) that counts, rather than just the CFM rating. The trouble is the FAD rating is rarely quoted.

Edited By Lathejack on 05/02/2015 22:46:07

Edited By Lathejack on 05/02/2015 22:52:21

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Edited By Lathejack on 05/02/2015 23:08:43

I use a BAMBI for Spraymist, very quiet (almost silent) but takes a few minutes to fill the tank. I also have a low cost 2HP compressor, originally bought to run Spraymist, similar noise level to Manx Norton with open pipes at full throttle, doesn't get used much indoors now.

Dave

I have found that the minimal amount of oil in these direct drive compressors can cause problems,particularly if is taken outside the workshop to inflate tyres,etc make sure the compressor is level,a slope in the ground can allow the oil to run to one end of the crankcase and starve the big end of oil.My neighbour had his compressor on a slope and seized it solid. I fitted larger diameter wheels on mine and it is a lot easier to move around,the supporting leg must also lengthened, In a workshop compressed air should never be used to clean machine tools,it blows swarf etc into the slides,only use it to blow swarf off of workpieces.

Direct drive compressors are much noisier than belt driven, if only because they usually run at a higher speed.

The oil does need to be changed regularly, as some water does get into it, and will eventually emulsify

Do note the difference between Displacement and Delivery. The latter is how much goes into the reservoir, and is always much less than Displacement. (Well, it couldn't be greater could it?)

With regard to draining the condensate, the advice when I bought my compressor, was to drain after every use, and to leave the drain valve open when not in use. Despite doing this, some condensate will still dribble out when the compressor is moved. But at least it has a chance to drain out, rather than staying in and causing rusting. Occasionally, I run the compressor with the drain open, in the hope of pushing out condensate still present.

I have fitted a water trap on the delivery side, and drain that regularly, also.

The thought comes to me that, as a pressure vessel, the reservoir ought to be tested periodically, although I must admit that I never have. (Mine is supposed to have a plastic lined tank, but corrosion might still have taken place).

Howard

I have just realised that I have two compressors. The other one is a home brewed concoction, an HGV brake compressor belt drive, into an old gas cylinder. This works well and is quiet (ish). Cheap to build and better than the real cheapos.

Interesting point, as far as industrial air receivers are concerned any thing over 250 bar/litre so an air receiver running at 10 bar and greater than 25 litres needs to be tested every couple of years. All but the smallest fall into this category but not sure how this effects home use or a model engineering society as we have a small one at our track for blowing out tubes, will ask on my next visit.

Bob

As previously mentioned we have one at work which is used to blow out threaded holes and displace rinse water after using the Ultra Sonic.

After about 2 years use it started to run for a long time before shutting down and I checked all the items like oil and draining water which came out brown. The next thing that happened was that the quick release valves started leaking and on opening one up found that the steel spring had rusted away. By this time we had replaced with a new compressor and I claimed the prize thinking I can fix all this but it seems I could not as the cost and complexity of replacing parts got bigger and bigger. Vibration was shaking things apart and I was forever having to replace the air filter after I found it on the floor, so I scrapped it and now I religiously vent the tank and check oil levels on the replacement which is a lot quieter and maintains pressure even over a weekend.

At a previous place of work I did a lot of routing in plastic using a high Rpm air motor. To drive this we had a Broom and \Wade vane type compressor which barely kept up with the air motor. The noise of the air motor and compressor combined was more than the nearby workers could stand so it was mostly used early and late for the work. The work consisted of routing out the dense foam for fitting of instruments into travel cases. All done with a jig and layers of foam glued together with some intricate shaping.

Clive