Compressor terminology and advice

[The Bear]

I have to admit I know nothing about compressors. I have searched the forum already but the posts I've found have been a bit over my head.
In the first instance I want to use an air nailer/brads, probably 18 gauge. I want to in the future be able to do a moderate amount of spraying which I understand is quite "thirsty" on the air.

So far I've ascertained I need a high free CFM (as opposed to piston displacement CFM). Other than that I don't really know what to look for.

In particular what is the benefits of

Direct drive vs Belt drive
Oil lubricated vs oil free.
Are connector types standard across the industry and interchangable at this level?
Do all compressors have valves to regulate the air pressure coming out or does it depend on what is in the tank?

I am at the moment considering the following two compressors with a £250 budget in mind.

This Axminster one, 8.5 cfm
http://www.axminster.co.uk/product.asp? ... =1&jump=44

and this SIP, 14 piston cfm which according to another site equates to about 9.3free cfm.
http://www.sipuk.co.uk/tools/info_SIP06242.html

Looking at them they seem almost identical and are probably rebadges of something else. Though why the Axi might need 16amp is a bit confusing. Would both these be a able to cope with moderate spraying?

Sorry if some of these Qs seem daft.

Mark

 

[RobertMP]

I'd suggest a smaller £100 compressor just for your air tools and a HVLP unit for spraying.

HVLP uses a thing called a turbine to produce the air. A bit like a vacuum cleaner blowing instead of sucking - lots of continuous low pressure air. Sprays well and much less atomised overspray floating around in the air compared to a high pressure compressor based spray.

Have a search on 'HVLP' they come in a range of prices and sizes.

 

[andycktm]

Belt drives are a LOT quieter

 

[Dibs-h]

I'd suggest a smaller £100 compressor just for your air tools and a HVLP unit for spraying.

HVLP uses a thing called a turbine to produce the air. A bit like a vacuum cleaner blowing instead of sucking - lots of continuous low pressure air. Sprays well and much less atomised overspray floating around in the air compared to a high pressure compressor based spray.

Have a search on 'HVLP' they come in a range of prices and sizes.

Yep - I'd go with RobertMP's advice. Spray painting in a small space with a traditional gun - overspray is putting it mildly! Not to mention the grunt required for the compressor with cost serious £££.

 

[FatFreddysCat]

So far I've ascertained I need a high free CFM (as opposed to piston displacement CFM).

The term you're searching for is "free air delivery". This is normally only quoted by the larger (and therefore more expensive) manufacturers

what is the benefits of
Direct drive vs Belt drive

Direct drive is normally only used on smaller compressors up to about 3 or 4HP. Seems to me that above that the starting resistance becomes too much for the motor (unless you want a very high startup surge). More industrial compressors are often of 2-stage design where the first one ofr two cylinders compress the air to say 70psi and another piston then compresses it further to about 130 to 150psi. Industrial compressors also tend to run the motors at 1500 or even 750 rpm meaning that the motors wear out less quickly and in addition they aren't as noisy in use.

Oil lubricated vs oil free

Oil-less compressors are generally very small capacity and are often incapable of running anything as "thirsty" as a spray gun

Are connector types standard across the industry and interchangable at this level?

No. There are literally dozens of types. The most commonly available are called "SPL" and were designed back before WWII. Still very common in the motor trade and probably the most readily available. They may not be the best in terms of air volume handled, but for a conventional spray gun they are more than adequate.

Do all compressors have valves to regulate the air pressure coming out or does it depend on what is in the tank?

No. This is an add-on extra as is the pressure gauge. If you decide to spray you'll need at least a 20micron coalescing filter (and preferably a 5 micron particulate filter downstream from that) to give you clean, oil-less, water-less (well, relatively) air.

Hope that clarifies things.

 

[andycktm]

Very good explanation ,but i think you will find a regulator valve on any compressor you buy

 

[The Bear]

Thanks for the replies

If I decide to go down the HVLP line for spraying (which does sound more efficient), I still want a compressor to run a nail gun etc.

In that case what "size" should I be looking for in terms of tank size, HP, and do I now need to worry about free air delivery CFM (if I do what size).

Should probably add this will get moderate use, it won't be running all day every day

Finally brands, any spring to mind?


Thanks in advance


Mark

 

[cambournepete]

If you like (relative) silence then get a Bambi.
I've got my eye on a BB24V for use with nailers and dust blowing on the lathe...
They're not cheap, but at 40dB vs 75dB rather quieter.

 

[The Bear]

Pete, I've just had a quick look in the Axi catalogue and thats too expensive for me I'm afraid.
It doesn't seem to have much "power" either, is that all thats required for a nail gun, blower etc???

Mark

 

[cambournepete]

Although the pump is small there is plenty of air available in the tank for nailing, stapling, airbrushing and operating pneumatic systems.

Designed to require minimal maintenance and to ensure years of trouble free use, our comprehensive range meets the needs of many applications including: air-brushing, exhibition stands, glue dispensing, pneumatic controls, stapling - anywhere where compressed air is needed silently!

So it should do.
Their website is here.
The BB24V is part of their budget range.

 

[The Bear]

Unfortunately still too expensive, £315 in Axi catalogue.
Looking up to £200, could be pushed for slightly more, but now bearing in mind I will want to buy a HVLP sprayer in future.

Mark

 

[RobertMP]

I use a £80 compressor that I got from Makro on one of their offers. It is about 4 cfm. Some of the very cheap ones do not have pressure switches and just purge when up to pressure. mine does have a switch and has a regulator for the 2 outputs. Considering a set of air tools was included in the price I wouldn't complain if it died tomorrow, but after 3 years it does not seem likely to. Like all similar compressors it is noisy when running but as it will not be on much for light use that is not a problem.

I have done some high pressure spraying with it and used it to drive a air file - both of which meant it ran near continuously but it managed it. I don't have a nailer but I have an air rivet gun and that is no problem to run.

I'd guess it compares to the £113 axminster one so if you don't mind the noise that should do you.

 

[The Bear]

Thanks for that. As I said at the start I know nothing about compressors so what is the difference between the pressure switch and regulator? I don't really understand what you are describing, and therefore what I should be looking for :?

Mark

 

[gidon]

You can run an HVLP gun off a compressor - a 3HP compressor like the ones you've researched will do it. I got the Axminster one first - it was faulty - kept blowing the 13A fuse. I swapped it for the SIP which was a bit more but better in my opinion.
I just gave away an HVLP gun Chris gave me - you can get one from Machine Mart for £30.
BUT the easier option is what Robert suggests - I just bought the Earlex HV5000 and can recommend it - subscribe to the Screwfix email letter and you can get it for £160. The turbine driven HVLP is so easy - you get instructions for one thing - and the gun and turbine are designed to work together (it is noisy though). I've wasted a LOT of time with both an HVLP gun and an expensive SATA RP gun running off my compressor. And got better results with the Earlex - have a look at some of my recent posts for more info. (That's not to say compressor driven guns are a bad idea - they are actually more versatile - but there are just more factors to get right if you've never done it before).
Cheers
Gidon

 

[RobertMP]

Pressure switch is the thing that cuts the motor off once the tank is pressurised to the right level... and turns the motor back on when you use some air and the tank pressure drops. Say it cuts off at 150 psi then it might turn back on at 100psi so the tank gets pumped back up to pressure. While you use up the air from 150 to 100 all is silent and the motor does not run. Once it hits the switch pressure all hell breaks loose (well not really but they are loud).

Air tools usually have a pressure they are designed to work at. The regulator lets you set the pressure for the output. The tank may be at 120psi but if you set the regulator to say 30 psi then that is all your air tool will ever see. Often you can just leave it set high to something like 80 - 100. Spraying is where you may knock it down to 30 or 40 psi or even less.

Regulators have a cap you (usually) pull up then turn to adjust and push back down to lock and a dial on the side to show the pressure. You may need to let some air through the hose to see lower pressures on the dial as it will read the outlet pressure.

 

[The Bear]

Ah I understand now
Thanks

Mark

 

[Dibs-h]

Don't forget air tools need oil in the supply - so either a mini oiler on the tool or a larger one in the line.

Try the Bay - cheap as chips, especially for a used one.

 

[RobertMP]

For hobby use I'd disagree with that

You certainly don't want an in line oiler (a device that puts a mist of oil in the air) for spraying. The main point is to stop the tool going rusty from the moisture in the air. I just spray some WD40 into the air inlet hole on the tool before use and have not had any problems. You could do the same with proper air tool oil if preferred.

Using a tool every day it does make sense to have in line lubrication.

 

[The Bear]

I think I have decided to have a seperate HVLP sprayer/turbine at some point in the future. So with that in mind a compressor suitable for a nailer only in the first instance is what I need.(Can't think of anything else other than a blower I might want to run off it)

The Bambi that Cambournepete suggested had the following specs
375W
Free air delivery of 1.4cfm
24 litre tank
120psi
As I said before, I though that sounded a bit small until Pete put me right.

So basically as long as I find a compressor that is of these specs or more I will be OK?
I want to clarify as if I can get a smaller one I like the look of the SIP and Bostich that have the cage around them. (I'm thinking of where I can put it, stack stuff over it etc)

Mark

 

[RobertMP]

Compressors do generate a bit of heat when running (compression of air releases heat) so I wouldn't plan on covering it too much.

Up to you really. Is there anywhere locally that sells small compressors where you could go and hear one running? The sound of a cheapie 3 or 4 cfm might not seem so bad when you hear it.