Air Compressors - how many bar

[Rick]

Intend buying a new Air Compressor, up to now have used an 8 bar Clarke model.

Looking at Machine Mart they have loads of compressors, many with little difference between them ... looking for a 24 litre air receiver .... Again there is plenty of choice .... But the key thing is Air Pressure ..... majority are 8 bar models 1.5hp ..... but you can get

10 bar, but they are about 45% more expensive.

I was just about to buy an 8bar 7cfm model on sale as a special at a big discount, and then chickened out at last moment. (would be more than double price to get the equivalent 10bar model)

Trying to understand if/why I would need 10 bar, all my air nailers etc. run at around 6 bar or less. When do you need 10 bar? .... Assume it can't be for spraying as here it would be cfm that is important not an extra 2 bar of pressure.

Anybody any idea ?

[The3rd Earl Of Derby]

How about...when you have two air tools on the go at the same time?

-- Sir Benjamin Middlethwaite

[Cicero]

=================== Sand blasters need the higher capacity and some of the tools like needle scalers etc. One difference to look for (regardless of size) is 'oil free' or otherwise.

Cic.

[Mark]

The most important thing with a compressor is Volume, CFM Bigger is _always_ better, since most air tools run below 150psi you are pursuing the wrong spec.

-

[Andrew Mawson]

receiver

If your receiver (tank) is pumped to the higher pressure then you have more energy stored so a given tool will run longer before the compressor has to start up again. Few tools 'need' more than 100 psi and run at a regulated lower o/p pressure, but things like sand blasters are dramatically more effective above 100 psi

AWEM

[Andy Hall]

I have a 10bar,2.2kW 150 litre compressor for my workshop airline ring main system (SIP 06646)

I was more concerned about having plentiful air storage and delivery rate than absolute pressure. The 10bar aspect came with that.

I use a number of air tools which use a lot of air as well as doing spraying. I also have a number of medium air use nailers and similar which, as you say, are happy at around 6 bar, and assorted things such as tyre inflaters and blow guns. There are then some pneumatic clamps and similar that I use on my table saw.

The compressor is connected directly to the ring main and then there are drops to filter/regulator/lubricator units, e.g.

give adjustable pressure outlets with and without misted oil lubrication for nailers etc.

Since the compressor is relatively large, it is hoisted high up out of the way in the roof space of the workshop. Clearly I don't want to keep climbing up and down the ladder to change the pressure for different purposes.

Having the 10bar maximum does mean that the motor runs less frequently during operation. However, the things to look for in choosing a compressor are the air production rate and receiver size, considering the application.

If you are mainly using nailers and the like, the 24litre type that you mention is more than adequate. It would also do a reasonable amount of spraying. If you wanted to use heavier air use tools or do a lot of spraying, then a more substantial compressor would be a good idea.

These smaller models also have a regulator and you can add a lubricator if you want it.

[Peter Parry]

How do you manage the condensate water drain from the tank with this installation (roof space mounting of a compressor is an option I'm looking at for a friends workshop)?

[Andy Hall]

I used an automatic electronic condensate drain made by Domnick Hunter

- RS carry a similar one - stock code 386-3422. I was fortunate to get a very good deal on one when I was buying a whole load of stuff for the project - normally they are about £100, but I paid around £40, which I thought reasonable for the convenience.

The principle of these is that they fit under the compressor receiver and condensate trickles down into a reservoir with a float switch which triggers a solenoid operated valve. There is a breather pipe which can be implemented in flexible tube that is connected to a tee into the location where the regulator goes on the top. The whole chamber remains under pressure. When the chamber fills, the valve operates for a second or two and compressed air forces the water out through a second tube. I run that into a large container which I empty periodically - although it could go straight outside.

An alternative would be to use a mechanical automatic tank drain. Most of the air equipment manufacturers like Norgren, SMC, Parker etc. make these e.g. RS stock code 234-1987 Prices around £35 or so. I would have gone for one of these had it not been for getting the electric one for a similar price. I have fitted one of these mechanical drains at each far corner of the airline pipework at a low point - the pipework is arranged with a slight slope to deal with it. A bit of air is lost with these, but I don't think that that matters a lot.

There are various installation options for these devices under compressor receivers, and the larger compressors have a venting fitting with a 3/8 thread in the bottom which can be removed.

The main issue was having enough height underneath the compressor to fit the drain accessory. Some of the larger ones come with wheels etc. To get around this issue and to improve noise and vibration (not that this compressor is noisy as its a belt drive running relatively slowly) I made a mount consisting of two rectangular timber frames one above the other. I fitted the two together using Paulstradyn anti-vibration mounts. e.g RS 367-8785 The compressor is bolted to the top frame and the bottom one in my case just sits on the boarded area in the roof. For good measure, I fitted eye bolts so that I can hoist the compressor up into the roof space.

The results are impressive. The compressor runs very quietly and the drain pops perhaps once a day or so if I'm using air tools for most of the day. Having the thing out of the way is a significant space saver as well.

[Andy Dingley]

10bar is more stored energy in the tank than an 8bar machine, even if you're still only using it at 6bar. This doesn't make much difference for continual sandblasting (you'll need real compressor capacity) but it does allow you to run a "thirsty" tool in short bursts which the compresor wouldn't otherwise have the volume capacity for.

[Rick]

Cheers for the links. I already use a triple set up ... water separator, pressure reg & oiler, and had that connected to my portable compressor (10Lit) tank using RECTUS type 25 connectors - in fact I use these connectors on all my air tools as the internal bore is so much larger than standard schrader fittings. Found that frame nailer & dry wall stapler would frequently jam on standard fittings (BeA rep advised change to RECTUS) .=2E. the sudden spurt of volume needed immediately after the drive action to retract the piston fully)

I want to keep to single phase and 24 Lit receiver for portability, as this has proved useful in the past ...

I also have a separate 50 litre receiver which I can plug into the compressor to give me larger volume should I need high volume of air at any time- but to be honest so far have never found a need for it.

Considering an 8 bar 7 cfm model ... a Clarke Ranger 35 (1.5Hp) which is reduced to =A360 +vat to get a 10bar ver the price hikes to =A3130 + vat and up to =A3150 +vat to get higher cfm of 8.7 (2Hp)

[Matt]

While the cfm is important it can (and is) so bodged by the various manufacturers to make their compressors always look better than they actually are. For air tool use like a nailer it makes little difference but this fraud really comes to light when you are using the compressor semi-continuously (for paint spraying for instance)

On just about *any* new compressor from every discount supplier costing sub 500 quid take the discharge cfm with a bag of salt. On anything sub 2000 quid take it with a pinch of salt. Above 2000 quid they just start to get into trustworthy territory because they usually quote the free air delivery (FAD) and that is what matters. Also don't believe the "HP" figures either, they are usually pure story book fantasy - witness 2HP compressors driven by 1.2kW motors. James Watt would be turning in his grave.

That 15"cfm" compressor complete with a 150psi, 50 litre tank may realistically only be able to produce 60psi @ 9cfm continuously.

[Roger R]

At one time I needed to test out the air equipment of a commercial vehicle the compressor of which developed around 150 psi (~ 10bar). The normal line pressure at the operating depot was 10 bar. 8 bar was just not enough to carry out satisfactory tests.

Next one I get will definitely be 10 bar.

Roger