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I am looking to buy a compressor, I am told it must be 10bar & 7cfm to run what I need it to run.
The cubic feet per minute bit is confusing me as one I looked at said it had a piston displacement of 7cfm but it's free air delivery is 3.5cfm.
I'm not sure what I should be looking for & which figures most of them display & I cannot find the relevant info on the net, so I thought I'd ask the experts.
Any recommendations, the receiver size can be 25 or 50lts
Free air delivery is the important number. Some air tools need a lot.
Yup, you want free air delivery of 7cf/m *at least*. We have a few air tools that have minimum cfm requirements the same as our compressors free-air CFM and they only just function properly.
Yep, look at the free air delivery, it's a bit like horsepower ratings in cars, quoted at the flywheel i.e engine on a dyno bench and not in a car. The horsepower at the wheels is probably 30% less on average. Don't know if that analogy helps.
Buy the biggest you can, as air tools consume loads. 3 horsepower motor is the most single phase power, but you need to wire that directly into the fuseboard. To get your 7hp you are going to need most of 12-13 cfm. You'll need all of the 50 litre tank, again go for as much as you can accomodate, space wise.
I have a 370 litre tank, with two 3hp motors, that start staggered, to give a 20cfm free air, 29.5cfm quoted by manufactuers. That's wire direct into 30 amp single phase fuse box, via a switched fuse of course. I believe that's the biggest single phase available.
I use it for car repair tools www.peterflynnclassiccars.com
If you only use the one one air tool and only use it intermitently then don't go crazy. If its a tool that runs continously (sanding, spraying, grinding) then if you are close to the free air margin you might find you have to keep stopping to let the compressor get its breath back, but if you are using the tool in short bursts (nailing, screw driving etc) then thats less of an issue. The benefits of a large tank are that the compressor is running less of the time, again if you are using a lot of air the compressor will be buzzing away all the time, driving you bloody nuts (and wearing out) bigger tanks give a more continuous air flow and moments of blessed silence.
If you are wanting to use the compressor for just the one tool, then I'd shop around for an air free alternative. Compressors are pain in the bloody arse, cheap compressors more so.
Thanks for the input so far guys.
It's actually to run a gas booster pump, & the specs in my first post were given to me by the supplier.
I am looking at this compressor below, but it does not actually give the cfm of free air. The booster pump is very thirsty & it will drain the receiver in no time, so the size of the receiver is not an issue, the compressor will be running constantly for the time I am using it which will be only for periods of up to 30min no more than a couple of times a week. Would this be suitable, or do you know of a better one in this price range?
http://www.aktivetools.com/sip-06250-air-compressor-airmate-25hp-24-litre-pro-tech-professional-1106-p.asp
11.0 CFM piston displacement
5 metre hose included
Oil lubricated
Extra large wheels and comfortable handle
Double fixed support for added stability
TECHNICAL SPECIFICATION:
PISTON DISPLACEMENT: 11.0 CFM
INPUT VOLTAGE: 230V ~ 50Hz
FUSE RATING: 13amp
MOTOR: 2.5hp - induction
RECEIVER TANK SIZE: 24 litres
MAX. PRESSURE: 10 bar
Personally i wouldn't touch a piston compressor if the reciever wont be up to the job , i found they pulse and in some applications can cause problems, problem is I guess you are going to be using single phase so will be limited to that type as vane and screw compressors are generally bigger (i dont like vane either). 10 bar is quite high as well and could you run a lower pressure? if you can you may be able to improve the cfm as it generally proportional. Oh and don't let it run dry they dont like it!