compressors

[BrokenBiker]

right, i have never really looked into comps, my father has had a few but ive never know anything about them apart form tank size.

i wanna know what to look for when buying a comp so it can run tings like an air impact wrench, die grinder, needle gun etc.

as with my blowtorch thread, its all about automotive work. not interested in using it for spraying, have my father kit for that.

i find the cordless impact guns i have tried not to be up to much when undoing stubborn bolts, but when i have gone to my mates garage and used his air driven one, the bolt flies out. electric die grinders are too bulky and cumbersome (have a bosch that i have just sold as i don't like using it) and never seen an electric needle gun

tank size needs to be small-ish, portability is key, don't need to store any air (I don't think) unless I cant find a comp with enough free delivery to run the tools

 

[BrokenBiker]

the impact gun and die grinder I have looked at say they need around 4-6CFM with a max pressure of 90psi, so a small 25L comp with 7.4CFM and max pressure of 116 should be good enough?

or wont it allow enough air when the tank is empty?

 

[Bill Edwards]

What cordless impact wrenches have you tried? I'm guessing you've not used the milwaukee ones!
To use an impact wrench for anything other than a couple of seconds I find you either need a big receiver or a very big pump, ideally both. Take the figures quoted by the compressor manufactures to be rather exaggerated, and take the consumption figures for the tools as being optimistic.
A 25l compressor that claims it delivers 7,4 CFM that runs of a domestic supply (as is normal for that size) will only run the impact wrench for a matter of seconds before you'll need to stop and let it build up air.
And I think you'll find that the good looking CFM figure is at 0 psi - i.e free air not under pressure - it's a little different at 100 psi.

 

[BrokenBiker]

ah. that puts a decent comp out of my budget then.

on a side note, seen a mains voltage impact gun that claims 450nM of torque, think it was a Clarke so maybe that's worth looking at?

 

[Rig Pig]

The other thing to consider is noise - small direct drive compressors are loud, if your neighbors are playing up a loud compressor will give them another excuse to hassle you

 

[Maker]

14 cfm (quoted) is the most you can get from a 3 hp compressor and you can't have more than 3 hp on a normal 13 amp supply. If noise is a concern I've heard of people putting them inside a sound proofed box and many people with bigger comp's put them in a tiny shed the other end of the garden. For what you want a 3hp sounds adequate but don't expect to run a spray gun or sandblaster.

 

[BrokenBiker]

don't need to worry about noise, not going to be spraying or blasting either. that said my fathers comps have always run off domestic supply in his shed and he was a sprayer for 20 years with them

 

[Maker]

You can get belt driven ones as opposed to direct drive which are quieter and cooler running because the pulley is shaped like a fan but they are only on 150+ litre tanks - better if you have the space and the money.

 

[wristpin]

The important figure is "free air delivered" not the theoretical output of compressor pump cylinder volume times rpm that takes no account of valve leakage and other inefficiencies. As far as tool consumption goes add twenty five percent to any figure quoted!

 

[steviec_lj]

Had an 18v Dewalt impact driver, big, bulky and f-ing awesome.

Some twit nicked it out the back of my van at a festival a number of years ago. Been meaning to replace it as I've still got the batteries and charger.

As said, you'll want a large receiver for ANY air tools to be honest. I've got a 3hp 50ltr direct drive that empties in seconds with an impact driver, the 3hp 200ltr isn't far behind on the speed it'll empty at if the nut/bolt is stuck.