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Air hose size
Steve Lovelock - 10/1/11 at 10:29 PM

Hello,

I have been given a 3HP, 50Ltr, 14CFM compressor for Christmas and now need to get an air hose to go with it. I seem to remember that the longer the hose the greater the pressure drop and I see that you can get lots of different sizes of internal bore. Does anybody have any recommendations for the lenght and bore size I should select?

Cheers
Steve

MakeEverything - 10/1/11 at 10:41 PM

The 30m halfords one will do.

blakep82 - 10/1/11 at 10:52 PM

think mine's 8mm hose? 'had' a 10m long one (but i ran it over and it split), and got a 15m one. does me

if you're using quick release connectors (as i'm sure you will) i can't see the point in going much bigger or smaller than the size of the hole in the end of the connector.

hillbillyracer - 10/1/11 at 11:17 PM

quote:
Originally posted by blakep82
think mine's 8mm hose? 'had' a 10m long one (but i ran it over and it split), and got a 15m one. does me

if you're using quick release connectors (as i'm sure you will) i can't see the point in going much bigger or smaller than the size of the hole in the end of the connector.



The reason for going bigger than the connector diameter is to overcome the "wall drag" of the pipe, a long length of 6mm bore pipe will suffer a massive pressure drop in comparison to a connector with a 6mm outlet.
We're fitting an airline into the workshop where I work & using 19mm bore to take it the lenth of 75ft long shed, but the outlet coupling are just the 6mm ones.

For DIY in a household garage I would'nt think you'd really any bigger than 10mm bore, & 8mm would do most jobs if the line is'nt too long but if you're going to use anything with an air motor (die grinder, air drill etc) it'll be a hungry thing, especially an impact gun as it'll not perform as well.

Here's a chart giving sizes of pipe against distance & flow rate:
http://www.goodyearrubberproducts.com/files/Dixon/DixonCatalog/DixonCatalog1.Page531.asp
It's really for things on an industrial scale but it'll give you an idea of how it works out.

blakep82 - 10/1/11 at 11:22 PM

^ ah well that explains it then thanks, when i've got some more cash i'll look at upgrading mine then.
i always thought you can move so much air through a 19mm hose, but the connector at the end will only slow it down, but i was wrong theres a lot more science to it!

hillbillyracer - 10/1/11 at 11:29 PM

Been looking into it a bit as we're doing the workshop, & I did'nt realise it made so much difference either! Took a bit to convince the boss, hope it works better than the 10mm that was in when I get all connected!

One hang-up the bigger you go I'm told is the water drops out of the air more & can puddle in the pipe, so you need to make sure on permament lines that there are no low points unless they have a drain on them so you get rid of the water. On the upside that's another way of getting more water out of the air which is a good thing, we'll know how inportant that is in a few weeks & see if the drain legs on the line fill up.

JoelP - 11/1/11 at 11:26 AM

i think my 8mm hose was the limiting factor that made my air wrench crap, so id say 10mm is a better bet depending on length. A bloke off here came round to help with his good air wrench, and it too was no good for the job at hand, so im fairly sure it was the hose.

I bought a crap cheap one recently because it was only really to blow tyres up (i have 22 tyres in regular use )

Peteff - 11/1/11 at 02:39 PM

I have a 20' hose with a 3/8" bore and have no problems with pressure drop from my old SIP 3hp compressor. I bought a cheap rattle gun from Aldi to undo a sprocket nut on the ZX9 engine and it ran it of no trouble. It also coped with the flywheel bolts on a Zetec 1800 which I had chased round the shed with an extension and socket before I remembered I had an alternative