Thread: Cost of reticulated compressed air

Given the relatively large capacity of your compressor are you going to have large enough piping to adequately meet the flow requirements for your applications?

Originally Posted by rob streeper

Given the relatively large capacity of your compressor are you going to have large enough piping to adequately meet the flow requirements for your applications?

45 cfm @ 120 psi will flow through 20m of 20mm pipe with a pressure loss of around 5% so I think we are OK.
The only reason the compressor is so big is that we got it at around the same price we budgeted for a 20 cfm compressor.

I like the concept of multiple points in the shed, and it has me thinking.

Now I admit that I know nothing about compressor capacity, but would a compressor of 20 cfm be sufficient for an 'average' shed? Uses would have to include the use of spraying equipment etc.

I friend of mine has one of those small 'Auto Cheap' compressors. You know the ones that are about $200 with extras. He uses that and has a couple of points available. It runs paint gun and sand blaster. What he has is a huge reserve tank like the size of a 1200mm high gas tank.

It takes a while to fill but if he is using it in bits and pieces as many shed workers would be he hardly ever empties it to the point that he has to wait for the compressor to build up.

I was thinking with my new cave (when it finally gets done) to have my old compressor set up as a reserve tank at one end and my main compressor at the other.

Thanks for the heads up on pricing & options, it is something I have been contemplating for some time.


Dave the turning cowboy

turning wood into art

Originally Posted by BobL

45 cfm @ 120 psi will flow through 20m of 20mm pipe with a pressure loss of around 5% so I think we are OK.
The only reason the compressor is so big is that we got it at around the same price we budgeted for a 20 cfm compressor.

I'm planning a dual use point setup with a similar run length and though I can do it with the diameter you suggest I use a number of air-hungry tools like die-grinders, pneumatic hammers and a needle scaler and as I only want to install the system once I'm going to use 25mm piping.

Originally Posted by cava

I like the concept of multiple points in the shed, and it has me thinking.
Now I admit that I know nothing about compressor capacity, but would a compressor of 20 cfm be sufficient for an 'average' shed? Uses would have to include the use of spraying equipment etc.

20CFM (as long as they are real CFM) is heaps.
Actually for a DIY even 10 REAL CFM is usually plenty

To work out the real CFM is not that difficult and you need to know the following

A) the volume of your tank in cubic ft (if you know it in litres, multiply the Litres by 0.0353)

B) The time it takes to recharge the tank in minutes.

C) the fractional pressure increase during the recharge. i.e. the PSI increase during the recharge divided by 14.5PSI. Lets say the pressure goes from 90 to 120 PSI so that's a gain of 30 PSI, now divided by 14.5 PSi so thats (120 - 90)/14.5 = 2

Now use this formula (A x C)/B

If the tank is 100L thats 3.53 Cubic ft, if it takes 1 minute to recharge from 90 to 120 PSI then
(A x C)/B - (3.53 x 2)/1 = ~7 CFM

Don't be surprised if your compressor fails miserably to meet the manufacturers specification

I think CFM is relative to a PSI. So a manufacturer may say 10 CFM at 70 psi. 70 psi is much easier to generate than 110 psi.


My 18v makita air blower can generate significant cfm air flow compared to my compressor but almost 0 PSI

I am happy to stand corrected.

Your calculations Bob look something worth me keeping to see if my compressor is up to the use of certain tools when I finally get around to having and setting up my cave


Dave the turning cowboy

turning wood into art

A filter/drier on the outlet of the compressor would eliminate any rust/drainage issues (not to mention just being good practise)

Originally Posted by BobL

45 cfm @ 120 psi will flow through 20m of 20mm pipe with a pressure loss of around 5% so I think we are OK.
The only reason the compressor is so big is that we got it at around the same price we budgeted for a 20 cfm compressor.

5% loss at 120psi may be significant for some tools / applications.

What tools are you likely to be connecting to the air supply?
what is the flow demand of those tools?
a very very quick Google, suggests that one model of air sander needs >10 cfm to operate

I'm not sure that I'd trust a men's shed with plumbed air.
It will be all too easy to grab the air hose to clean up at the end of the day

Originally Posted by ian

5% loss at 120psi may be significant for some tools / applications.
What tools are you likely to be connecting to the air supply?
what is the flow demand of those tools?
a very very quick Google, suggests that one model of air sander needs >10 cfm to operate

We have no air powered tools at the moment and none are on our current wish list - that was why we originally targeted a 20cfm compressor
The most likely first thing we will buy that needs air is a plasma cutter.

I'm not sure that I'd trust a men's shed with plumbed air.
It will be all too easy to grab the air hose to clean up at the end of the day

That is almost certainly what will happen.

doing that will sort of make venting the dust collector outside pointless

Originally Posted by ian

doing that will sort of make venting the dust collector outside pointless

Doing what?

Originally Posted by BobL

Doing what?

using compressed air to blow the surface dust, shavings, etc into the shed's air

Which pipe solution did you end up going with??

Also with the copper pipe could it be sourced cheaper if you know someone in the trade ie a plumber?