Air Compressor - Header Size?

[waskillywabbit]

Air compressor: 175 cfm
120'-0" of header
7 stations
15 cfm needed at each station
stations consist of 3/4" drop, pressure regulator, quick connect
No more than 3 on at one time
To be used for running simple air tools

How do I go about sizing my 120'-0" of header?

Thanks.

 

[TD2K]

You don't say what pressure you are planning to operate this system at. Assuming it's 100 psig and your tools need this pressure, you want to size the header so the pressure drop is relatively small for your 175 cfm (which I assume is at standard conditions).

Basically, you want to size your pipe so your piping pressure drops are minor. You've spent the money compressing the air, you don't want to lose lots of that pressure just flowing through your piping system.

dP per 100' for 1" sch 40 is 6.6 psi, too high IMO.
dP per 100' for 1 1/2" sch 40 pipe is about 0.73 psi.
dP per 100' for 2" sch 40 pipe is about 0.20 psi.

These are out of Crane's technical paper 410.

If you run sch 80 pipe, both dPs will increase by about 40% due to the smaller ID. For your system and assuming you see no need for more capacity in the future, the 1 1/2" should be fine. If you might increase air flow later, put in a 2".

 

[saxon]

wabbit, As TD2K has pointed out the first place to start is to size the header for minimum pressure drop to the farthest T.O. from the station. This will give you a minimum size. Now you need to take into consideration future expansions. If the header is sized only for the present, future expansion will make it too small. Also, you need to take into consideration volume capacity of the system. By building this into the header system, it minimizes header pressure fluctations which can cause equipment operations problems, and at the same time mimimizes fast cycling of the compressors to make up for the header pressure fluctuations. This also reduces wear and tear on the compressors which translates into lowered M/O costs and extends the life of the units.

So as general rule of thumb, size the header so that a mimimum pressure drop occurs, then add in an extra 15%-25% above the min. for future and capacity. As to which percentage to use, this is where experience comes into play based on the application.

Hope this helps.
saxon

 

[MJCronin]

To all,

TD2K said it all...

In my opinion, all air systems seem to be about the same general size and cover about the same general area. Your compressed air need seem to be on the more modest side...

All of the compressed air headers I have seen have been 2" hard-copper....except for one really, really big/plant, that had a 2-1/2" header

MJC