Sizing Pipes and Lines for an Air Compressor

What is your total run length and will you use a distribution loop or a straight run?

Transair (Legris) has a great flow calculator on their website, but it looks like the link is broken right now. I have a down-loaded copy on my home PC and will run the numbers for you tonight. If you have not previously considered it, I would strongly recommend adding an air receiver tank to each of your loops at the point furthest away from your header connection. How long to you anticipate your header run to be, and what is the outlet pipe size of your compressor?

the outlet pipe size of my compressor is 2 in. you mean to say that for every end of a loop i need to add a receiver tank? what size shall it be? ...Can you please give a copy of your downloaded items so that i can use that as my reference. thanx..and more power...

The calculator I use is here. Yes, I would strongly recommend a 200 gal. tank on each loop at the furthest point from your header connection. It will do wonders to even out peak demand surges. If your compressor outlet is 2", I would go with Ozzb's suggestion and run 2" or larger everywhere if you can find a good deal on pipe. Do not use black pipe or PVC, no matter what! Black will scale faster than you can say "crud" and PVC is just not durable. If you can manage, copper is best, but $$$. Also take a look at the Transair system. The material cost is high, but installation is fast. I've used it several times and never regretted. Had two inexperienced guys on a scissor lift hang over 1600' in less than 1 day (no leaks!) - try that with threaded pipe.

thanks a lot csm. have a nice day...

Thank you for the link CSM! I looked at it and put it right into my favorites.

I found another copy!

To keep your pressure drop under 5psi, it looks like you should use 63mm (2-1/2") pipe in both loops. Actual pressure drop in the 200m loop will be 1psi and in the 300m loop, 1.3psi. If you step down to 40mm (1-1/2"), drops become 9 & 13.3 psi, respectively. These calculations assume the worse case that the entire 313 scfm could be flowing through a single loop at one time! If you have a better idea of the actual air consumption in each loop, or if you want to just split 50/50 between each loop, let me know. Also, let me know if you want numbers for your header run. If you do know your individual loop demands, we can use that info to step your header down after the first loop. Good luck!

Hey CSM,

I am trying to size the air line pipe for a spray room. I have a 45 gallon compressor that has 3.5 Running Horse Power and has 10.1 SCFM @ 90 PSI and 12.0 SCFM @ 40 PSI. I have 60 feet of run. No loop. Any suggestions on pipe size? Is schdule 40 PVC acceptable? Thanks in advance? KW

Use 1/2 or 3/4 Shedule 40. If you use plastic try the green stuff that is rated for compressed air.

i have here a 500 m closed loop system. and each end loop has a auto-drain with valve connection. my initial design was 2.5" dia for the main pipe. i will use 75hp air compressor with 313 scfm. thank you.

Go 3"

How much loss can you stand?

I would not worry about sizing the main line and any branch lines unless one piece of equipment is going to utilize the entire 313 cfm. I would size them larger than necessary. Let the additional size of the pipe be air storage.

I am running a 50 hp with 246 cfm with 2 inch pipe as a main and branch lines.

Look for a deal on the pipe of a size larger than necessary.

The size of main pipe is 1 1/4 inch or 1 1/2 inch. If the length of line is too long then the size is smaller and the opposite.

http://www.engineeringtoolbox.com/air-flow-compressed-air-pipe-line-d_1280.html

and

http://www.engineeringtoolbox.com/compressed-air-pressure-loss-d_1014.html

Good work CSM!

If a schedule 10 lightwall pipe is used, the flow losses will be less than standard schedule 40, and cheaper also. This pipe is much better at corrosion resistance than regular steel pipe, and can therefore be trusted to be clean for most applications. By oversizing the piping, and creating a loop, a surge tank/storage tank may not be needed. The piping can be utilized as storage. The cost difference between 2 1/2" and 4" is marginal. Utilizing victaulic-type couplings will also speed the process.

The enlarged piping can also serve to trap condensate and particulates, due to slow velocities. The take-offs should be on top of the pipes to maintain as dry an air as possible.

Will you have an after-cooler, water separator, or refrigerated air dryer?

What is the application? What is the peak load you will experience?

As always, there are more questions than answers.

Larger pipe with less pressure drop is good, pressure drop is wasted energy and $$$ out the door. Size the piping for 5% or less pressure drop. CSM has the right idea.

Also agree that depending on the length and diameter of pipe, the volume in the main line could take the place of a receiver. However, if using a recipricating compressor, a receiver will dampen pulsations in the air piping and might be neede for that purpose.

WHITE PAPER: #1 IN A SERIES - Conveying Air - Tom Kreher http://journals.aol.com/tkreher/ALLABOUTAIR

Compressed air has been called "the fourth utility". It is used commonly and often nearly forgotten. Like water from the tap we expect compressed air to be there when we want.

I have seen it written that the air compressor may be the greatest consumer of electricity in many industrial plants and mills. Commonly the cost of compressed air prompts talk of the cost of air leaks. Leaks are hard to eliminate. There is a better way to reduce the cost of compressed air

Often the compressor is adjusted to produce the highest design pressure, say 125 psig Just as often pressure lost conveying the air from the source to the application results in 80 psig 'mill air' (sound familiar?). This is a loss of 36%.

What to do.

In the case of compressed air, larger air lines will convey air with less loss.

Someone will say, "We cannot afford the expense of larger pipes for our air lines .

The cost of the larger air lines is a one time expense. The cost of pressure drop through smaller lines is continuous. At approximately 4 scfm per compressor horse power (746 Watts) it is not hard to determine the cost of pressure loss .

If our compressor discharge pressure is 110 PSIG and we retain 85 psig at our applications the loss is 21% . 1 Horse Power–hour = .746 Kw -hour

For example

Loss = 30 HP-hour x .746 Kw-hour/Hp-hour x 21% = 4.7 KW-Hour x Hours x $/Kw-Hr.

The pressure lost in compressed air through transmission lines, fittings, valves etc. is largely caused by turbulence. Increase the size of the manifold or pipe until the flow become laminar. This will eliminate the majority of the pressure drop. Get the flow below 20 IFPS or 1200 feet per minute. This works wonders for the efficiency of transporting the compressed air

From the example above; a 30 HP compressor will produce approximately 120 scfm. When the designer checks charts they list 1" schedule 40 pipe for 150 scfmat 100 psig for a line loss of 5% per 100 feet and seems the natural choice.

A 2" pipe would pass six times as much, 900 scfm, with a 5% loss.

With approximate 2" I.D. each foot of 2" schedule 40 would hold .17 scf at 100 psig.

120 scfm / .17 scf/f = 706 fpm [under the turbulent velocity of 1200 fpm.

The loss of 120 scfm at 100 psig in 100 feet of sched. 40 would be approximately 4% .

The loss of 120 scfm at 100 psig in 100 feet of sched. 40 would be less than 1% .

Converting every fitting, valve, etc. to 'equivalent feet' of pipe would help add all the potential loss or savings. The savings of equivalent length multiplied by approximately 3 1/2% continuously would easily justify the one time expense of the larger pipe. Higher retained pressure to do more work is a potential secondary benefit.

Thomas W. Kreher tkreher

you can purchase pipe sizing programs here www.eng-software.com/products/pipeflo/professional/2007New.aspxh#isometric_grids_&smarttext

Yes! Trans-Air Legris Helps how to calculate the loop size. But first you need to knew the total length of your loop. 63 mm may good enough for your system after the receiver. Anyway your compressor will compressed the air inside your pipe. Just make sure that you avoid lots of bends to minimize pressure drops.

Almost all programs, charts and graphs that are available for sizing pipe, tube and hose for compressed air are based on a pressure drop of 5% or 10% of the applied pressure in 100 feet. This is absurd!!!! If you follow conventional wisdom you will find that many can only maintain 80 psig in the shop or production area from what started at the compressor as 110 psig. That is an accumulated loss of almost 30%. To make matters worse the highest pressure air requires the most work or energy to compress. It is easier to squeeze a cubic foot of atmospheric air into a pipe or reservoir that has low pressure, say 80 psig than it is to force that same cubic foot of atmospheric air against 100 psig. Those who try to save on the price of pipe by buying smaller that will cause a parasitic drag on every bit of air ever used are just not thinking.

The greatest cause of pressure drop in transmitting air is turbulence. In smooth, laminar, flow the resistance is a result of the viscosity of air which is minimal. When the air travels in turbulent flow pressure is lost with each and every air to air and air to object collision. Velocity of the air makes the difference. The same amount of air in a large area moves slower than the same amount of air that is squeeze through small plumbing. What is the pressure loss from a reservoir? The loss caused by flow rate is usually nil due to the very large volume to flow ratio.

If you size your plumbing for under 1200 feet per min. you will be a happy camper, save energy and have more air for work. 2 1/2" Schedule 40 pipe would be adequate. consider using 3" for your main header. No such thing as too large and a secondary benefit is the reservoir effect of larger lines. Now with very little pressure drop you can reduce the outlet pressure at your compressor to 90 psig, save energy and wear and still have 80 psig in your production area.

As a rule of thumb, double any pipe, tube or hose size size suggested in popular charts.