/ Resources · Sizing

Is your air pipe big enough?

Every psi you lose in the pipe is a psi the compressor has to make and you pay for. Put in the run and see how much you lose, and what pipe size fixes it.

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The run

updates as you type

Air flow through the pipe (SCFM) The most air this run carries at once. Pressure at the start of the run (psig) Usually the receiver or dryer outlet. Straight pipe length (ft) Receiver to the farthest point of use. Pipe size (Schedule 40 steel) Inside diameter, if not Sch 40 (in) Aluminum, copper, or plastic pipe: use the maker's inside diameter. Target drop (psi) 3 psi is about 3% at 100 psi, the common design target.

Fittings on the run

Long radius elbow Standard elbow Tee, air turns out the side Gate valve, open Globe valve, open

Each fitting adds drag, counted as extra feet of straight pipe. Source: equivalent lengths from CAGI, Compressed Air and Gas Handbook, Table 4.15, "Loss of Air Pressure Through Screw Pipe Fittings". Schedule 40 inside diameters per ASME B36.10M. * 1-1/4", 2-1/2", and 5" are not in the CAGI table; their fitting lengths are estimated: interpolated from CAGI Table 4.15, a straight line on inside diameter between the sizes above and below.

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How much drop is OK?

Design to about 3 psi

Size the pipe so you lose no more than 2 to 3% between the receiver and the point of use. At 100 psi that is about 3 psi.

Never near 10%

A good system loses much less than 10% of compressor pressure from the receiver to the tool. Past that, people turn the compressor up, and every 2 psi costs about 1% more power.

Go one size up

Drop falls fast as the pipe gets bigger, roughly with the 5th power of the inside diameter. One size up often cuts the drop by more than half.

Source: US DOE / ORNL Better Plants compressed air training, Session 6 (2 to 3% between receiver and point of use). US DOE / Compressed Air Challenge Sourcebook, "Improving Compressed Air System Performance" (much less than 10% of discharge pressure; about 1% more power for every 2 psi of added pressure). This tool covers one run. Drops through dryers, filters, hoses, and quick couplers come on top.

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Fitting table

feet of straight pipe

Fitting	1/2"	3/4"	1"	1-1/4" *	1-1/2"	2"	2-1/2" *	3"	4"	5" *	6"
Long radius elbow	0.62	0.82	1.05	1.38	1.61	2.07	2.47	3.07	4.03	5.05	6.07
Standard elbow	1.55	2.06	2.62	3.45	4.02	5.17	5.57	6.16	7.67	11.44	15.2
Tee, air turns out the side	3.1	4.12	5.24	6.89	8.04	10.3	12.31	15.3	20.2	25.31	30.4
Gate valve, open	0.036	0.048	0.061	0.08	0.094	1.21	1.44	1.79	2.35	2.95	3.54
Globe valve, open	17.3	22.9	29.1	38.30	44.7	57.4	68.56	85.2	112	140.04	168

Source: CAGI, Compressed Air and Gas Handbook, Chapter 4, Table 4.15, equivalent length in feet of Schedule 40 pipe, shown as published. * Columns marked with a star are estimated: interpolated from CAGI Table 4.15 (straight line on inside diameter between the neighbouring CAGI sizes).

Re-piping or adding a drop?

Send us the run. We'll quote the pipe, fittings, drops, and ball valves, in steel, copper, or an aluminum system, and check the size against your flow.

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