Air Compressor Pipeline Sizing

There is a formula for air velocity in pipe.

It's easy to find if you search for it.

Instead of asking us to find the formula for you, why not accept the fact that practical experience and common sense may be better than formulas, and do as ozzb suggests.

More info on the use of air is required.

Dealing with the compressor supplying the air at 0.45 m3/hour. This is free air at atmospheric pressure.

When compressed to 30 bar it will occupy a much smaller volume according to the pressure ratio; which is the absolute working pressure divided by the absolute atmospheric pressure (assumed to be 1.0132 bar) thus (30 + 1.0132)/1.0132 = 30.61. Thus the volume becomes 0.45/30.61 = 0.0147 m3 or 14.7 litres

This volume is given by the (A) area x (L) length of pipe holding it. So whatever area you choose you get an associated length. That length will be the distance the air travels in one hour. You can change the units of length and minutes or seconds to suit.

Next consider the volume of the cylinder you say is 250 litres. Is that the actual dimensional volume, or is it the free air volume?. If the former then a 250 litre vessel at 30 bar will hold the equivalent of 250 x 30.61 = 7,652.5 litres. How long will it take to use this air? and how far away are you from the cylinder?.

But taking 250 litres of air at 30 bar and an area of pipe of your choice you again calculate the length of pipe that will hold this amount of compressed air. This coupled to the flow rate of usage gives you the velocity.

You the have to match this velocity to the distance the air has to travel to in order to assess the pressure loss down the pipe.

Do you have or can you get a copy of Crane Technical Manual 410, Flow of Fluids Through Valves Fittings and Pipes? If you can review chapter 4, and page b-15. This will explain most of your questions.

There is a velocity table for all fluids u can pick from that table

Thanks to all for taking interest in my query.