The final distance connecting the end-use-equipment to the compressed air system is fondly referred to as the “last dirty thirty”. This is because the final 30 feet is often riddled with inefficiencies due to often needing to get things up and running quickly once the long-awaited equipment is finally in place … resulting in the facility using whatever is readily available in terms of pipe, tubing, hose, clamps, fittings, valves, filters, etc. The consequence: Pressure Drop.

Pressure drop is the result of the restriction created by the pipe or hose.  Anyone who has tried to breathe through a straw will know that trying to force a large flow of air through a small tube can be problematic. This is because the smaller the diameter, the greater the velocity that is required for the air to travel through the hole. Higher velocities cause more friction, friction constricts flow, which in turn results in pressure drop. With pipes and hoses, the loss is multiplied by the length of the pipe.

Flexible hose in actual use typically contains many bends and loops and as such it makes it extremely difficult to precisely calculate pressure drop; however we can get a generic baseline calculation and you can know that actual pressure loss would be significantly worse if the hose were reeled up or had several sharp bends.

See Chart below:

This chart illustrates the estimated pressure drop, per 50ft, of a 1/2 in hose at varying pressures and flow.

So by way of example, let’s say we have a 50ft hose delivering 40 CFM at 70 PSI. At the very best this would result in a prssure drop of 7 PSI per 50 ft of hose. If this hose were reeled up, or had any sharp bends, the pressure drop would be worse.