The Pressure loss through a hose is often approximated using coarse heuristics, but utilization of more accurate correlations increase the efficiency of pump and piping designs. This article presents more accurate methods to estimate the pressure loss in various type of hoses using multiples of the pipe length. Methods of estimating pressure loss caused by couplings, curves and coiled hose are also detailed.
Traditional rules of thumb regarding pressure loss in hoses are coarse and do not consider the construction or arrangement of the hose. A common estimate is "the pressure drop from hard piping of 3 times the length of the actual hose". Through more considered estimation of pressure loss in hoses we can estimate separately the pressure loss due to the frictional losses in the hose material when straight, as well as any additional losses introduced by the hose being coiled or curved.
In principle there are three common flexible hose constructions; rubber, wire reinforced and corrugated steel. Rubber hoses may also be reinforced with woven fabrics, however this does not effect the flow properties of the hose.
Pressure loss through Straight Hose
The pressure loss through a straight hose is directly proportional to the length of the hose, therefore the simplest method to quantify the pressure loss is to substitute the length of steel pipe required to provide an equivalent pressure drop. The table below provides the equivalent pipe length using a clean carbon steel pipe with a pipe roughness of 0.05 mm.
|Hose Type||Equivalent Length|
|Rubber Hose, Smooth||0.6-0.9|
|Rubber Hose, Wire Reinforced||0.7-1.3|
The variability of wire reinforced hose can be attributed to the degree to which the wire reinforcing impacts on the interior surface of the hose. In hoses with a thick internal rubber lining the wires will cause minimal variation to the internal diameter and the hose will behave as if it were smooth. While in hoses where the wire is closer to the internal surface it will cause ridges (see diagram above), and increase the pressure loss.
Pressure Loss through Bends and Couplings
The methods utilized for calculating bend pressure loss in piping may be applied to hose pressure loss calculations. There are many methods for estimating the pressure loss from pipe fittings, please refer to this summary of methods for estimating pressure loss from fittings to determine which method best suits your requirements.
For quick calculations where high accuracy is not critical the easiest method to apply is the equivalent length method. Information is available for long radius elbows and hose couplings which are applicable to hose pressure loss calculations.
Alternatively the friction factor for flow in coils and curved pipe can be calculated and utilized to determine a more accurate pressure loss for a coiled or curved hose.