The traditional rule of thumb for pressure loss in plas […]
The traditional rule of thumb for pressure loss in plastic hoses is vague, without considering the structure or arrangement of the hose. The usual estimate is "the pressure drop of the hard pipe is 3 times the actual hose length". Through more careful estimation of the pressure loss of the hose, the friction loss in the straight hose material, and the loss caused by the coil coiling can be estimated separately.
In principle, there are three common flexible hose structures: rubber, steel wire reinforcement, and corrugated steel. Rubber hoses can also be reinforced with woven fabric, but this will not affect the flow properties of the hose.
1. Pressure loss caused by straight pipe
The pressure loss through a straight pipe is proportional to the length of the hose, so the simplest way to quantify the pressure loss is to replace the length of the steel pipe required to provide an equivalent pressure drop.
The variability of the steel wire reinforced hose can be attributed to the degree of impact of the steel wire reinforcement on the inner surface of the hose. In thicker rubber-lined hoses, the wires minimize variations in the inside diameter, and the hose behaves like it is smooth. In the hose, when the wire is closer to the inner surface, it can cause bulging and increase pressure loss.
2. Pressure loss caused by bending and coupling
The method used to calculate pipe bending pressure loss can be applied to hose pressure loss calculation. There are many methods to estimate the pressure loss of the fittings. Please refer to this method to estimate the pressure loss of the fittings to determine which method is best for your requirements.
For fast calculations where accuracy is not critical, the simplest method is the equivalent length method. Information on long radius elbows and hose fittings suitable for hose pressure loss calculations is provided.
Alternatively, the coefficient of friction flowing in the coiled tubing and the bent tube can be calculated and used to determine a more accurate pressure loss for coiled or bent hoses.