Pressure Drop
The pressure the oil loses to friction while passing through a line, valve or filter. Reducing hose diameter grows the loss very quickly; all of the lost pressure turns into heat and is the main source of a system heating up unnecessarily.
Four factors determine pressure drop: flow velocity, line diameter, line length and the viscosity of the oil. Of these, the effect of diameter is far stronger than the others, because at the same flow rate halving the diameter quadruples the flow velocity.
- Flow velocities of around 3-6 m/s are targeted in pressure lines and around 0.6-1.2 m/s in suction lines. If velocity rises in suction there is a risk of cavitation.
- Cold, thick oil increases the loss; that is why motions are heavy on the first start in winter and you should wait until the system warms up.
- A clogged filter, a crushed hose and an unnecessarily narrow fitting all give the same symptom: motion slows down, the oil heats up quickly.
Measurement is simple: a gauge is connected on each side of the element and the difference is read. If the loss is above expectations the element must be replaced. A large loss in the line is a performance problem pronounced enough to overshadow the benefit of electronic improvements such as a retrofit kit.
Where this term is used: How Are Manual Hydraulic Levers Controlled Remotely? A Comparison of 6 Methods