Pressure Drop in Hydraulic and Pneumatic Systems 15

Pressure Drop in Hydraulic and Pneumatic Systems 15 -Sep-21

What Is Pressure Drop? • Pressure drop is the difference in the pressure of a fluid as it enters one end of a hydraulic hose assembly and the pressure of that fluid as it leaves the other end. There will be a difference in pressure, and it will be less. How much less depends on what is between the beginning and end of the hose assembly. • In general mechanical components and fluid properties can influence pressure drop. 15 -Sep-21

Contributions to Pressure Drop • Mechanical components such as valves, flow meters, quick disconnects, adapters, couplings, tubing, hose, etc. , all contribute to pressure loss. • The amount of pressure loss in mechanical components is impacted by criteria such as cross-sectional area, internal surface roughness, length, bends, and geometric complexity. • Fluid properties such as density, viscosity, heat capacity, and bulk modulus will also contribute to pressure loss. Fluid properties are impacted by temperature, pressure, contamination, and time. Fluid velocity has the most impact. Fluid velocity is a direct product of flow rate and crosssectional area. (Bulk Modulus is a measure of a substance’s resistance to compression – a substance which is very hard to compress has high Bulk Modulus) 15 -Sep-21

Examples of things that can influence the amount of pressure drop • FRICTION — This is the rubbing of fluid against the inside walls of the hose assembly. Result is pressure drop and heat generated. • TYPE OF FLUID — Different fluids behave differently under pressure. Thicker fluids are moved with greater difficulty and will exhibit greater pressure drop. • TEMPERATURE OF THE FLUID — Warming fluid thins it so it flows more easily, as with automotive oil. • LENGTH OF HOSE ASSEMBLY — The longer it is, the more surface there is for friction to decrease pressure. • SIZE (I. D. ) OF HOSE — Affects the fluid velocity for a given flow rate. Higher velocities result in greater pressure drop. Therefore, a larger I. D. hose will produce less pressure drop. • TYPE OF COUPLINGS & ADAPTERS — Any change in bore or change in direction (such as with 45 or 900 elbows) can increase the amount of pressure drop. • FLOW RATE — Pressure drop increases with flow rate for same size hose. 15 -Sep-21

Why Does Pressure Drop Matter? • If there is excessive pressure drop in a system, pumps will have to work harder, use more energy, and the working fluid will increase in temperature. Depending on the source of the additional pressure loss, it could raise the whole system pressure, increase wear, and introduce potentially dangerous over-pressure conditions, render some tools or equipment functions inoperable because of inadequate operation pressure, or create damaging cavitation and loss of net positive suction head 15 -Sep-21

What Can Be Done to Reduce Pressure Drop? • Check pressure drop when non-identical replacement parts or ongoing system problems are observed. • Use straight adapters and bent-tube couplings whenever possible. • Replace worn parts and old fluids. • Lower the fluid velocity. 15 -Sep-21