Tuesday, July 15, 2014
What Is Pressure Drop? Friction is defined as the resistance an object encounters in moving over another; solids, liquids, and gases all exhibit friction in their motion. In hose and piping systems, the result of this friction is pressure drop and heat generation that may be accurately estimated with engineering models. 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 (NPSH). What Affects Pressure Drop? The factors which contribute to pressure loss may be broken down into two general categories: mechanical components and fluid properties. 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 cross-sectional area. 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.