Glossarypump |


Dynamic viscosity

can be defined as the ratio of shearing stress to the rate of deformation. As viscosity varies with temperature it is always expressed at a specific temperature. A change in viscosity alters liquid handling characteristics of the pumping system; more or less energy may be required to perform the same amount of work. In a centrifugal pump the increase in viscosity reduces the pressure energy (head) produced while increasing the

Vapour Pressure

Pressure at which a pure liquid can exist in equilibrium with its vapour at a specified temperature. Fluids at temperatures greater than their specified (critical) temperature will exist as a vapour with no distinction between gas and liquid phases. This is a single phase liquid. At less than the critical temperature, the two fluid phases can coexist; the denser fluid phase exists as a liquid and the less dense phase


Resistance of a fluid to sheer motion – its internal friction. The viscosity of a fluid varies with temperature. The molecules of a liquid have an attraction for each other, and they resist movement. This resistance to flow is expressed as its viscosity.


The vertical distance between pumping level and the bottom of the pump or jet assembly. Submergence must be sufficient to insure that the suction opening of the pump or jet assembly is always covered with water, while maintaining enough clearance from the bottom of the well to keep it out of sediment (at least 10 feet clearance is recommended).

Total Head Discharge

The total pressure or head the pump must develop. It is the sum of the depth to pumping level, the elevation, the service pressure, and the friction loss expressed in the same units, usually feet of head, before adding them together.

Service Pressure

The range of pressure in the pressure tank during the pumping cycle, usually expressed in pounds per square inch gauge

(P.S.I.G) Setting

The vertical distance from the level at which the discharge pipe leaves the well to the bottom of the pump or jet assembly in the well.


The net positive suction head required (NPSHR) remains unchanged for a given head. Flow, rotational speed, and impeller diameter, but changes with wear and liquids

Friction Loss

The loss of pressure or head due to the resistance to flow in the pipe and fittings. Friction loss is influenced by pipe size and fluid velocity, and is usually expressed in feet of head