Brochure

Useful Definitions
Flow is a volume measure to establish pump capacity per
unit of time, usually as GPM.
Head is a pressure measurement represented by how high
the pump can lift a column of liquid, usually in feet. To
convert the popular pressure expression P.S.I. to feet of
water, multiply P.S.I. X 2.31.
Horsepower (H.P.) is the amount of power available to
drive the pump.
Brake Horsepower (BHP) is the amount of power
required to drive the pump.
Net Positive Suction Head Required (NPSHR) is a
pressure measure – in absolute units – expressed in feet,
and indicates the pressure required at the pump suction
to prevent cavitation. Reducing the pressure at the pump
flange below the vapor pressure of the liquid can cause
formation of vapor pockets in the impeller passes. This
condition (cavitation) will interfere with pump performance,
and is usually accompanied by noise as the vapor pockets
collapse. NPSHR can be thought of as the amount of
pressure in excess of vapor pressure required to prevent
the formation of vapor pockets.
Net Positive Suction Head Available (NPSHR) is the
pressure available at the pump suction flange. If NPSHA is
less the NPSHR, cavitation problems should be expected.
Pump efficiency represents the portion of brake
horsepower converted into useful work. Pump efficiency,
along with flow, head, and liquid specific gravity affect the
power required to drive the pump. The more efficient the
pump, the less power required to drive it.
Specific Gravity (S.G.) is the relative weight of a liquid
when compared with water (water = 1.0 S.G.)
R.P.M. is the rotational speed of a pump.
Shut-Off Head is the head developed by a pump at zero
flow.
Static Head is the pressure at the pump discharge which
the pump must overcome before it can produce flow. Static
head is a difference in elevation and can be computed for a
variety of conditions surrounding a pump installation.
System Resistance is the pressure on the pump
discharge resulting from the resistance to flow created by
friction between the fluid and the piping system. This value
will vary with flow rate.
Suction Pressure is the pressure observed at the pump
suction connection. This may be a positive pressure or a
negative pressure.
Discharge Pressure is the pressure at the discharge
connection. This will always be a positive pressure.
Differential Pressure is the algebraic difference between
the discharge and suction pressures. This value represents
pump head.
Service Factor is the reserve power available from an
electric motor when operating under normal conditions.
System Curve is a graphical representation of the hydraulic
characteristics of a piping system. When the pump
performance curve is laid over the system curve, the
intersection indicates the flow and head pressure of the
pump when coupled to the hydraulic system.
Constant Speed is the RPM of a pump upon which a
published pump curve is based.
Commercial Hydronic
Application Information
4.