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.