Hale SMR - Manual (Page 16)

Introduction
2-2 Stainless Max Series Pumps
The velocity at which the fluid travels from the center directly relates
to the diameter of the disk and the speed of rotation.
When water is confined in a closed container (such as the pump
body or volute), the velocity is converted to pressure and this pres-
sure rises to a level that depends on the speed of rotation. There
are three interrelated factors that regulate the performance of a
centrifugal pump:
❑ SPEED (RPM) If the speed of rotation increases with flow held
constant, fluid pressure increases.
❑ PRESSURE Pressure is usually measured in Pounds Per
Square Inch (PSI or BAR).
If pressure changes with speed held constant, the flow,
measured in gallons or liters per minute (GPM/LPM), changes
inversely; that is, if pressure increases, flow decreases.
❑ FLOW Flow is usually measured in the number of gallons of
fluid per minute (GPM or LPM) that a pump can deliver when
supplied from draft. If the pressure is held constant, the flow
increases with an increase in the speed of rotation.
A centrifugal pump is preferred by the fire protection service due to
its ability to fully utilize any positive suction inlet pressure, reducing
the amount of work done by the pump.
For example, if the required discharge pressure is 120 PSI (8.3
BAR), and the inlet pressure is 45 PSI (3.1 BAR), the pump must
only produce the difference in pressure or 75 PSI (5.2 BAR). This
contributes to low engine and pump speeds with reduced mainte-
nance. Decreased maintenance is aided by the fact a centrifugal
pump has few moving parts; such as the impeller, shaft and seal.
Note: SM Series pumps are single stage pumps, meaning there is a
single impeller on a common shaft.
As the impeller rotates, the water moving outward in the impeller
creates a vacuum in the suction eye allowing the pump to lift the
fluid into the volute (or body).
As water is evacuated from the suction passage atmospheric
pressure pushes the water through the suction passage.
Pump Stages
The number of impellers on a common shaft determines the number
of pump stages.