HALE AP, Technical Manual

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area compresses and warms as it descends. The warming inhibits the formation of clouds,
meaning the sky is normally sunny in high pressure areas. But haze and fog still might form. Just
the opposite occurs within an area of low atmospheric pressure. Atmospheric pressure affects a
pumps ability to pump from draft. Higher pressures will increase a pumps performance, while
lower pressures can cause a noticeable decrease in lift.
2.4.1.2
Cavitation
The definition of cavitation is the formation of empty cavities (low-pressure bubbles) in a liquid
being moved by means of mechanical force (such as the rotation of an impeller) which is then
followed by their immediate and sudden implosion. The resulting forces can be as damaging as
striking the metal with a hammer. Cavitation within a pump may sound as if the pump were filled
with gravel or being struck with a hammer. See Section 3.5, Cavitation (Details), for more details.
2.4.1.3
Dead Heading
Operating a pump without any discharge is known as dead heading. Lack of flow causes temper-
atures to rise inside the pump.
2.4.1.4
Impeller And Clearance Rings
The impeller is the primary working part of a centrifugal pump. The impeller moves the water. An
impeller consists of two discs surrounding curved vanes. The vanes force water to rotate within
the discs resulting in the water being thrown outward at high velocity. The water from the impel-
ler discharges into the volute, converting the high velocity energy into pressure.
The clearance rings minimizes the amount of water that bypasses the discharge and returns to
the suction side of the impeller reducing pump performance (gpm). The wrap around clearance
ring reduces the bypass even more than the typical style ring (see Figure 3). Clearance rings are
ware items that protect the volute from experiencing the ware generated by the moving water
and especially the debris (sand, salt, etc.) when present.
Figure 3. Clearance Ring Water Flow
2.4.1.5 Priming Pump
An auxiliary pump attached to provide positive displacement of air out of the booster pump creat-
ing a vacuum which initially draws water into the pump. The type of priming pump used (by Hale)
for the AP, CBP, MBP, and RSD pumps is an electric motor driven rotary vane pump. Once the
main pump is primed and pumping, the priming pump is turned off.
2.4.1.6
Relief Valve
An automated valve with a control mechanism that maintains the pump pressure within 30 psi
when the pump discharge is gated (reduced) or closed (off). The valve maintains a set pressure
by diverting a portion of the pump discharge flow into the pump suction.