Cavitation, Process of cavitation – Hale SMR User Manual
Page 47
Stainless Max Series Pumps
3-13
Operating Procedures
4. When the pump is not in operation, turn the hand wheel clock-
wise back to a position slightly above the normal operating
pressure. More complete and detailed information can be found
in the relief valve manual.
CAUTION!
THE PRESSURE INDICATOR ON THE PANEL IS ONLY A ROUGH INDICA-
TION OF TPM SETTING. ALWAYS USE THE ABOVE PROCEDURE TO
PROPERLY SET THE “TPM” RELIEF VALVE SYSTEM.
CAVITATION
Cavitation can occur while pumping from draft, in relay, or from a
hydrant. The operator must be aware of the warning signs and correct
the situation, or serious damage to the pump and impeller will occur.
Cavitation can damage the impeller and other sensitive components,
impair pump performance, and reduce flow capacity. The damage
done during any one period of cavitation is not great, but the effects are
cumulative. Implosions occurring during cavitation break away or erode
tiny pieces of metal from the internal parts and the pump casing. When
enough metal has been chipped away, the impeller becomes unbal-
anced causing a strain and vibration on bearings, bushings and shafts.
The way to eliminate cavitation is to increase the flow to the pump,
decrease the amount of water being discharged from the pump, or
reduce the pressure in the pump by decreasing engine speed.
Process of Cavitation
When increased discharge demand exceeds the intake, bubbles
form in the low-pressure region (eye) of the impeller. The pressure
of the water in the pump drops as it flows from the suction flange
through the suction nozzle and into the impeller.
As flow from the pump increases, the vacuum at the impeller in-
creases. As the vacuum increases, the boiling point of the water in
that vacuum decreases until it reaches a point near the impeller eye
where it boils and vaporizes.
Once the vapor pockets, or bubbles, enter the impeller, the process
begins to reverse itself. As the vapor reaches the discharge side of
the pump, it is subjected to a high positive pressure and condenses
back to a liquid.