Net Positive Suction Head (NPSH):
NPSH is the difference between suction pressure and vapor pressure.
NPSH Available (NPSHA): The
absolute pressure at the suction port of the pump.
NPSH Required (NPSHR):
The minimum pressure required at the suction port of the pump to keep the pump
from cavitating.
NPSHA must be greater than NPSHR for the
pump system to operate without cavitations.
Cavitation:
High velocity liquid flowing through pump impeller tends to flash due to
reduction in pressure leading to bubble formation. These bubbles explode as
they approach higher pressure region causing damage to the pump internals. This
phenomenon is known as cavitation.
Staggering of stages:
Operation of Centrifugal Pumps:
Steps for starting a centrifugal pump:
— 1. Turn
on the cooling water system for the pump bearings, stuffing boxes &
mechanical seals, if these
parts are liquid cooled.
— 2. Start
the auxiliary lube oil pump, if one is fitted & check the oil flow to the
bearing & other parts of
the pump.
— 3. Close
all the drains in the casing & suction & discharge piping.
— 4. Open
the suction gate valve & close or open the discharge gate valve, depending
on the starting
procedure to be followed.
— 5. Prime
the pump.
— 6. Open
the warm up valve if the pump is not at the right temp.
— 7. Open
the recirculating valve.
— 8. Start
the driver & bring the pump into speed.
— 9. As
soon as the pump is up to rated speed, open the discharge gate valve slowly.
— 10. Check
the leakage from the stuffing boxes.
— 11. Adjust
sealing liquid flow to ensure packing lubrication. A flow of 1 to 2 gpm to each
stuffing box is usually sufficient.
— 12. Check
the pump bearings for lube oil flow.
— 13. When
there is sufficient flow through the pump, close the recirculating valve.
— 14. Check
the pump suction discharge, lube oil, cooling water& sealing water pressure
& temperatures.
Operating Checks:
•
Bearing temp
•
Suction & discharge pressure
•
Lube oil temp & pressure
•
Leak off flow
•
Discharge flow meter
•
Stuffing box leakage
•
Discharge temp and pressure
•
Pump driver current the oil level in the
pump & driver bearings. Keep an hourly record of all these readings, using
the logbook.
Pump Shutdown:
•
Partially close the discharge valve.
•
Shut off the power.
•
As soon as the power is off close the
suction and discharge valves.
Parallel Operation of Pumps:
Series Operation Of Pumps:
