Never operate a centrifugal pump without liquid in it.
How to check that the pump is primed?
Opening all valves between the product source and the pump suction should get a product to the suction, but does not always ensure that the pump is primed.
Open the bleeder valve from the pump casing until all vapor is exhausted and a steady stream of product flows from the bleeder.
It may be necessary to open the bleeder again when the pump is started, or even to shut down and again bleed
off vapor if pump discharge pressure is erratic.
CLOSE THE DISCHARGE VALVE.
For low and medium-specific speed pumps close the discharge valve and open the suction valve.
Some users ask a question Why we should start up the pump at a closed discharge valve. It seems that open discharge valve facilitates the start. To answer this question let's consider the power curve of the centrifugal pump and electric motor characteristics.
The closed discharge valve creates a minimum load on the driver when the pump is started.
Let’s look at the power curve of the centrifugal pump. We see that at the zero flow the power I minimum. It facilitates electric motor start. On the contrary, If the discharge valve is open and the pipe is not filled the system has no or minimum resistance. But take into account that axial flow pumps have maximum power at the zero flow and should be start at the open discharge valve.
START THE PUMP AND LOOK AT THE PRESSURE GAUGE
The pressure should be built up to H at Q=0
If the discharge pressure does not built.
Start the pump. Confirm that the pump is operating by observing the pressure gauge. If the discharge pressure does not build up, stop the pump immediately and determine the cause.
Wrong direction of rotation
Air leaks through suction pipe connection or bottom valve.
The impeller is worn out or clogged
OPEN THE DISCHARGE VALVE
Open the discharge valve slowly, watching the pressure gauge.
The discharge pressure will probably drop somewhat, level off and remain steady.
If it does not drop at all, there is probably a valve closed somewhere in the discharge line. In that case, close the discharge valve. Do not continue operation for any length of time with discharge valve or line blocked.
If the discharge pressure drops to zero or fluctuates widely, the pump is not primed. Close the discharge valve and again open the bleeder from the casing to exhaust vapor. If the pump does not pick up at once, as shown by a steady stream of product from the bleeder and steady discharge pressure, shut down the pump and driver and check for closed valves in the suction line. A dry pump will rapidly destroy itself.
CHECK NOISE AND VIBRATION.
Carefully check the pump for abnormal noise, vibration (using vibration meter) or other unusual operating conditions. An electrician and machinery engineer should be present when pumps are initially commissioned
SOURCES OF ABNORMAL NOISE AND VIBRATION
CHECK THE BEARINGS TEMPERATURE
If the temperature bearings is rising possible reasons can be
Check the oil level
Pump and motor Alignment
The Pump operating point is far from the operating range
Be careful not to allow the bearings to overheat.
Recheck all lube oil levels.
CHECK THE PUMP SEAL OR STUFFING BOX FOR LEAKAGES.
If gland packing is used, check the leakages and if necessary adjust
Mechanical seal. If mechanical seal leaks. It is necessary to replace it.