what`ll happen if centrifugal pump runs with discharge valve closed?

Question

further if recirculation valve is not provided/
what will happen n same case for multi stage centrifugal pumps

Answer 1

Good Morning! I saw your question and had to try this one. A few years back I worked for Stanley Hydraulic Tools and the discharge pumps we sold we centrifugal pumps as well. These pumps as yours are designed to move large volume not pressure. Closing the discharge side off should not damage the pump.....housing or impeller. We had a hydraulic motor that spun the pump/impeller. The hydraulic motor was constantly bathed in oil and even in a stall or a closed discharge valve situation the pump was protected. I would encourage you to find out who the manufacturer of your pump assembly is and make this question out directly to them but I hope this in its self helps! Hyway.

Answer 2

Often it is required to start a centrifugal pump with its discharge valve closed to start the pump "unloaded" reducing current surge in the drive motor. The pump with run at shutoff head (the highest discharge pressure it can produce). If there is no recirculation flow, the water in the pump will heat up (perhaps to steam!) and the bearings that are usually lubricated by the cool liquid being pumped may fail. As the discharge valve is slowly opened, the pump will move more and more water increasing the load (and current) of the motor. At some point (perhaps valve fully opened) pump discharge pressure will match system resistance and maximum system flow will occur.

Answer 3

Reiterating what Kes has said with a couple of corrections.
Starting a centrifugal pump with the discharge valve closed will not affect the motor inrush current. Inrush current is typically 6 - 8 times full load current regardless whether the motor is started coupled or uncoupled. Inrush current is totally independent of load current.
When a cage motor is started the inrush current peaks withing 3 or 4 cycles and decays very quickly as the motor accelerates to full speed.
Cage motors at start exhibit a very low power factor (typically .2 .3 PF. this causes high inductive reactive currents to flow. As the motor accelerates, the PF rises towards unity as the load (watts) increase. When the motor is at full load the power factor is typically between .7 and .95 depending on the size and motor design.
Again, to reiterate what Kes has said, running a centrifugal pump with the discharge valve closed (shut off head) will drop the watts load on the motor to a point where only mechanical losses in the motor/pump are apparent plus the copper and iron losses in the motor. However there can be quite high EI (reactive amps) flowing in the circuit due to the low PF. Also of course as the impeller is thrashing the water in the pump, the temperature can rise and boil.

Answer 4

yeah Centrifugal Pump can dead head, the casing temp climbs, but no drama, and yes high pressure multi stage Centrifugal Pumps temps climb real quick (and usally have temp based pressure relief valves). so all the above answers are correct, but note, dont dead head a positive displacement pump, (that doesnt have a pressure relief plate arrgt.) or your break something.

Answer 5

Almost nothing. The pressure at the outlet will rise up to a certain value, and the rotor will have a little more of a resistance, but it can't be broken. Only cavitation may occur, if You close the inlet..

Answer 6

After some time the temperature of the fluid will rise and that will damage the mechanical seal all of this will depend on for how long time it has been running without discharge and the temp. of the fluid.

Answer 7

Eventually, with no recirculation flow or bearing cooling flow, the water in the pump housing will overheat and probably cause failure of seals and bearings.

Answer 8

not much
cos its actual use is only to obtain discharge not to generate pressure
so after some time when the resistance increases to a certain limit it will stop and cavitation may occur