How to start a centrifugal pump with opened discharge valve??

[sunny_ahanwu]

We all know the centrifugal pump shall be started with closed discharge valve. But in some cases, the pump will be started with a open discharge vale. What's the difference between these two ways?

In API 610 7.1.6, "Some pumps are equiped with bypasses, in which case alternative starting conditions should be used.", how to understand this?

[josefreitas]

If one centrifugal pump starts without a valvle in close position, the head is near zero and the flow is infinite. Or the pump fails or the motor fails. This pump characteistic is done with nominal speed of the motor. But if you start the pump with a VFD then the pump starts can be with increase controlled flow (if the piping is filling - but take care with the reverse flow)

[sunny_ahanwu]

Thanks for you reply. But in the fire system, fire pumps are started with open discharge valve.
As we known that the centrifuagl pump shall be started with closed discharge valve, it is the best way for fix speed pump.
But when fixed speed pump was started with open discharge valve (e.g fire pump ), are there some differences from that started with closed discharge valve? e.g : choose larger motor or other something.

[sunny_ahanwu]

If one centrifugal pump starts without a valvle in close position, the head is near zero and the flow is infinite. Or the pump fails or the motor fails. This pump characteistic is done with nominal speed of the motor. But if you start the pump with a VFD then the pump starts can be with increase controlled flow (if the piping is filling - but take care with the reverse flow)

Thanks for you reply. But in the fire system, fire pumps are started with open discharge valve.
As we known that the centrifuagl pump shall be started with closed discharge valve, it is the best way for fix speed pump.
But when fixed speed pump was started with open discharge valve (e.g fire pump ), are there some differences from that started with closed discharge valve? e.g : choose larger motor or other something.

[josefreitas]

Use, here You have a great diference blecaute the circuito is pressurized, só the centrifugas pump have a compressivos pressure and the pump can status without valve because the pump flor is determinated by This pressure

[sunny_ahanwu]

Use, here You have a great diference blecaute the circuito is pressurized, só the centrifugas pump have a compressivos pressure and the pump can status without valve because the pump flor is determinated by This pressure

Thanks for your reply.
In API 610 11th, clause 7.1.6,"Some pumps are equipped with bypasses, in which case alternative starting conditons should be used", what does it mean? It means to start the pump with VFD??

[josefreitas]

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