starting pump vithout discharge pressure 1

[lorang]

I have to start submerge centrifugal pump with inducer without discharge pressure. The pipe is empty because the liquid is evaporated. There are a valve to regulate flow, but is at 25m of the pump, so when I simulate the starting sequence, the pump is over runout flow during few second.
The manufacturer of the pump says that the flow will be limited by the inducer near runout flow. I don't understand why the inducer can limit the flow if I have enough pressure at pump inlet(no problem of NPSH).
Could someone can help me and could give some information about running over runout during few second.

Sorry for my english.

 

[Artisi]

You have given very little detail to work with and more information would help the guys in the forum to make some meaningful contribution to your request.
I would however suggest that if runout at startup is momentary then you shouldn't have any problem.


International College
Naresuan University
Phitsanulok
Thailand

 

[rmw]

Your english is just fine. You have nothing to apologize about. However, the level of detail that you provide for us to be able to help is not.

Unless your pump vendor is making the case that the inducer will help fill the pump, as well as the discharge piping rapidly enough so that the total system head loss will become the limiting factor, his comment does not make sense based on what you have provided. Every passage in your pump and/or piping can be considered as an individual orifice, and there is a limit to how much can flow through a given point without pressure losses becoming unreasonable.

He may be saying that the inducer will reach a point that it is trying to "stuff" more fluid into the pump suction (or volute, or discharge) than the pump itself can overcome, and it will be self limiting.

Picture, if you will, attaching a HUGE pump to the suction of your pump, and then starting it with many times more flow than it can pass. Well, the pump itself will act like a giant resistance to the huge pump, and limit its flow.

That is the only way his comment makes any sense to me. He appears to be saying that the inducer will act in this way.

Many pumps are started just as you describe, and have to fill empty piping as they start up. In very large pumps, a big concern is the inertia of the moving slug of fluid as it finally fills the empty piping and all that energy is suddenly stopped by a valve (or elbows, etc.) Therefore it is mandatory to fill the discharge systems by other means before starting the pump.

If this doesn't answer your question, please post back more information, and we will go from there.

rmw

 

[lorang]

Thanks all for your reply. I understand better how it work.