Two suctions

[mwinn]

I have a small 30 gpm centrifugal 3 hp 3500 rpm pump with two suctions. One suction is small and close to pump, the other if large but far more distant. Both are same elevation. When starting up the flow favors the nearer chamber and quickly empties it first. I attribute this to the much lower inertia of the water in the small chamber. My solution was to nearly close the valve to the nearer smaller chamber. I will probably change that to a small orifice. My question is this: How do I predict such a difference in startup flow between the two chambers? And how do I size the restrictive orifice to the smaller chamber? Note that the two chambers are piped together just before the pump suction. The smaller chamber contains the pump start stop switch based on level. No need to tell me it was a messy design. It was hemmed in by location requirements.

 

[yazguli]

I don't know how apart your chambers are. If not so far, I think you'd better join the two chambers with a second pipe of large enough size at bottom. This may act as an equalizer and keep the level in the two chambers equal.

 

[LittleInch]

" I attribute this to the much lower inertia of the water in the small chamber ". Err, no. This is due to the lower frictional resistance in the smaller line compared to the bigger, but longer line at the same flow and hence the flow will increase in the smaller line until the frictional looses become the same.

To attempt to get equal flow, which is what I assume you want, you need to get the overall frictional losses, assuming there is no head difference, a equal as you can. This will be difficult with any fixed device like an orifice so some sort of variable control is advised if you really want to get true equal flow.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[yazguli]

As mwinn has mentioned,"The smaller chamber contains the pump start stop switch based on level.",so equal flow will empty the smaller one first and the pump will stop before the larger one is emptied.
By the way, mwinn , I doubt if "a pump with two suctions " is a proper term for what you mean.

 

[LittleInch]

Good point. Also w don't know how fast these empty. It implies that it happens quite quickly.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Artisi]

Don't think we really know anything, a sketch or photo might throw a bit of light onto what is going on and hence the problem.


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[yazguli]

And if you are going to send more and detailed information, tell us if this is a mixing process of two different liquids or not.