Partially closed pump discharge valve question
Partially closed pump discharge valve question
(OP)
Hi all,
Just got a quick question here wondering if you guys can help me out.

Right now I have the yellow pump curve and the orange 2 inch system curve , producing around 120 gpm against around 110 ft of head. If I expand the piping from 2 inch to 3 inch I end up with the grey system curve. The grey system curve doesn't intersect with the pump curve so this way of operating is not possible in my understanding; However, using the grey system curve, if I partially close the pump discharge valve to artificially increase the head so that the total head becomes 110 ft, would the new operating point be the same as before (120 gpm against 110 ft of head)? Similarly, if I partially close the discharge valve so that the total head becomes say 100 ft, would the operating point be around 130 gpm against 100 ft of head?
Any help is appreciated, thank you guys.
Just got a quick question here wondering if you guys can help me out.

Right now I have the yellow pump curve and the orange 2 inch system curve , producing around 120 gpm against around 110 ft of head. If I expand the piping from 2 inch to 3 inch I end up with the grey system curve. The grey system curve doesn't intersect with the pump curve so this way of operating is not possible in my understanding; However, using the grey system curve, if I partially close the pump discharge valve to artificially increase the head so that the total head becomes 110 ft, would the new operating point be the same as before (120 gpm against 110 ft of head)? Similarly, if I partially close the discharge valve so that the total head becomes say 100 ft, would the operating point be around 130 gpm against 100 ft of head?
Any help is appreciated, thank you guys.





RE: Partially closed pump discharge valve question
How was the grey system curve derived, using diameter ^5.
Throttling the discharge you can select what ever flow you want at the corresponding head - but why increase the pipe diameter and then throttle the pump?
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.)
RE: Partially closed pump discharge valve question
Hi, sorry I didn't include these information in the post. Here are the background information.
1. The pump curve is the manufacturer pump curve, I just jotted down the points from the original graph and made a trend line in excel so I could play around with it haha
2. Both system curves were derived by calculating friction losses (fittings accounted for) on top of the static head.
3. I got two of these pumps here, currently we just run one pump and the orange system curve, but I'm trying to increase the flow. By increasing the pipe size to the grey system curve would intersect the pump curve with two of these pumps running in parallel and would get me increased flow and head that we need(I didn't show the parallel curve in the graph, but they intersect). However, just in case if we ever run just one pump for some reason, the curves won't intersect. I am doing this for a back-up option I guess.
You said "Throttling the discharge you can select what ever flow you want at the corresponding head," that means my assumptions in the original post would be correct right? By throttling the discharge valve is essentially just moving the system curve left-ward right?
Thank you
RE: Partially closed pump discharge valve question
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.)
RE: Partially closed pump discharge valve question
RE: Partially closed pump discharge valve question
The reality is the a single pump will meet the system curve, but you would be running off the published max flow and may get one of the following problems / issues
Excess power / amps on the motor
Decrease in efficiency
vibration
NPSHR increase and possible cavitation
Or for a basic pump it might just work ok, especially if this is only an occasional operation. That is a pretty steep pump curve though - you don't often see a 50% reduction in head over a usable flow range.
But otherwise artisis response is very good.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Partially closed pump discharge valve question
RE: Partially closed pump discharge valve question
The larger pipe was installed to run 2 pumps.
Currently 1 pump runs to gain an slight increase in flow.
Throttling the discharge will move the system curve left until the required (increased)flow is achieved.
Will overall pump efficiency increase or decrease - no pump curve so its an unknown.
Will the pump be mechanically sound as this increased duty - without full curve detail efficiency / NPSHr etc again not clear, however for such a small increase I don't foresee and upsets.
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.)