how does pump efficiency curve change with pump age?
how does pump efficiency curve change with pump age?
(OP)
I'm working on recommendations for an upgrade to controls for an unusual water distribution system (but not because of the pumps).
Part of the system includes six vertical turbine pumps, nominally 1000 gpm w/ 100 hp motors. There are two different types having two different book curves. The pumps were installed in 1963, 1974, and one in 1989.
When tracking down the curves for the 1974 pumps, the manufacturer's rep cautioned me against using the "book curve" . When doing simulations on the system, I had to seriously increase the minor losses in the suction lines to get a calibration.
As someone will probably want the new control system to help the pumps operate efficiently, I am wondering if re-built pumps become less efficient with age. I've seen the threads on testing for head vs. flow but am not sure if it is reasonable or feasible to test for efficiency.
Thanks
Mary





RE: how does pump efficiency curve change with pump age?
mac
RE: how does pump efficiency curve change with pump age?
all the best.
raj
RE: how does pump efficiency curve change with pump age?
Raj:
Thanks for the answer. But how do I construct a "true" efficiency curve? I can measure hydraulic horsepower, and can get amp readings. How do you measure the actual motor horsepower?
Mary
RE: how does pump efficiency curve change with pump age?
RE: how does pump efficiency curve change with pump age?
There is a rule of thumb that says 5% to 10% the cost of a pump is in the intial purchase price, the other 90% to 95% is in the lifetime energy use. On pumps this large, a full-on energy analysis, possibly including replacement with optimal new pumps is quite feasible. These may not be PE or EE motors, but probably should be per economics. Perhaps beyond the scope of your obligations though.
Pumps generally do better than their pump curves...no one wants to get caught short and get sued. Pump curves are rather dangerous in my book. For instance, how do you know for sure what size impellers are in those pumps? One test is to deadhead the pump and compare pressures to the curves for different size impellers to zero in on the one you have. Find someone with a good ultrasonic meter, rent it. As some else stated, recirculation problems can create some very unexpected results that could leave lots of egg on your face if you rely only on pump curves.
Hope this is some help, Pacific Steve
RE: how does pump efficiency curve change with pump age?
Of course, if the original impeller was polished & backfiled, then....no dice.
Further, polishing and backfiling only temporarily increases the efficiency becuase as the impeller wears, the vanes are not as sharp and smooth.
Tim