Impeller Trimming
Impeller Trimming
(OP)
Good day,
We're considering trimming the impellers on our 6 vertical turbine Pumps. Pumps are consuming too much power and we'd like to reduce it by trimming them. I would like to know, is there any particular method / procedure to trimming impellers? The impellers are semi open impellers. Do you simply skim off 1/4 or 3/4 of an inch as necessary off the impeller O.D.?
Thanks
We're considering trimming the impellers on our 6 vertical turbine Pumps. Pumps are consuming too much power and we'd like to reduce it by trimming them. I would like to know, is there any particular method / procedure to trimming impellers? The impellers are semi open impellers. Do you simply skim off 1/4 or 3/4 of an inch as necessary off the impeller O.D.?
Thanks





RE: Impeller Trimming
Before you make the decision, increase the lift 10-20% and check. Not sure of pump size, but this shouldn't be more than 0.010" or so. This reduces efficiency, so reduces head but increases power.
But if the impellers are rubbing the liners at current lift, you can eliminate the rub and your power reduction will be greater than the increase due to lost efficiency...
If they are multistage, you can reduce labor by trimming only the top stage, do not go below manufacturer's minimum diameter.
But the procedure is trim, underfile, balance, reinstall.
RE: Impeller Trimming
Changing lift is not something I've done much, but it can help.
Another thing to remember is excessive trimming of the impeller will degrade the efficiency of the pump and can be counter-productive. If there is a good pump curve available, try and plot the head at each proposed diameter and compare with existing process data. Understand what your process is doing to require "too much" power.
RE: Impeller Trimming
Thanks Again!!
RE: Impeller Trimming
For this situation, 0.2" trim on semi open, trying to leave the back shroud would only complicate the process. Never heard of doing this on a semi-open.
Service is water? Can you coat the hydraulic passages on the bowl to improve surface condition (and improve efficiency)?
RE: Impeller Trimming
I'd be curious to see how exactly the system works, because if you're turning down these pumps enough to wreck bearings, the larger impellers are well off what you were expecting.
Do what 1gibson said, and keep the shrouds as flow guides. You'll still get some recirculation at the tip depending on the system demand, but it should keep things relatively stable.
RE: Impeller Trimming
We coat the bowls and columns on all of our big vertical turbine water pumps. I believe it not only improves the efficiency, but it increases the life of the parts by delaying or eliminating the corrosion.
Johnny Pellin
RE: Impeller Trimming
RE: Impeller Trimming
Do you have an accurate system curve, how do you know you need 191 ft of pump head?
Did you know that 76.4% of all statistics are made up...