Minimally trimmed impellers
Minimally trimmed impellers
(OP)
Hi everybody,
First of all you guys form a great community.
My questions is: does anybody know the harms in having minimally trimmed impellers for vertical turbine pumps?
Some vendor is offering 6 stage pumps with impellers in stages2-6 to be trimmed to the minimum diameter possible.
It feels like an undersirable design because of the raw river water supply (30000 ppm solids), but I can't technically explain why. I think its reasonable to have mid-trim or below mid-trim design, but not to the point of having the minimum impeller diameter possible.
Can anyone comment?
Thanks,
Tronical
First of all you guys form a great community.
My questions is: does anybody know the harms in having minimally trimmed impellers for vertical turbine pumps?
Some vendor is offering 6 stage pumps with impellers in stages2-6 to be trimmed to the minimum diameter possible.
It feels like an undersirable design because of the raw river water supply (30000 ppm solids), but I can't technically explain why. I think its reasonable to have mid-trim or below mid-trim design, but not to the point of having the minimum impeller diameter possible.
Can anyone comment?
Thanks,
Tronical





RE: Minimally trimmed impellers
RE: Minimally trimmed impellers
Why the trim at all? How far off of BEP are you?
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Minimally trimmed impellers
Addressing your question, presumably, the first of the 6 stages is full diamter, although this is not stated in your posting and without a set of performance curves for the pump it is hard to say what their intention is, however, if the remaining impellers are trimmed to their minimum diameter, I would suggest that the pump is probably not a good hydraulic fit for the duty -- but as noted, without a set of curves etc it is hard to give you any definite advice at this point.
Naresuan University
Phitsanulok
Thailand
RE: Minimally trimmed impellers
As for not trimming the first impellor, a guess may be to assist in NPSH, the curve for that may be best if the impellor is at full trim, a chart with NPSH vs trim are not very common, may be it was only tested at full trim.
Hydrae
RE: Minimally trimmed impellers
VTP's do have much smaller clearances. Although his impeller was minimally trimmed, pumps were operating to the right of BEP! just a bit though.
But with VTPs, between the minimum and maximum diameter possible is usually a few percent (<10), so its that uncommon to see minimally trimmed impellers since the clearance is so tight (at least relative to slurry pumps).
Anyways we met with vendors and the minimum impeller vendor was rejected. The guy can't even remember why he offers minimally trimmed impellers.
He was also the highest bidder, more than twice the next highest bidder.
Thanks for your input guys
RE: Minimally trimmed impellers
Naresuan University
Phitsanulok
Thailand
RE: Minimally trimmed impellers
What can you tell about a pump house intake design with two vertical turbine pumps positioned in-line, one behind the other, in a narrow channel?
The first pump is normally not running, (stand-by pump) the second pump has a capacity of 5100 m3/h at 25 m WC
Any comment?
Erik
RE: Minimally trimmed impellers
Naresuan University
Phitsanulok
Thailand
RE: Minimally trimmed impellers
This is just a pump sizing issue - the larger the pump, the more it costs. The smaller trimmed impellers are needed to meet the flow requirements. Sometimes you just cannot get a good fit.
Performance-wise, there is no problem with minimum trimmed impellers - just don't trim below manufacturers minimum recommended trim or you will get recirculation in the pump - which results in erosion, vibration - and the pump curve is no longer accurate.