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hydraulic development

hydraulic development

hydraulic development

(OP)
Dear all,
to achieve performance, we trimmed impellers to lower the head. but after trimming serious droop is observed at shut off. wondering why it is? can any one help me??????

RE: hydraulic development

i think you trimmed the impeller too much. each casing will have a max and minimum impeller dia.

RE: hydraulic development

(OP)
To Raj,
No sir, trimming is well within the limit

RE: hydraulic development

As you increase clearance between impeller OD and the cutwater you can see a droop of CV pressure. There are ways around this problem and is dependant on how the OD of the impeller is machined, but if the impeller is already trimmed it's now too late.

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: hydraulic development

Did it droop before?

Can you post any curves?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: hydraulic development

It is possible that the trim for that particular pump was only to be applied to the vanes, and the impeller shrouds should have been left at the full diameter. Common on low specific speed pumps, high head low flow (where the impeller looks like a pancake.)

RE: hydraulic development

Who trimmed it?. You or the vendor?

You, then it`s your fault.

The vendor? Ask him.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: hydraulic development

Is the droop at shut-off a problem, it shouldn't be, as running near to or at shut-off is a NO-NO anyway.

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.)

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