Impeller/casing gap

[TPJ07]

Dear Forum,

I am checking some centrifugal pump's drawing and I need to know if the gap, between impeller OD and casing ID, is correct.

OD impeller 237 mm
ID casing 241 mm
Gap 2 mm

Flow 3600 l/min at 12 barg
4000 RPM

Could someone help me!

Thanks a lot

 

[Cheddarcaveman]

It would be useful to know what pump this is.
From your description you are refering to the gap between the impeller OD where it discharges into the casing volute? If this is the case I would say that 2mm is a very small gap.
Or are you talking about wear-ring clearance?

 

[TPJ07]

Thanks Cheddarcaveman,

It is a fire truck pump and here attach there is a section of.

Dear

 

[Artisi]

I would assume that the designer / pump manufacturer would know what the correct gap should be between the impeller OD and the casing. Why would you think otherwise??????

 

[JJPellin]

The gap you are referring to is sometimes called the "A" gap. There are a number of rules-of-thumb for an ideal A-gap. One of those was included in "The Pump User's Handbook" by Bloch and Burdis. They recommend an ideal A-gap of 1.2 to 1.5 mm. But, most of their recommendations are based on API and ANSI pumps. Your pump configuration seems a bit unusual and could have other issues that would make a larger gap preferable. The 2 mm gap does not seem at all unusual to me. Is the impeller full diameter or has it been trimmed? If it has been trimmed, then you could consider trimming only the impeller vanes and leaving the shrouds full diameter

Johnny Pellin