Seal chamber pressure question 1

[v7042800]

Hi folks. My question is in regards to an overhung API pump with closed impeller, wear rings and BALANCE HOLES.

I would like to ascertain if the pressure acting behind the impeller, in the area where the balance holes are located (adjacent to seal chamber), if it is only slightly above suction pressure. (assume no seal flush flow)

I am having trouble accepting the 25% of deltaP estimation for this particular type of impeller design...

 

[JJPellin]

It depends on the particular design and the condition of the parts. We have pumps of this configuration in vacuum service where the design was deliberately altered to maintain positive pressure in the seal chamber. We have others where I know that the balance holes are large enough to maintain the seal chamber at suction pressure. As the back wear-ring wears, the amount of leakage passing through the balance holes increases and this pressure may go up some. But, in general, you are correct. For most pumps of this arrangement, the pressure will be less than the 25% rule-of-thumb. If it is a new application, the OEM should be able to tell you the expected seal chamber pressure. If it is an existing installation, put a pressure gauge on it and check.

Johnny Pellin

 

[v7042800]

Thank you, sir !!

 

[flexibox]

see if the attached helps. I agree with Johnny's comments