Stuffing Box Pressures for Non-API Multistage Centrifugal Pumps
Stuffing Box Pressures for Non-API Multistage Centrifugal Pumps
(OP)
Afternoon
Looking for any help on calculating stuffing box pressures on a multistage centrifugal pump with an equalizing line.
I am told (by pump/seal mfg's)that you cannot calculate a true value as there are simply too many variables to take into consideration and as such the industry assumes that the stuffing box pressure = the suction pressure through the use of an equalizing line. Please see the attached technical reference on how to calculate stuffing box pressures for different pumps.
I am looking for some clarification if the above is true. Is there no real way to calculate a true value?
I have heard of some theoretical ways to calculate these values depending on the number of impellers, pump design, pump tolerances, whether equalizing lines are used, location of stuffing box in relation to the area where the impellers is turning, type of axial thrust balancing employed, peripheral speeds + pressure in seal areas combined into a PV value to determine frictional heat developed, liquid temperatures, etc etc.
Any help or advice is muchly appreciated.
Looking for any help on calculating stuffing box pressures on a multistage centrifugal pump with an equalizing line.
I am told (by pump/seal mfg's)that you cannot calculate a true value as there are simply too many variables to take into consideration and as such the industry assumes that the stuffing box pressure = the suction pressure through the use of an equalizing line. Please see the attached technical reference on how to calculate stuffing box pressures for different pumps.
I am looking for some clarification if the above is true. Is there no real way to calculate a true value?
I have heard of some theoretical ways to calculate these values depending on the number of impellers, pump design, pump tolerances, whether equalizing lines are used, location of stuffing box in relation to the area where the impellers is turning, type of axial thrust balancing employed, peripheral speeds + pressure in seal areas combined into a PV value to determine frictional heat developed, liquid temperatures, etc etc.
Any help or advice is muchly appreciated.





RE: Stuffing Box Pressures for Non-API Multistage Centrifugal Pumps
RE: Stuffing Box Pressures for Non-API Multistage Centrifugal Pumps
The pressure at the higher pressure side will very much depending on the construction of the pump, and the balancing line dp use by the pump manufacturer. The balancing line dp are based on the pump head and fluid properties at the design condition. Operating away from this conditions will change all the parameters.
For a more critical application such as low SG and high vapor pressure liquid, it is best to consult the pump vendor. Too low a pressure in the seal chamber may cause the liquid to flash and too high pressure may cause insufficient flushing liquid flow over the seal faces.
RE: Stuffing Box Pressures for Non-API Multistage Centrifugal Pumps
You can calculate an order of magnitude estimate by having the curve and flush stream data handy with reasonable assumptions of head loss across the system. It isn't rocket science, just time consuming. I've had seal vendors calculate theoretical stuffing box pressures before and they are usually within +/-10% of the test pressure (using a gauge on the box itself)
Highly recommend that you consult both the pump and seal vendor and get them to communicate so that you have adequate stuffing box conditions.
RE: Stuffing Box Pressures for Non-API Multistage Centrifugal Pumps