API Plan 23
API Plan 23
(OP)
Hi guys! Please clarify?
Here are two contradicting views on the clearances for the throat bushing in a API plan 23 environment overhung pump.
One view is the throat bushing must be installed at the bottom of the seal cavity to help isolate the seal chamber from the pump flow, close clearances are not required.Diametral clearances of 0.025 in to 0.030 in are adequate.
The other view is
A close clearance throat bushing is to isolate the stuffing box from the pumping area,it should be as tight as possible depending on the material. If the stuffing box is not isolated from the pumpage the desired cooling would not be achieved,the pressures would equalize, it would however restrict turbulence in the chamber which would have some effect on the movement of product from the stuffing box but not as effective as the tight throat bush. Also excessive throat bush clearance would create too large a duty on the heat exchanger for effective cooling (stuffing box volume plus behind impeller).
However the pump manufacturer does not recommend using a back wearing on this pump so as to reduce load on the thrust bearing, the impeller is a single suction type with no balance holes.
Here are two contradicting views on the clearances for the throat bushing in a API plan 23 environment overhung pump.
One view is the throat bushing must be installed at the bottom of the seal cavity to help isolate the seal chamber from the pump flow, close clearances are not required.Diametral clearances of 0.025 in to 0.030 in are adequate.
The other view is
A close clearance throat bushing is to isolate the stuffing box from the pumping area,it should be as tight as possible depending on the material. If the stuffing box is not isolated from the pumpage the desired cooling would not be achieved,the pressures would equalize, it would however restrict turbulence in the chamber which would have some effect on the movement of product from the stuffing box but not as effective as the tight throat bush. Also excessive throat bush clearance would create too large a duty on the heat exchanger for effective cooling (stuffing box volume plus behind impeller).
However the pump manufacturer does not recommend using a back wearing on this pump so as to reduce load on the thrust bearing, the impeller is a single suction type with no balance holes.





RE: API Plan 23
RE: API Plan 23
However, after spewing all that, several seal manufacturer's seem to be recommending floating throat bushings on Plan 23's. On a 3" shaft, Clearances would be in the .004" to .006" range. I have yet to hear any positive or negative feedback, or any reduction in cooling water requirments.