Thrust/End play/float calculations for centrifugal pumps?

[MechEngineer2012]

Hello Engineers,
I have been self teaching myself about pumps and have a theoretical question about centrifugal pump design.

When a new pump is manufactured, during assembly of pump, a thrust clearance or End play is left. For example, On a typical horizontal single stage overhung pump (OH2 per API 610), the thrust ball bearings hit bearing housing on one side and hit the end cover of bearing housing on the other side, when the shaft is moved axially. This gap is usually between 0.002"-0.006". My question is, how is this calculated and determined for a new pump during design phase? What happens when it is too high or too little? I am thinking the purpose of this gap is to have some room in case the process fluid temperature goes up and internal parts expand.

 

[quadtracker]

Your correct the gap end play is based on the temperature of the fluid allowing for shaft expansion and too little gap will put too much load on the thrust bearing may cause it to over heat and lose lubrication on the rolling elements (anti-friction type) or score pad faces on kingsbury thrust brg. causing excessive wear. These Gap specifications are suggested by the pump or bearing manufacturer. Too much gap will cause mechanical seal problems and other moving parts such as impeller rubbing stationary casing areas.

 

[jsalas1]

Agreed with quad, in an OH2 pump, it is a function of the deflection due to thrust load, thermal growth, and the tolerance stack up of the components. In multistage BB5 pumps, we normally measure float on the magnitude of .050". The available float dictates the axial setting of the pump and the location of the thrust bearing. Generally we set them "in the middle" of the float, as pumps can experience reverse-thrusting if they operate far right on the curve.