temp and press profile of canned motor pump.

[wookiyo]

Reagarding canned motor pump, With the API 685, that says Vendor furnish the temp. and press. profiles of the fluid recirculation flow path through the pump and rotor chamber.

What reasons (purpose) to be checked the temp & press profile ?
and How does the vendor expect the profiles? Use the sensor to catch it at each locaton?

 

[vanstoja]

Motor internal coolant and fluid film bearing lubricant flow in process-liquid-cooled canned motor pumps often employs a so-called auxiliary impeller to circulate the fluid within the motor. That impeller has an NPSH required inlet pressure to prevent fluid cavitation and the fluid circuit between the auxiliary pump inlet and discharge experiences pressure drops throughout the circuit due to restrictions like the can annulus gap which causes the motor rotor to have an axial hydraulic thrust load that may add to or subtract from the impeller axial hydraulic thrust load consequently affecting fluid film thrust bearing loading. One must know the pressure distribution within the motor internal coolant system to assure that thrust bearings are not overloaded and that there is sufficient NPSH for non-cavitating flow in the internal flow system. Temperature gradients exist throughout the internal coolant flowpath and it may be desirable to know the fluid temperature in the vicinity of radial and thrust bearings for assurance of adequate minimum fluid film thicknesses. Determination of internal coolant pressure and temperature profiles in canned motor pumps is generally a difficult analytical problem and the pump supplier would probably measure temperatures and pressures at selected locations in the flowpath for at least one unit of each particular design. Test results can usually be applied to all other units of the same design.

 

[vanstoja]

For an excellent description of API 685 canned motor pump circulation plan options and examples of temperature-pressure plots for determination of vapor pressure margins for motor cooling see Forsberg,R., 2001, "Selecting Sealess Pumps and Circulation Systems for Difficult Pumping Applications", Pumps and Systems Magazine, February, pp. 15-26. The author is from Sundyne Corp. and the pumps illustrated are probably of Sundyne design with hollow rotor shafts for fluid return to the main pump suction or discharge and without external heat exchangers. Rather than thrust bearings, thrust balancing chambers are employed as is common in many small, low power canned motor pumps. High power (more than 15 horsepower)water-cooled canned motor pumps usually have auxiliary impellers, external heat exchangers, separate thrust bearings and a motor-only recirculation system for motor cooling which,after initial filling, does not mix with primary fluid in the main pump.