Hi..Critical speed depends on the mass of rotor, distance between two supports & rotor diameter.
Critical speed =4.76x106xD2xF /(KL2)
D = Diameter of shaft in inch
F = select 1 for motors (both side free supports)
L = Distance between two supports in inch
K = Safety factor take 1.2 to 1.5...
Yes, same problem is happened with us also.The root cause was, after pump preventive maintenance for 4 hours, suction valve of the pump opened & pump started immediately. As soon as pump started pump got seized, as there was no enoufg time to accomodate expansions due to hot water.
Other causes...
For newly installed pumps, rise of bearing temperatures for a day or two days is normal,but it should nor cross temperature above 85 degree.If it is persisiting continuosly check the following installation related issues
Check alignment
Ensure pump is operating within rated load
Check...
