VTP Down Thrust

[PUMPTESTER]

Does anyone have any experience in measuring down thurst of a VTP type pump during operation? Need to measure on a pump that has a 2400 HP driver and around 100,000 lbs down thrust.

 

[smckennz]

This answer probably isnt much help, but on some heavy equipment, such as mills and pressure vessels with variable inventory, we use load cells with reasonable success.The cell is normally just a strain gauge fastened to an appropriately dimensioned strain member.
On some of the hydro turbines I work on, we use thrust bearing oil jacking systems, which show a residual pressure
while running. It would take some pretty fancy math to deduce the thrust, however. Probably next to impossible with any reasonable level of accuracy.
If you are after temporary readings, the humble portapower cylinder and pressure gauge may be of some use, as the loads you are looking at arent especially high. With a little vibration to break stiction, the pressure X area gives reasonable accuracy. You can calibrate against a test load, and check against the pump deadweight. Obviously you will have to deduct in-service clamping loads, which may have an unacceptable effect on accuracy.
If the pump is mounted on a full contact bedplate, I dunno.
Perhaps remote anchored dial gauges and testweight(s) with assumed stiffness characteristic.
Whats wrong with pressure times discharge area, or are you looking for a transient?
Sorry about the woffle; may encourage a more coherent response.

Cheers

Steve

 

[scalleke]

What type of bearing is taking the thrust?

If it is a tilt pad bearing, do you not have the possibility to drill a hjole in one of the pads and measure pressure?

Best regards,

Scalleke

 

[vanstoja]

Axial thrust measurements on vertical (or horizontal)centrifugal pumps are generally not made during normal operations to my knowledge, but rather are done by pump manufacturers during engineering tests conducted for a particular pump design. Special thrust measuring instruments are generally needed to make in-shop axial thrust load measurements. You should ask the manufacturer of your vertical turbine pumps whether the design was thrust tested in the shop and whether or not the same instrumentation scheme could be applied in the field.
The placement of axial thrust test instrumentation whether load cells, strain gages or piston-type displacement devices depends heavily on the pump and motor driver radial and thrust bearing types and locations. For fluid film bearings in both motor and pump, the upper end of the motor shaft (coupled to the pump shaft) is a plausible place to install some kind of special thrust measurement "dome" having either a fluid activated piston or a strain gage calibrated shaft extension preferrably threaded into the upper end of the motor shaft. If rolling element bearings are used in the motor only, then the pump shaft below the coupling is the preferred thrust measuring site. With rolling element bearings in both pump and motor you would have to measure between the pump bearings on the pump shaft or on the bearing cages, a very difficult, if not impossible, accessibility problem.