Turbine Hunting 1000 KW Backpressure

Any one or several of many different causes can cause swinging load and or twirling valve stems.

Not knowing the design or the manufacturer of the turbine/valve I cannot comment too much about that other than to suggest that if the lock nut on the stem is not tight or there is no anti-rotation pin, lever, plate or other provision to stop the rotation, valve plugs are prone to spin in the housing. Whether this is a serious problem or not is a matter of the design of the valve trim, linkage (if any), coupling and actuator.

The swinging is another matter which could be due to valve problems, usually sticking or hysteresis which causes lost motion in the valve control network.

If the linkage between the actuator and the valve stem is loose and wondering about, this also causes sloppy control and frequently causes swinging.

If there is a hydraulic or pneumatic actuator with bad piston seals, gunked up positioner, or something else flailing about or bound up, this can also cause swinging.

It could also be due to tuning of the speed, back pressure or load controller or some multiple of them.

Is this a synchronous or induction generator?

What kind of valve actuator is being used?

What Kind of Governor?

Does the swing stop if the back pressure controller is temporarily disabled?

???

It is possible that this machine is not even the one originating the swing. Another machine on the same intake or exhaust header or even a pressure reducing valve on one or the other header could cause this.

TT3