What causes a control valve to hunt?

What causes a control valve to hunt?

The common reasons for control valve hunting are stiction and positioner overshoot. The output response of a valve with stiction is shown in figure1.

What is hunting in steam turbine?

When a turbine can not maintain it’s designed speed, it is termed as hunting in turbine. It is an oscillatory instability. Speed fluctuates from low to high continuously.

What causes steam turbine overspeed?

The steam turbine overspeed event occurs when little or no energy is being consumed by the driven equipment, whether a generator, pump or compressor, and too much steam is provided to steam turbine. All steam turbines have overspeed systems.

What is throttle governing in turbine?

In throttle governing the pressure of steam is reduced at the turbine entry thereby decreasing the availability of energy. The flow rate is controlled using a partially opened steam control valve. The reduction in pressure leads to a throttling process in which the enthalpy of steam remains constant.

What causes pump hunting?

A pump with a drooping curve could rapidly “hunt” or oscillate (fluctuations in pressure and flow resulting in instability) when operated in certain ranges—in other words, it is unstable. Another reason may be that the system resistance curve was not correctly calculated.

What is hunting in control system?

In control system: Basic principles. overcorrect itself, a phenomenon called hunting may occur in which the system first overcorrects itself in one direction and then overcorrects itself in the opposite direction. Because hunting is undesirable, measures are usually taken to correct it.

What causes steam turbine Governer hunting in reaction turbine?

Loss of inlet steam pressure to turbine is one of the cause. of governor hunting in reaction or impulse turbine.

What are the do’s and don’ts of steam turbines?

DO’S & DON’TS OF TURBINE DON’T…. 1. Try to tune the servomotor while m/c in operation. 2. Operate the m/c with the governor hunting. 3. Meddle with the manual knob of I/H converter when m/c is in operation. 4. Raise the speed fast when MOP/ Governor are taking over.

How to regulate the speed of a steam turbine?

1. Try to tune the servomotor while m/c in operation. 2. Operate the m/c with the governor hunting. 3. Meddle with the manual knob of I/H converter when m/c is in operation. 4. Raise the speed fast when MOP/ Governor are taking over. 19. EMERGENCY STOP VALVE 20. OVERSPEED TRIP PIN ASSLY 21. CHANGEOVER VALVE FOR QCNRV 22. TRIP SOLENOID VALVE 23.

Why are there governor valves in STEM turbines?

Hunting of governor valves in a stem turbine assembly could occur due to many factors. The most common types of valve hunting scenarios during operation are :