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How does a EHC valve works using Mark VI controls VSVO/TSVO boards?
Bharat,
This <b>seemingly</b> simple question does <b>not</b> have a simple answer.
You need to be more specific about what it is you want to know. There are too many components and elements to provide you with a good answer to the question you asked.
An electro-hydraulically controlled valve requires hydraulic pressure and flow to open/close the valve (or IGVs for a GE-design heavy duty gas turbine). The flow of hydraulic pressure to the hydraulic actuator which opens/closes the valve is controlled by an electro-hydraulic servo-valve, which converts an electrical signal (usually DC milliamps) to a flow of hydraulic oil at pressure to/from the hydraulic actuator. When there is a flow of hydraulic oil to/from the actuator the actuator will move. When there is no oil flowing to/from the actuator, the actuator--and the valve (or IGVs)--the actuator opens/closes will remain at some position.
Some hydraulic actuators are single-acting, and hydraulic pressure is used to open the valve--usually against spring pressure (in most cases the spring is trying to close the valve and hydraulic pressure/flow is required to open the valve). Most hydraulically-operated devices will remain at a desired open position when the flow of hydraulic oil to the actuator is reduced to zero. When hydraulic oil is ported away from the actuator, the spring will then close the valve (usually).
Some hydraulic actuators (such as are used on IGVs) are double-acting, meaning that flow to one side of the piston of the actuator is required to open the valve, and to close the valve flow has to be directed to the other side of the piston.
In essence, the Mark VI determines a reference for the valve (or IGVs) in the application code ("sequencing" or "logic"). The reference could be position, or flow-rate, or angle, etc., for the electro-hydraulically controlled device (valve or IGVs, etc.).
That reference is compared to a feedback (position, or flow-rate, or angle, etc.) and sent to the VSVO, which is connected to the TSVO, which is a terminal board to which the electro-hydraulic servo-valve is connected. The electro-hydraulic servo-valve controls the flow of hydraulic oil to/from the device's actuator.
Sometimes the feedback device(s) are connected to the TSVO, and sometimes they are not. When the feedback is equal to the reference, the output essentially goes to "zero". But, most servo-valves requires a small current to keep the flow of hydraulic oil at zero to keep the feedback equal to the reference.
Sometimes the comparison of the feedback and the reference are done by the application code running in the Mark VI. Sometimes the comparison is done by regulator software running on the VSVO). It depends on the application (type of EHC device) and GE's control philosophy regarding that device.
That is a very general and broad explanation. Sometimes the current is bipolar (meaning it goes positive to shut off the flow of fuel or air or steam), and it goes negative to increase the flow of fuel or air or steam. Sometimes, the current is just linear, and increases (goes more positive) when flow or position needs to increase, and decreases (gets less positive) when flow or position needs to decrease. It depends on the type of actuator used and, again, GE's control philosophy.
You can look up single-acting and double-acting actuators on the world wide web using your preferred search engine. You can also look up electro-hydraulic servo-valves on the world wide web.
If you want a better answer, you need to provide a <b>***LOT***</b> more information about the specific "EHC valve" and the application (gas turbine; steam turbine; hydro turbine; etc.). If you are experiencing some particular issues, you need to tell us what they are.
I hope this helps!
This <b>seemingly</b> simple question does <b>not</b> have a simple answer.
You need to be more specific about what it is you want to know. There are too many components and elements to provide you with a good answer to the question you asked.
An electro-hydraulically controlled valve requires hydraulic pressure and flow to open/close the valve (or IGVs for a GE-design heavy duty gas turbine). The flow of hydraulic pressure to the hydraulic actuator which opens/closes the valve is controlled by an electro-hydraulic servo-valve, which converts an electrical signal (usually DC milliamps) to a flow of hydraulic oil at pressure to/from the hydraulic actuator. When there is a flow of hydraulic oil to/from the actuator the actuator will move. When there is no oil flowing to/from the actuator, the actuator--and the valve (or IGVs)--the actuator opens/closes will remain at some position.
Some hydraulic actuators are single-acting, and hydraulic pressure is used to open the valve--usually against spring pressure (in most cases the spring is trying to close the valve and hydraulic pressure/flow is required to open the valve). Most hydraulically-operated devices will remain at a desired open position when the flow of hydraulic oil to the actuator is reduced to zero. When hydraulic oil is ported away from the actuator, the spring will then close the valve (usually).
Some hydraulic actuators (such as are used on IGVs) are double-acting, meaning that flow to one side of the piston of the actuator is required to open the valve, and to close the valve flow has to be directed to the other side of the piston.
In essence, the Mark VI determines a reference for the valve (or IGVs) in the application code ("sequencing" or "logic"). The reference could be position, or flow-rate, or angle, etc., for the electro-hydraulically controlled device (valve or IGVs, etc.).
That reference is compared to a feedback (position, or flow-rate, or angle, etc.) and sent to the VSVO, which is connected to the TSVO, which is a terminal board to which the electro-hydraulic servo-valve is connected. The electro-hydraulic servo-valve controls the flow of hydraulic oil to/from the device's actuator.
Sometimes the feedback device(s) are connected to the TSVO, and sometimes they are not. When the feedback is equal to the reference, the output essentially goes to "zero". But, most servo-valves requires a small current to keep the flow of hydraulic oil at zero to keep the feedback equal to the reference.
Sometimes the comparison of the feedback and the reference are done by the application code running in the Mark VI. Sometimes the comparison is done by regulator software running on the VSVO). It depends on the application (type of EHC device) and GE's control philosophy regarding that device.
That is a very general and broad explanation. Sometimes the current is bipolar (meaning it goes positive to shut off the flow of fuel or air or steam), and it goes negative to increase the flow of fuel or air or steam. Sometimes, the current is just linear, and increases (goes more positive) when flow or position needs to increase, and decreases (gets less positive) when flow or position needs to decrease. It depends on the type of actuator used and, again, GE's control philosophy.
You can look up single-acting and double-acting actuators on the world wide web using your preferred search engine. You can also look up electro-hydraulic servo-valves on the world wide web.
If you want a better answer, you need to provide a <b>***LOT***</b> more information about the specific "EHC valve" and the application (gas turbine; steam turbine; hydro turbine; etc.). If you are experiencing some particular issues, you need to tell us what they are.
I hope this helps!
