In this article, I will explain to you about hand jack and vibration loop used while working with the control valve. Those who have work with it have a really good idea about it but those who don't know anything about this then article is for them.
HAND JACK :
As per the name, hand jack means something which is hand operated need to use when a valve with a main actuating supply fails.
Some pneumatic valve actuator comes with hand jack which needs to position manually in the event of the air supply failure.
So, the handwheel is nothing but a rotating wheel which comes with a valve in regard to manual operation.
Following is the image of the hand jack which you can see. Here, three manual valves are used and out of the two are block valve. Mostly gate valve is used to block the flow and a second one is the bypass valve.
If the main control valve fails then using block valve you can block the flow and allow flow to pass through the bypass valve as you can see the direction of the flow.
In such a condition it is very important in many processes as the valve can be failed due to the long run of the service and with such combination of a valve, you can have time to repair valve without interruption.
You can identify a state of the valve from images by seeing a stem position. As you can see that in both block valve stem is clearly visible means the valve is open and in the bypass valve stem is not visible indicating close valve position.
VIBRATION LOOP :
To minimize strain on the metal tube from the vibration, the vibration loop is used in the control valve.
To make vibration loop you can bend the pipe which you can clearly see in the above-mentioned image. The vibration loop exists in between a valve actuator and an air supply pipe.
The vibration occurs in liquid due to cavitation and flashing but in gas service vibration occurs due to choked flow as cavitation and flashing never occur in gas service.
Vibration in the long pipeline also occur due to mechanical damage or due to any type of shock happen in the pipeline.
To detect such vibration we can use accelerometer which detects the rate of change in velocity, also we can measure displacement to trigger safety interlocks.
Hope you may have a better idea on vibration loop and hand jack. If you like this article then please do share among your friends.