In this article, I will cover hand jack and vibration loop in brief. Those who have work with it have a really good idea about it but those who don't have any about this, this article belongs to them.
HAND JACK :
Some pneumatic valve actuator comes with manually position the valve 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 you can see. Here, 3 manual valves are used, out of the two are block valve and mostly gate valve is used to block the flow and one is bypass valve.
If the main control valve fails using block valve you can block the flow and allow flow to pass through the bypass valve as you can show the direction of the flow.
Such a condition is very important in many processes as the valve can be failed due to the long run of the service and with such combination, you have time to repair valve without interruption.
You can identify a valve from images by 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.
To make vibration loop you can bent the pipe as you can clearly see in the above figure, the vibration loop exists in between valve actuator and air supply pipe.
Vibration occur 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.