When the valve is opened, several turns should remain on the screw rod – why can’t the valve rod be pulled out completely?
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When the valve is opened, several turns should remain on the screw rod – why can’t the valve rod be pulled out completely? What is the reason?
This post was last edited by dqkwb on 2017-4-16 at 19:13. This is to prevent damage to the valve when there are large temperature changes, as the expansion coefficients of the valve stem and the valve body differ; when the valve stem is fully open, it comes into contact with the packing at the dead center, which helps to protect the valve.
After the valve is fully open, turn the handwheel slightly in the opposite direction to ensure a tight fit between the threads, thereby preventing loosening and damage. For straight-stem valves, remember the position of the stem when the valve is fully open and fully closed, to avoid hitting the dead center when it is fully open. It also facilitates checking whether it is functioning properly when fully closed. If the valve seat comes loose, or large debris gets trapped between the valve core seals, the position of the valve stem when the valve is fully closed will change. Damage to the valve sealing surface or the valve handwheel.