Turn the gate valve’s handwheel and put it in the off position. This lowers the gate into the fluid flow and effectively shuts it off. You can then install the gate valve lock over the handwheel.
The gate valve lock will not lock by itself. You will have to use a personal safety padlock to properly secure the gate valve lock. Gate valve locks come with at least one hole that can accommodate padlocks, making it easy to lock closed. However, while gate valve locks are easy to secure, they are not easy to break into.