valves are very similar to a faucet style knob in your bathroom or
the garden hose spigot outside. These type of valves are not a common
pool valve on new installations, but were the only valve used on pools
over thirty years ago.
These valves are commonly
found to be leaking air and or water. You can repack the valve using
plumber's tape, if the valve is leaking air or water from under the
nut. These valves may be easier to replace with something of a plastic
variety if they leak or if the handle just spins and spins....
A common problem with gate valves is that the paddle will eventually deteriorate with years of water and harsh chemistry. If you find a gate valve unable to close, it may be best to replace the valve. Connecting brass and pvc is a difficult challenge, leaks are the usual result.