I just bought a house built in 1984 it has PEX plumbing. I need to remove a toilet to install a new floor and I noticed the water supply line to the toilet connects to a water shut off valve that I’ve never seen before. It looks like a PVC bonnet or nut cap thing With a half crescent ring that you turn left or right to turn the water on or off. Are these reliable or should I replace with a quarter turn ball valve. I really don’t want to do anything unnecessary but a PVC shut off valve gives me anxiety as an inexperienced DIY homeowner
With a manifold system, each branch has its own valve, so it is more common to not have a valve at the point of use. If you are more comfortable with an additional valve next to the toilet, you can certainly add a typical 1/4 push-fit shut off valve.
If for some reason the manifold doesn't have individual valves or something is wrong with them, you would simply need to turn off the main water valve to the house so you could remove that straight fitting and replace it with a valve like you would do in an older home.