what is angel valve
Suppose you want to connect a washing machine to the building plumbing, and plumbing has already been created. If the lid is used at the end of the pipe, you have to cut off the water of the entire building to connect the washing machine hoses, and then connect the hoses. But if you use a piston valve at the end of the plumbing, you can easily connect the hoses and open the water.
You can also adjust the pressure of the outlet water from the piston valve and use it for a long time without changing it.