(1) The pressure point should be located in the proper position of the pressure regulating valve. The pressure should be greater than 2 times the diameter of the pipe before the valve, and the pressure should be greater than 6 times the diameter of the pipe after the valve.

 (2) Self-operated valves can be smaller than pipe diameter according to calculation, while globe valves, cut-off ball valves, bypass valves and filters can not be smaller than pipe diameter.

Source: Baidu Encyclopedia