Single-seal type control valves such as single-seat valves, high-pressure valves, and single-sealing sleeve valves without balancing orifices require flow direction selection.

     Open and closed flow have advantages and disadvantages. The open-type valve works relatively stable, but has poor self-cleaning performance and tightness, and has a short life. The flow-closed valve has a long life, self-cleaning performance and good sealing performance, but when the diameter of the valve stem is smaller than the diameter of the valve core, the stability is poor. .

     Single seat valve, small flow valve, single seal sleeve valve is usually selected to open, when the flushing or self-cleaning requirements can be selected flow closure. Two-type quick opening characteristics control valve selection flow closed type.