Which valves need to choose the flow direction and how to choose?

Single-sealed regulator valves such as single-seat valves, high-pressure valves, and single-sealed sleeve valves without balance holes require choosing flow direction.

There are advantages and disadvantages to flow-to-open type and flow-to-close type. The flow-to-open valve works stably, but the self-cleaning performance and the sealing performance are poor, and the service life is short. The flow-to-close valve has a long service life, self-cleaning performance and good sealing performance, but the stability is poor when the valve stem diameter is smaller than the spool diameter. 

Single-seat valves, small-flow valves, and single-seal sleeve valves are usually selected for flow-to-open. When flushing is strong or self-cleaning is required, flow closure is optional. The two-position quick-opening characteristic regulating valve is selected forflow-to-close type.