Operating positions for 2-port valves might be either shut (closed)
to ensure that no flow whatsoever undergoes, fully open for max flow, or
sometimes partially available to any degree among. Such valves are
already called by various names for example regulating, throttling,
metering, or wafer ball valve .For
example, needle valves have elongated conically-tapered discs and
matching seats for fine flow control. For a lot of valves, there might
be a mechanism to point because when much the valve is open, but on many
occasions other indications of flow rate are engaged, including
separate flow meters.