Usually by handwheel.  Other options possible on request (cylinder, etc.)

These valves work on the piston valve principle. Adapting this to small diameters means that areas of build-up can be kept to a minimum while keeping the decrusting effect when the piston withdraws. The piston movement dislodges any solidified chemicals that might have penetrated into the valve body.

Flanged, tapped half-sleeve, socket-weld, or "wafer" sandwiched between pipe flanges.

Integral steam jacket, flush or projecting piston, metal/metal seat, etc.