Here is an overview of how a typical stainless valve works:
Construction:
Stainless valves have a valve body made of stainless steel or alloys like 316L that provide corrosion resistance.
Seats:
There are valve seats, usually made of PTFE (Teflon) or similar material, that create seals.
Stem:
The valve stem transmits motion from the actuator (handwheel or motor) to open/close the valve.
Ball or Disc:
Located inside the valve body, the ball or disc rotates or slides to block or allow flow.
Packing/Seals:
Packing rings or O-rings around the stem prevent leaks between the moving stem and fixed body.
Operation:
Actuators turn the valve stem to rotate the ball/disc and shift from the open (perpendicular to flow) to closed (parallel to flow) position.
Sealing:
In the closed position, the ball/disc presses firmly on valve seats, compressing the seat material to form a tight seal.
Flow Control:
Partially opening the valve throttles flow through the partial opening between ball/disc and seats.
Stainless materials and a simplistic design allow these valves to withstand corrosive fluids in industries like chemicals, oil/gas, mining and more. Proper maintenance keeps them sealing effectively for years.