Pneumatic angle seat valves are valves where the valve seat is placed at an angle. A spindle is moved in a linear motion by an air-operated piston to move the seal towards or away from the valve seat. This seal is usually PTFE (teflon) and the valve housing is usually brass or stainless steel. Due to the Y-shape the medium can flow through relatively easily (few bends). As a result, these valves have a high flow capacity and Kv value in comparison with vertical globe valves. Angle seat valves are reliable, require low maintenance and are characterized by a long lifespan with millions of cycles. They can be applied with gases, vacuum or (viscous) liquids and seal in two directions. Other names for these valves are valve shut-off valve, Y-valves or angle seat piston valves. The valve generally closes in the same direction as the flow direction. There are special versions where the valve closes against the flow direction, in order to reduce the risk of water hammer.