These are angle way valves , which have adjustable opening pressure and cover the differential pressure range 2-8 bar (29-116 psi)
The valve can be closed manually e.g during plant service and has back seating, enabling the spindle seal to be replaced with the valve still under pressure.
The valves are specially designed to prevent fluttering due to low velocity and/or low density. In consequences it is possible to apply the valves with wide fluctuations in capacity demands ,i.e from maximum performance to part load. A flexible o -ring provides perfect sealing over the seat.