Pressure reducing valve with quick opening function

Installation:

Reducing station with quick-opening devices are used to safeguard the steam network downstream of the turbine. They are arranged as a by-pass to the turbine and let off to the steam network in the shortest possible time the steam volume upstream of the machine in the event of quick –action shut-down of the turbine. Since the steam is taken over by the reducing station within the space of 1 second, pressure or temperature variations are excluded. 

Operation:

The reducing station with quick-action opening is equipped with two separate drives, A and B. Drive A is used for regulating the valve whereas drive B is used as a locking device respectively as a release of the valve spindle. 

The compressed air drive B and the spring cylinder are used for fast opening of the valve. If it is intended to regulate by means of the reducing station, the compressed air drive B is pressure-released to start with. This is effected via the two 3-way solenoid valves arranged at the side of the compressed air cylinder. They permit passage from the compressed air cylinder to atmosphere. Using regulating drive A the reducing station can be operated in the same way as a standard reducing valve. After completion of the regulating process the reducing station is closed and the solenoid valves at compressed air cylinder B are closed against atmosphere. Now compressed air is led into the compressed air cylinder B with pressure. This results in blocking the regulating spindle, by pressing the latter onto the valve seat. Regulating drive A remains functional, i.e. the load states arriving from the turbine are imposed on it via a load dependent controlled variable. Since the regulating spindle is kept in closed position by the compressed air cylinder B, it is necessary to store the path for the regulating drive A in a spring. The stored spring path corresponds exactly to the valve stroke which would have been executed by the regulating spindle in the normal way. 
In the event of fast opening the pressure in the compressed air cylinder is let off to atmosphere by an appropriate circuit on the solenoid valves. The spring in the spring cylinder, which is in a state of more or less pronounced compression lifts the regulating spindle off the valve seat. In doing so, the regulating spindle opens, within less than one second, to the pre-set spindle stroke, which was imposed on the reducing station by the regulating drive A at the time of switching off the turbine. Following the fast opening, further control can be exerted immediately by means of the regulating drive A.