1. Field of the Invention
The present invention relates to a quick-action flap according to the preamble of claim 1.
2. Discussion of Background
A quick-action fitting together with an intercept valve are placed in steam turbines between the respective reheater and the intermediate pressure turbine. In dependence on the steam data and the type of mounting, the quick-action fitting can be a valve or a flap, preferably a swing flap. The opening of this quick-action fitting occurs hydraulically, closing is initiated via a spring. A swing flap possesses the advantage over a valve that it does not have to deflect the steam and therefore, naturally causes lower flow losses. Furthermore, a swing flap facilitates an advantage arrangement on the intermediate pressure turbine. On the other hand, it is to be noted that a swing flap is subjected to this flow to a greater degree than a valve and thus experiences greater mechanical loading, i.e., in respect of loading, the swing flap structure is highly stressed. If the flow processes in a swing flap are considered, it is to be noted that, during the closing process, the steam pressure on the outflow side of the flap falls and thus the pressure difference at the disk of the flap rises. The entire swing flap is speeded up by the force growing in the flow direction to such an extent that a high, and for the construction of the swing flap, dangerous impact speed of the flap disk against the seating ring in the flap casing occurs. Although the conclusion could be drawn that the construction should be strengthened, with increased mass the kinetic energy would also rise. The impact speed could be reduced by means of a hydraulic brake; however, any deceleration causes braking forces (mass times deceleration) which would greatly load the entire mechanism of the swing flap. It is also to be borne in mind that, even if the mechanism of the flap withstands the loading caused by the braking force, a hydraulic brake designed for a low closing speed would have the great disadvantage for such a flap that the closing speed would be too low in respect of the task and correspondingly the closing time would be too long, not to mention the fact that, in such a constellation, the steam pressure behind the flap would fall even further, which would cause the pressure difference and thus the force on the flap to rise even more.
In addition, the smaller the chambers through which there is flow, between the quick-action flap and the entry to the blading, the quicker the pressure behind the flap disk must drop due to falling accumulation effect, which in turn must have a negative effect on the impact speed of the flap against the seating ring. If this were to be remedied, one would have to provide long lines in each case behind the flap, which alone could provide large accumulation capacities. However, it is part of the definition of the object to place the fittings directly in front of the turbine;
in order to minimize the accumulation capacity, in order to avoid damage to the turbine due to excessive speed of rotation; PA1 because of more favorable use of space.