| 摘要 |
1513775 Fluid-pressure servomotor systems KRAFTWERK UNION AG 18 June 1975 [26 June 1974 26 Sept 1974] 26045/75 Heading G3P [Also in Divisions F2 and G6] A safety valve 8, Figs. 1 and 2, in the live steam line 2 of a nuclear reactor installation, comprises a normally open valve-member 22 controlled by a mechanism sensitive to pressure to rapidly close or almost close the valve when the pressure falls below its normal operating value and to re-open the valve by at most half its fully-open throughflow cross-section if the pressure subsequently rises above a predetermined value in excess of the normal operating value. The valve 8 is located in a safety envelope 3 of the installation together with steam generator 1 and safety valve 13. Outside the envelope the line 2 is associated with a branch 16 having a further safety valve 17 and blow-off regulating valves 20. The valve, Fig. 2, is normally forced fully open by the steam pressure in line 2. However, should the steam-pressure fall, e.g. due to a fracture in the line, sensors would cause hydraulic pressure fluid to be supplied from an accumulator 50 to the space above piston 36 and thereby force the valve-member 22 to close. If, thereafter, the steam-pressure increases to a dangerous level, e.g. because the reactor is not shut-down quickly, it re-opens the valve-member 22 but only by an amount set by an adjustable stop 42. The amount is up to one-half, preferably 30%, of its fully-open flow cross-section. Additionally an adjustable stop 47 may be provided so that when the valve-member 22 is moved towards its closed position it is prevented from completely closing for a short time, e.g. 20 seconds. Alternatively, the final closing movement of the valve may be controlled by a clockwork timing mechanism. In an alternative valve, Fig. 6, the valve-member is actuated by a pair of pistons 116, 121 operating in a common cylinder, the steampressure upstream of the valve-member being communicable with opposite ends of the cylinder via two 2-3 way pressure-responsive valves 126, 128. In the event of damage to the steam system, steam is delivered through valve 128 to act upon piston 116 and close the valve-member 102 as shown. If steam-pressure thereafter rises to about 80 bars, the valve 126 switches to allow the steam to act on piston 121 which, assisted by steam-pressure acting on the valve-member, causes the latter to partially open until piston 121 abuts a stop 122. If the steam-pressure rises further to 88 bars then the valve 128 switches to exhaust the steam from above the piston 116 whereby the valve-member is further opened by an amount determined by stops 142. Complete closure of the valve-member can be effected by delivering compressed air through conduit 134. A pointer 145 and scale 146 indicate the position of the valve-member. Alternative reactor installations incorporating the valve are illustrated in Figs. 3 and 4 (not shown). |
