Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
2003-08-26
2004-10-12
Scherbel, David A. (Department: 3753)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C137S489000, C137S492500, C251S026000, C251S029000
Reexamination Certificate
active
06802339
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to an assembly comprising a fitting and a control device having at least two spring-loaded control valves which each actuate a dedicated control part, for opening the fitting which is opened by pressure relief by means of a control line.
These are fittings which are actuated by their own medium, preferably safety valves for reducing undesirable excess pressures in pressure lines or pressure vessels. The fittings which are actuated by their own medium are opened by a control valve when a critical pressure is reached in a pressure vessel or a pressure line and should be closed by the same control valve when the pressure falls below a critical level. The control valves are spring-loaded. The preferred application area for fittings which are controlled by their own medium in this way is in the primary circuit of nuclear power plants, in particular pressurized-water reactors.
Spring-loaded control valves per se are sufficiently well known in the prior at and are already supplied for these purposes by various companies. A safety valve of this type is known, for example, from German patent DE 455 133. In a control valve arrangement which operates on the relief principle, the system pressure (pressure in the pressure vessel) operates against a spring and an additional magnetic load and opens a pilot valve, downstream of which a nonreturn valve is arranged. As a result, a valve disc of this nonreturn valve is lifted counter to the force of a further spring and lifts a nonreturn valve cone out of its valve seat; as a result, the control line of a pressure-vessel safety valve is opened and the pressure in the control space of the safety valve is relieved. The safety valve opens. It closes again when the system pressure has fallen sufficiently far for the pilot valve and the nonreturn valve to close.
The valve arrangement of a second manufacturer operates on the loading principle. It essentially comprises only a valve with spring and magnetic loads (similar to the abovementioned control valve) and—as soon as a setpoint has been reached—passes a mass flow out of the pressure vessel into the control line, which leads to the control space of the safety valve and presses it open.
The control valve produced by a third manufacturer actuates a plurality of valve bodies which are connected to one another and which are used both to pressurize the control space of the safety valve (closure of the safety valve) and to relieve the pressure on this control room (opening).
Spring-loaded control valves have a relatively high probability, which does not correspond to that of the main fitting, of failing to close. The inability of a spring-loaded control valve to close is 10
−2
/demand, i.e. the is probability is that the valve will fail to close once in only 100 demands. By contrast, the probability that the main fitting will fail to close is 10
−4
/demand. However, the relatively high probability that the control valve will fail to close means that the low probability of the main fitting failing to close has no effect.
Even with a relatively recent internal development of a control valve, the probability of the valve failing to close is still not entirely satisfactory. In this device, a pressure-displacement converter is connected to a control valve, the pressure-displacement converter being mechanically connected to a filling cone and to a relief cone, and both cones being moved in the same direction. In a first step, the filling cone can be moved onto a seat by a relatively low force, with the result that a control line of the control valve is blocked. In a second step, only a relatively high force is able to lift the relief cone off its seat, with the result that the control line of the control part is connected to a line which is open to atmosphere and the pressure on the safety valve is relieved (i.e. the valve is opened).
Theoretical calculations revealed that the probability of control valves failing to close can be reduced by connecting a combination of these control valves in series. By way of example, connecting two valves in series would lead to a probability of (10
−2
)
2
/demand, i.e. of 10
−4
per demand, of failure to close. A closure failure probability of this level is very similar to the closure failure probability of the main fitting.
Engine control valves which are connected in series are known in the prior art. They are in some cases also used in combination with a primary circuit safety valve. However, since these engine control valves operate on the working principle, according to the relevant safety regulations they should not be used on their own. For example, German Regulations TRD 421 state that if there are three safety valves protecting a pressure vessel, only one safety valve may have control valves which operate on the working principle. The other two safety valves which are present must have control devices which operate on the static principle.
The only known series-connected control valves which operate on the static principle are solenoid valves. However, these valves cannot be used in the primary circuit of a nuclear power plant, since they may open in the event of a voltage loss.
Known spring-loaded control valves, as described in the introduction, for example, cannot be connected in series on account of their design. For this reason, spring-loaded control valves are currently generally only used in single control valve arrangements in the primary circuit, i.e. even if a plurality of valves are provided, ultimately only a single control part which applies or relieves the load on the safety valve is present in the control line of the safety valve. The relatively high probability of the valve failing to close is accepted as inevitable.
SUMMARY OF THE INVENTION
The object of the invention is to provide a spring-loaded tandem control valve which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which specifies a control device for a fitting which, although it may contain loading springs, nevertheless leads to a low probability of the fitting failing to close.
With the above and other objects in view there is provided, in accordance with the invention, an assembly, comprising:
a fitting communicating with a control line and being opened by pressure relief via the control line;
a control device having at least two spring-loaded control valves each actuating a dedicated control part, for opening the fitting by pressure relief via the control line;
wherein the control parts are arranged at the control line and are configured to open the fitting only when all the control is parts are in a position in which the load on the fitting is relieved, and the control parts closing the fitting as soon as a single one of the control parts is in a position imposing a load on the fitting.
In an alternative embodiment, there is provided, in accordance with the invention, an assembly, comprising:
a fitting communicating with a control line and being opened by pressure imposed via the control line;
a control device having at least two spring-loaded control valves each actuating a dedicated control part, for opening the fitting by pressure imposed via the control line;
wherein the control parts are arranged at the control line and are configured to open the fitting only when all the control parts are in a position in which a load is imposed on the fitting, and the control parts closing the fitting as soon as a single one of the control parts is in a position relieving the load on the fitting.
In other words, the invention specifies a control device by means of which a fitting, in order to be opened, can either be relieved or loaded by means of a control line, i.e. the fitting can operate either according to the relief principle or according to the loading principle. The control device may also operate without additional electromagnetic or other loads.
To achieve the above and other objects of the invention, the control device has at le
Conrads Hermann-Josef
Laurer Erwin
Model Jürgen
Framatome ANP GmbH
Greenberg Laurence A.
Krishnamurthy Ramesh
Locher Ralph E.
Scherbel David A.
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