Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Patent
1998-10-27
2000-08-15
Michalsky, Gerald A.
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
137907, 454 61, G05D 701
Patent
active
061020702
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to a safety valve or a containment.
2. Background Art
A glove box is a closed containment that makes it possible to handle dangerous items such as chemicals or radioactive materials. In order to protect the operator, gloves boxes are maintained in a permanent state of negative pressure in order to avoid leakage of dangerous materials to the exterior of the glove box. The negative pressure inside glove boxes is regulated such as to remain between an upper and a lower threshold.
A containment generally comprises two ventilation circuits: extraction in the event of a leak in the confinement; the aim of this additional extraction is to ensure that the leak in the confinement is met by a dynamic confinement by forcing air into the confinement at a velocity of the order of 0.5 m/s.
The valve of the invention is designed to be fitted to this type of safety circuit.
A safety circuit is designed to limit variations in absolute pressure caused inside a containment in the event of:
In the event of a rapid, significant variation in relation to the reference pressure, and depending on the design and state of the ventilation system parameters, the safety circuit may also ensure all or part of the safety flow rate.
The ON/OFF circuit contributes to attaining the safety throughput rate in the event of an unexpected breach of the containment, if, for example, a glove breaks off.
While the gloves are being used under normal conditions this type of circuit should never open, even fleetingly, in order to preserve the filters. It must instantaneously ensure the safety throughput rate in the event of a leak.
Safety circuits of the known art may be fitted with the standard valve shown in FIG. 1, fitted with a lightweight piston to limit unwanted opening while the gloves are being used.
This type of valve 10 comprises: opening into the main branch 11, valve; depending on the operating mode required, the piston may be weighted or not,
A containment under negative pressure 16, for example a glove box, is connected to an extraction collector 17 via piping 18 comprising a filter 19. Valve 10 described above is incorporated into the said piping. The upper section 20 of the main branch is connected to containment 16 via piping 18 and the lower section 21 of the main branch is subject to a reference pressure, for example atmospheric pressure, via a filter 22. Secondary branch 12 is connected to extraction collector 17.
The valve 10 controls the regulation of negative pressure above piston 13. If the negative pressure in the containment is reduced, the piston drops and connects the containment to extraction collector 17 until normal negative pressure is re-established. If the negative pressure of the containment rises the opposite happens. For a given negative pressure the extraction throughput rate required inside the containment is obtained by adjusting the internal weighting of the piston.
However, when the containment is breached piston 13 descends but does not travel its entire course, being too light; this limits the rate extracted. When, however, a high safety throughput rate is required several valves must be connected in parallel.
The balance of piston 13 is the result of the equilibrium between two directly opposed vertical forces: resulting from the pressure difference on the bearing surfaces of the piston.
The lower bearing surface of the piston is in contact with the ambient air and is subject to no force. The negative pressure of the system downstream of the valve has equal effects on the top and bottom of the piston and the resultant is therefore nil.
In normal operation, therefore, the negative pressure in containment 16 is applied to the upper bearing surface. The resultant is greater than the weight of piston 13 that thus remains in the upper position with a nil safety flow rate. When, however, the gloves are used the negative pressure inside the containment 16 varies such that when the resultant is less than or equal to the weight of piston 13 there i
Alnet Remy
Busin Michel
Compagnie Generale des Matieres Nucleaires
Michalsky Gerald A.
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