Fluid handling – Destructible or deformable element controlled – Destructible element
Patent
1997-12-17
1999-08-10
Fox, John
Fluid handling
Destructible or deformable element controlled
Destructible element
137 6823, F16K 1740
Patent
active
059343079
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an overpressure protector to be arranged between two separate spaces for preventing an excessive pressure difference between said spaces, comprising a body portion of single crystal silicon having a front surface and a back surface, a burst flow conduit processed by means of chemical etching and extending through the body portion, and a membrane supported by the front surface of the body portion, covering the burst flow conduit and responding to a pressure difference, said membrane being produced by means of growing prior to etching the burst flow conduit.
It is previously known to use overpressure protectors formed of metal films or films of other materials, as well as spring-loaded overpressure protectors for protecting probes of various kinds or the overall structure. Overpressure protection devices of this kind operate within the range from hundreds of millibars up to thousands of bars. The drawbacks of the conventional overpressure protectors are their costliness and large dimensions, especially when operating at small pressure differences. A spring-loaded overpressure protector placed in a measuring circuit of a control device, for instance, may also cause significant errors to measurement values, and thus even dangerous malfunctions when left leaking.
An overpressure protector for relatively low pressures is known from EP Patent Application 519 585, according to which crossing slits have been cut in a membrane formed of plastic film for dividing the membrane into four independent parts. On the membrane, a metallic conductor strip supporting the parts of the membrane and connected to an electrical indicator circuit is arranged, the portions of said strip supporting the different parts of the membrane cross at the crossing point of the slits in the membrane. A weakened portion at the crossing point of the conductor strip is used for predetermining the pressure at which the conductor strip will break. Breakage of the conductor strip, in turn, is detected by means of the electrical detector circuit.
An overpressure protector for protecting vessels and pipings is known from U.S. Pat. No. 5,279,321. In that protector, a thermoplastic material is used as the membrane responsive to pressure, conductor wires being embedded in said material, thus providing, in addition to reinforcement for the membrane, information on breakage of the membrane.
Membranes of thermoplastic materials, however, cannot be used as overpressure protectors at low pressures, as it is not possible to restrict their breakage or rupturing in a reliable manner to a narrow pressure range.
U.S. Pat. No. 4,275,406 and East German Patent 281 457, again, disclose piezoresistive pressure probes which have the features mentioned in the introduction, and in which a piezoresistor separated by an insulation layer has been grown on the surface of a bending silicon film. These pressure probes are intended for pressure measurement and are based on stretching of the membrane to which the piezoresistors are provided. These pressure probes are not suited for use as an overpressure protector because they have several structures, such as insulation layers that do not allow rupturing or breakage of the membrane structure at small pressure differences or within a predetermined narrow pressure range. In these pressure probes, the invention has been to provide the membrane with certain elastic properties instead of certain rupturing properties, as would be necessary when an overpressure protector is concerned.
The object of the present invention is to provide an overpressure protector which is also suited for use at small pressure differences, and which may be dimensioned to operate within a predetermined pressure range, yet enabling small manufacturing tolerances without the production costs rising too high. This is achieved with an overpressure protector in accordance with the invention, which is characterized in that the membrane is a thin-film, arranged to break when the pressure difference acting across the membrane exceeds a prede
REFERENCES:
patent: 4275406 (1981-06-01), Moller et al.
patent: 4978947 (1990-12-01), Finnegan
patent: 5601109 (1997-02-01), Muddiman
Halonen Eero
Lehto Ari
Orpana Markku
Utriainen Aarne
Fox John
Oy Beamex AB
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