Low pressure burst disk sensor

Abstract: An ultra low pressure flow sensor consisting of a support gasket (12) defining a flow way and having a thin, pliable membrane (14) extending thereacross with right angle slits (26,28) formed totally across the flow way portion. An electrical conductor strip (16) is then bonded across each pair of opposing quadrants (32,36 and 34,38) of the membrane in continuous connection to an electrical indicator circuit. The conductor strip across each pair of membranes is centrally notched (at 54,56) to a preselected depth of cut thereby to control the flow pressure break strength.

Description: The present invention relates generally to rupturable burst disk sensors for low pressure applications. Safety pressure relief apparatus of the rupturable type has often been utilized in applications where continual indication of the operating condition of the apparatus is desirable or necessary. Fluid pressure rupturable apparatus generally includes one or more rupture disks sealingly clamped between annular supporting members or heads which are then bolted together or suitably clamped between bolted flanges in a conduit or flow line. Indication of the rupture disk failure may not be given other than by the resulting change in the vessel or flow line pressure. In some situations, the pressure condition of the system may not change appreciably and the failure of a rupture disk could go unnoticed for a considerable period of time. Known monitoring devices are for example, shown in US-A-3770918 which is directed to a monitoring device for a reversible rupture disk that includes electric probes positioned behind the rupture disk. US-A-4342988 is directed to a rupture disk alarm system that includes a signal carrying means in contacting relationship with a rupture disk. US-A-4408194 is directed to a rupture disk monitor apparatus that includes capacitor means positioned in sensing relationship to a rupture disk. US-A-4978947 is directed to a device (according to the preamble of claim 1) for sensing flow in flow line, comprising an insulative support member defining a central flow way adapted to be seated between inlet and outlet head means which define a central flow way and are in sealed retention in alignment with said flow line; an insulative membrane supported on said support member and extending across said central flow way and having at least one slit formed therein; a flexible strip of electrical conductor extending across the membrane, first and second ends of said conductor being connectable to means for providing an indication that the conductor has broken. While such rupture disk monitoring devices and systems have achieved varying degrees of success, they still have some shortcomings. Specifically, it is a problem to obtain a reliable break limit as well as an indication of rupture disk failure in very low flow pressure situations. Accordingly, the present invention is characterised in that said slits are formed such that at least two membrane petals normally extend across the central flow way; in that said electrical conductor is bonded across said membrane petals and in that said electrical conductor has a weakened portion with predetermined break strength disposed over the at least one slit. Such a burst disk sensor is operable in very low pressure systems. The burst disk sensor may be employed in such as a relief flow line adjacent a low pressure rupturable disk or the like which is clamped, normally upstream of the sensor, across the flow line by means of inlet and outlet head members. The petals are maintained closed across the flow way by means of the one or more conductors bonded thereon and continuous thereacross. Thus, the resistance of the membrane is eliminated from the break strength equation as only the conductor minimum break point senses the flow of fluid and consequent flow pressure presence, e.g., as a result of the upstream rupture of a rupture disk. An electrical indication and/or alarm may then be actuated in response to the conductor breakage or open circuit. In order that the present invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings in which:- Figure 1 is an exploded perspective view of one embodiment of burst disk sensor according to the invention, with an upper gasket; Figure 2 is a top plan view of the burst disk sensor of Figure 1 in assembled form; and Figure 3 is a view of the burst disk sensor in section as installed in a flow way shown in cutaway with block diagram representation of indicator circuitry. The illustrated ultra low pressure burst disk sensor 10 consists of a support gasket 12, a plastic membrane 14 and a conductor strip 16 bonded thereon. An upper sealing gasket 18 is then employed in most applications; however, the upper gasket 18 is entirely for sealing purposes and contributes nothing to the burst disk sensor operation. The support gasket 12 has an outer and inner circumferences 20 and 22, the diameter of the inner circumference 22 generally conforming to the diameter of the conduit flow way wherein the sensor 12 will be seated. Gasket 12 is formed of a suitable gasket material on the order of 4.76 mm thickness and it includes a radially aligned rectangular tab 24 which serves to support a coupling element described below. The support gasket 12 may be formed from any number of electrically insulating gasket materials. The membrane 14 is formed of a suitable plastic film of selected thickness consonant with stiffness requirements, e.g., 0.076 mm film. Any of various plastic materials may be used so long as they are resistant to high temperature deformation or deterioration and are corrosion resistant. Preferred materials are polyesters, polyamides, polyolefins or the like. The membrane 14 includes crossed, 90° slits 26 and 28, each of which extends across the internal flow way area or internal diameter 22 of support gasket 12. The slits 26 and 28 cross at centre point 30 to define four quadrature arrayed petals 32,34,36 and 38 which form free and independent flaps. Stiffening for pressure interference of the petals 32-38 is then provided by the conductor strip 16 which is bonded to membrane 14 in a generally figure-of-eight (8) configuration. The conductor strip 16 includes two crossed conductor strip portions 40 and 42, a folded interconnection 44 on one rim of membrane 14 and conductor strip portions 46 and 48 extending outward to form contactor strips 50 and 52, these portions being bonded onto support gasket tab 24. The cross strip portions 40 and 42 are each formed with a respective central notch 54 and 56, the depth of which determines the specified break strength for the burst disk sensor. The notches 54 and 56 are aligned over the centre point 30 of membrane 14, and the conductor strip 16 is selected to be a conductive metallic material of sufficient thickness to maintain petals 32-38 rigid in low pressure blockage of the flow way, yet thin enough that it can be selectively notched for very low flow pressure breakage. Such metallic strip material may consist of silver, nickel, chromium, iron, copper or alloys, and a preferred material is a foil strip of nickel-chromium alloy sold under the trade mark INCONEL. Referring to Figure 3, the burst disk sensor 10 may be employed adjacent a rupturable disk 60 of predetermined safety pressure relief. The rupture disk 60 may be a type which opens at pressures as low as 38.1 mm water column, i.e., 0.735 bar differential. Thus, the rupture disk 60 will open fully when subjected to the proper burst pressure albeit a very low pressure, and the low pressure burst disk sensor 10 will fail at the conductor strip notches, either one or both notches 54 and 56, to provide output indication. Fluid pressure is directed as shown by the arrow 62 through conduit 64, which is connected to a clampable flange member 66 which forms an inlet head 68 that provides an annular seating surface 70 for receiving an inlet gasket 72, the rupture disk 60 and an outlet gasket 74. A separator ring 76 is then seated on gasket 74 to provide an annular face 78 for receiving the burst disk sensor 10, which is positioned with support gasket 12 adjacent annular face 78 and supporting the membrane 14 with conductor strips 16 and upper gasket 18 adjacent an annular face 80 of an outlet flange 82 that forms an outlet head 84 in continued connection to conduit 64. A plurality of circumferentially spaced secure bolts 85 connect flanges 82 and 66. An electrical connector 86 connects to the tab 12 and contactor strips 50 and 52 to provide electrical connection via leads 88 and 90 to an alarm and indicator circuitry, including an electric current source 92, a relay 94 and a rupture indicator 96. The electric current source 92 is returned through relay 94 to provide a holding current for continuing rupture indication. In operation, the burst disk sensor 10 responds to a failure of rupture disk 60 to provide an indication when either one or both of conductor strips portions 40 and 42 are broken or opened electrically. Since the conductor strip portions 40 and 42 are securely bonded to the membrane petals 32,34,36 and 38, the full fluid flow force or pressure from the total area within the flow way is applied to the conductor strip 16. No resistance can be attributed to the membrane 14 since it is cross-slit across the entire flow way. The notches 54 and 56 in respective conductor strip portions 40 and 42 are pre-cut to a depth adjusting the break strength of the respective conductor strips thereby to select a breakpoint requiring very little fluid flow pressure. In this way, an ultra low burst disk sensor is provided, one which operates reliably and opens as low as 0.0034 bar gauge. It is also contemplated that a strip type burst disk sensor could be provided in which a membrane or plastic film strip is extended across a flow way while being slit at a central point. One or more notched conductor strips, bonded to the strip, would maintain the strip in position transverse of the flow way until venting of sufficient process fluid to exceed the conductor break strength. In effect, the insulative membrane and the conductor strip work in concert to form a composite rupture membrane as the conductor strip itself actually becomes a part of the rupture member. The burst disk sensor of the invention has the capability of providing indication of disk failures at ultra low system pressures, which is of great benefit in low pressure applications wherein the operation does not enjoy the destructive benefits of a sonic shock wave at the instant of rupture, and gentle flow pressures can be sensed to cause a gauged breakage for the purpose of providing an alarm or other visual indication. The device is relatively simple and reliable and can be constructed of a number of different configurations, plastic films, conductive strip materials and the like.

Claims: A device for sensing flow in flow line, comprising an insulative support member (12) defining a central flow way adapted to be seated between inlet and outlet head means (68,76,84) which define a central flow way and are in sealed retention in alignment with said flow line (64); an insulative membrane (14) supported on said support member and extending across said central flow way and having at least one slit (26,28) formed therein; a flexible strip (16) of electrical conductor extending across the membrane, first and second ends (50,52) of said conductor being connectable to means (86-96) for providing an indication that the conductor has broken, characterised in that said slits are formed such that at least two membrane petals (32,34,36,38) normally extend across the central flow way; in that said electrical conductor is bonded across said membrane petals and in that said electrical conductor has a weakened portion (54,56) with predetermined break strength disposed over the at least one slit. A device according to claim 1, characterised in that said insulative membrane (14) has two 90° oriented slits (26,28) formed through the central flow way, thereby to form a quadrature array of membrane petals (32,34,36,38). A device according to claim 2, characterised in that said flexible strip of conductor (16) is bonded to each of opposing pairs (32,36 and 34,38) of the quadrature array of membrane petals to form a crossed pattern (40,42) of conductors, and each conductor weakened portion (54,56) overlies the respective two slits (26,28) formed across said membrane. A device according to claim 3, characterised in that it is disposed downstream from a low pressure responsive rupture disk (60). A device according to any preceding claim, characterised in that a gasket means (12,18) define said central flow way and are secured between the insulative membrane and said outlet head.

Inventors: ELLIS JIM E, ROOKER MITCHEL L, TOMASKO JOHN A, ELLIS, JIM E., ROOKER, MITCHEL L., TOMASKO, JOHN A.
Applicants: BS & B SAFETY SYSTEMS INC, BS & B SAFETY SYSTEMS, INC.
Application year: 1992
Main classification: F16K17
IPC codes: F16K37, F16K17, G01F1