VACUUM RELIEF UNIT WITH MEANS PREVENTING THE EFFECTS OF AN ACCIDENT

Abstract: The invention relates to a vacuum relief unit for pressure equalisation between the ambient atmosphere and a tank in a tanker, wherein the vacuum relief unit comprises: a valve housing (10) with a first opening (12), whereby the valve housing (10) is able to communicate with the tank, and a second opening (24) with a seat (30) for a valve body (40) that is configured for being conveyable into the valve housing (10) to permit inflow of air to the tank; and a mechanism (100) configured for being able to prevent passage of seawater through the valve housing (10) in case of an accident, wherein the tanker is at least partially immersed into seawater, which mechansim (100) features a first movable part (160) that is arranged outside the valve housing (10) and whose movement can be controlled by the liquid pressure of the sea water; a second movable part (150) that can be advanced within the valve housing (10) and that is movably coupled to the first movable part (160). The invention is characterised in that the second movable part (150) is configured for being conveyable to abut on the valve body (40) by an increasing movement of the first movable part (160) to cause the valve body (40) to return to its abutment on the seat (30).

Description: Vacuum relief unit with means preventing the effects of an accident The present invention relates to an improved vacuum relief unit for pressure equalisation between the ambient atmosphere and a tank in a tanker, wherein the vacuum relief unit comprises: a) a valve housing with a first opening, whereby the valve housing is able to communicate with the tank, and a second opening with a seat for a valve body that is configured for being conveyable into the valve housing to allow inflow of air into the tank; and b) a mechanism configured for preventing the passage of water through the valve housing in case of an accident when the tanker is at least partially immersed into seawater, said mechanism having a first movable part that is arranged outside the valve housing and whose movement can be controlled by the liquid pressure of the seawater, and a second movable part that can be advanced within the valve housing and is movably coupled to the first movable part. The term "movably coupled" as used in this context is intended to designate that a movement of the first part is transmitted to a movement of the second part. An important field of application for vacuum relief units of this type is use onboard tankers for oil products and chemicals. Vacuum relief units are used in tankers for ensuring a pressure equalisation when the tank of the vessel is emptied and to serve as safety measure in case of erroneous operation of the tanker's filling plant, eg as described more specifically in US patent No. 5,607,001. US patent No. 5,607,001 specifically teaches a vacuum relief unit, shown by the reference numeral 50. The vacuum relief unit has a valve body that is automatically conveyed away from a valve seat at a given pressure difference to allow inflow of air into the tank. One inconvenience in connection with this and similar vacuum relief units is that usually they do not take into account the extraordinary situation where, following an accident, the tanker is completely or partially immersed into the sea water. In such situation, the direct contact of the water with the valve body may be able to cause the valve body to move away from the valve seat, thereby allowing seawater to flow into the tank and slowly displace its content of oil and chemicals. Hereby a pollution of the seawater may occur. It has previously been attempted to provide vacuum relief units that are able to prevent inflow of seawater into the tank in case of an accident. Such vacuum relief unit is described in US patent No. 3,868,921. However, that solution is of a complex structure with many components, which - on the one hand - makes the unit expensive to manufacture and - on the other - increases the risk of malfunction of the unit in case just one of the many components fails. As mentioned above, the invention relates to an improved vacuum release unit, whereby it is possible, by means of a modest number of components, to restrict the movement range of the valve body away from the valve seat in case the vessel wrecks. The invention is suitable for use in particular in connection with valve devices of the kind taught in US patent No. 5,607,001; but it may also be applicable, however, in connection with valve devices that do not feature a pressure relief device. The invention distinguishes itself by being suitable, in many cases, for utilisation in connection with restructuring valve devices that are already in existence of precisely the kind described in the latter patent disclosure. The above advantages are achieved in accordance with claim 1 by the second movable part being configured for being conveyed into abutment on the valve body by an increasing movement of the first movable part in order to cause the valve body to return to its abutment on the seat. Thus, the invention relies on the finding that the hydrostatic pressure that attempts to move the valve body away from its abutment on the valve seat when the vessel is immersed can be used to close the valve body by providing means that are per se influenced by the hydrostatic pressure and that influence the valve body by a force that can move the valve body towards the valve seat. Advantageous embodiments of the invention will appear from the independent claims. The vacuum relief unit can thus in a simple manner be configured as featured in claim 4. The invention will now be described in further detail with reference to the drawing, wherein Figure 1 is a cross sectional view through a preferred embodiment of the vacuum relief unit for mounting on a tanker; and Figure 2 is an enlarged sectional view of Figure 1. Albeit in the drawing the invention is shown as an integral part of a valve device that also comprises a vacuum relief device, the vacuum relief device according to the invention can obviously be configured as a unit that is built into a tanker separately from the pressure relief device. In the drawing, I is used to designate a preferably vertically oriented valve device with a socket 4 that has, at its lower end, a flange 5 that can be bolted to a bead on a tank or to the upper end of a pressure equalisation pipe that is connected to one or more tanks in the tanker. The socket 4 has a lateral opening 6 to which a vacuum relief unit 10 according to the invention is connected. A pressure relief unit 8 that is arranged above the lateral opening 6 will not be subject to more detailed description, as it does not form a part of the present invention. The pressure relief device 8 can be for instance of the kind taught in US patent No. 5,607,001. As shown, the vacuum relief unit 10 comprises a valve housing 20 that has, at its one end, a connecting part 22, whereby the valve housing 20 can - by means of conventional connecting means - be connected to the lateral opening 6, to a pressure equalisation tube or directly to a tank in a vessel. The connecting portion 22 defines a first opening 12 of the valve housing 20. The valve housing 20 also has a second opening 24 in which a valve seat 30 is arranged that features a guide 32 for a valve bar 45. The valve seat 30 forms an abutment for a valve body 40 that carries said valve bar 45 and has, on the side that faces towards the valve housing 20 interior, a central area 42 with adjoining face portions 44. The internally and externally pressure- influenced surfaces, respectively, of the valve body 40 that produce a movement away from and towards the valve seat 30, respectively, has an area A3. The valve body 40 has a predetermined mass and may optionally be spring- biased. Hereby a certain abutment force F1 is obtained between the valve body 40 and the valve seat 30, whereby a given sealing of the second opening 24 can be ensured. It will be understood that, in case of a sub- atmospheric pressure in the tank, the valve body 40 will be lifted away from its abutment on the valve seat 30, whereby air is, in normal operating conditions of the vessel, able to flow into the tank from the outside and permit a pressure equalisation. Underneath the valve seat 30 a pushbutton-like device 21 is also arranged that enables checking of the performance of the vacuum relief unit 10 during normal operation. At the top, the valve housing 10 has a flange 28 that delimits a third opening 26 in the valve housing 10, and to which a mechanism 100 is firmly bolted that may, as will be described more detailed below, be released automatically in case the ship sinks. Apart from that, the configuration of the valve housing 10 corresponds to the teachings of US patent No 5,607,001 , wherein said third opening is covered by a firmly bolted board. The mechanism 100 is shown in an enlarged scale in Figure 2 and comprises a bottom plate 110 that is intended for being secured in close abutment on the flange 28. Upwards from the bottom plate 110 a preferably cylindrical housing 120 extends that has an upper cover plate 130 with mounting apertures 134. The housing 120 is mounted in close abutment on the bottom plate 110 by means of a sealing means 116. The cover late 130 is secured to the bottom plate 110 by means of a number of bar elements 140 that extend through the mounting apertures 134 and are mounted in indentations 114 in the bottom plate 110. By means of bolts 145 it is possible to remove the cover plate 130 to obtain access to the interior of the mechanism 100. Interiorly of the housing 120, a first movable part is arranged in the form of a piston 160 that is firmly connected to a second movable part in the form of a piston rod 150 and has a surface area A1. The housing 120, the piston 160 and the bottom plate 110 define between them a space 102 that is preferably filled with air or other readily compressible gas. The piston rod 150 is displaceably joumalled in a through-going aperture 112 in the bottom plate 110, whereby the piston can be moved in the direction of the arrow P. A spring 155 serves to bias the piston 160 in a direction towards the starting position shown in Figures 1 and 2, where the top face of a bolt 152 that serves to fixate the piston rod 150 to the piston 160 abuts on the underside of the cover plate 130. Along with the spring 155 the pressure Pc of the gas in the space 102 will, to a certain extent, counteract a downward movement of the piston 160. In the embodiment shown the piston 160 is in the form of a rigid plate; it may, however, be configured in other ways, eg as a resilient membrane that is connected to the piston rod 150. The elasticity of the membrane may, in that case, be utilised to the effect that the spring 155 can be eliminated. In the starting position shown, a space 103 occurs between the cover plate 130 and the top face of the piston 160, and this space 103 communicates with the exterior via openings 132 in the cover late 130. Above the cover plate 130 an open-mesh grid 105 or alike is preferably arranged that serves merely to prevent entry of insects or the like to the mechanism 100. As will appear, the piston 160 is sealed relative to the inside of the housing 120 by a sealing means 165, and the piston rod 150 is sealed relative to the interior of the valve housing 20 by a sealing mans 117. As will also appear, the piston rod 150 has an end 152, whose surface area A2 is significantly smaller than the surface area A1 of the piston 160. Said end 152 enters in the valve housing 20 interior immediately above the central area 42 of the valve body 40, as will appear clearly from figure 1. It will be understood, that the piston rod 150 and the valve body 40 are preferably controlled such that the end 152 and the central area 42 move linearly towards each other by pressure influences on the piston 160 and the valve body 40, respectively. The area A1 of the piston 160, the length of the piston rod 150, the spring force of the spring 155 and the resistance to the movement 160 of the piston due to the pressure Pc interiorly 102 of the housing 120 is, in accordance with the invention, dimensioned such that the end 152 of the piston rod 150 will, in case of usually prevailing sub-atmospheric pressure in the tank, move towards the central area 42 of the valve body 20, but not so far that the end 152 arrives to abut on the central area 42 before the valve body 40 has moved slightly away from the valve seat 30 having allowed an equalisation of the difference in pressure. Following this pressure equalisation, the piston 160 will move back to the starting position. Such dimensioning must thus take into account the abutment force F1 between the valve body 40 and the valve seat 30. In case of an accident where the ship is immersed a certain distance below sea level, seawater will flow into the space 103 between the cover plate 130 and the top face of the piston 160 and influence the piston 160 with a downwardly oriented force corresponding to the hydrostatic pressure, whereby the piston 160 is moved downwards. The end 152 of the piston rod 150 will reach the central area 42 of the piston body 40 shortly after the hydrostatic pressure of the water has given rise to a movement of the valve body 40 away from its abutment on the valve seat 30. When the hydrostatic pressure increases due to the vessel being further immersed, the end 152 of the piston rod 150 will move further into the valve housing 20 and press the valve body 40 back in abutment on the valve seat 30. Hereby further inflow of seawater is avoided. In order to take into account the accident scenario, dimensioning of the 10 mechanism 100 and the valve body 40 must thus make sure that the above- described state can be brought about. In the show exemplary embodiment the following condition must thus be complied with: (A3 x Py) - (A3 x Pi) + F1 = (A1 x Py + F2) - (A1 x Pc + F4) wherein Py is the hydrostatic pressure; Pi is the pressure within the tank; F2 is the force as a result of the mass of the piston 160; and F4 and Pc are the spring force and the pressure in the interior 102 of the mechanism, respectively, when the end 152 of the piston 160 is advanced towards the valve body. Albeit in the drawing the piston rod 150 is shown to be arranged immediately opposite the valve body 40 and thus will move opposite the movement direction of the valve body 40, obviously nothing prevents the mechanism from being arranged in any other manner, as long as the piston rod 150 can, by its movement, cause the valve body 40 to abut on the valve seat 30.

Claims: C l a i m s 1. A vacuum relief unit for pressure equalisation between the ambient atmosphere and a tank in a tanker, wherein the vacuum relief unit comprises: a valve housing (10) with a first opening (12), whereby the valve housing (10) is able to communicate with the tank, and a second opening (24) with a seat (30) for a valve body (40) that is configured for being conveyable into the valve housing (10) to permit inflow of air to the tank; and a mechanism (100) configured for being able to prevent passage of seawater through the valve housing (10) in case of an accident, wherein the tanker is at least partially immersed into seawater, which mechanism (100) features a first movable part (160) that is arranged outside the valve housing (10) and whose movement can be controlled by the liquid pressure of the sea water, a second movable part (150) that can be advanced within the valve housing (10) and that is movably coupled to the first movable part (160), characterised in that the second movable part (150) is configured for being conveyable to abut on the valve body (40) by an increasing movement of the first movable part (160) to cause the valve body (40) to return to its abutment on the seat (30). 2. A vacuum relief unit according to claim 1 , characterised in that the valve body (40) is configured for being conveyed essentially linearly into the valve housing (20); and that the second movable part is configured for being conveyed linearly into the valve housing (20) opposite this direction. 3. A vacuum relief unit according to claim 1 or 2, characterised in that the valve housing (10) comprises a third opening (26); and that the mechanism (100) comprises a housing (120) arranged in association with said opening (26). 4. A vacuum relief unit according to the preceding claim, characterised in that the first movable part (160) is a piston and that the second movable part (150) is a piston rod that is firmly connected to the piston (160); that the piston (160) and the housing (120) forms a sealed space (102); that the piston (160) has a surface that is configured for being able to be influenced directly by said liquid pressure; and that the piston rod (150) can be advanced into the valve housing (10) through said opening (26). 5. A vacuum relief unit according to the preceding claim, characterised in that the mechanism also comprises a spring (155) configured for providing a resistance to the movement of the piston (160). 6. A vacuum relief unit according to claim 4 or 5 characterised in that the housing (120) comprises a cover plate (130) provided with apertures (132), whereby the piston (160) can be influenced by said liquid pressure, and that the cover plate constitutes a limitation to the movement of the piston (160). 7. A vacuum relief unit according to any one of claims 3-6, characterised in that said third opening (26) is configured in a detachable wall portion (110) of the valve housing (20).

Inventors: SOERENSEN EMIL AARESTRUP, SOERENSEN, EMIL, AARESTRUP
Applicants: PRES VAC ENGINEERING AS, SOERENSEN EMIL AARESTRUP, PRES-VAC ENGINEERING A/S, SOERENSEN, EMIL, AARESTRUP
Application year: 2001
Main classification: B63B25
IPC codes: B63B1, B63B25, B63J2, F16K17, F16K24