GB2478581A

GB2478581A - Pressure relief vent

Info

Publication number: GB2478581A
Application number: GB1004039A
Authority: GB
Inventors: Christopher Coxon
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-03-11
Filing date: 2010-03-11
Publication date: 2011-09-14
Also published as: GB201004039D0

Abstract

A pressure relief vent comprises a vent housing 4 defining an aperture and a plurality of vent blades 6 mounted in the vent housing 4 to be pivotable in the same rotational sense about each of first and a second spaced pivot axes by a respective differential air pressure across the vent aperture. The blades 6 are pivotable from a common first position in which the vent blades cooperate with the vent housing and/or any adjacent vent blade to close the vent aperture, towards a second or a third position, at which positions the vent aperture is open. Each vent blade 6 returns to the first position when there is no differential air pressure across the vent aperture.

Description

Two Way Pressure Relief Vent One approach to extinguishing a fire in the room of a building is to inject a cooling fire extinguishing gas into the room to cool the seat of the fire and to deprive the source of the fire of oxygen.

When the gas is first injected into a room the air contracts due to the cooling effect which results in a drop in pressure of the room relative to the exterior of the room. It is known to provide a motorized pressure relief vent in a wall or ceiling of a room which is automatically opened to allow equalisation of the pressure in the room with the surroundings. The gas subsequently heats up any overpressure that may be caused by the gas expansion is avoided by virtue of the open pressure relief vent, which is kept open by the motor that initially opened the vent.

Such pressure relief vents have the advantage that they can be opened to a position that allows gas flow in both directions through the vent when in its open position. However, such pressure relief vents rely on a control system to cause the motor to open the vent at the appropriate time which not only requires appropriate sensors and back up power supplies in case of mains power cuts but being an active system also has a number of potential failure points.

A pressure relief vent without these drawbacks is a pressure relief vent comprises a vent housing with one or more pairs of vent blades pivotally mounted in the vent housing. Each vent blade is pivotable in both rotational senses on a pivot by a respective differential air pressure across the vent aperture from a first position at which position the vent blades co-operate to close the vent aperture to a second position atwhich position the vent aperture is open. -This provides an entirely passive pressure relief vent able to allow pressure relief in two directions (i.e. to allow gas flow into and out of a room) which, after allowing relief of pressure, will automatically return to a closed position with the vent closed, as required by fire regulations in certain circumstances.

In order to provide a closed vent when the blades are in the closed position, adjacent vent blades have to seal to each other to an acceptable degree and in a manner that allows the moving ends of the vent blades to readily move in each of the two rotational senses relative to the fixed end of the adjacent vent blade and to return to the sealed position afterwards. The need to meet both criteria places constraints on the design of the vent in order to achieve satisfactory sealing in an entirely passive vent aperture opening and closing system.

The present invention seeks to provide a pressure relief vent without all these constraints. Accordingly, the present invention provides a pressure relief vent comprising a vent housing defining an aperture, at least one vent blade mounted in the vent housing so as to be pivotable in the same rotational sense about each of a first and a second, spaced-apart pivot axes, by a respective differential air pressure across the vent aperture, from a first position, at which position the vent blade co-operates with the vent housing and/or any adjacent vent blade to close the vent aperture, towards a second and a third position, respectively, at which positions the vent aperture is open and in which each vent blade returns to the first position when there is no differential air pressure across the vent aperture.

Because each vent blade rotates to open the pressure relief vent in the same rotational sense whatever side of the vent is exposed to the higher pressure, the seals between each vent blade and the adjacent vent blade or vent housing can be designed with fewer constraints as the seal is, in each case, broken by the same relative movement. This is in contrast to the prior known arrangements where the seals must be designed to be broken in two oppositely directed relative movements.

In a preferred embodiment, a first end of each vent blade has a pivot means mounted in, and movable along, an arcuate guide means an end of which acts a stop when the vent blade is in the first position and an opposite second end which rests against a stop means when the vent blade is in the first position.

When a differential air pressure applied to the vent urges the vent blade in a direction which pushes the second end of the vent blade against the stop the first end of the vent blade moves as the pivot means moves along the arcuate guide so opening the vent, the vent blade rotating about the stop which defines a pivot axis. When a differential pressure is applied to the vent in the opposite direction, the first end of the vent blade is maintained in place as the pivot means is at the end of the arcuate guide while the second end is pushed away from the stop so, again, opening the vent.

Considering a vent with a pair of such vent blades, the ends of the adjacent blades can be fully interfinked, in an overlapping manner, as the overlap is broken by the same relative movement whatever the differential pressure: either the upper end of the lower vent blade rotates away from the lower end of the upper vent blade or the lower upper end of the lower vent blade end of the upper vent blade rotates away from the upper end of the lower vent blade.

The pivot means may be rotatably mounted in a carrier plate which, in turn, is pivotably mounted on the stop.

Generally, embodiments of pressure relief vent according to the present invention will have at least two vent blades and adjacent vent blades interlink when in the first position.

The vent blades may be interconnected so that they are constrained to pivot together.

Preferably the adjacent vent blades interlink when in the first position to form a continuous barrier, conveniently by means of a male/female arrangement.

There may be included closing means for urging each vent blade towards the first position to provide that the vent blades return to the closed position when there is no differential pressure across the vent. Other passive means may be employed, for example suitably weighted vent blades.

A particular application of two-way vent is for the pressure relief of an enclosure where a halocarbon gas suppression system has been installed. Studies and directives indicate that the negative pressure to be relieved for such an enclosure is greater, by a factor of about four in some cases, than the positive pressure to be relieved. As the vent doesn't need to present the same open area in each direction it is possible to restrict the degree of rotation of the vent blades when venting the positive pressure from a room thereby reducing the depth of the pressure relief vent in comparison to one were equal venting is presented in both venting directions.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic isometric view of an embodiment of a pressure relief vent according to the present invention; Figures 2, 3 and 4 are schematic cross-sectional end views of the vent of Figure 1 in the closed position and after the vent is opened by airflow from the left and right side, respectively.

Referring to Figures 1 and 2, a pressure relief vent 2 has a 1.5mm steel housing 4 into which fit a series of 1.0mm double sheet steel vent blades 6 which are fixed to a pair of 10mm diameter steel pivot pins 8 and which are free to rotate inside the top of a carrier bracket 10 which is made from 2.0mm steel with a fold down one side for stiffness. The carrier brackets 10 are each attached to a bearing via an MlO cap head bolt 12 and can rotate about a respective pivot 14.

The bearing about which each carrier arm 10 rotates sits in a top hat" style sheet metal pressing which is attached to the vent housing 4 by 3 x M5 Clynch studs 16. The head of each MlO cap head bolt 12 extends into the housing aperture and acts as a stop for the bottom of each vent blade 6 about which they rotate where there is a positive on the to right hand hole as shown in Figure 4. A counter weight 1 8 made of 2.0mm steel acts to balance the weight of the vent blade assembly 6 and carrier bracket 10 so as to keep this assembly upright when no air pressure is acting on it and no pressure relief is required in direction N of Figure 4. Additional weights can be added to the counter weight 1 8 to adjust the pressure at which the vent will open in the "positive" direction of Figure 4. Slots 20 allow pivot pins 8 free movement along the slots 20 whilst the vent blades 6 are moved open for the "positive" pressure relief up to the extent of the slot. In this embodiment the slot is of a length which limits the "positive" pressure relief to approximately 50% free vent area. These slots 20 also stop the vent blades 6 from falling forwards.

Referring now to Figure 2, the vent unit 2 is shown in cross section with the vent blades 6 in the closed position. The double skinned blade design of the vent blades can be seen. A top skin 30 is of 1.0mm sheet steel is attached to central chassis bar 32 which is a "U" section of 1.5mm steel which holds it apart from a top skin 34 by 10mm. Each blade skin 30, 34 has a 15mm radius curve at one end. These cross over each other in a fully overlapping manner when the vent blades are in the closed position of Figure 2 to stop flames from passing through the vent in the event of a fire. Z' sections 36 act as a fire stop at the top and bottom of the casing when engaged with the adjacent vent blade 6. A 10mm diameter steel pivot pin 38 which has half of its diameter machined away to form a flat which sits on the blade section and which is riveted to each vent blade 6. This offsets the weight of each blade assembly from carrier arm pivot point 12 and helps to keep the carrier arm upright when in Negative' pressure relief mode as shown in Figure 3 and the blade in the upright, closed position. This offset pivot also helps to keep more mass of each vent blade 6 over pivot point 1 2when in Positive' pressure relief mode so as reducing the amount of counter weight required to return the blades to the upright position when the positive' pressure has subsided. See Figure 4.

Referring now to Figure 3, vent blades 6 are shown rotated about pivots 38 from pressure of air in first, negative direction from direction M. In this direction each blade 6 is free to open to 90 degrees from upright giving the vents maximum free vent area which taking the 10mm profile of each blade into account will equate to 90% free vent area. The counter weight 1 8 and air pressure keep the carrier arm 10 upright. The air flow acting on the curve on the lower (right hand end as shown) of the blade 6 makes most efficient use of its force by being at the furthest point from pivot point 38 and therefore helps to effect the free vent area provided at low air flow and pressure. At the same time the curved upper end of the vent blades 6 acts to direct air underneath each blade. In the closed position these curved ends of adjacent vent blades interlink and cross over to act as a flame barrier in the event of a fire.

Referring now to Figure 4 louver blades 6 and carrier arm 10 are shown rotated about pivot point 1 2 under pressure from air movement in a second direction N. In this example the vent blades 6 are limited to 30 deg angle of rotation by the arcuate guide 20 which by forming a gap of approximately 50mm at points G gives a 30% free vent area. Each blade pivot 12 is 100mm apart and so for a three-bladed vent the aperture height is 300mm so two, 50mm gaps equates to 100mm or 33% free vent area, slightly exceeding the approximately 25% required. It is possible for this design to provide the same free vent area in both directions but in the direction illustrated in Figure 4 this would require a larger counter weight to bring the blade assemblies to the upright position after the air pressure had subsided the more venting required. Also in this example it can be seen that the curved part of the upper end of each blade allows the air force to act at the most mechanically advantageous point relative to pivot point 1 2. The curve on the lower end of each blade now acts to direct airflow over each blade.

It is not possible to use such blade sections in this way with a single pivoting blade where each blade goes from 90 degrees in one direction from upright to degrees in the other since any kind of blade profile as in this arrangement it will simply either only work in one direction or if applied to each face of the blades just cancel each other out.

Referring again to Figure 1, the vent blades 6 are being acted on by air flow in the direction N and counter weight 1 8 acts about pivot points 1 4 via its own pivot point 40 which consist of an MS Clynch standoff fixed into the carrier arm 10, over which an 8mm diameter hole in the counter weight 18 sits and is held in place with a washer and a rivet inserted into the threaded hole of the standoff. The weight of the counter weight 1 8 about the pivot 14 acts to close the vent blades 6 when the pressure acting on them subsides.

The illustrated configuration is intended to allow 90% venting in one direction and up to 33% in the opposite direction. This design is far simpler than a two way vent where the blades need to be interlinked and performance testing also confirms that this new invention performs far better with low pressures. It is common to have to keep a room pressure under 250 Pascals during a gas suppression discharge and the blade design that is used in this invention has been proven to perform to 100% of its available free vent area at pressures as low as 100 Pascals. This is due to this unique double pivoting design with allows for the use of light weight sheet steel blades with curved ends that can utilize the maximum effect of the air flow over the blades to achieve higher free vent areas at low pressures.

Claims

CLAIMS1. A pressure relief vent comprising; a vent housing defining an aperture; at least one vent blade mounted in the vent housing so as to be rotatable in the same rotational sense about each of a first and a second, spaced-apart pivot axes, by a respective differential air pressure across the vent aperture, from a first position, at which position the vent blade co-operates with the vent housing and/or any adjacent vent blade to close the vent aperture, towards a second and a third position, respectively, at which positions the vent aperture is open; and in which each vent blade is arranged to return to the first position when there is no differential air pressure across the vent aperture.
2. A pressure relief vent as claimed in claim 1, in which a first end of each vent blade has a pivot means mounted in, and movable along, an arcuate guide means an end of which acts a stop when the vent blade is in the first position and an opposite second end which rests against a stop means when the vent blade is in the first position.
3. A pressure relief vent as claimed in claim 1 or 2, in which there are at least two vent blades and adjacent vent blades interlink when in the first position.
4. A pressure relief vent as claimed in any preceding claim, and including closing means for urging each vent blade towards the first position from the second and third positions.
5. A pressure relief vent as claimed in any preceding claim, in which the vent blades are interconnected so that they pivot together.
6. A pressure relief vent substantially as hereinbefore described with reference to, and/or as show in, the accompanying drawings.