GB2083353A

GB2083353A - Fluid pressure controlled time delay apparatus

Info

Publication number: GB2083353A
Application number: GB8124844A
Authority: GB
Original assignee: Chubb Fire Security Ltd
Current assignee: Chubb Fire Ltd
Priority date: 1980-08-20
Filing date: 1981-08-14
Publication date: 1982-03-24
Also published as: EP0046378A2; AU541137B2; NZ198079A; GB2083353B; AU7433481A; EP0046378A3

Abstract

A time delay device, particularly for use with CO2 or other fire fighting installations, to introduce a predetermined delay for evacuation etc between the raising of alarm and the discharge of the fire fighting medium. The device comprises a chamber 15 with an inlet controlled by a restricted orifice 16 and an outlet controlled by a bursting disc 17. When the alarm is raised high pressure gas is supplied to the orifice 16 into the chamber 15 until the pressure in the chamber causes the disc 17 to rupture, the time taken for rupture depending on the size of the orifice 16, the capacity of the chamber 15 and the bursting pressure of the disc 17. When the disc ruptures a surge of pressurised gas passes through the outlet 11A to a pneumatic relay (not shown) to cause release of the fire fighting medium. <IMAGE>

Description

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GB2 083 353A 1

SPECIFICATION

Fluid pressure controlled time delay apparatus

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The present invention relates to fluid pressure controlled time delay apparatus and is particularly, though not exclusively, concerned with time delay apparatus for use in connection 10 with fire fighting systems of the type frequently installed e.g. in commercial and industrial premises for releasing a fluid fire extinguishing/prevention medium, such as carbon dioxide vapour, into the environment 15 in the event or threatened event of fire.

In fire fighting installations of this type it is customary to employ a device which introduces a predetermined time delay between the initiation of a fluid-releasing sequence and 20 the actual discharge of the medium into the environment. This is in order to permit personnel to evacuate before there is any risk of the environment being rendered irrespirable or otherwise harmful by the medium itself. It is 25 furthermore advisable to delay the discharge of the medium until sufficient time has elapsed for fire doors to be closed, ventilators to be shut down etc., in order to maximise the effects of the medium when discharged. The 30 typical time delays provided by these devices range from a few seconds to about a minute.

It is preferable, for reliability, that the operation of the time delay apparatus is independent of external electricity or other power 35 supplies and hence various types of device have been proposed hitherto which rely for their operation on a source of stored fluid pressure. Such devices, as exemplified e.g. by United States Patent Specifications nos. 40 2537009, 2663153, 2819865 and

2865592, typically comprise a chamber of predetermined volume into which the pressurised fluid is metered through a restricted flowpath provided e.g. by an orifice or capil-45 lary tube. The pressure within the chamber is applied to one side of a piston exposed on its other side to a reference pressure, and the piston controls a valve which, when opened, connects the primary pressure source directly - 50 to some pressure-responsive means for releasing the fire fighting medium. Initiation of the release sequence is accomplished by establishing communication between the pressure source and the chamber, but actual discharge 55 of the fire fighting medium does not occur until the pressure in the chamber has risen to a value sufficient to move the piston and open the associated valve, and with a given source pressure the time taken to reach any selec-60 ted pressure in the chamber depends upon the capacity of the chamber and the characteristics of the restricted flowpath by which it is connected to the pressure source.

Time delay devices as described above are 65 relatively complex and the parts of the piston/

valve assembly need to be made to close tolerances; hence they are expensive to produce. The present invention seeks to provide fluid pressure controlled time delay apparatus 70 suitable for the same service as described above but being significantly simplified in its construction and operation, and hence amenable to more economical production.

In a first aspect the invention accordingly 75 resides in time delay apparatus comprising a chamber of predetermined volume; a restricted flowpath for communicating a source of pressurised fluid with said chamber; and an outlet from the chamber normally closed by a 80 bursting disc.

By a "bursting disc" is meant an element which is adapted to rupture to open the said outlet to the transmission of fluid pressure from the chamber when a predetermined pres-85 sure differential across the element is established. In use, with a reference pressure on the downstream side of the disc, the time taken to establish a selected burst pressure differential will depend upon the source pres-90 sure, the capacity of the chamber and the characteristics of the restricted flowpath, as in the case of the prior art devices referred to above. However, on rupture of the disc the resultant surge of pressure from the chamber 95 can be used directly through suitable pres-sure-responsive means to release a fire fighting medium or perform other functions in other applications of the device, so that the need for a piston/valve assembly in the delay 100 apparatus can be eliminated. This leads not only to a simplification in the construction of the time delay apparatus but also to a simplification in, and consequently a potential increase in the reliability of, the operation of the 105 apparatus, no moving parts being required. Furthermore, with a given source pressure, chamber capacity and restricted flowpath characteristics, selection of different time delays can be very simply and effectively 110 achieved by the substitution of bursting discs with different burst pressures.

In a second aspect the invention resides in a time delay system comprising a source of pressurised fluid; a chamber of predetermined 115 volume; a restricted flowpath for communicating said source of pressurised fluid with said chamber; an outlet from the chamber normally closed by a bursting disc; first means operable to establish communication between 120 said source and chamber through said flowpath; and second means for performing a function in response to the transmission of fluid pressure from said chamber upon rupture of said bursting disc.

125 Such a system will involve a time delay between the operation of the first means and the response of the second means determined by the time taken for the pressure within the chamber to rise to a value which causes 130 rupture of the bursting disc, as previously

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described. When such a system is incorporated in a fire fighting installation of the type discussed the operation of the first means -which may comprise e.g. a valve or piercer 5 mechanism associated with the pressure source - may be effected automatically or manually in response to the automatic detection of a fire or otherwise upon the raising of alarm, the second means comprising a mecha-10 nism operable to release the fire fighting medium upon the transmission of fluid pressure from the aforesaid chamber. However, apparatus and systems according to the invention are of general utility in the provision of se-15 lected time delays between a first event and a second event conditional upon the first, and are not restricted to the field of fire fighting.

The invention will now be more particularly described, by way of example, in the context 20 of an application to a fire fighting installation, reference being made to the accompanying drawings in which:

Figure 1 is a schematic diagram of the installation; and 25 Figure 2 is a more detailed sectional view, to an enlarged scale, of the time delay device incorporated in the installation of Fig. 1.

Referring to the drawings, the installation comprises a source of fluid fire fighting me-30 dium illustrated as a bank of cylinders 1 of compressed C02, each of which is communicable through an individual knuckle valve 2 with a manifold 3 by which the gas is distributed to the areas to be protected in the event 35 or threat of fire. Operation of the valves 2 to release the stored gas can be effected by a pneumatic relay 4 having a piston 5 which, when pressure is transmitted to the cylinder of the relay, moves to withdraw a connecting 40 cable 7 to which the valves 2 are all linked.

The power for operating the relay 4 is derived from a cylinder 8 of compressed inert gas, such as nitrogen. On the raising of alarm the cylinder 8 is opened to supply gas to a 45 delay device 9 interposed in the line 10/11 between the cylinder 8 and relay 4, in the illustrated embodiment the outlet from the cylinder 8 being equipped with a frangible closure 12 which can be pierced by a pin 13 50 connected to a hand lever 14 to place the cylinder in communication with the delay device.

The delay device 9, which is more clearly shown in Fig. 2. comprises a pressure vessel 55 15 having an inlet fitting which includes a restricted orifice 16 and an inlet adaptor 1 OA for connection to the line 1 0. The vessel 1 5 is also equipped with an outlet fitting which includes a bursting disc 1 7 and an outlet 60 adaptor 1 1A for connection to the line 1 1. In use, when the cylinder 8 is opened nitrogen gas passes through the line 10, adaptor 10A and orifice 1 6 into the chamber defined within the vessel 1 5, but is initially prevented 65 from reaching the relay 4 by the bursting disc

17. Pressure builds up within the vessel 15 at a rate determined by its capacity and the size of the orifice 16, until after a certain interval the pressure differential across the disc 17 (its 70 downstream side being exposed to the ambient pressure in the relay cylinder 6 and line 11 at this time), reaches the value which causes the disc to rupture. When this occurs a surge of pressurised nitrogen passes from the 75 vessel 15 through the adaptor 11A and line 11 to the relay cylinder 6 to move the piston 5 and thereby release the fire fighting medium from the cylinders 1.

For a given source pressure the time delay 80 introduced by the device 9 between operation of the lever 14 and the release of the fire fighting medium depends upon the capacity of the vessel 15, the size of the orifice 16 and the burst pressure of the disc 1 7. Variation of 85 the delay can be achieved by changing the effective capacity of the vessel 15 or the size of the orifice 16, but most simply and effectively can be achieved by substituting discs 1 7 with different burst pressures. The discs 90 are typically made from nickel-silver or copper, discs of this type being commercially available and reliably adapted to rupture at pressures within closely prescribed limits. In one example of a delay device constructed as 95 illustrated in which the capacity of the vessel 1 5 is approximately 230ccs and the diameter of the orifice is 0.015" (0.38mm), and working from a 1400 psi (97 bar) pressure source, a disc 1 7 with a burst pressure of 600 psi 100 bar) gives a delay of 7 seconds while a disc with a burst pressure of 700 psi (48 bar)

gives a delay if 21 seconds. As shown in Fig. 2, the disc 1 7 is clamped peripherally between a pair of washers 18 which in turn are 105 clamped between a cone ring 19 and a seating ring 20 provided on the vessel 1 5, the assembly being secured by a locking ring 21 screwed onto the ring 20 and retaining the ring 19. To change the disc 17 the locking 110 ring 21 is simply unscrewed to permit the rings and washers to be separated.

It will be appreciated that the details given above of the means by which pressurised fluid is made available to the delay device 9, 11 5 and of the means which respond to the rupture of the disc 17 and the functions performed thereby, are given for the purposes of illustration only and are capable of considerable variation without changing the essential 120 construction and operation of the delay device itself.

Claims

1. A fluid pressure controlled time delay 1 25 apparatus comprising a chamber of predetermined volume: a restricted flowpath for communicating a source of pressurised fluid with said chamber; and an outlet from the chamber normally closed by a bursting disc. 1 30 2. A fluid pressure controlled time delay

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system comprising a source of pressurised fluid; a chamber of predetermined volume; a restricted flowpath for communicating said source of pressurised fluid with said chamber;

5 an outlet from the chamber normally closed by a bursting disc; first means operable to establish communication between said source and chamber through said flowpath; and second means for performing a function in re-

10 sponse to the tranmission of fluid pressure from said chamber upon rupture of said bursting disc.

3. A time delay apparatus or system according to claim 1 or claim 2 wherein said

15 flow path is restricted by means of an orifice of predetermined cross-sectional area at the inlet of said chamber.

4. A time delay apparatus or system according to any one of claims 1 to 3 wherein

20 said bursting disc is mounted to close said outlet by being clamped at its periphery between a pair of ring members associated with said chamber and secured together in demountable fashion.

25 5. A fire fighting installation incorporating a time delay system according to claim 2 or to either of claims 3 and 4 when appended thereto, wherein said second means comprise a mechanism arranged to release a fire fight-

30 ing medium in response to the transmission thereto of fluid pressure from said chamber upon rupture of said bursting disc.

6. A fire fighting installation according to claim 5 wherein said first means are arranged

35 to operate in response to a signal from automatic fire detection means.

7. A fluid pressure controlled time delay appratus according to claim 1 and substantially as hereinbefore described with reference to

40 Fig. 2 of the accompanying drawings.

8. A fluid pressure controlled time delay system according to claim 2 and substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

45 9. A fire fighting installation according to claim 5 and substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd.—1982.

Published at The Patent Office, 25 Southampton Buildings,

London, WC2A 1AY, from which copies may be obtained.