GB2156574A

GB2156574A - Vents for electric storage batteries

Info

Publication number: GB2156574A
Application number: GB08407742A
Authority: GB
Inventors: Norman Shanks; Michael Edward Mcguire
Original assignee: Chloride Group Ltd
Current assignee: Chloride Group Ltd
Priority date: 1984-03-26
Filing date: 1984-03-26
Publication date: 1985-10-09
Also published as: GB8407742D0

Abstract

The vent comprises a rounded annular shoulder 16 extending around a vent opening 13, an elastomeric vent member 19 resting on the shoulder and normally closing the vent opening and a support 24 situated within the vent opening and engaged by the vent member. Basing means constituted by a vent closure plug 17 engages the vent member 19 via a resilient upstanding tube 22 which is moulded integrally with the vent member 19. <IMAGE>

Description

SPECIFICATION Vents for electric storage batteries The present invention relates to vents for electric storage batteries, in particular recombination batteries, so called drain dry battery and dry charged batteries. In such batteries and in particular in lead acid recombination batteries it is desirable that if any gas should be evolved within the battery only a very small superatmospheric pressure should be permitted to develop within the battery but that no atmospheric air should be permitted to enter the battery since this substantially accelerates the rate of self discharge. It is thus desirable to provide a vent which opens to vent the interior of the battery at even a small superatmospheric pressure within the battery but which functions reliably as a non-return valve to prevent any inflow of air into the battery.

British Patent Specification No. 2085217 of the present applicants discloses a vent which fulfils this function. The vent disclosed therein comprises a rounded annular shoulder around a vent opening and an elastomeric vent disc which engages the shoulder and is pressed into contact with it by a closure member which deforms the central portion of the vent disc into the vent opening. The precise distance by which the vent disc is deformed into the vent opening determines the pressure with which the disc engages the shoulder and thus the pressure differential at which the vent opens to vent the interior of the battery.

In the prior specification referred to above the vent disc is engaged by a T-section closure member which is a snap fit within the vent body. The pressure with which the vent disc engages the shoulder is thus dependent on the distance between the end of the closure member and the annular shoulder, that is to say on the precise dimensions of the closure member and of the vent body and on the dimensions and accuracy of the snap connection between the closure member and the vent body. As a manufacturing practicality it is not possible to predetermine all these parameters precisely and the result of this is that the pressure at which the vent opens varies from vent to vent.

In order that the characteristics of a large number of batteries provided with a vent may be made predictably the same it is necessary that all the vents open at the same pressure and accordingly it is an object of the present invention to provide a vent for an electric storage battery which is of the general type disclosed in the prior specification referred to above but does not suffer from the disadvantage referred to and in which the pressure with which the vent disc is pressed against the shoulder and thus the pressure differential at which the vent will open are reliably predeterminable.

According to the present invention a vent for an electric storage battery comprises a rounded annular shoulder extending around a vent opening, an elastomeric vent member resting on the shoulder and and normally closing the vent opening, a support situated within the vent opening and biassing means engaging the vent member and deforming it into contact with the support, the vent member and/or the biassing means including resilient means permitting relative movement between the biassing means and the vent member.

Thus in the vent in accordance with the present invention the support is engaged by the vent member and thus predetermines the distance by which the vent member is deformed by the biassing means. Accordingly the pressure with which the vent member engages the shoulder and thus the pressure differential at which the vent opens are precisely predetermined. The resilient means permits relative movement of the biassing means and the vent member and thus compensates for any dimensional tolerances of the type referred to above.

The resilient means may constitute a spring connected to or otherwise associated with either the biassing means or the vent member. Alternatively, the biassing means may incorporate a member of rubber, elastomeric or other compressible material which may be compressed to accommodate the dimensional tolerances. However, in the preferred embodiment the vent member has a compressible member extending therefrom which is engaged by the biassing means. This compressible member is preferably integral with the vent member, i.e. formed from the same material, and in the most preferred embodiment comprises an upstanding tube whose walls may bow outwardly on the application of a longitudinal force thereby reducing its length and may thus compensate for dimensional tolerances.

Preferably the support is integral with, e.g.

part of the same plastics moulding as, the annular shoulder. This permits the distance between the surfaces of the shoulder and the support to be precisely predetermined and it will be appreciated that it is this distance which determines the force with which the vent member engages the shoulder.

The resilient means is preferably constructed to permit relative movement of the biassing means and the vent member of 1 mm, 2mm or even 3mm or more.

Further features and details of the present invention will be apparent from the following description of one specific embodiment which is given by way of example only with reference to the single accompanying drawing which is a scrap side sectional elevation of a lead acid recombination battery incorporating a vent in accordance with the present invention.

The vent is generally similar in construction and operation to that disclosed in the prior specification referred to above, the disclosure of which is incorporated herein by reference.

The lid 11 of the battery is formed with a well 12 in the floor of which is a vent opening 13. Extending around the opening 13 is a wall 15 at whose upper edge is a rounded shoulder 16. A vent disc 19 of ethylene propylene closed cell polymer, in this case an ethylene/propylene rubber cross-linked with a diene monomer, 2mm thick engages the shoulder 16 and normally closes the vent opening 13.

The top of the well 12 is closed by a closure member 17 which is retained in position by a snap connection and which is circular in horizontal cross section and T-shaped in vertical cross section and has a depending stem 18. The head of the closure member is formed with a plurality of passages 21 to permit the escape of gas from the interior of the battery. The space within the well 12 below the head of the closure member is traversed by a disc 20 of gas-permeable, flame-retarding material, such as that sold under the Trade Mark VYON in which a central hole is formed which accommodates the stem of the closure member as a sliding fit.

Upstanding from the upper surface of the vent disc and moulded integrally therewith is a centrally disposed tube or hollow cylinder 22. Extending across the vent opening are two or more intersecting bars or spokes 23 moulded integrally with the wall 15. A flattopped support 24 projects upwardly from the central intersection point of the spokes.

In use, when the closure member 17 is snap fitted into position, its stem 18, which constitutes the biassing means, engages the tube 22, which constitutes the resilient means, and deforms the vent disc 19 into the vent opening and into contact with the support 24. The vent is so dimensioned that even at the extreme of the possible dimensional tolerances the vent disc is pressed into contact with the support 24. At all other points in the tolerance range the tube 22 compensates by being outwardly deformed, as indicated diagrammatically by the chain line 22'. The normal position of the vent disc is thus precisely predetermined by the support 24 and any dimensional tolerances are compensated for by deformation of the tube 22.In this position the vent disc forms a seal with the shoulder 16 and if necessary the sealing surface of the vent disc may be coated with petroleum jelly to close its surface and ensure the integrity of the seal.

If the pressure within the battery should rise to a pressure, e.g. 0.05 bar, at which the edge of the vent disc lifts off from the shoulder gas is permitted to flow into the well and then flows through the flame-retarding disc 20 and then to the atmosphere through the passages 21. This pressure is determined by the parameters of the vent disc and by the pressure with which the disc engages the shoulder which in turn is determined by the distance between the support surfaces of the support 24 and the shoulder 16. If the pressure within the battery should fall to subatmospheric the support 24 positively prevents the vent disc from being sucked into the vent opening, in which position it would be unable to fulfil its intended sealing function.

Claims

1. A vent for an electric storage battery comprising a rounded annular shoulder extending around a vent opening, an elastomeric vent member resting on the shoulder and normally closing the vent opening, a support situated within the vent opening and biasing means engaging the vent member and deforming it into contact with the support, the vent member and/or the biasing means including resilient means permitting relative movement between the biasing means and the vent member.

2. A vent as claimed in claim 1 in which the vent member has a compressible member extending therefrom which is engaged by the biasing means.

3. A vent as claimed in claim 2 in which the compressible member is integral with the vent member.

4. A vent as claimed in claim 3 in which the compressible member comprises an upstanding tube whose walls may bow outwardly on the application of a longitudinal force thereby reducing its length.

5. A vent as claimed in any one of the preceding claims in which the support is integral with the annular shoulder.

6. A vent for an electric storage battery substantially as specifically herein described with reference to the accompanying drawing.

7. An electric storage battery including a vent as claimed in any one of the preceding claims.