Vent valve and a storage cell including it

Details Vent valve and a storage cell including it Vent valve and a storage cell including it

2001-12-20

2004-03-30

Ryan, Patrick (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Means externally releasing internal gas pressure from closed...

C429S082000, C429S054000

Reexamination Certificate

active

06713208

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based on French Patent Application No. 01 00 077 filed Jan. 4, 2001, the disclosure of which is hereby incorporated by reference thereto in its entirety, and the priority of which is hereby claimed under 35 U.S.C. §119.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vent valve which can be used as a safety valve for a storage cell, for example an aqueous electrolyte storage cell. The invention also relates to a storage cell equipped with the vent valve.
2. Description of the Prior Art
Aqueous electrolyte storage cells, for example nickel-cadmium storage cells, generally include a casing that is sealed to prevent electrolyte from leaking out and oxygen and pollutants from entering. The electrochemical system of this kind of cell can give off large quantities of gas in operation, or the cell may become overheated. This increases the pressure of the gases and/or air trapped in the casing of the cell. In particular, this occurs if the cell is subjected to intense, or even abusive, operating conditions, under which it delivers excessive electrical currents. This increase in pressure can deform the casing of the cell and cause the casing to leak or even explode. To prevent this, storage cells are generally equipped with safety valves that evacuate the gases to the outside if the pressure inside the casing exceeds a given threshold.
There is a first type of safety valve that includes an elastomer member that is ruptured by the pressure inside the storage cell if it exceeds a particular threshold. This type of vent valve has the drawback that it can be used only once: once broken, the membrane no longer seals the cell, even if operating conditions return to normal.
A second type of safety valve includes a seal blocking an orifice in the casing of the storage cell. The seal opens to free the orifice and allow the gas to escape from the interior of the casing if the pressure exceeds a given level, and then closes again when the pressure inside the casing falls below that given level. Operation of this device relies on retaining the seal, which takes the form of a gasket, against the perimeter of the orifice in the casing by means of a resilient member such as a spring. This solution has the drawback of necessitating a large space to house the gasket and the spring. It also has a high unit cost because of the number of components and the need to assemble them to the cell.
FIGS. 1
,
2
a
and
2
b
show a further solution. The vent valve
1
is on the outside of a cover plate
2
. The cover plate
2
seals the top part of the casing of the storage cell, not shown. The vent valve
1
includes a vent cap
3
on the outside of the cover plate
2
. The area of the cover plate
2
including the vent cap
3
is flat; the portion of the cover plate
2
shown diagrammatically in
FIG. 1
is limited to this area. The vent cap
3
takes the form of a section of a circular cylindrical tube
4
delimited in the lengthwise direction by two planes perpendicular to its axis and one end of which is closed by a bottom
5
. The other end of the section is fixed to the cover plate
2
. The bottom
5
is flat and parallel to the flat area of the cover plate
2
including the vent cap
3
. An orifice
6
in the cover plate
2
establishes communication between the inside of the casing of the cell and the inside of the vent cap
3
. The orifice
6
is substantially coaxial with the cylindrical tube section
4
. Two vent holes
7
a
and
7
b
are provided in the cylindrical tube section
4
at a level adjacent the bottom
5
. The vent holes
7
a
and
7
b
are diametrally opposed. A seal
8
is provided inside the vent cap
3
, to be more precise between its bottom
5
and the cover plate
2
. The seal
8
is shown in
FIGS. 2
a
and
2
b
. The seal
8
has the following external shape. It includes a part
9
in the shape of a circular cylinder section delimited in the lengthwise direction by two planes perpendicular to its axis. On each of the disk-shaped opposite faces of the part
9
is a respective frustoconical part
10
a
,
10
b
coaxial with the part
9
. The diameter of the frustoconical parts
10
a
,
10
b
decreases from a diameter equal to the diameter of the part
9
. Each of the frustoconical parts
10
a
,
10
b
is delimited by a plane perpendicular to the axis common to the part
9
and the frustoconical parts
10
a
,
10
b
. As a result the seal
8
has two parallel plane disk-shaped faces
11
a
,
11
b
. The seal
8
is made from an elastomer. At rest, when it is not fitted, the height of the seal
8
—i.e. the distance between the two faces
11
a
and
11
b
—is greater than the distance between the bottom
5
of the vent cap
3
and the cover plate
2
. On the other hand, the diameter of the part
9
of the seal
8
is less than the inside diameter of the tube section
4
of the vent cap
3
. The seal
8
is placed inside the vent cap
3
with the face
11
a
pressed against the bottom
5
of the vent cap
3
and the other face
11
b
pressed against the cover plate
2
. As a result the seal
8
is compressed between its two faces
11
a
and
11
b
. This is how the vent valve
1
works. Under normal operating conditions of the storage cell, the face
11
b
of the seal
8
is pressed elastically against the cover plate
2
, around the orifice
6
, because of the compression of the seal
8
between the bottom
5
of the vent cap
3
and the cover plate
2
. Consequently, the seal
8
seals the orifice
6
in the cover plate
2
. If the pressure inside the casing of the storage cells exceeds a given threshold, it further compresses the seal
8
against the bottom
5
to the point of allowing the gases to find a path for themselves between the face
11
b
and the cover plate
2
and thereby reach the free area defined between the circumference of the seal
8
and the tube section
4
, whence the gases escape freely through the vent holes
7
a
and
7
b
to the external environment of the storage cell. The path taken by the gases is indicated by the arrows G in FIG.
1
. When the pressure inside the casing returns to a value below the threshold, the seal
8
is again sealed to the cover plate
2
, around the orifice
6
. Consequently, the orifice
6
is blocked again.
This solution has a number of drawbacks. Firstly, the seal
8
is fabricated by injection/compression of an elastomer, which implies a high fabrication cost. To increase productivity, either the number of fabrication molds or the number of imprints per mold must be increased. Apart from the cost of the tooling, the second of these approaches causes variations in the height of the seal, and consequently variations in the pressure at which the vent valve
1
opens.
Furthermore, precise calibration of the pressure at which the vent valve
1
opens also depends on correct centering of the seal
8
relative to the orifice
6
. This centering is achieved by the tube section
4
of the vent cap
5
. The orifice
6
is centered relative to the tube section
4
, which centers the seal
8
. The seal
8
is centered in the tube section
4
by the part
9
of the seal
8
, which has a diameter close to the inside diameter of the tube section
4
. Nevertheless, for the vent valve
1
to be able to operate, the diameter of the part
9
of the seal
8
must be less than the inside diameter of the tube section
4
in all situations, in particular if the diameter of the seal
8
increases because of the compression of the seal
8
between its two faces
11
a
,
11
b
, due to the manner in which it is mounted, but also because of the action of the gases via the orifice
6
. Otherwise, the circumference of the part
9
would be pressed against the inside surface of the tube section
4
. There would then be a seal between these two components, which would restrict or even render impossible evacuation of gases toward the vent holes
7
a
,
7
b
in the event of an increase in pressure in the casing of the storage cell. Consequently, the vent valve would no

Affiliated with

Also associated with

Rating

Vent valve and a storage cell including it does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Vent valve and a storage cell including it, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Vent valve and a storage cell including it will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3188099