Resealable vent valve for containers such as batteries

This invention pertains to a novel resealable pressure relief vent valve for use in normally sealed containers such as sealed electric batteries or cells wherein said vent valve includes an outer rigid plate, an inner flexible disc forming part of the interior of the container, said disc having one or more vent holes and a compressible rubber disc positioned in partially compressed condition between the outer rigid plate and inner flexible disc and situated over each of said vent holes whereby the inner flexible disc flexes upward breaking its seal over the said holes venting the interior of the container when excessive internal pressures occur.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention pertains to a novel resealable pressure relief vent valve 
which can be used in containers which are air and fluid tight. More 
particularly, the present invention relates to an improved resealable 
pressure relief vent valve which is capable of relieving the build-up of 
excessive gas pressures within a closed container such as an energy cell. 
When said pressure is relieved, the vent closes providing the cell with 
its air and fluid-tight configuration. 
The valves of the present invention have particular application in 
containers such as electrical batteries or cells which are inexpensive yet 
which must be provided with a reliable valve which has good endurance to 
function the entire life of the battery or cell. Therefore, the valves of 
the present invention are particularly characterized by their relative 
inexpensive cost of manufacture, simplicity of design and reliability. 
The term battery is generally used to describe a single unit comprising one 
or more cells which supply electrical energy. The electric current is 
produced directly by chemical reaction which occurs within the battery. 
The terms battery and cells will be used hereinafter interchangeably. 
The resealable vent devices of the present invention are useful in sealed 
cells in contrast to vented cells. A sealed cell, in its normal operation, 
does not require the venting of gas to the atmosphere. However, in a 
vented cell, venting is part of the normal operating behavior of the cell. 
Although sealed cells contain a vent mechanism, they are still referred to 
as "sealed" cells because the vent operates only as a safety measure when, 
as a result of a malfunction or an abuse of the cell, the cell obtains an 
abnormally high internal pressure. 
In a sealed cell, the safety vent mechanism is designed to open if the 
pressure exceeds a certain limit. After the vent releases the excess 
pressure to the atmosphere, it automatically closes, sealing the cell. For 
this reason, it is called a resealable safety vent. The vent is 
incorporated in the cell or battery to protect the cell by opening to 
relieve damaging high pressure, and resealing the cell so that it does not 
remain open to the atmosphere and cause the electrolite to dry out. 
The vent devices of the present invention have a resealing capability. 
Resealable safety vents are generally preferred to non-resealable vents in 
sealed cells for various reasons. Resealable vents can be tested prior to 
assembly into a cell casement to help assure reliable operation. The 
resealing feature allows the cell to operate after the excess pressure has 
been relieved. Cells containing a non-resealable vent will not function 
properly after venting because the electrolite within the cell will dry 
out as the vent remains open. 
While the resealable safety vents of the present invention may be utilized 
on most sealed cells which potentially could experience increases in 
internal pressure, nickel-cadmium cells are discussed in greatest detail 
herein. Such cells are merely illustrative and examples of other cells 
that may be used include carbon-zinc dry cells and "alkaline" cells. The 
operating pressures for each of these cells and other cells vary from 
those of nickel-cadmium cells and the resealable vent devices of the 
present invention may be suitably adapted to be used at pressures other 
than those in nickel-cadmium cells. 
As used herein, the term vent pressure means that internal pressure that 
will cause the vent in the cell to open. 
2. Description of the Prior Art 
Resealable pressure relief vent valves of various designs have been used in 
the past for releasing high internal gas pressures from the inside of a 
sealed electrical cell or battery such as a nickel-cadmium cell. These 
valves generally utilize a valve member such as a flat rubber gasket which 
is situated in a sealing position over a vent orifice by means of a 
resilient member such as a helical spring. The resilient member or spring 
is set to yield at a certain predetermined internal gas pressure which 
momentarily breaks the seal and allows the gas to escape through the vent 
orifice. Examples of such pressure relief vent valves are described in 
U.S. Pat. No. 3,664,878 in the name of H. K. Amthor; U.S. Pat. No. 
3,484,301 in the name of E. E. Gray; and U.S. Pat. No. 3,293,091 in the 
name of J. L. S. Daley. All of these patents disclose devices whose 
configuration require critical tolerances to enable the valve system to 
function properly. As brought out in U.S. Pat. No. 3,644,878, a major 
problem encountered with such valves is that they are bulky and difficult 
to incorporate into the cell assembly. 
Conventional devices utilizing metal springs are extremely costly and 
require very close tolerances to attain the desired force exerted by the 
springs. Moreover, the labor costs in fixing the springs in the cell is 
substantial. The vent device of the present invention has none of these 
disadvantages attributed to spring-type vents. 
Another advantage of the vent device of the present invention over the 
conventional spring vent devices is that it requires substantially less 
space, particularly for its height, in the cell. The reduction in height 
is attributed to the elimination of the spring component in the vent 
device of the present invention. By reducing the space required for the 
vent section, a battery containing the vent device of the present 
invention can contain more energy-producing materials yielding a battery 
having an increase in energy density over a comparable cell utilizing 
conventional vent devices. 
The resealable vent device of the present invention overcomes these and 
other problems and provides numerous additional advantages over known 
resealable pressure relief valves.

SUMMARY OF THE INVENTION 
According to the present invention, there is provided a resealable pressure 
relief valve capable of relieving the excessive build-up of internal 
pressure within a closed container by venting gas from the container to 
the atmosphere and resealing the cell after the internal pressure is 
sufficiently reduced, said valve comprising: 
an outer rigid plate; 
an inner flexible disc forming part of the interior of the container and 
which contains one or more vent holes; and 
a compressible rubber gasket situated in partially compressed condition 
between the outer plate and inner disc and over the said vent holes; 
wherein said plate is bound to the inner disc by means passing through an 
open area of the gasket interconnecting the upper surface of the inner 
disc and the lower surface of the outer plate; and wherein said valve 
vents gas when a predetermined internal pressure is reached within the 
container, which pressure causes the inner disc to flex upward yielding a 
non-uniform gap between the surfaces of the inner disc and rigid plate 
transmitting a non-uniform compression to the rubber gasket including 
reduced compression of the gasket in the area adjacent said vent holes 
causing the gasket to break its seal over the vent holes providing a vent 
path for the venting gas. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The Drawings 
FIGS. 1 and 2 illustrate the cross-section and top views of a battery 
incorporating a resealable vent valve of the present invention. The 
battery comprises a nickel-plated steel can or casing 1 in which is 
contained a battery coil 2 which consists of a positive plate 2a and a 
negative plate 2b separated by separator insulative layers 2c which are 
wound together to form the battery coil 2. A tab 3a connected to or 
integral with the negative plate 2b is secured to the bottom of the casing 
1. Another tab or strap 3b connected to or integral with the positive 
plate 2a is secured to a positive terminal located in an electrically 
conductive button 4 which is welded to the top surface of the rigid metal 
plate. 
The upper end of the battery is formed by the can 1 being bent forming a 
groove 5 and rolled or further bent over an insulating seal ring 6 and 
inner metal disc 7 providing a crimp closure. 
The resealable safety vent device of the present invention comprises an 
outer rigid metal plate 8, an inner flexible metal disc 7 containing vent 
holes 9, and a rubber gasket 10 sandwiched between the outer rigid plate 
and inner flexible disc. 
In the embodiment shown in FIGS. 1-4, a dimple or boss 11 in the upper 
surface of the inner flexible disc 7 protrudes upward through an open area 
in the center of the gasket 10 and that dimple is bonded to the bottom 
surface of the rigid plate 8. In another embodiment (not shown), the 
dimple or boss is located in the bottom surface of the metal plate cover 
and projects downward through the gasket opening to be bonded to the 
flexible metal disc. The height of the dimple or boss is chosen so as to 
cause the sandwiched gasket to attain the desirable compression as will be 
discussed more fully below. 
In FIG. 1 the vent device is in the venting condition as would occur if the 
internal pressure exceeded a predetermined set limit. The path of the gas 
escaping through the vent holes 9 is shown by the arrow. The inner metal 
disc 7 is flexing upward as a result of the excessive internal pressure of 
the battery while the dimple 11 and the outer metal plate 8 remain rigid. 
The change in the plane of the inner disc 7 with respect to the plane of 
the rigid plate 8 causes a non-uniform gap between the surfaces and a 
non-uniform compression on the rubber gasket 10. When the vent pressure is 
reached, the compression on the rubber gasket 10 is sufficiently reduced 
in the area near the vent holes 9 to cause a break in the seal between the 
rubber gasket and the inner metal disc yielding a vent path outward from 
the inner container of the cell. 
After the internal pressure of the cell is reduced below the vent pressure, 
the inner disc returns to its flat configuration, thus resealing the vent 
holes in the inner metal disc. 
In the enlarged cross-section view in FIG. 4 the vent is shown in a sealed 
condition where the flexible inner disc 12 is flat causing the rubber 
gasket 13 in its compressed condition to cover and seal the vent holes 14. 
The Vent Device And Its Operation 
The resealable vent device of the present invention, when incorporated in a 
sealed nickel-cadmium cell, is designed to open in the pressure range of 
about 100 to 400 psig. The lower value for the range is determined by the 
minimum optimum pressure required to carry out the electrochemical 
reaction in the cell. The upper value for the range is determined by the 
maximum internal pressure at which the cell's container will safely 
maintain its integrity. 
The rubber gasket which is sandwiched between the rigid metal plate cover 
and flexible internal metal disc is actually the sealing member which 
covers the vent holes in the internal disc. Therefore, the material of the 
gasket must not be porous to the gases generated within the cell or to the 
atmosphere. The gasket must have memory characteristics. When its 
compression is reduced as the inner disc flexes under excess internal 
pressure, its seal over the vent holes will be broken. As the disc returns 
to its flat configuration when the internal pressure is within prescribed 
safe limits, the gasket returns to its originally compressed state forming 
the seal with the inner disc over the vent holes. The gasket material must 
also be resistant to caustics and other chemicals within the cell. An 
example of a suitable material for the gasket would be an 
ethylene-propylene rubber. 
The inner flexible disc in combination with the rubber gasket seals the 
upper end of the cell or battery. The crimped closure for the top of the 
cell is formed around the edges of the inner flexible disc by causing a 
seal ring of a flexible and non-porous material to be sandwiched between 
the edge of the inner flexible disc and the rolled edges of the can. 
Because the inner disc forms a substantial portion of the top cover of the 
cell, it must be sufficiently strong to withstand the internal pressures 
within the cell below the vent pressure and be resistant to normal 
physical abrasion on the external surface. 
The inner disc may be composed of a nickel plated steel which has 
sufficient flexibility and memory or temper to function properly in the 
vent of the present invention. By having memory or temper is meant that 
the steel should have minimum hysterisis and be capable of flexing at the 
vent pressure to a sufficient degree and distance to reduce the 
compression on the rubber gasket and form a vent path from the vent hole 
in the inner disc to the atmosphere. The resealable safety vent of the 
present invention should preferably vent with a deflection of the inner 
disc in the order of about 0.020 inches. Therefore, the degree of flexing 
of the inner disc should be determined by reverse engineering utilizing 
the desired vent pressure and size of disc. 
The internal pressure at which a vent path will be formed from the vent 
holes in the inner disc to the outside will depend upon a number of 
variables in the components of the vent device. Most significant of these 
variables are the durometer of the gasket, the degree of compression of 
the gasket, the dimple height, the flexibility of the inner disc, the 
diameter of the vent hole, and the location and number of the vent hole 
with respect to the center of the inner flexible disc. While there appear 
to be a large number of variables, once the vent pressure for a given size 
battery is chosen, and the materials to be used in the vent device are 
chosen, the actual structure and dimensions of the vent components can be 
determined. 
In the approximate center of the inner disc is located a dimple or boss. 
The upper surface of this boss is utilized to bond or adhere to the outer 
rigid metal cover. The dimple or boss must have a sufficient cross-section 
to be able to be bonded or welded to the rigid metal plate. The height of 
the dimple above the surface of the flexible disc determines the degree of 
compression for a given rubber gasket. 
The degree of compression for the rubber gasket should be sufficient to 
cause a force downward onto the surface of the inner disc which exceeds 
the force exerted by the normal operating pressure of the cell but which 
is less than the force exerted by the internal pressure when it exceeds 
the vent pressure. It is preferred to choose a rubber gasket having a 
durometer whereby the desired degree of compression is achieved with a 20% 
or less compression or reduction in the thickness of the gasket. The 
greater the degree of compression, the greater the distance the inner disc 
must flex in order to reduce the compression. For a large diameter disc, a 
more highly compressed gasket may be used than for a smaller diameter 
disc. In general, there is an advantage to use as high a compression of 
the disc as possible. As the degree of compression for the gasket 
increases, the criticality for the assembly parts is reduced because the 
same tolerance of error for a part will have a smaller effect on larger 
degrees of compression. 
The actual dimensions of the gasket must be considered both in the 
compressed and uncompressed state. As described above, the gasket is of a 
donut shape. The inner diameter of the donut must be sufficiently small to 
cover the vent holes in the inner flexible disc. If the inside diameter of 
the gasket becomes too close to the vent holes, small increases in 
internal gas pressure can expand or distort the inside diameter causing a 
relocation of the gasket, causing the internal gas to act on the gasket in 
different directions. On the other hand, the inside diameter of the gasket 
must be sufficiently large so as to fit around the dimple or boss in the 
inner flexible disc without sliding out of position. 
As a general rule, the closer the vent holes in the flexible disc are to 
the center line of the disc, the greater the flexing angle required for 
the disc in order to form a vent path. Hence, as the vent holes are moved 
closer to the outside diameter of the flexible disc, the angle of flexing 
is reduced for forming a vent path. As a matter of practicality, the 
smaller the diameter of the overall cell, the closer the vent hole must be 
to the center line of the cell. Therefore, depending upon the materials 
chosen for the venting device, there may be a minimum diameter for cells 
which may use the vent device of the present invention. For most materials 
used for the vent device of the present invention, it is recommended that 
cells should have a minimum diameter of about 0.875 inches. This would be 
equivalent to a sub-size C cell or larger. 
A diameter of the vent holes themselves are also an important factor in 
determining the number of holes that should be present in the disc as well 
as their location. It is suggested that vent holes have a diameter in the 
range of 0.080-0.090 inches. The border around a vent hole formed by the 
rubber gasket should be about 0.030-0.040 inches to assure proper sealing 
of the vent hole. 
The rigid metal plate of the vent device an be comprised of any durable 
metal such as a nickel-plated steel. It must be rigid and flat and have a 
surface which is compatible for welding or bonding to the inner flexible 
disc. The rigid metal cover may have a diameter less than that of the 
inner metal disc, as small as one-half the diameter of the inner disc. 
The top or cover of the cell must contain the positive terminal which is 
electrically connected to the positive plate. The upper rigid plate of the 
vent device may also function as the cover of the cell. Optionally, a high 
hat or electrically conductive button can be welded to the outer surface 
of the metal plate to form a positive terminal for the cell. The strap or 
tab connected to the positive plate can be welded to the bottom surface of 
the inner flexible disc which is electrically connected to the upper rigid 
plate by the attachment through the boss or dimple. 
This configuration represents an important advantage of the vent device of 
the present invention over conventional devices. Due to the spring vent 
designs in conventional cells, a metal strap from the roll assembly 
(positive plate) must be bonded to a non-uniform, non-flat surface on the 
underside of the cover. Due to this non-uniform, non-flat surface, the 
target area for welding the strap is small and therefore the labor costs 
involved in attaining the weld in conventional valves are high. In the 
design of the valve of the instant invention, the surface of the inner 
disc is flat, significantly reducing the cost and difficulty in welding 
the strap. 
The pressure relief valve of the present invention provides a significant 
savings in manufacturing costs compared with helical-spring type valves 
used in conventional energy cells, with no sacrifice in reliability. The 
valve of the present invention provides a significant saving in assembly 
costs because there is minimal labor required in the orientation of parts 
for the valve providing for automatic assembly thereof. Compared with 
conventional spring-type valves, the valve of the present invention 
provides not only a saving in manufacturing and assembly costs but it also 
has a smaller space requirement in the cell. Cells containing the valve of 
the present invention can be improved by utilizing the additional space 
attributed to the more streamline valve.