Battery vent plug

A battery vent plug providing repeated relief of a pressure condition within a battery at relatively low internal pressures. The vent plug is arranged to prevent dropping of the internal pressure to zero upon venting while yet having a small relief-reseal pressure range. The vent plug includes a relief valve within a housing defined by a rubber cylinder releasably engaging an annular seat on the housing about an inlet to a vent chamber within the housing. The rubber cylinder is maintained under a preselected compression assuring sealing thereof to the seat at pressures below a preselected venting pressure. Upon removal of the sealing portion of the cylinder from the seat, the pressurized gas escapes around the cylinder and through a hole in the housing to atmosphere.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to battery vent plugs and in particular to battery 
vent plugs provided with low pressure relief valves. 
2. Description of the Prior Art 
In U.S. Pat. No. 3,201,284 of Grenville B. Ellis, a vent valve for 
batteries is shown having a pair of seal rings provided with abutting 
tapered annular portions which are deflected from their normal abutting 
association by pressure acting outwardly through a vent passage 
communicating with the interior of the battery. The rings are carried in 
an outwardly opening annular groove on the body of the plug so as to vent 
the battery to atmosphere through the resulting opening therebetween. 
Robert A. Warren et al, in U.S. Pat. No. 2,934,584, show a control vent 
having a resilient sealing disc engaging the edge of a cup containing the 
battery cell elements, and means for clamping the disc against the cup 
edge. A gap is provided in the edge so that sealing pressure is exerted by 
the resilient strain of the less combined portions of the sealing disc 
adjacent the gap so that pressurized gas may lift the edge of the sealing 
disc at the gap and escape from the cup. 
In U.S. Pat. No. 3,096,216, Robert A. Warren shows a vent valve adapted for 
venting an alkaline cell at gas pressures of 135 lbs. psi. The valve 
includes a sealing disc lying over a groove or notch, which is pushed 
slightly into the notch by the high pressure. By urging the sealing disc 
portion sufficiently into the notch, the seal with the sealing cup is 
momentarily broken to permit gas to escape. 
Robert A. Warren discloses, in U.S. Pat. No. 3,114,659, a valve wherein a 
nylon gasket, a steel diaphragm, and a neoprene gasket are caused to bow 
outwardly by the pressure of the gas. When a certain predetermined 
pressure is reached, the seal between the sealing cup and the neoprene 
gasket is weakened sufficiently to permit venting therebetween. Upon 
reduction of the pressure, the steel diaphragm urges the structure back to 
the normal position, reestablishing the seal. 
A common problem in the known battery pressure relief valve is the 
reduction of the pressure within the valve substantially to ambient or 
zero psig, as a result of each pressure relief operation. Thus, it is 
conventional in the known pressure relief valves to permit continuous 
bleeding until internal pressure in the battery reaches zero. A number of 
prior art vent devices which tend to maintain an internal pressure at all 
times have a relatively high relief pressure. One such structure is 
defined by a rubber disc with a narrow slit in the center thereof. 
SUMMARY OF THE INVENTION 
The present invention comprehends an improved low cost battery vent plug 
which provides low pressure relief of the battery cell chamber such as at 
pressures below 10 psig. 
The vent plug of the present invention has a small relief-reseal pressure 
differential of approximately .+-.2 psig. 
The vent plug of the present invention effectively maintains a positive 
pressure within the battery cell upon each venting operation. 
The vent plug is formed of suitable materials unaffected by the corrosive 
materials in the battery. 
The improved vent plug is defined by a housing having a mounting portion 
adapted to be mounted in a battery cover opening, a vent chamber, an 
annular seat confronting the vent chamber, an inlet opening through the 
seat to the vent chamber, and an outlet opening through a portion of the 
housing spaced from the inlet, a resilient body in the chamber having a 
sealing portion adjacent the inlet, and a force transfer portion opposite 
the sealing portion, and means on the housing for applying a compressive 
force to the force transfer portion directed through the body to urge the 
sealing portion against the seat for releasably sealingly closing the 
inlet, the resilient body being compressed toward the force transfer 
portion as a result of a preselected elevated fluid pressure in the inlet 
to space the sealing portion from the seat and permit flow of the fluid 
through the vent chamber about the resilient body to the outlet and to 
permit the resilient body to have the sealing portion resealed to the seat 
upon dropping of the fluid pressure below the preselected fluid pressure. 
In the illustrated embodiment, the resilient body is defined by a right 
circularly cylindrical rubber member. 
The resilient body, in the illustrated embodiment, defines parallel, 
opposite end surfaces defining the sealing portion and force transfer 
portion of the resilient body, respectively. 
The vent chamber defines an annular space extending about the resilient 
body for providing communication between the inlet and outlet when the 
sealing portion is spaced from the seat. 
The inlet opens to the vent chamber coaxially of the resilient body sealing 
portion in the illustrated embodiment. 
In the illustrated embodiment, the seat comprises an upstanding annular 
projection on the housing defining an annular knife-edge portion engaged 
by the resilient body sealing portion. 
In a modified form, the seat is defined by an O-ring carried by the 
housing. 
A sealing gasket may be provided for sealing the housing mounting portion 
to the battery cover. 
In the illustrated embodiment, the seat is defined by a projection having 
frustoconical radially inner and outer surfaces intersecting at a 
knife-edge engaged by the resilient sealing body. 
The battery vent plug of the present invention is extremely simple and 
economical of construction while yet providing improved low pressure 
relief of a battery, such as lead-acid battery.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the exemplary embodiment of the invention as shown in FIGS. 1-3 of the 
drawing, a vent plug generally designated 10 is shown to be sealingly 
mounted to the top wall 11 of a battery 12 which illustratively may 
comprise a lead acid battery. 
At times, such as at overcharge of the battery, gas is generated by 
electrolysis of water in the electrolyte. In hermetically sealed lead-acid 
batteries, the battery is effectively sealed so as to maintain an oxygen 
cycle therein such that oxygen gas generated at the positive electrode of 
the battery diffuses to the negative electrode thereof where it is 
electrochemically reduced to form water. Resultingly, buildup of hydrogen 
gas within the battery is minimized and water loss is thereby minimized. 
However, it is desirable to provide in such sealed lead-acid batteries some 
means for venting the battery in the event of the internal pressure 
thereof exceeding a preselected elevated pressure. The present plug 10 
provides such desirable pressure relief at relatively low operating 
pressures while yet effectively maintaining pressure within the battery. 
The vent plug is provided with a mounting portion 13 which is fitted into 
an opening 14 in the battery cover, or top wall, 11. The body 15 of the 
vent plug defines a vent chamber 16. In the illustrated embodiment, a plug 
cap 17 cooperates with the body 15 and mounting portion 13 in defining the 
vent plug housing 18. 
As best seen in FIG. 2, mounting portion 13 defines an outturned annular 
flange 19 provided with a radially inwardly opening annular recess 20 for 
receiving an outturned annular flange 21 at the inner end of the plug cap 
17. 
As further illustrated in FIG. 2, the plug cap 17 defines a transverse wall 
22 outwardly of the flange portion 21 and has a central through opening 23 
in direct communication with the cell interior and defines an inlet to the 
vent chamber 16. Transverse wall 22 and opening 23 may have any 
configuration desired as long as communication between the battery cell 
and vent chamber 16 is maintained. 
Plug cap 17 defines an outer circularly cylindrical surface 24 which is 
secured to a complementary inner cylindrical surface 25 of mounting 
portion 13 of body 15 as by suitable adhesive 26, ultrasonic fusion, or 
the like. Thus, as indicated above, the plug cap is secured in association 
with body 15 to define the vent chamber 16. 
As shown in FIG. 3, top wall 27 of body 15 is provided with a pair of 
diametrically oppositely positioned vent openings 28 defining outlets from 
the vent chamber 16. 
Outwardly adjacent flange 19, body 15 is provided with an annular support 
flange 29. In one configuration, a plurality of thin vertical ribs 30 are 
spaced at 90.degree. about the axis of body 15 and extend from an upper 
edge 31 spaced above top wall 27 to a lower edge 32 formed integral with 
the flange 29. 
Mounting portion flange 19 defines upwardly facing inclined surface 33 
cooperating with the battery cover wall 11 in defining a bayonet mount of 
the mounting portion to the cover. To provide a seal of the vent plug 10 
to the cover, a rubber sealing gasket 34 is mounted to mounting portion 13 
subjacent flange 29 so as to be compressed against the edge of the battery 
cover defining opening 14 when the vent plug is locked into position by 
the bayonet-type mount defined by flange surfaces 33 engaging the inside 
surface of the battery top wall. 
Vent chamber 16 effectively defines a right circularly cylindrical chamber. 
Coaxially received in the vent chamber is a right circularly cylindrical 
resilient valve body illustratively formed of rubber, having a 
cross-sectional diameter slightly less than that of the vent chamber so as 
to define therebetween a coaxial annular vent space 36. 
As shown in FIG. 2, the axial length of valve body 35 is preselected so as 
to cause the valve body to be compressed between top wall 27 of the 
housing body 15 and an annular upstanding seat 37 on the transverse wall 
22 of plug cap 17. More specifically as shown in FIG. 2, the outer end of 
valve body 35 defines a planar surface 38 in facial engagement with top 
wall 27 and the inner end of the valve body 35 defines a planar surface 39 
parallel to surface 38 and defining the sealing portion of the valve body 
engaging the seat 37. 
In the embodiment of FIG. 2, seat 37 defines an annular knife edge formed 
by an inner frustoconical surface 40 and an outer frustoconical surface 
41. The knife edge 42 provides an effectively positive seal to the valve 
body 35 in the normal disposition of vent plug 10, as illustrated in FIG. 
2. 
Vent plug 10 is arranged to vent gaseous fluids from the interior of the 
battery 12 when the pressure thereof reaches a preselected pressure. 
Internal battery fluid pressure acts through opening 23 in plug cap 17 
against the surface 39 of valve body 35 so as to space surface 39 upwardly 
from the knife edge seat 42 at the preselected vent pressure. As will be 
obvious to those skilled in the art, the specific preselected pressure at 
which the vent plug 10 vents the gas from battery 12 is a function of the 
resiliency of the material making up valve body 35 and the amount of 
precompression applied to the valve body in urging the surface 39 against 
the knife edge seat. As will be further obvious to those skilled in the 
art, other parameters of the structure, including the diameter of the vent 
holes 28 and the radial dimension of the coaxial annular vent space 36 may 
be preselected in further controlling the pressure at which the vent plug 
operates. 
Illustratively, in one form of vent plug 10 embodying the invention, the 
vent plug opened to relieve the battery internal pressure at a pressure of 
8 psig, with a partial resealing of the valve body against the valve seat 
at a pressure of 6.5 psig, and with a positive stable resealing of the 
valve body to the valve seat when the pressure dropped to approximately 5 
psig. Thus, illustratively, the vent plug may be arranged to provide a 
relatively small pressure differential in effecting the venting operation 
while maintaining a positive gas pressure within the battery at all times. 
In the illustrated embodiment, the components of the vent plug, other than 
valve body 35 and sealing gasket 34, may be formed of a suitable molded 
synthetic resin resistant to corrosion by the battery acid. The valve body 
35 and gasket 34 may be formed of suitable rubber material also resistant 
to attack by the battery acid. 
As will be further obvious to those skilled in the art, other forms of 
seats may be utilized within the scope of the invention. Thus, as shown in 
FIG. 4, an O-ring 43 may be installed in a suitable annular recess 44 in 
the transverse wall of the plug cap in lieu of the knife edge seat 
illustrated in FIG. 2. Where the O-ring is formed of rubber, the rubber 
material may be preselected to resist corrosion by the battery acid. 
Thus, the present invention comprehends an improved vent plug structure 
which is adapted to provide venting of a sealed storage battery over a 
small pressure differential range. The vent plug further is arranged to 
effect such venting while maintaining a positive pressure within the 
battery. The invention comprehends control of the parameters of the 
construction of the components of the vent plug so as to provide such 
venting at a preselected pressure, such as in the range of approximately 1 
psig to 20 or more psig. 
It is contemplated that the vent plug housing may have any shape or 
configuration desired so long as the plug cap cooperates with the housing 
and valve body to form the desired fluid seal and to provide a fluid 
passage which, upon excess pressure buildup within the cell, permits the 
valve body to unseat to vent the excess pressure to the atmosphere as 
described. Likewise, the vent opening or openings in the housing may be 
positioned in any convenient location so long as fluid communication is 
maintained with the atmosphere upon the valve body venting the excess 
pressure. Further, it may be desirable to design the plug cap to 
facilitate drainage of liquid electrolyte back into the cell from the vent 
chamber or to reduce the chances of electrolyte entering the vent chamber. 
Thus, it is contemplated that the vent plug embodying this invention may 
take many shapes and other features may be included as desired without 
departing from the spirit and scope of the invention as defined in the 
appended claims. 
The foregoing disclosure of specific embodiments is illustrative of the 
broad inventive concepts comprehended by the invention.