Tire pressure indicator

A tire pressure indicator for visual observation of tire pressure including a screw-on cartridge containing a spring-biased piston with a movable shield which covers a central indicator pilot when tire pressure is up to requirements. When pressure is below what it should be, the piston retracts to allow the shield to expose indicator pilot to the view of an observer, thus serving as a warning that inflation is required.

FIELD OF INVENTION 
Pressure indicators incorporated in the valve stem of a vehicle tire to 
indicate to an operator the condition of inflation. 
BACKGROUND OF INVENTION 
As early as 1914 inventors were devising ways for the operator of a motor 
vehicle to observe the inflation pressure of tires as exemplified in U.S. 
Pat. No. 1,089,326 to Chilson. More recent examples of pressure indicators 
are found in U.S. patents to Bordwick, U.S. Pat. No. 3,357,240 (1967), and 
Yabor, U.S. Pat. No. 3,789,867 (1974). In earlier years, when tires and 
tubes were formed of natural rubber, they required much more attention 
relative to inflation since the material was porous and the tires tended 
to deflate by leakage through the walls. With the more recent use of 
synthetic rubber and tubeless tires, the tires retain the initial inflated 
condition for a relatively long time. Under these conditions a vehicle 
operator tends to become careless about checking his tires. 
It is an object of the present invention to provide an inflation indicator 
which will register "under inflation" at a glance with no need to bend 
down and read any calibrated scale. A color signal will warn the observer 
if there is a deflation condition which requires attention. 
It is a further object to provide a tire pressure indicator which can be 
readily mounted on a valve stem in a manner to depress the basic 
springbiased valve and substitute a secondary seal. 
It is a further object to provide an indicator which can be readily removed 
so that the air supply nozzle to permit inflation can be applied to the 
standard valve stem. 
Additional objects and features of the invention will be apparent in the 
following description and claims in which the principles of the invention 
are set forth together with details to enable persons skilled in the art 
to practice the invention, all in connection with the best mode presently 
contemplated for the invention.

DETAILED DESCRIPTION OF THE PRINCIPLES OF THE INVENTION AND THE MANNER AND 
PROCESS OF USING IT 
With reference to the drawings, in FIGS. 1, 2 and 3, the top threaded end 
of a standard tire valve stem 20 is illustrated showing a standard valve 
stem 22 which, when depressed, opens the primary valve (not shown). 
The pressure indicator, according to the present invention, has a main 
cylindrical body 24 with a three-step bore. The bottom and largest is the 
bore 26 which is internally threaded to screw onto the valve stem 20. A 
second bore 28 terminates at the bottom in a shoulder 30 where an O-ring 
32 is located to seal the top of the stem 20. At the top of the bore 28 is 
a second shoulder 34 which locates an O-ring 36. 
At the bottom of the body 24 is a spider 40 (FIGS. 1, 2 and 8) which 
carries a depending pin 42 on the bottom of which is a small disc 44. This 
disc will depress the valve stem 22 of the primary valve when body 24 is 
screwed onto the valve stem 20. 
A piston 50 with an O-ring seal 52 is slideable on the bore 28 and has an 
upstanding, preferably opaque, hollow stem 54 which is axially slotted at 
the top end 56. This stem serves as a shield for a visual indicator to be 
described. 
The top end of body 24 is reduced in size at 60 to receive a sleeve-like 
skirt 62 of a cap 64. The cap has a top plate 66 with a central rod-like 
extension indicator or post 68. Viewed from the top, as in FIG. 7, it will 
be seen that a C-shaped opening 70 is provided around the indicator post 
68. The top plate 66 serves as a spring retainer for coil spring 72 which, 
at its other end, bears against the piston 50. The slotted end of the 
piston stem 54 slips through the C-shaped opening 70 in a sliding 
relationship This end may be colored green. 
A dust seal cap 80, formed of transparent plastic, overlies the cap 64 and 
has an atmospheric vent opening 82. The cap 64 is secured to the main body 
by a suitable adhesive or sonic welding. Similarly, the transparent cap 80 
is secured to cap 64 by an adhesive or sonic welding. 
The rod-like indicator post 68 is preferably formed of or covered with a 
colored material such as red. 
The spring 72 can be calibrated for any desired pressure such as 26, 28, 
30, etc. pounds per square inch. 
IN THE OPERATION 
With the parts assembled as shown in FIG. 2, the main body 24 is screwed 
onto a standard valve stem 20. Disc 44 will press down the standard valve 
step 22 admitting the tire pressure to the piston 50. If the pressure 
within the tire can overcome the calibrated spring 72, the piston will 
move against the spring and up against the seal 36 to provide a secondary 
seal for the air within the tire. In this position, the opaque hollow stem 
54 will be covering the post 68 so that only the green sleeve 54 is 
visible through the transparent cap 80. 
If the pressure in the tire reduces to a point that the calibrated spring 
72 can move the piston down, the red indicator post 68 will be exposed so 
that an observer can see that the tire needs inflation. 
FIG. 9 illustrates a modified valve stem depressor in the form of a ring 90 
carrying suitable spider arms to support the depending disc 92. An O-ring 
seal 94 serves to seal the body 24 to the valve stem.