Pressure gauge with a movable interior scale

A pressure gauge with a movable interior scale is provided including an elongated hollow body having a closed chamber, an intake passage communicating with the closed chamber, and an air inlet communicating exteriorly of the pressure gauge. A charge port is provided between the closed chamber and the intake passage and a discharge port is provided communicating with the closed chamber and exteriorly of the pressure gauge. In addition, a spring-biased charge valve is disposed at the charge port and is normally biased to close the charge port. At the same time, the spring-biased charge valve is driven to open the charge port when pressurized air enters the intake passage. A sliding member is mounted in the closed chamber in sealing engagement with the chamber, and slidable in the chamber upon entry of pressurized air. A pressure indicating scale is carried by the sliding member and a display hole is formed in the body and aligned with the scale so that the scale is visible through the display hole. A spring-biased discharge valve is disposed at the discharge port and is normally biased to close the discharge port, but is manually openable to release pressurized air in the closed chamber. A spring is connected at an upper end to the charge valve and at a lower end to the sliding member for biasing the sliding member to ruturn to a normal position when pressurized air is released from the closed chamber.

BACKGROUND OF THE INVENTION 
This invention relates to a pressure gauge, and more particularly to one 
which has a movable interior scale. 
The improvement of this invention is directed to a conventional pressure 
gauge shown in FIG. 1 which is typically used to measure the air pressure 
in a tire. The conventional pressure gauge includes an adapter A for 
coupling with a tire's air valve, a tubular body B, and a movable scale C 
inserted partially into the tubular body B. The reading of the scale C is 
difficult. In addition, when impurities enter the interior of the tubular 
body B, the precision of the pressure gauge may be reduced. 
SUMMARY OF THE INVENTION 
It is therefore the main object of this invention to provide a pressure 
gauge with a movable interior scale. 
According to this invention, a pressure gauge includes an elongated, hollow 
body having a closed chamber therein, an intake passage communicated with 
the closed chamber and having an air inlet communicated with the exterior 
of the pressure gauge, a charge port provided between the closed chamber 
and the intake passage, and a discharge port communicated with the closed 
chamber and the exterior of the pressure gauge. A spring-biased charge 
valve is disposed at the charge port for being biased to close the charge 
port so as to stop air flow between the closed chamber and the intake 
passage when no pressurized air enters the air passage and for being 
driven by pressurized air entering the air passage to open the charge 
port. A sliding member is mounted slidably in the closed chamber and is 
slidable as sealed in the closed chamber when pressurized air enters the 
closed chamber. The discharge port is positioned between the charge port 
and the sliding member. A pressure indicating scale is carried on top of 
the sliding member. A display hole is formed in the body and aligned with 
the scale so that the scale is visible through the display hole. A 
spring-biased discharge valve is disposed at the discharge port for being 
both biased to close the discharge port and driven to open the discharge 
port. A magnifier is fixed within the display hole so that the scale can 
be seen clearly. A spring is connected to the sliding member for biasing 
the sliding member to return to its normal position when the pressurized 
air is removed from the closed chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 2 and 3, a pressure gauge of this invention includes an 
outer tube 1, an adapter 2, a transparent inner tube 3, a pressure 
measurement unit 4, and a pressure discharge unit 5. The outer tube 1 
includes an internally threaded upper end 11, a clip 12 attached to its 
upper end, a display hole 13 formed in its middle portion, an indicating 
line 14 provided on its outer surface and terminated at the adjacent edge 
of the display hole 13, an internally threaded lower end 15, and a first 
discharge port 18. A magnifier is fit into the display hole 13. An 
externally threaded lower seal 16 is engaged with the lower end of the 
outer tube 1 and has a central bore 17 therein. The adapter 2 has an 
externally threaded lower end engaged with the upper end of the outer tube 
1, and an air passage 22 having an inlet 21 and an outlet 23. 
The adapter 2 is also provided with a conventional mechanism for depressing 
the tire valve to enable pressurized air from the tire to flow into the 
passage 22. This mechanism includes a chuck 24, a rubber ring 25 disposed 
about the chuck, and a tubular retaining member 26 for locking the ring 25 
to the chuck 24. Chuck 24 is adapted to connect with the air valve of a 
tire in a conventionl manner. The inner tube 3 extends through the outer 
tube 1 to engage tightly with the bore 17 of the lower seal 16 and has a 
second discharge port 31 aligned with the first discharge port 18 of the 
outer tube 1, and an internally threaded upper end 32. 
The pressure measurement unit 4 includes a charge valve member 41 having an 
outward flange formed at its upper end, an externally threaded lower end 
431, an interior air passage 432, and an inward flange 433 formed at its 
lower end for defining a charge port inside of the inward flange 433. A 
compression spring 44 is placed in the air passage 432 so that a headed 
charge valve rod 451 extends through the spring 44. A charge valve 452 is 
formed in its upper end surface with a threaded hole which is engaged with 
the externally threaded lower end of the charge valve rod 451 to close the 
charge port. The outward flange of the charge valve member 41 is clamped 
between the adapter 2 and the inner tube 3. An O ring 42 is clamped 
between the upper ends of the valve member 41 and the inner tube 3 for 
establishing an air-tight seal therebetween. A sliding member 47 includes 
a seal 471 dividing the interior of the inner tube 3 into two closed air 
chambers. A scale 48 is formed in its lower end portion with a hole 
through which a tongue of the sliding member 47 is inserted tightly so 
that the scale 48 is carried on top of the sliding member 47 and moves 
therewith. A tension spring 46 is sleeved tightly on the externally 
threaded lower end 431 of the charge valve member 41 at its upper end and 
connected securely to the sliding member 47 at its lower end for biasing 
the sliding member 47 to move upward. 
The pressure discharge unit 5 (see FIG. 2A) includes a hollow, truncately 
conical coupling element 51 bridging the gap between the outer tube 1 and 
the inner tube 3 for the defining of an exhaust passage between the first 
discharge port 18 of the outer tube 1 and the second discharge port 31 of 
the inner tube 3. As illustrated, an air-tight seal is established between 
the small-diameter end 52 of the coupling element 51 and the second 
discharge port 31 of the inner tube 3 and between the large-diameter end 
53 of the coupling element 51 and the first discharge port 18 and the 
outer tube 1. A discharge valve unit is constructed in a similar manner to 
the charge valve unit and includes a headed discharge valve rod 56, a 
discharge valve 57 secured to the discharge valve rod 56, and a 
compression spring 55 sleeved on the discharge valve rod 56, as shown in 
FIG. 2A. The discharge valve 57 is normally closed and can be opened by 
pushing the head of the discharge valve rod 56. 
Referring to FIG. 4, when the adapter 2 is coupled with a tire (not shown) 
in such a manner that when the air passage 22 of the adapter 2 is 
communicated with the air valve of the tire, pressurized air impels the 
charge valve 452 to move downward so that the charge port is opened. The 
pressurized air therefore flows into the inner tube 3 to move the sliding 
member 47 downward against the biased force of the tension spring 46. When 
the scale 48 stops, the mark of the scale aligned with the indicating line 
14 can be seen through the magnifier. When the pressure gauge is removed 
from the air valve of the tire, the charge valve 452 is pushed upward by 
the spring 44 to close the charge port so that the sliding member 47 and 
hence the scale 48 are rendered immovable for a more convenient reading of 
the pressure value being measured. 
When it is desired to reset the pressure gauge after use, the discharge 
valve rod 56 is pushed inward to open the discharge port, permitting the 
pressurized air to flow out of the interior of the inner tube 3. 
With this invention thus explained, it is apparent that numerous 
modifications and variations can be made without departing from the scope 
and spirit of this invention. It is therefore intended that this invention 
be limited only as indicated in the appended claims.