Nixon & Vanderhye
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. 
G
G01L
inventional
Tien-Tsai
Huang