How Do Tire Pressure Guages Work?

Three basic types of tire gauges, they all work with the same principle. Devices have different readout methods

Maintaining proper air pressure in your car's tires is a simple preventative maintenance step you can perform to avoid such troubles as bad gas mileage, premature tire wear, and poor tire to road contact. An invaluable tool for this procedure is a tire pressure gauge. And just a note here, don't trust the gauges connected to the air hose at a service station. They can be notoriously inaccurate due to misuse and mishandling There is a myriad of shapes, sizes, and costs to consider when shopping for a gauge, however, they all boil down to 3 basic types. The dial, digital, and stick. The gauges may look different, and display results differently, but all use the same principal. When the gauge is pressed onto the stem of a wheel, the air pressure in the tire pushes against some type of plunger which in turn actuates the readout section of the gauge assembly. The following article describes the similarities and differences between the different types of gauges.

The first and most common gauge is the stick type, also known as the pen type. On the air input end is a ball or tube shaped body that presses onto the wheel stem. Inside the opening of this ball is a centered pin. This pin pushes against the pin in the valve stem to open the valve, letting air into the gauge. The gauge's pin is surrounded by rubber to seal the gauge to the valve stem. The gauges long metal tube is lubricated with light oil, and contains a rubber piston that is forced away from the air input end when the gauge is pressed onto the valve stem. The piston is pushed in direct relation to the air pressure coming from the tire. The piston is pushed against a spring that is calibrated in such a way that a certain amount of air will compress it a certain amount. The spring is wound around a stick or rod with gradations printed on it. When the piston pushes the spring and the rod, the rod is pushed out the end of the gauge by a calibrated amount. The user then simply reads the number on the rod. The rod is not connected to the spring or the piston, so when the gauge is removed from the valve stem, the spring returns the piston to its starting point, but the rod stays where it is until the user pushes it back into the body of the gauge. The rod is larger in diameter inside the gauge, so as not to be shot out the end of the tube.

The second type of gauge is the dial type. These gauges are easier to read, but more expensive and less robust than the stick variety. In this gauge, air from the tire enters a C-shaped tube inside the gauge. The air forced into the tube causes it to uncoil, much like a party noisemaker. The end of the tube is connected to an indicator needle by a series of levers and springs. When the tube straightens out, the needle deflects accordingly. Almost all dial gauges have an air bleeder valve; if the air pressure is too great in the tire, hold down the button and air will be released until the desired pressure is achieved.

The third type is the digital tire gauge. These gauges are the easiest to use, they have a direct LCD readout, and some even talk! These gauges use an electronic component known as a strain gauge. Air from the tire goes into the body of the gauge, where it pushes against the strain gauge. The resultant flexing of the strain gauge changes its resistance. This resistance change is input to a microprocessor where the resistance change is converted to a binary signal used to drive LCD readout. These gauges come in a variety of shapes and sizes, are very accurate and very durable.

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