What Is an Air Gauge?
An Air Gauge is an instrument used to measure the pressure of high-pressure air when handling it.
It may refer to a pressure gauge for high-pressure air pipes or tanks, or it may refer to an instrument that measures the pressure of air in tires. Both have similar construction and principles.
It is important to routinely check the pressure of high-pressure air pipes and tanks to ensure their proper operation. Pneumatic tires are filled with high-pressure air, and proper air pressure must be maintained for the tires to perform as they should.
Therefore, air gauge has an important role to play in measuring air pressure.
Uses of Air Gauges
Air gauges are used to check air pressure. Air gauges for high-pressure air lines and tanks are used to verify that the actual pressure matches the required pressure for the equipment.
Air gauges for tires are useful for checking the air pressure in inflated tires for automobiles, motorcycles, or bicycles.
Principle of Air Gauges
1. Bourdon Tube Gauge
The most commonly used analog air gauge is the Bourdon Tube Gauge. This gauge uses a bent metal tube that is blocked at one end. When pressure is applied, the tube’s bend stretches. The needle rotates in conjunction with the deformation of the metal tube to indicate the pressure. Although highly accurate, these gauges are mechanical and precise, and their vulnerability to shock is a drawback.
2. Spring-Type Gauge
Spring-Type Gauges are often used in the same way as Bourdon Tube Gauges. The pressure is antagonistic to the spring, and the pressure is indicated by the indicator needle in conjunction with the contraction of the spring. It is characterized by its simple structure and relatively high shock resistance. These gauges are used in portable air gauges for tires and in pressure gauges for daily inspections of high-pressure piping.
3. Diaphragm-Type Gauge
A diaphragm is a membrane. A diaphragm is used to measure pressure by detecting the pressure that causes the diaphragm to cave in. There are two detection methods: One is to connect the diaphragm to a Bourdon Tube Gauge and measure mechanically, and the other is to read the deformation of the diaphragm electrically.
Types of Air Gauges
1. Pressure Gauges for high pressure air piping and tanks
Pressure gauges for high-pressure air piping and tanks are sometimes called air gauges. They are used to check if the pressure is within the normal range during daily inspections, and the most common type is the durable spring type.
2. Air Gauge for tires
When we call them air gauges, we generally refer to those for tires. There are analog and digital display methods, and mechanical and electrical methods for converting detected pressure to display. In the case of analog types, most gauges are either Bourdon-Tube or Spring-Type Gauges.
They range from small, simple portable gauges to large, precise gauges that are regularly used at gas stations and maintenance shops. Since Bourdon tube gauges are sensitive to shocks, the entire gauge is usually covered with rubber.
Some gauges are integrated with air injection valves and operating devices. An example of this type of gauge is one that is inserted into the air valve of a tire and is inflated when the grip is held short and inflated when held long. This type is connected to an air tank.
Other Information on Air Gauges
Air Pressure Units
The SI unit of pressure is Pa. In general, air pressure gauges are also displayed in Pa. For safety reasons, it is especially important for gauges used for high-pressure air pipes and tanks to use the same units, and SI units are strictly enforced. On the other hand, most gauges for tires are calibrated in units of 100 kPa.
This is because the air pressure of passenger car tires is around 200 kPa, and this scale is easy to read. Another reason is that in Japan, kgf/cm2 has been used for tire pressure.
Since 100 kPa is approximately 1 kgf/cm2, by using the scale in units of 100 kPa, people familiar with either unit can handle the gauges without much discomfort. Gauges with kgf/cm2 and bar indications are still sold today.
Foreign-made air injectors and other equipment may be denoted in units common in foreign countries. In the UK, they may be denoted in psi. As a guide, 30 psi is equivalent to about 200 kPa.