What happens when you inflate a balloon past its holding capacity? It pops.
What happens when you pressurize an air tank beyond its rated pressure? It fails catastrophically and ruptures in a spectacular way that you wouldn’t want to witness firsthand.
Most air compressors have a number of precautions built in to avoid the risk of a tank rupture. The compressor itself will probably have an automatic shut-off control that turns off the motor once the maximum tank pressure is reached.
In case the auto-shutoff switch fails, there will typically also be a safety valve built into the tank. Such safety valves, such as the Conrader hard seat valve shown above, are rated to specific pressures. A 100 PSI valve will open up at ~100 PSI in order to vent excess air to keep the pressure at or below 100 PSI.
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Essentially, safety valves have spring-loaded pistons. Below their factory-set pressures, internal springs hold the pistons downward, creating a seal. But once the pressure inside a tank or device overcomes the built-in pressure limit of a safety valve, the piston is pushed upwards, opening the valve seal to lower and equalized the air pressure.
Safety valves typically also have loops attached to the pistons so that you can manually rapidly depressurize a device or air tank. You should check safety valves every now and then to ensure they can open freely.
There are two main types of safety valves – hard seat and soft seat valves. Hard seat valves are rugged and inexpensive, but typically leak a little bit. Soft seat valves are a little less rugged and more expensive, but they are built with better seals that aren’t as prone to leaking.
I went with Conrader hard seat valve for a recent project, but there are other good brands as well. Safety valves are available in a wide range of pressures and in different styles.
Amazon carries a couple of valves directly and through 3rd party vendors, but your best bet is to check with Grainger, Zoro, McMaster Carr, or another industrial suppliers that have wider selections.