A diving compressor is an air compressor that provides breathing-quality air to a diver. This can be done by filling diving cylinders (tanks) or by providing constant air at the surface. Compression condenses the breathing gas, removing the water and allowing a certain volume of gas to be contained or stored.
Diving compressors are large three or four stage reciprocating air compressors. They can use oil or some have ceramic lined cylinders with O rings so that no lubrication is needed. Those that use oil must only be lubricated with the oil specified by the manufacturer. Filters are installed to remove water and oil residue. Be aware that just because an air compressor is oil-free it does not mean the gas output will be of breathable quality.
A diving compressor will meet certain criteria- including air quality. They operate at much higher volumes than the standard garage’s air compressor. Compressors used to fill cylinders must provide high pressure and low volume whereas compressors used at the surface will provide low pressure but high volumes of breathing gas because they are normally supplying more than one diver with air.
Those looking to purchase a diving compressor should be trained and certified in inspecting scuba equipment. Being a Professional Scuba Inspector (PSI) means the diver will know how to safely fill and inspect a diving cylinder. Incorrect procedures can mean life or death in the waters.
A certified inspector will first make sure the cylinder is in compliance (meaning it has been recently tested.) They will then remove or bleed out air until the tank is at five or ten pounds PSI- a tank should never be fully emptied. With the tank mostly empty the inspector will shake the tank, checking for loose objects or water.
The inspector will then examine the valve- looking for rust or damage. Then he will begin to fill the tank. The cylinder will be placed in a cool bath and filled slowly (at less than one bar per minute.) This is to prevent the cylinder from becoming heated, which can cause an unsafe reduction of pressure in the tank when cooled.
Some diving compressors come with a bank. Compressors used to fill dive cylinders may have a bank that will fill storage tanks when it is at idle. Surface supplied compressors will have a bank filled with back up breathing gas in case of mechanical failure.
As stated above, compressors remove water from the gas, which is good for the dive cylinder because it prevents the formation of rust. It will also prevent the regulator from freezing. This, however, does make the air very dry, leaving divers at greater risk for dehydration. It’s crucial to make sure the divers are adequately hydrated before and after the dive to prevent decompression sickness.
Decompression sickness occurs when a diver ascends too rapidly, and the body becomes overly saturated with nitrogen. Decompression sickness can be fatal if severe. Along with making sure they are hydrated divers should make sure to complete several decompression stops on their way back up from a dive.
Diving compressors are an important part of the safety of scuba diving. Therefore, it’s very important to make sure cylinders are properly filled and inspected by certified divers. Those looking to own a diving compressor themselves should be aware that the equipment is an investment and know how to properly care for and use the compressor. A diving compressor will be the most expensive piece of equipment a diver can own, so it is often only purchased by those looking to open their own dive shops or scuba tours.