The Schrader valve is a clever pneumatic valve that nearly every vehicle in the world has on its tyres. So what’s it got to do with air conditioning?
It’s a good question, and the answer is tied up with how the Schrader valve works. When you remove the dust cap from your car tyre before putting air in, you see the valve stem, which is the bit sticking out from the tyre. The valve core is threaded inside it. The valve core has a seal which is attached to a pin. When you push the air line hose on to the valve, it presses on the pin and it opens the valve to allow the air in. The valve ensures that the air already in the tyre is retained when you connect the air pump to the tyre and top up the air – the valve is closed until a tool is introduced that opens it.
The reason that Schrader valves are widely used in air-conditioning systems is that they allow engineers and maintenance crew to conduct tests and carry out work without losing pressure from the system or having to take the entire system down, especially if it is pressurised. In air conditioning, the Schrader valve allows the operator to service the cooling system and to diagnose any problems that are causing the unit to run less efficiently.
Using the Schrader Valve for Maintenance
The operator will use various tools and hoses to suck refrigerant out of the system if necessary – for example, if the system has been overcharged with refrigerant. Alternatively, if there has been a leak, they can top up gases or liquids as required without having to stop the system. In addition, the gas pressure in the system can be measured.
Schrader valves perform very well unless they are tightened too much or too little – in other words, the torque has to be right. Over- or under-tightening can result in leaks from the valve. So you do need air-conditioning professionals to work on your system. They’re aware of these kinds of issues and will make sure they get the torque on the valves right.
It’s important, too, to select the right kind of core in the Schrader valve. The valves come in different materials and grades, and the oil pressure, temperature and type of refrigerant can all influence the type of Schrader valve chosen. Many manufacturers make their own recommendations, so the installer or maintenance provider needs to be aware of this. In some cases, hexagonal caps are used on the valves, because they can be carefully adjusted to the correct torque using a spanner.
Because of their vital role in servicing and maintaining air-conditioning systems, the position of the Schrader valves should be marked on the system drawings so that they are easy to locate if there is a problem.
How many times have you driven away from the garage air pump and left the dust caps neatly lined up on the top of the compressor unit? Heating and ventilation engineers carry spares, of course, and they always check that the cap is back on – it’s vital to keep dirt and dust out of the valve.