What is a decompression valve?
The cylinder of a chainsaw contains a mixture of gases. When you start the machine, this mixture needs to compressed in order for ignition to succeed. But, excessive pressure requires you to put a lot more effort into starting the engine. When the starter cord is pulled, the piston inside the cylinder moves, compressing the fuel and air mix and increasing the internal pressure. Overcoming this pressure on chainsaws with a larger engine capacity takes considerable effort, but a decompression valve reduces the pressure, making the engine easier to turn over.
How does the STIHL decompression valve work?
Opening a decompression valve releases gas to ensure that the peak pressure when starting the engine is reduced. This compression release means less effort is required when starting your chainsaw. As soon as the engine starts, the decompression valve automatically closes again, compression increases, and the start-up momentum of the cylinder initiates normal combustion operation so you experience full engine performance.