The blow-off valve may be familiar to anyone who enjoys the sound it produces. This valve, which is also called scavenged air valve, pop off valve, or drain valve, is located in the engine compartment and produces a striking noise when used. However, many are unaware of how this noise originates and what is actually the benefit of such a valve.
The function of a blow-off valve
Put simply, a blow-off valve allows excess pressure to escape from the intake of the engine. Specifically, this valve is always used in combination with a turbocharger. To explain the process, first briefly the functioning of the turbocharger be explained. The turbocharger's exhaust gas turbine is driven by the exhaust gas flow during acceleration and uses a compressor wheel to compress the air in the intake tract on the other side. When the acceleration stops, the throttle closes, but the exhaust flow continues to drive the turbocharger, so pressure continues to build up despite the throttle being closed.
This continual pressure can cause significant material fatigue, especially in turbocharged turbochargers. To prevent this, the blow-off valve is used. This will allow the excess pressure to escape as soon as the throttle closes. As the pressure escapes, so does the familiar sound. However, there are two types of blow-off valve, of which only one produces the distinctive noise. The closed version allows the escaping air back into the intake tract in front of the turbocharger, so that the noise is not heard so clearly here. The open version of this valve simply lets the air into the atmosphere, with the sound clearly audible.
Installation of a blow-off valve
When retrofitting a blow-off valve, make sure that the important components in the surrounding area remain accessible despite the installation. Basically, the valve is installed between the throttle and the turbocharger, which is already a little tighter on most vehicles. However, many newly built turbo engines already have such a valve as standard. If the valve to be installed is an open model, it must be avoided to return the air. For this purpose, special aluminum covers are suitable. The disadvantage of a blow-off valve for any tuning friend, however, is that it is not allowed in Germany. Accordingly, it should be carefully considered whether you want to block this valve. If you want to buy a blow-off valve, you can prepare yourself for a wide price range. Cheap valves start already at 30 Euro. However, the price is not yet exhausted on higher quality models even at 500 Euro.
Of course that had not happened yet!
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