A blowoff valve , exhaust valve or compressor bypass valve ( CBV ) is a pressure release system that exists in most turbocharged engines. The main purpose is to remove the turbo load when the throttle is suddenly released.
Video Blowoff valve
Characteristics
The compressor bypass valve (CBV), also known as a pressure relief valve or switch valve, is a vacuum-driven manifold valve designed to release pressure in the turbocharged loaded vehicle intake system when the throttle is lifted or closed. This air pressure is re-circulated back to the non-pressurized intake tip (before the turbo) but after the airflow sensor.
A blowoff valve, (sometimes "hooter valve" or BOV) performs the same task but releases air into the atmosphere instead of circulating it. This type of valve is usually an aftermarket modification. The blowoff action produces a variety of different hissing sounds, depending on out design. Some blowoff valves are sold with trumpet-shaped exit doors that intentionally amplify sound. Some turbocharged vehicle owners can buy blowoff valves solely for hearing effects even when those functions are not required by normal machine operation. Motor sport organized by the FIA ​​has made it illegal to vent the blowoff valve into the atmosphere.
The wind blower valve is used to prevent compressor surges, an easy phenomenon when lifting the throttle from an unventilated turbocharged engine. The resulting sound is called turbo flutter (slang term "choo-choo" is sometimes used). When the throttle plate on the turbocharged engine closes, the high-pressure air in the intake system is trapped by the throttle and the pressure waves are forced back into the compressor, the resulting collision of the pressure waves creates an effect similar to cavitation producing a unique sound.
Maps Blowoff valve
Operation
A blowoff valve is connected by a vacuum hose to the intake manifold after the throttle plate. When the throttle is closed, the relative manifold pressure drops below atmospheric pressure and the resulting pressure differential operates the blowoff valve piston. The excess pressure of the turbocharger is then released into the atmosphere or recirculated to the upstream intake of the compressor inlet.
Disadvantages
In the case where the airflow sensor (MAF) is used and located upstream of the blowoff valve, the engine control unit (ECU) will inject excess fuel as air-fed air is not subtracted from the measurement of the intake charge. The machine then operates briefly with a rich mixture of fuel after each valve actuation.
Rich mixing can cause doubt or even stall the engine when the throttle is closed, the situation worsens with a higher push pressure. The occasional occurrence of this type may only be a nuisance, but frequent events may eventually disrupt the spark plug and destroy the catalytic converter, since inefficient fuel burns produce soot (excess carbon) and unburnt fuel in the exhaust stream can produce soot in the converter. and drives the converter outside its normal operating temperature range.
An alternative method to utilize MAF and blowoff valves is to have MAF down stream between intercooler and throttle plate. These are known as Blow-throughs rather than traditional Draw-through settings. Care should be taken to the MAF position to prevent damage to sensitive elements. For example, on a SR20DET engine, MAF must be at least 12 "(30cm) from the throttle plate, and the blowoff valve should be 6" (15cm) from the MAF sensor. By using the blow-through method, the MAF will not be affected by the opening of the blowoff valve because the pressure is released before air reaches the MAF.
One approach used to reduce the problem is to reduce the push pressure, which reduces the volume of ventilation required and results in less over-calculated costs by the ECU. Air can also be recirculated back to the intake, a typical stock arrangement for cars with upstream MAF sensors. This situation can also be corrected by diverting the fuel measurement system to an absolute manifold pressure sensor, a conversion that usually requires a compatible ECU or compatible piggy-back fuel controller. The MAP sensor monitors absolute pressure in the manifold at any time and will detect changes that occur when the valve is out, allowing the ECU to reduce fuel metering.
See also
- Wastegate
- Water hammers
References
Source of the article : Wikipedia
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