Saturday, July 6, 2013
The Uses Of PCV Valve
By Fred Gagnon
The blowby vapors that finish up in an engine's crankcase hold moisture and also combustion byproducts and unburned fuel vapors. The crankcase is covered to avoid the get away of these gases to the atmosphere, however the vapors need to be taken out so as to avoid oil contamination that will cause sludge formation. The positive crankcase ventilation (PCV) system siphons these vapors from the crankcase and tracks them into the intake manifold so that they can be reburned in the engine.
The primary component in the PCV system is the PCV valve, which is typically found in the valve cover. A hose attaches the PCV valve to the intake manifold. An additional hose between the air cleaner and crankcase or another valve cover (V6 or V8 applications) gives fresh air to help purge the vapors from the crankcase. Some engines have a split air filter for the PCV breather hose positioned inside the air cleaner.
The PCV valve is a spring-loaded valve with a particular hole size made to confine the amount of air that's siphoned from the crankcase to the intake manifold. This is crucial because air drawn over the valve from the crankcase has a hovering effect on the fuel mixture exactly the same as a vacuum leak. So, air flow by the valve need to be managed within certain limits. At idle, air flow is decreased because little blowby is made. When the engine is traveling and vacuum is quite high, airflow through the entire PCV valve is at an optimum to free the blowby vapors from the crankcase.
You must be aware that PCV valves are assessed for special engine applications. A poor PCV valve for an application can pass way too much or too little air leading to drivability difficulties. Varnish remains can obstruct the valve, so replacement for protective maintenance is advisable (every 50,000 miles usually).
Only some engines have PCV valves. Some ventilate the crankcase with a tiny breather hose and calibrated pinhole. There's no spring-loaded PCV valve. On those applications, no maintenance tasks is usually required.
The primary component in the PCV system is the PCV valve, which is typically found in the valve cover. A hose attaches the PCV valve to the intake manifold. An additional hose between the air cleaner and crankcase or another valve cover (V6 or V8 applications) gives fresh air to help purge the vapors from the crankcase. Some engines have a split air filter for the PCV breather hose positioned inside the air cleaner.
The PCV valve is a spring-loaded valve with a particular hole size made to confine the amount of air that's siphoned from the crankcase to the intake manifold. This is crucial because air drawn over the valve from the crankcase has a hovering effect on the fuel mixture exactly the same as a vacuum leak. So, air flow by the valve need to be managed within certain limits. At idle, air flow is decreased because little blowby is made. When the engine is traveling and vacuum is quite high, airflow through the entire PCV valve is at an optimum to free the blowby vapors from the crankcase.
You must be aware that PCV valves are assessed for special engine applications. A poor PCV valve for an application can pass way too much or too little air leading to drivability difficulties. Varnish remains can obstruct the valve, so replacement for protective maintenance is advisable (every 50,000 miles usually).
Only some engines have PCV valves. Some ventilate the crankcase with a tiny breather hose and calibrated pinhole. There's no spring-loaded PCV valve. On those applications, no maintenance tasks is usually required.
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