What is a PVC valve? Signs of damaged PVC valve?

PVC valves are an important part of a car’s exhaust system that helps remove exhaust gases from the crankcase of an internal combustion engine. Therefore, checking and identifying signs of damage to the PCV valve is essential to help the vehicle always operate stably. Below CARON PRO will share with you useful information to identify damaged PVC valves so they can be repaired promptly.

What is a PVC valve?

PVC valve

When a car engine operates by burning a mixture of fuel and air, a small amount of excess air usually flows to the lower part of the crankcase (crankcase). Even though the piston rings are sealed, gaps still exist between the piston rings and the cylinder wall, allowing gas in the combustion chamber to escape.

The release of air into the crankcase causes many problems, including degrading the quality of the engine oil inside the crankcase, increasing the pressure below and hindering the forward movement of the piston, as well as pushing. Oil passes through seals and gaskets, leading to reduced efficiency of the lubricating oil system.

That is why we need a crankcase ventilation system (Positive Crankcase Ventilation – abbreviated as PCV) to remove excess air from the crankcase.

Structure of the crankcase ventilation system:

  • Snorkel: The snorkel is connected from the engine’s intake manifold and is responsible for providing a stream of clean air (fresh air) to push excess air out of the crankcase. In the snorkel there is usually a baffle or filter to prevent oil vapor.
  • PCV valve: The PCV valve (also known as crankcase vent valve or crankcase vent valve) is a one-way valve connected from the engine’s cylinder head to the intake manifold. The PCV valve’s job is to use the engine’s vacuum force to suck excess air from the crankcase out. Then, this gas is introduced into the intake system and mixed with fresh air to enter the engine and participate in the combustion process. However, before entering the intake system, excess air passes through a filter to remove oil vapor.

Additionally, the PCV valve also helps prevent backfires and fires by preventing pressure from the intake system from entering the crankcase. When an engine undergoes turbocharging or backburn, pressure from the intake system can cause damage to the crankcase’s gaskets and seals. Therefore, when this pressure is encountered, the PCV valve will close to prevent pressure from entering the crankcase.

PVC valve structure?

PVC valve structure

The structure of the PCV valve is designed very precisely with two specially sized valve heads. In between, there are precisely calibrated valve balls and springs. The more the engine works, the more exhaust gas is emitted. However, when the engine is running at idle, these emissions are very small. Therefore, the PCV valve must be able to flexibly adjust the amount of exhaust gas corresponding to each engine working mode. To achieve precise regulation, the PCV valve is designed to operate based on vacuum pressure in the intake manifold. Because this pressure always changes with the engine speed.

Flexible PVC valve regulates the amount of air corresponding to each engine’s working mode
  • When the engine operates at idle or light load, the vacuum force in the intake manifold increases, reducing the amount of exhaust gases that need to be released from the crankcase. This vacuum force will push the PCV valve closed, leaving only a narrow gap for a small amount of exhaust gas from the crankcase to enter the intake manifold, avoiding losing the concentration of exhaust gas.
  • When the engine is operating at high load or under heavy load, at high rpm, the vacuum suction is reduced, and the spring opens the PCV valve to allow larger amounts of exhaust gases to escape.
  • When the engine stops, there is no vacuum force, the spring pushes the PCV valve closed.
  • In case of backfire, the increased pressure in the suction pipe will force the PCV valve to close.

Although the PCV ventilation system brings many benefits, it also has a disadvantage: it can lead fuel and combustion gases back into the intake system, causing the valves and cylinders to become black.

Signs of damaged PVC valve?

When exhaust gases flow through the PCV valve for a long time, it can cause a buildup of oil, causing a blockage. Therefore, if the PCV valve is clogged or stuck closed, the following signs may appear:

  • The engine has mud or dirt around the PCV valve area.
  • Oil leak from PCV valve system.
  • The check engine light on the dashboard illuminates, indicating a system problem.
  • There is a strange sound coming from the engine, like a grinding or hissing sound.
  • PCV valve gasket or seal is blown or damaged.
  • Exhaust smoke color has unusual signs such as gray, black or blue.
  • The engine is difficult to start or tends to vibrate unsteadily.

The above signs may indicate that the PCV valve is clogged or not working properly. Addressing this problem is important to ensure the PCV valve system operates effectively and maintains engine stability.

How to check PVC valve?

How to repair PVC valve

When detecting signs of suspected damage to the PCV valve, the user can check the PCV valve in one of the following ways:

  1. Open the oil tank cap when the engine is running: When the engine is running, the user can open the oil tank cap to check. If the oil tank cap is sucked inside the engine and is difficult to remove, this indicates high vacuum pressure in the crankshaft system or possibly a damaged PCV valve.
  2. Using PCV pipe clamps: Users can use PCV pipe clamps and observe the engine rpm. If you see a change in engine rpm, it may imply that the PCV valve is stuck and the engine may vibrate or shut down.
  3. Check for sludge buildup: When you see blue smoke coming from the exhaust pipe or there are signs of oil leakage due to high engine pressure, check to see if there is a buildup of sludge and dirty oil inside the pipe. If the PCV valve is excessively contaminated, the user needs to clean it before continuing to use it.
  4. Blow air into both ends of the PCV valve: Remove the PCV valve and blow air into the crankshaft end and intake air line to check the level of valve blockage.
  • On the crankcase side, if there is no air flow, this indicates the valve is stuck closed. On the contrary, if there is air flow through, the PCV valve operates normally.
  • On the intake side, if there is air flowing through, this indicates the valve is stuck open. Conversely, if there is no air flow, the PCV valve operates normally.

Reputable car maintenance address?


CarOn Pro – 5S standard car service system

Caron Pro is trusted and known by customers as a chain of 5S standard auto repair service centers. With extremely modern equipment, genuine spare parts, skilled technicians, a full range of services at extremely affordable prices and quality. With a variety of services and products, CarOn is committed to providing the most dedicated quality and service.

Please contact us immediately via Hotline: 1900633612 or 0919009069

Facility 1 – CarOn Xuan Phuong
Lot P3, Thi Cam Street, Xuan Phuong, Nam Tu Liem, Hanoi
Phone: 0919009069
Facility 2 – CarOn Hoang Quoc Viet
455 Hoang Quoc Viet, Co Nhue 1, Bac Tu Liem, Hanoi
Phone: 1900633612
Facility 3 – CarOn Lai Xa
Km14, National Highway 32, Lai Xa, Kim Chung, Hoai Duc, Hanoi (next to Hoai Duc welcome gate)
Phone: 0384653472
Facility 4 – CarOn Care Thai Nguyen
76 Viet Bac Street, Dong Quang, Thai Nguyen
Phone: 0975782639
Facility 5 – CarOn Care An Khanh
Bao Son Paradise Villa Area, Hoai Duc, Hanoi
Phone: 0963598600

Trả lời

Email của bạn sẽ không được hiển thị công khai. Các trường bắt buộc được đánh dấu *