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Understanding the crankcase ventilation system
Understanding the crankcase ventilation system
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Understanding the crankcase ventilation system

On your vehicles, the crankcase ventilation system is essential for preserving the engine and its lubrication system. Why is this? By regulating the pressure in the crankcase, it prevents excessive engine wear and oil leaks, ensuring optimum performance. In the face of today's environmental challenges, the importance of this system cannot be underestimated. It captures noxious gases charged with oil mist, preserving our atmosphere and our health. What's more, by reinjecting the collected oil into the lubrication system, it reduces engine oil consumption. To fully understand this system, let's go back to basics: the four-stroke engine.

A closer look at how the combustion engine works

A 4-stroke engine operates in four distinct phases: 1. intake, 2. compression, 3. expansion and 4. exhaust.
During intake, the piston creates a vacuum in the cylinder, allowing air to enter via an intake valve. During compression, the piston moves upwards, compressing the air while an injector introduces fuel. The resulting explosion of the air-fuel mixture pushes the piston down, generating a rotary motion that is transmitted to the vehicle's wheels. When in operation, the burnt gases are expelled via a valve and discharged through the exhaust system.
At the same time, the lubrication system reduces friction between parts by lubricating them with engine oil, stored in the crankcase.
⚠️During engine operation, various phenomena occur in the oil sump, in particular the formation of blow-by and oil vapours, which can cause engine malfunctions.

Blow-by: definition, origin and composition

In an engine, blow-by is a leak of combustion gases from the cylinders into the oil sump. This leak is the result of a poor seal between the piston and the cylinder, mainly due to ring wear. Over time, the friction between pistons and cylinders wears down the rings, making them less effective at retaining combustion gases.
Made up of combustion gases, blow-by is a threat to the engine and the environment. It contains pollutants such as unburnt fuel, nitrogen oxides, carbon oxides, water vapour, sulphur oxide and particles from component wear.
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Oil mist in the crankcase

When the engine is running, the oil is heated to high temperatures, causing it to evaporate and form an oil mist inside the crankcase. Mixed with blow-by, this new vapour-gas mixture poses a threat to the engine.
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What are the risks for the engine?

The main risks associated with the combustion gas-oil vapour mixture are :
  • Excessive pressure in the crankcase: An accumulation of gases and vapours in the crankcase generates excessive pressure in the system, exerting too much force on the seals. This high pressure leads to leaks, even threatening the lubrication system.
  • Engine oil contamination: Once in the crankcase, blow-by gases contaminate the oil, diluting it and altering its lubricating properties. Contaminated oil can cause premature wear to components as it circulates through the lubrication system.

The risks involved also include a drop in engine performance due to reduced compression of the air-fuel mixture. This results in increased fuel consumption to maintain acceptable performance. In addition, oil leaks require more oil to compensate for these losses.
To counter these threats, it is imperative to establish effective crankcase ventilation, which is essential to depressurise the system and deal effectively with these gases and vapours.
⚠️Unlike four-stroke engines, two-stroke engines do not require a crankcase ventilation system. Why is this? Because their combustion cycle comprises just two phases: intake and combustion. Inside, the oil is mixed directly with the fuel to lubricate the moving parts. In this way, oil vapours and blow-by gases are burnt with the air-fuel mixture during combustion, eliminating the need for crankcase ventilation.

The crankcase ventilation system

As environmental standards have evolved, crankcase ventilation systems have had to improve. Older vehicles used OCV (Open Crankcase Ventilation) systems that vented gases and vapours into the atmosphere. Some were equipped with filters to capture engine oil. However, with increasingly stringent regulations, open systems have been replaced by closed CCV (Closed Crankcase Ventilation) systems.
The CCV system, also known as the "PCV system" (Positive Crankcase Ventilation), is now widespread and even compulsory on new vehicles. What's special about it? It prevents the release of noxious gases into the atmosphere.
How does it work? Gases and vapours are drawn into the system. They are passed through a coalescing filter. Thanks to its filter media, this retains the oil and contaminants present in the combustion gases. The oil is returned to the crankcase, while the gases are reintroduced into the intake manifold via the PCV valve to be burnt during combustion.
🔍What is the PCV valve? The PCV valve is a valve located in the crankcase, connecting it to the intake manifold. Inside is a diaphragm and a spring. In practical terms, when the pressure reaches a certain level, the spring collapses and the diaphragm deforms, allowing the gases to reach the intake and causing the pressure within the crankcase to drop.

What are the advantages of a ccv system?

  • Crankcase pressure stabiliser: This system maintains the crankcase pressure at the correct level. Excessive pressure can lead to oil leaks, faulty seals and damage to mechanical parts. Conversely, insufficient pressure can lead to lubrication problems. Pressure regulation therefore ensures optimum engine performance, prolonging its life.
  • Reduce oil consumption: Thanks to the coalescing filter, oil droplets present in the vapours are captured. This oil is returned to the crankcase for reuse, minimising oil consumption.
  • Reduce pollutant emissions: By redirecting the gases towards the air intake, this system allows them to be burnt in the combustion chamber instead of being released into the atmosphere. This contributes significantly to a cleaner environment by limiting harmful emissions.
  • Preserving the engine and its performance: By capturing contaminants and soot in the combustion gases, the filter prevents premature engine wear and ensures efficient combustion. As a result, the engine maintains its performance over the long term, ensuring reliable, long-lasting vehicle operation.

How coalescing media work

What is coalescence? It's when the oil molecules in a gas come together to form larger droplets. In a VCC system, this happens thanks to a glass fibre filter. These glass microfibres are hydrophobic, meaning that they do not absorb liquids, enabling highly efficient coalescence.
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How does this filter work?

Oil vapours and gases enter the coalescing filter. Inside, the fibres resemble a very tight labyrinth. This arrangement forces solid particles and aerosols to constantly change direction, reducing their speed until they are captured by the glass fibres. The droplets eventually flow down the fibres, coalesce into large drops and reach the outside of the filter media. By gravity, they fall and accumulate in the tank of the filter housing. The collected oil returns to the housing. At the same time, the gas freed of oil and impurities is directed towards the intake for combustion.

The HIFI FILTER® range

Discover our wide range of crankcase ventilation filters at HIFI FILTER®. To browse our catalogue or get more information, please contact us. Find the perfect filter for your engine now and ensure optimum performance.
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"When should I replace my filter?"

To determine when to replace your coalescing filter, follow the manufacturer's recommendations, as the replacement interval depends on operating conditions, the vehicle and the type of load. In dusty environments or with heavy loads, replacement may be more frequent. To detect a faulty filter, look out for the following signs:
  • Oil leaks: When a coalescing filter is clogged, the combustion gas-oil vapour mixture is not evacuated efficiently, leading to a rise in crankcase pressure.
  • Blue smoke in the exhaust: If the oil is not properly separated from the combustion gases, it can be drawn into the air intake system and burnt in the combustion chamber, causing blue smoke to be emitted in the exhaust.

If your equipment shows any of these symptoms, check or change your crankcase ventilation filter immediately.

"How can we slow down the blow-by?"

Although blow-by is a natural phenomenon linked to engine wear, regular maintenance can slow it down. Adopt these maintenance habits:
  • Change the engine oil and oil separator filter regularly: This removes contaminants that can accelerate wear on engine components, particularly cylinders and piston rings.
  • Use quality fuel: Good quality fuel ensures better combustion, limiting contamination of the crankcase.