What Is an Exhaust Valve?
An exhaust valve is installed as integral parts of a vehicle’s exhaust system and open and close to control gas flow, optimize engine backpressure, and improve performance and acoustic control.
The exhaust valve is located in the cylinder head of an internal combustion engine.
When the fuel/air mixture ignites in the cylinder, spent gases are pumped out of the engine through this valve.
In a typical internal combustion engine, the exhaust valve is larger than the intake valve.
This is because it is more difficult to clear the exhaust gases from the cylinders than it is to introduce fuel and air into the combustion chamber.
A key feature in building horsepower and fuel economy in modern engines is the ability to optimally time the opening and closing of the exhaust valve.
Uses for Exhaust Valves
The camshaft is at the center of control, grinding lobes to clear the cylinder to take full advantage of the valve’s capabilities.
By opening the exhaust valves at critical times in the combustion process, the piston is able to push all of the exhaust gases from the cylinder out of the combustion chamber without sacrificing the flow of intake charge into the cylinder.
Several factors are involved in assisting the exhaust valves.
Valve pockets in the cylinder head are very important.
Like exhaust valves, valve pockets and bowls must be unrestricted so that spent gases can exit the combustion chamber quickly and without restriction.
The exhaust port must also be free of obstructions, and gasket matching is a common way to accomplish this.
Principle of Exhaust Valves
By grinding the exhaust ports and exhaust manifold of the cylinder head to the same size as the openings in the exhaust gasket, the gases do not contact the blunt edges of the gasket or exhaust manifold and impede flow.
This smooth transition eliminates backpressure that would otherwise impede the flow of exhaust from the engine.
Smoothing the radius of the exhaust bowl in the cylinder head also aids flow by providing a smooth unobstructed path for flow out of the cylinder.
When grinding the valve seat of an exhaust valves, six different angles can be ground on a single valve face for high-performance applications.
Each angle corresponds to an existing angle ground into the valve seat of the cylinder head.
The engagement of the angles not only provides a proper seal when the valve is closed, but also provides a smooth path around the edge of the valve for gas to flow.
In a typical street vehicle, exhaust velocity is not as critical as in a racing engine, so a three-angle valve grind is used.
Exhaust Valve Construction
Exhaust valves are used in sealed vessels and piping, for example, to prevent destruction when internal pressure rises.
The basic structure of an exhaust valves are that when the internal pressure rises, the valve body or ball section is pushed up and the valve opens to vent the internal pressure to the outside. After the pressure is discharged, the valve is no longer pushed up by the pressure, so the valve drops under its own weight to stop discharging pressure.
Until now, exhaust valves has not been seen very often in daily life. Recently, however, we are seeing more and more masks with exhaust valves in factories and other places. When working with a mask, humidity and temperature inside the mask rise, making it difficult to breathe. When breathing in, the valve is pulled closed by negative pressure. Conversely, when you exhale, the valve is pushed open by exhalation, expelling the humidity and heat inside.
Exhaust valves are not included in safety valves or air vent valves when divided by genre or category. But they are similar in that they vent internal pressure.
Safety valves are intended to prevent serious accidents such as rupture or destruction of equipment or structures due to pressure buildup. Safety valves work by releasing pressure to the outside when a set pressure is reached in an enclosed container or piping.
Air vent valves prevent air from mixing with water or other fluids. To give an example, if air gets mixed in with a pump for fluid, the propeller that generates the water flow will spin out of control and be damaged. To prevent this phenomenon, known as air biting, air vent valves use the pressure of the fluid that flows into the air vent valve to push up the valve to expel the air remaining inside.
Structure of Intake and Exhaust Valves
Intake and exhaust valves are valves that incorporate a gas intake structure into an exhaust valves. By being able to perform intake as well as exhaust, the valve can be used against negative pressure. When no negative pressure is generated, the operation is the same as that of an air vent valve. However, when negative pressure is generated, the valve can take in gas through the air intake port to break the vacuum.
In general, the structure is such that under atmospheric pressure, the gas is discharged by the operation of a float. When the inlet side where fluid flows in becomes negative pressure, the float operates to open a space for a valve such as a disk or diaphragm to operate. The valve then operates to take in the gas and relieve the negative pressure.