Friday, February 25, 2011

CrazyEngineers Forum - Mechanical & Civil Engineering

CrazyEngineers Forum - Mechanical & Civil Engineering

Valves

Posted: 25 Feb 2011 04:06 AM PST

Hello friends,
Many a times you must have heard of valves many times. ever wondered what a valve is?Let us talk what a valve is with reference to an engine.
Each engine by default is provided with two valves.The intake and the exhaust valve.
The intake valve is the passage for air fuel mixture to enter the cylinder.
While the exhaust valve opens at the end of exhaust valve.

So there are basically four types of engine valves and the engines are named accordingly.The valves can be arranged in various ways in the cylinder block.

1.L-head engine:
The valves and camshaft are located in the cylinder block.Ever seen a lawn mower? you have a high probability to see this type of arrangement there.
Disadvantages:
1.Cannot be designed for high compression ratio
2.It has excessive exhaust emissions.
This arrangement was popular in 1950's but now out of service.

2.Overhead valve engines:
These valves have high compression ratios.The valves are located directly above the piston.This also provides clearance volume.It has got more engine torque and power.

3.Overhead-camshaft engines:
Here the camshaft is placed over cylinder head.These are called OHC engines.
In this type pushrods and rocker-arm have got inertia.This resists changing speed and direction.So these push rods bend slightly before they open the valve.This bending has little effect at lower speed. But increases as the speed increases.This causes increasing lag in valve action that tends to limit speed.

4.Multivalve engines:
This engine has many valve per cylinder.but to increase power output mostly 4 valves are used per cylinder.
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