DJA3032 CHAPTER 7

CHAPTER 7:VALVE AND COOLING VALVE
by
MOHD SAHRIL BIN MOHD FOUZI, Grad. IEM (G 27763)
DEPARTMENT OF MECHANICAL ENGINEERING
© MSF @ POLITEKNIK UNGKU OMAR
(DJA3032) INTERNAL COMBUSTION ENGINE

General Objective:
To understand the structures and types of valves
Specific Objectives:
At the end of this unit you should be able to:
1. describe the types of valves
2. draw and label the different parts of a valve
3. explain types of materials used in valves
4. explain the process of coating a valve
5. explain the function of an interference angle valve
6. explain the purpose and operation of valve rotation
7. explain the heat zones and working temperature of a valve.
8. explain how working temperature is maintained by sodium cooled valves.
9. explain the purpose and operation of DOHC engine.

Introduction
 In this chapter we are to discuss about valves in an engine. Valves can either be in
the block, or in the cylinders. Valve location is used to classify an internal
combustion engine.
Types of valve location for the internal combustion engine
 Valves in the block (flat head), are also called L Head engine, because the
cylinder and combustion chamber are in the shape of an inverted ‘L’.
 Engines with valves in the block have the intake valve on one side of the cylinder
and the exhaust valve on the other side, these are called T Head engines.
 Valves in head ( overhead valve), are also called I-Head engine because the
cylinder and combustion chamber are in the shape of an ‘I’.
 One valve in head ( usually intake ) and one valve in block, are also called F head
engine; this is less common.

Arrangement of valve
FIGURE 7.1: ARRANGEMENT OF VALVE

Valve Parts
FIGURE 7.2: PARTS OF VALVE
 A valve has several parts and they are in the tip or
rocker arm contact area, valve spring retainer lock
grooves, valve stem, fillet, face, margin and valve
head. The head of the valve is the part that is inside
the combustion chamber.
 The valve can be designed with different head shapes
such as :
i. oval head
ii. flat head
iii. concave head
iv. recessed head
 The more metal on the head of valve, the more rigid the valve is.
 Less metal means the valve will be able to conform to the seat more effectively.
These valves are said to be elastic.
 Rigid valve does not seat that well. Elastic valves seat better, but they may not
last long.

Flat head Concave head Oval head Recessed head
FIGURE 7.3: TYPES OF HEAD VALVES
Valve Materials
 Intake and exhaust valve materials include :
i. alloy steel valves with aluminized face and chrome stem
ii. silchrome valve with aluminized face
iii. austenitic steel with aluminized face and chrome stem
iv. SAE 21-2steel with nickel-plated face
v. Satellite
vi. Sodium-filled stems ( for valve cooling ).

Valve Protection
 Corrosion tends to cause pitting on valve seat faces, as a result of which the hot
gases start to leak through, eventually burning a channel locally through which
compression is lost .
 Due to this, coatings are applied for protection against corrosion. Materials that
are used for coatings include alloy containing :
i. nickel
ii. manganese
iii. cobalt
iv. chromium
v. silicon
vi. molybdenum
vii. tungsten
viii. titanium

 However these materials are costly. Due to that, a much economical coating
system has been developed . This coating system is called ‘Aldip process’ in
which application of an aluminum coating is used.
 The process is :
i. Aluminum material is sprayed in the form of a paste after valve seats have
been finished – machined and the stems rough grounds.
ii. The component, in a jig, are then dipped for a few seconds in a molten flux
bath at 7600 C.
iii. Later it is removed from bath before surplus aluminum is blown off.
 The outcome is a smooth permanently adhering coating of aluminum on an iron
alloy underlay. No further finishing is necessary.

Valve Seat
 Valve seat is defined as a circular surface that is machined into the cylinder block
or head. There are two types of valve seats;
i. integral
ii. insert
 The integral type is cast directly as part of the cylinder head , the insert type uses a
metal ring as the seat.
 It is pressed into the cylinder block and ground to the correct angle. Insert valve
seats can be made from cast iron, hardened cast iron, hi-chrome steel, and satellite
(very hard steel).
 Valve seats are ground to a specific angle for correct operation. They are either 30 o
or 45 o . An interference angle is very common when grinding the valve.

FIGURE 7.4 : AN INTERFERENCE ANGLE
 Figure 7.4 shows the valve is ground to 44o
while the seat is ground to 45o. This interference
angle tends to cut through any deposits that have
been formed on the seat.
Valve Rotators
 Valve rotators are used on certain engines. If valve are rotated a small amount
each time they are opened, valve life will be extended. This is especially true
when using leaded fuel.

 Below are the effects of using valve rotators :
i. minimize deposits of carbon on the stem of the valve,
ii. keep the valve face and seat clean,
iii. prevent valve burning caused by localized hot spots,
iv. prevent valve edge distortion,
v. help to maintain uniform valve head temperatures,
vi. help to maintain even valve stem tip wear, and
vii. help to improve lubrication on the valve stem.
 There are several types of valve rotators. Most operate on the principle that as the
valve spring compressed, small balls inside the rotator roll up an inclined surface.
This action causes the valve rotates slightly as it is being compressed.
FIGURE 7.5 : VALVE ROTATOR

FIGURE 7.5: ROTORCAP VALVE ROTATOR OPERATION
Valve Temperature and Cooling
FIGURE 7.6: ZONES OF HEAT
 Exhaust valve temperature may reach approximately 704o
C to 815o C. This means that they are in fact running red
hot. Good heat transfer, therefore, is essential.
 It is important that valve can be fully seated when they
are closed. The exhaust valve is closed approximately two
– third of the time while the engine is running.

 It is during this time that a large part of the heat is transferred from the valve
head to the seat. The heat from the seat is transferred to the engine coolant.
 Figure 7.6 shows the zones of heat and working temperature of the exhaust
valve. The remaining heat transfer takes place from the valve steam to the
valve guide then to the engine coolant.
How Sodium Cooled Valves Can Maintain Working Temperature.
 Some exhaust valves also use a metallic sodium inside the stem. The sodium
becomes a liquid at operating temperature.
 Valve movement causes the liquid sodium transfers heat from the head of the
valve to the valve stem and then to the valve guide, which helps the valve head
to run cooler. Figure 7.7.
 Intake valve temperature is considerably lower than exhaust valve temperature.
 In coming air-fuel gases cool the intake valve while the valve is open. The
valve seat has a great deal to do with good heat transfer.

FIGURE 7.7: SODIUM-FILLED
STEM IMPROVES
COOLING
FIGURE 7.8: DOUBLE OVER HEAD CAM WITH
FOUR VALVES PER CYLINDER
Overhead Camshaft
 Overhead camshaft (OHC) assembly procedures vary considerably between
SOHC and DOHC, split or full circle cam bearings.
 OHC may operate the valve directly through bucket-type cam followers,
through pedestal-mounted cam followers, or by rocker arms.

 On DOHC engines with four valves per cylinder, there is one camshaft for intake
valves and one for exhaust valves. Now, most engines which have DOHC, operate
without rocker arm, that means the engine is less inertia from the valve linkage.
The engine produces good performance. Figure 7.8shows DOHC.

DJA3032 CHAPTER 7

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DJA3032 CHAPTER 7