Unit - WordPress.com · Web viewI-Head and F-Head valve. 10.2 Valve Parts. A valve has several parts and they are in the tip or rocker arm contact area, valve spring retainer lock

VALVE AND VALVE COOLING J3182 / UNIT10/1

Unit 10Title : Valve and Valve Cooling

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 woking temperature is maintained by sodium

cooled valves.


9. explain the purpose and operation of DOHC engine.

Input This section introduces the subject matter that you are going to learn.

10.0 IntroductionIn this unit 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.

10.1 Types of valve location for the internal combustion enginea. 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’.

b. 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. Figure 10.1 shows the L-Head and T-Head valve.

c. Valves in head ( overhead valve), are also called I-Head engine because

the cylinder and combustion chamber are in the shape of an ‘I’.

d. One valve in head ( usually intake ) and one valve in block, are also called

F head engine; this is less common. Figure 10.2. shows the I-Head and

F-Head valve.


Figure 10.1: Types of L-Head and T-Head valve

Figure 10.2: I-Head and F-Head valve

10.2 Valve Parts

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.

Figure 10.3 shows the valve parts.

Figure 10.3: Parts of valve


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. Figure 10.4 shows the different head

shapes of valves.

Flat head concave head Oval head Recessed head

Figure 10.4: Types of head valves

10.3 Valve MaterialsIntake and exhaust valve materials include :

a. alloy steel valves with aluminized face and chrome stem


b. silchrome valve with aluminized face

c. austenitic steel with aluminized face and chrome stem

d. SAE 21-2steel with nickel-plated face

e. Satellite

f. Sodium-filled stems ( for valve cooling ).

10.4 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 :

a) nickel

b) manganese

c) cobalt

d) chromium

e) silicon

f) molybdenum

g) tungsten

h) 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 :

a) aluminum material is sprayed in the form of a paste after valve seats have

been finished – machined and the stems rough grounds.


b) The component, in a jig, are then dipped for a few seconds in a molten

flux bath at 7600 C

c) 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.

Activity 10AThis section tests your understanding of the subject matter. You are to answer the following questions.

10.1 List down 3 types of valve location

10.2 Draw and label the diagram of valve parts

10.3 List 4 Intake and exhaust valve materials


Input 10.5 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 10.3 shows the valve is ground to 44 o while the seat is ground to 45 o.

This interference angle tends to cut through any deposits that have been formed

on the seat.


Figure 10.3 An interference angle

10.6 Valve RotatorsValve 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.

45o

44


Figure 10.4: Rotorcap Valve Rotator Operation

10.7 Valve Temperature and Cooling.

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 10.5 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.

Figure 10.5: Zones of Heat

10.8 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 10.6.

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 tranfer.

Figure 10.6: Sodium-filled stem improves cooling

10.9 Overhead Camshaft

Overhead camshaft

(OHC) assembly procedures

vary considerably between

SOHC and DOHC, split or full


circle cam bearings. OHC may operate the valve direcly through bucket-type

cam followers, through pedestal-mounted cam followers, or by roker 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 roker arm, that means the engine is less inersia from the valve

lingkage. The engine produces good performance. Figure 10.7 shows DOHC.

Figure 10.7: Double Over Head Cam With Four Valves Per Cylinder

Activity 10B


This section tests your understanding of the subject matter. You are to complete the following activity..10.4 What is an integral valve seat ?

10.5 Common valve face angle are ___________ and ___________ degrees.

10.6 Give four (4) effects of using rotators to extend the life of valve

i._______________________________________________________________

ii._______________________________________________________________

iii.______________________________________________________________

iv.______________________________________________________________

10.7 Based on Figure A10.1 below , label the heat zone according to the number.

Figure A10.1


Self –AssessmentSelf-assessment evaluates your understanding of each unit.Question 10-1

List down 4 major head shapes of a valve

Question 10-2

What is the cause of pitting on a valve seat face ? How do we prevent it and what are the material required?

Question 10-3

Describe in detail the Aldip process?

Question 10-4

Name the important materials when we produce the valve.

Question 10-5

Explain how sodium can maintain working temperature

Question 10-6

Why are there many cars with ‘DOHC’ engine ?

Documents

Unit - WordPress.com · Web viewI-Head and F-Head valve. 10.2 Valve Parts. A valve has several parts and they are in the tip or rocker arm contact area, valve spring retainer lock