Sizing of Valves

Breathing abilities are limited by throat size….

P M V SubbaraoProfessor

Mechanical Engineering Department

The Driving Force for Flow Through Intake System

How to Size the Valves ????

Exhaust Pipe

Geometrical Nomenclature for Valves

• The instantaneous valve flow area depends on valve lift and the geometrical details of the valve head, seat and stem.

• There are three separate stages to the flow area development as valve lift increases.

Stages of Valve Lifting

Instantaneous minimum Available Flow area: Low Lift

• For low lift valves, the minimum available flow area corresponds to a frustum of right circular cone.

• The conical face between valve and seat is, perpendicular to the seat, defines the flow area.

0cossin

vLw

The minimum area is:

2sin

22cos v

vvm

LwDLA

Instantaneous minimum Available Flow area : Intermediate Lift

cossintan

42

22

wLww

D

DDv

m

s

2/122tan wwLDA vmm

wDD vm Dm is mean diameter of seat :

• For the second stage, the minimum area is still the slant surface of a frustum of a right circular cone.

• However, this surface is not perpendicular to the valve seat.

• The base angle of the cone increases from (900-) toward that of a cylinder.

• For this stage:

•When the valve lift is sufficiently large, the minimum flow area is no longer between the valve head and seat.•It is the port area minus the sectional area of the valve stem.

tan4

2/1

222

wwD

DDL

m

spv

Then, 22

4 spm DDA

Instantaneous minimum Available Flow area : High Lift

Valve Lift Vs Flow Area Curves

Stream Tube formed by Flow Through Valves

Equivalent Converging-Diverging Nozzle Configurations:

Mild Separation.Severe Separation

Capacity of A Valve Passage

Mass flow rate through any cross section of area A

)()()( xuxAxm