Page 208 - Know and Understand Centrifugal Pumps

Mechanical Sea Is

of the faces. Therefore the average pressure between the faces is 50
psig.

r-l I I
1 In2= 200 Lbs
100 psi
Fiaure 13-11

By varying the area of contact (in this case, projecting 2-in.2 of area
exposed to pressure, over 1-in.2 of contact area) between the seal faces
with a constant pressure, the closing force between the faces can be
manipulated (Figure 13-1 1 ).

Fiaure 13-12

The illustration above (Figure 13-12) shows the same concept, but in
the opposite direction. In this case 1 in.2 of area exposed to pressure is
projected over 2 in.2 of contact area. The closing force is 50 lbs.

A common example utilizing the same concept is a woman's poir ited high heel shoes.
Iltl,,sLa210n of her shoe heel
,e*,- imnr;nt mevlrr nn e %,;n\,l Gin flnnr frnm ;m..rz.cc;
She can leave t~~~ptt~tt iiiaiha UI I a vqltyl Lllc lluul
points. Another example would be the Eskimo, who can walk on soft snow without
sinking by varying the area of co ntact of his footprint with broad snowshoes.

The pressure drop across the faces is not always linear. It may be convex
or concave (Figure 13-13).

mr-Jp The pressure drop is
High

not always linear. It may
/
/
Pressure drop be concave or convex.
across faces to
atmosphere
Fiqure 13-13

191