mechanic seal pump

1. 1
Hydraulic Balance

2. 2
Balanced mechanical seal
Carbon ring Stationary
Product +Springs
Product +Springs
Contact face pressure
Contact face pressure
> STRESS S
PRESSURE P

3. 3
Unbalanced mechanical seal
Stationary
Carbon ring
Product + Springs
Product + Springs
Contact face pressure
Contact face pressure
<
PRESSURE P STRESS S

4. 4
FACE AND SEAT AREA EQUAL 100% BALANCE
F = P * A F = S * A
P * A = S * A
P = S
A = Contacted
Surface area
S = Contacted
Surface stress
P = Product
+
Spring pressure
F = Acting force
S
P
=
100
%
A
P
Carbon ring
A
S
Stationary ring

5. 5
HYDRAULIC BALANCE OF SEALS 50 % BALANCE
F = P * A1 F = S * A
A
S
P * A1 = S * A
S
P
=
50
%
0.5
A
A1
P
P
P
=
S
P
A1
A
A = Contacted
Surface area
A1 = Projected area
of P
S = Contacted
Surface stress
P = Product
+
Spring
pressure
F = Acting force

6. 6
HYDRAULIC BALANCE OF SEALS 75 % BALANCE
F = P * A1 F = S * A
A
S
P * A1 = S * A
0.75
A
A1
P
S
P
= 75
%
=
S
P
A1
A
A = Contacted
Surface area
A1 = Projected area
of P
S = Contacted
Surface stress
P = Product
+
Spring
pressure
F = Acting force

7. 7
OPTIMUM HYDRAULIC BALANCE
Above 85 % ------------- WEAR
Below 65 % ------------- LEAK
Optimum Balance 75% for medium pressure seals
.
Balance percentage is a compromise
:

8. 8
P
S A1 ( projected area of P)
(
product + spring pressure
)
(
contacted surface stress
)
=
A ( contacted surface
area)
120
cm2
230
cm2
=
Mechanical seal has the following data
:
A = contacted surface area = 230 cm2
A1 = ( projected area of P) = 120 cm2
Calculate the hydraulic balance Percentage
SOLUTION
=
0.52
*
100
=
52
%
Hydraulic balance % is less than 65
%
This Mechanical is prone to leak

9. 9
P
S A1 ( projected area of P)
(
product + spring pressure
)
(
contacted surface stress
)
=
A ( contacted surface area)
180
cm2
200
cm2
=
Mechanical seal has the following data
:
A = contacted surface area = 200 cm2
A1 = ( projected area of P) = 180 cm2
Calculate the hydraulic balance Percentage
SOLUTION
=
0.9
*
100
=
90
%
Hydraulic balance % is more than 85
%
This Mechanical is prone to wear

10. 10
P
S A1 ( projected area of P)
(
product + spring pressure
)
(
contacted surface stress
)
=
A ( contacted surface area)
24
cm2
30
cm2
=
Mechanical seal has the following data
:
A = contacted surface area = 30 cm2
A1 = ( projected area of P) = 24 cm2
Calculate the hydraulic balance Percentage
SOLUTION
=
0.80
*
100
=
80
%
This Mechanical is hydraulic balanced
as it is in between 65 % and 85
%

11. 11
Hydraulic Balance - Benefits
• Increased pressure range for the seal
– this simple modification allows much higher
pressures to be sealed.
•Reduced heat generation
–ideal for unstable and low SG fluids
–less heat to be dissipated - less cooling required
•Reduced wear rate
–longer life
•Reduced power required to drive the seal
–lower running costs