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Balancing Back Pressure
Flow rates and/or viscosity differences between compo-
nent materials can create different pressure drops from
the proportioner to the manifold, causing unequal back
pressure. This will effect mix ratio accuracy.
To calculate pressure loss:
Pressure Loss = 0.000273 x Q x V x L
Q = Flow (GPM)
V = Viscosity in centipoise
L = Length of pipe in feet
4
D
= Pipe diameter (in inches) to the 4th power
Example: If you need to pump 1 gpm of high solids paint
(40 seconds in a Zahn #2 cup = 100 cp) 100 ft. in a sys-
tem using 1/4" pipe (0.364 in. ID):
Pressure Loss = 0.000273 x 1 gpm x 100 cp x 100 ft.
Pressure Loss = 152 psi
310676A
4
D
.018
Reduce pressure loss by using:
•
Large diameter pipe or tubing
•
Constant tubing or pipe size
•
Long runs without bends
•
Long radius elbows
You can balance differences in component back pres-
sure by adjusting hose diameter and length.
4
D
= .018 for 1/4" pipe
.06 for 3/8" pipe
.15 for 1/2" pipe
Using the previous example
(.000273 x 1 x 100 x 100 = 2.73):
Pressure drop: 1/4" pipe = 152 psi
3/8" pipe = 46 psi
1/2" pipe = 18 psi
Balancing Back Pressure
3
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