Calculating duct resistance – Grizzly G1028Z/G1029Z User Manual

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G1028Z/G1029Z Dust Collector

Calculating Duct Resistance

Adding duct work, elbows, branches and any
other components to a duct line increases airflow
resistance (static pressure loss). This resistance
can be minimized by using rigid (smooth) pipe
and gradual curves, as opposed to flexible pipe
and 90˚ elbows.

To help you think about this resistance, imagine
riding a bicycle in a tunnel that is an exact replica
of your duct work. If the inside of the tunnel is very
bumpy (flexible pipe) and has a lot of sharp turns
(90˚ elbows), it will take a lot more effort to travel
from one end to the other.

The purpose of calculating the resistance is to
determine if it is low enough from the machine to
the dust collector to meet the given CFM require-
ment for the machine. Use the charts in

Figure 26

to calculate the resistance of duct work.

Duct

Dia.

Approximate

Static Pressure

Loss Per Foot of

Rigid Pipe

Approximate

Static Pressure

Loss Per Foot

of Flex Pipe

Main

Lines

at 3500

FPM

Branch

Lines

at 4000

FPM

Main

Lines

at 3500

FPM

Branch

Lines

at 4000

FPM

.091

.122

.35

.453

2.5"

.08

.107

.306

.397

.071

.094

.271

.352

.057

.075

.215

.28

.046

.059

.172

.225

.037

.047

.136

.18

.029

.036

.106

.141

.023

.027

.08

.108

.017

.019

.057

.079

Fitting

Dia.

90˚

Elbow

45˚

Elbow

45˚

Wye(Y)

90˚

Wye(Y)

.47

.235

.282

.188

.45

.225

.375

.225

.531

.266

.354

.236

.564

.282

.329

.235

.468

.234

.324

.216

.405

.203

.297

.189

Figure 26. Static pressure loss charts.

Additional Factors

Static Pressure

Seasoned (well used)

Dust Collection Filter

Entry Loss at Large

Machine Hood

In most small/medium shops it is only necessary
to calculate the line with the longest duct length or
the most fittings (operating under the assumption
that if the line with the highest resistance works,
the others will be fine).

To calculate the static pressure of any given

line in the system, follow these steps:

1. Make a list of each size duct in the line, includ-

ing the length, and multiply those numbers by
the static pressure value given in

Figure 26.

2. List each type of elbow or branch and multiply

the quantity (if more than one) by the static
pressure loss given in

Figure 26.

3. Add the additional factors from Figure 27 to

your list.

Figure 27. Additional factors affecting static

pressure.

4. Total your list as shown in the example in

Figure 28 to come up with your overall static
pressure loss number for that line.

Note: Always account for a seasoned filter,
so you don't end up with a system that only
works right when the filter is clean.

Figure 28. Totaling static pressure numbers.

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