Oriflow Cobra User manual

Cobra
Duct Leakage Tester
User Manual

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Cobra Tester User Manual © Copyright 2021
Links to Online Help
(QR Code)
Video –Duct Leakage Testing
Online Technical Library
Online Max Leakage Calculator
(SMACNA Leakage Class)
Online Max Leakage Calculator
(% Allowable)

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Cobra Tester User Manual © Copyright 2021
Table of Contents
Introduction
Introduction ……………………………………….………………………….…………… 3
Safety Precautions
Safety Precautions ………… READ FIRST! ……….….……………….……………… 3
Prior to Testing
Are You Using the Correct Tester? …………………………………….…...…………. 4
System Preparation …………………….……………….…………….……...….……… 4
Power Requirements …………………………………....…………….……...….……… 4
Extension Cord Requirements ………………………....…………….……...…………. 5
Flex-Duct Length ………………………………………...…………………….……...…. 5
Determining Maximum Allowable Leakage ….………..……………...…….….……… 5
FREE Oriflow duct test summary form (SMACNA or DW/143) ………….….………. 5
Determining Which Orifice Plate to Use ……………....……………..……..…………. 6 - 7
Duct Leakage Test Setup and Procedure
Install Orifice Plate and Upper Tube Section ……………………………..………..…. 8 - 9
Connect Flex-Duct to Orifice Tube ………………........…………….……...….……… 9
Connect Flex-Duct and Static Pressure Tap to Duct System ………….……………. 10 - 11
Duct Leakage Test Setup (SUPPLY) ………………….………….….……..…………. 12
Duct Leakage Test Setup (RETURN/EXHAUST) …………………..……..…………. 13
Zeroing Pressure Gauges ……………………………………………..……..…………. 14
Avoiding Over-Pressurization …………………………..……………...…….…………. 15
Obtaining System Test Pressure ……………………………………...…….…………. 15 - 16
Determining Leakage Rate……………………………………………..….….…………. 16 - 17
Troubleshooting
Can’t obtain system test pressure (DUCT PRESSURE TOO LOW) …………….…. 18
Can’t obtain system test pressure (DUCT PRESSURE TOO HIGH) …….……….… 19
ORIFICE PLATE gauge reading maxed out ………......……………...….…....……… 19
GFCI/GFI trips …………………………………………………………………………….. 19
Error Codes ………………………………………………………………………….…….. 19
Zero or very small reading on ORIFICE PLATE gauge .………………........……..…. 20
DUCT SYSTEM Gauge (Digital) Displays UFL or OFL ……………………………….. 21
ORIFICE PLATE Gauge (Digital) Displays UFL or OFL ……………………………….. 21

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Cobra Tester User Manual © Copyright 2021
Introduction
The COBRA duct leakage tester is the most widely used tester in the U.S. It is the simplest to
use tester on the market backed by unparalleled customer service and technical support. Call
us, find out.
The recommended recalibration interval for the plates is 5 years. Note the authority having
jurisdiction may override this requirement, and if so, Oriflow has reasonable rates for re-
calibrating orifice plates manufactured by Oriflow. Call us at 727-400-4881 to receive lead
time and pricing for calibration. After you order the calibration, just ship the two orifice tube
sections along with the Oriflow orifice plates to:
Oriflow Calibrations
2125 Range Rd., Suite B
Clearwater, Florida 33765
Safety Precautions
Before operating your tester, read the following safety precautions:
✓DO NOT operate the tester outdoors, in the rain, or where it will get wet,
✓DO NOT operate the tester while it is near or in water,
✓DO NOT operate the tester with a damaged electrical cord or plug,
✓DO NOT operate the tester without an inlet safety screen,
✓DO NOT put fingers, hands or any object near inlet of blower while it is running,
✓DO NOT touch the blower wheel when the unit is plugged in,
✓DO NOT look into the discharge end of the tester when the unit is plugged in,
✓DO NOT use the tester as a ladder or step stool,
✓DO NOT allow children near the tester,
Things you SHOULD DO:
✓Use an extension cord of the proper gauge (see Table 3 on page 5),
✓Make sure unit is electrically grounded,
✓Use the proper voltage and phase listed on the Voltage/Phase/Hz label (front panel),
✓Lock the casters when the tester is positioned horizontally,
✓Use the tester on level ground,
✓Secure the tester when transporting it,
✓Wear proper hearing protection, safety glasses and work gloves,
✓Seek assistance when lifting the tester (e.g., loading onto truck, going up or down
stairs).

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Cobra Tester User Manual © Copyright 2021
Prior to Testing
Are you Using the Correct Tester?
See Table 1 for the maximum capacity for each duct tester when using the largest orifice
plate.
Table 1 –Duct Leakage Tester Capacities
Model
Maximum Leakage Capacity (cfm)*
System Test Pressure (in.wg.)
0.10
1
2
4
6
7
8
9
10
12
14
16
Cobra
680
cfm
650
cfm
645
cfm
600
cfm
465
cfm
405
cfm
350
cfm
250
cfm
—
—
—
—
Panther
1400
cfm
1350
cfm
1320
cfm
1210
cfm
1065
cfm
970
cfm
875
cfm
875
cfm
615
cfm
270
cfm
—
—
Rhino
1700
cfm
1630
cfm
1550
cfm
1420
cfm
1330
cfm
1255
cfm
1185
cfm
1185
cfm
1035
cfm
895
cfm
660
cfm
480
cfm
* Direct hookup (no flex) and using the largest sized orifice available for the model listed.
System Preparation
Cap off all ends of system using clear plastic and duct tape or sheetmetal duct end caps.
Make sure you test the part of the duct system that leakage testing is required. Usually, this is
from the system fan up to, but not including, the VAV boxes (terminal units). Refer to the
engineer's specifications and all applicable codes and test standards.
Power Requirements
Do you have an adequate power supply for your tester (see Table 2)?
Table 2 –Tester Amp Draw
Tester Model
Voltage
Flow Control
Option
Full Load
Amps
Cobra
115
Slide Gate
12.8
Cobra
115
VFD
14.0
Cobra
230
Slide Gate
6.4
Cobra
230
VFD
8.0

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Cobra Tester User Manual © Copyright 2021
Extension Cord Requirements
If you need an extension cord, is it the proper gauge? See Table 3 below for extension cord
requirements. Note these are minimum requirements. Always error on the side of thicker wire.
Table 3 –Required Extension Cord Wire Gauge
Tester Model
Flow Control
Option
Voltage
Extension Cord
Length (feet)
Minimum
Wire Gauge
Cobra
Slide Gate
115
10 to 50
14
50 to 100
12
Cobra
Slide Gate
230
10 to 50
14
50 to 100
14
Cobra
VFD
115
10 to 50
14
50 to 100
12
Cobra
VFD
230
10 to 50
14
50 to 100
14
Flex-Duct Length
Make sure you have enough flexible-duct with your tester for the job. Each
tester includes 12.5 feet, which is enough for most applications. Extra lengths
of flexible-duct are available at
https://oriflow.com/products/accessories/flexible-duct/.
Determining Maximum Allowable Leakage
To determine the maximum allowable leakage for the project, use ORIFLOW’s
free online programs to make these calculations
(https://oriflow.com/software/).
In the U.S., calculations are done for either of the two typical specifications:
1. SMACNA Leakage Class, or
2. Percentage of system flow.
In Europe, Australia and other countries outside of the U.S., the following DW/143
specification is commonly used:
1. Pressure Classification (Class A, B, C or D)
If the specification uses SMACNA Leakage Class or Pressure Classification, you will need to
calculate the total duct system surface area.
Oriflow has a FREE Adobe test summary sheet that will calculate duct surface area,
leakage factor, allowable leakage, actual leakage and Pass/Fail criteria. You can find
this test summary sheet using the QR code to the right. It’s an excellent tool that can
be printed or emailed.

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Cobra Tester User Manual © Copyright 2021
Determining Which Orifice Plate to Use
After determining the allowable leakage at the system test pressure, refer to the following
tables for the capacities of each orifice plate.
The proper orifice plate is the smallest orifice where the specified allowable leakage falls
between the minimum and maximum leakage at the system test pressure.
For example, if you are testing a system at 4 in.wg. pressure and the maximum allowable
leakage is 350 cfm, you will need a 3-inch orifice plate (See Table 6: 350 cfm falls between
82 and 375).
Table 4 –Tester Capacity using the 1-inch Orifice Plate*
System Test
Pressure
(in.wg.)
Minimum
Leakage**
(cfm)
COBRA Tester
Maximum
Leakage
(cfm)
0.10
9
47
1
9
44
2
9
42
3
9
39
4
9
36
5
9
32
6
9
29
7
9
24
8
9
19
9
9
12
* If you need to measure lower flow rates, contact us about the ‘low-flow’ orifice plate.
** Minimum based on 0.40 in.wg. across orifice plate.
Table 5 –Tester Capacity using the 2-inch Orifice Plate
System Test
Pressure
(in.wg.)
Minimum
Leakage**
(cfm)
COBRA Tester
Maximum
Leakage
(cfm)
0.10
34
180
1
34
170
2
34
165
3
34
155
4
34
140
5
34
125
6
34
115
7
34
95
8
34
75
9
34
45
** Minimum based on 0.40 in.wg. across orifice plate.

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Cobra Tester User Manual © Copyright 2021
Determining Which Orifice Plate to Use (continued)
Table 6 –Tester Capacity using the 3-inch Orifice Plate
System Test
Pressure
(in.wg.)
Minimum
Leakage**
(cfm)
COBRA Tester
Maximum
Leakage
(cfm)
0.10
82
440
1
82
420
2
82
410
3
82
390
4
82
375
5
82
340
6
82
290
7
82
245
8
82
195
9
82
130
** Minimum based on 0.40 in.wg. across orifice plate.
Table 7 –Tester Capacity using the 4-inch Orifice Plate
System Test
Pressure
(in.wg.)
Minimum
Leakage**
(cfm)
COBRA Tester
Maximum
Leakage
(cfm)
0.10
175
680
1
175
650
2
175
645
3
175
630
4
175
600
5
175
545
6
175
465
7
175
405
8
175
350
9
175
250
** Minimum based on 0.40 in.wg. across orifice plate.

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Cobra Tester User Manual © Copyright 2021
Duct Leakage Test Setup and Procedure
Install Orifice Plate and Upper Tube Section
The orifice plate that was determined from the previous section should now be installed with
the serial number facing upwards so the corresponding calibration certificate may be
referenced after installation. Refer to Figures 1 through 4.
Figure 1 –Install Orifice Plate and then Rotate Clockwise
Figure 2 –Rotate Orifice Plate Clockwise until it Locks in Place

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Cobra Tester User Manual © Copyright 2021
Install Orifice Plate and Upper Tube Section (continued)
After the orifice plate is locked in place, place the upper tube section over the bolt/wing nut
set, rotate clockwise, and tighten wing nuts (Figures 3 and 4).
Figure 3 –Install Upper Tube Section and Rotate Clockwise
Figure 4 –Tighten Wing Nuts after Rotation

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Cobra Tester User Manual © Copyright 2021
Connect Flex-Duct to Orifice Tube
See Figure 5 below for securing the 5-inch end of the flexible duct to the orifice tube. Slide the
flexible duct so that it overlaps the orifice tube 2 to 3 inches, and tighten clamp using a 5/16-
inch nut driver.
Figure 5 –Installing Flex-Duct on Tube
Connect Flex-Duct and Static Pressure Tap to Duct System
Refer to Figures 6 and 7. Connect the 6-inch end of the flex-duct to the duct system. Find a
convenient location on the duct system where the tester has easy access. Make sure the
connection is a sturdy, tightly sealed connection. You don’t want to create a leaky connection
thereby adding to the system leakage.
To monitor the system static pressure, you need to drill a 5/16-inch diameter hole for the grey
plastic static pressure tap to measure system static pressure (Figure 7).
If the static pressure tap is missing, locate the hole at least 3 feet away (farther is better) from
flex-duct connection, and insert the pressure tubing from the DUCT SYSTEM gauge so that 6
to 12 inches of tubing is inside the duct system. [Face the end of the pressure tubing away
from the flex-duct connection so that air entering the system does not blow into the tubing,
creating a false high system pressure reading.] Using putty or duct tape, seal the connection.
See Figure 8.

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Cobra Tester User Manual © Copyright 2021
Connect Flex-Duct and Static Pressure Tap to Duct System (continued)
Figure 6 –Flex-duct Connection to Duct System
Figure 7 –Connection to Duct System using Static Pressure Tap

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Cobra Tester User Manual © Copyright 2021
Duct Leakage Test Setup (SUPPLY)
See Figure 8 for the test setup for SUPPLY duct system testing (positive pressure testing).
On the backside of the DUCT SYSTEM pressure gauge, move the pressure tubing to the
pressure port labeled SUPPLY SYSTEM.
Figure 8 –Duct Leakage Test Setup for a SUPPLY System

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Cobra Tester User Manual © Copyright 2021
Duct Leakage Test Setup (RETURN/EXHAUST)
Refer to Figure 9 for the test setup required to measure air leakage of a RETURN/EXHAUST
system (negative pressure testing). On the backside of the DUCT SYSTEM pressure gauge,
move the pressure tubing to the pressure port labeled RETURN SYSTEM.
Connect the 6-inch end of the flex-duct to the inlet of the blower so that air from the system is
drawn into the blower. You will determine the leakage of the system since the air drawn from
the blower is discharged through the orifice plate.
Figure 9 –Duct Leakage Test Setup for a RETURN/EXHAUST System

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Cobra Tester User Manual © Copyright 2021
Zeroing Pressure Gauges
Before turning on the tester, make sure both gauges have been zeroed.
Zeroing Analog Gauges
Using a small slotted screwdriver, turn the zero-adjustment screw on the gauge until
the needle is aligned with the zero reading unless the calibration certificate for the
pressure gauge shows a different set value for true zero. Turning the screw clockwise
increases the pressure reading; turning it counterclockwise decreases the reading.
See Figure 10.
Figure 10 –Zeroing Analog Gauges
Zeroing Digital Gauges
If gauges do not turn on automatically (VFD tester models), turn on both gauges by
pressing the black (or red) button located on the backside of each gauge.
Use the following steps to zero each digital gauge:
1. Press MENU button once.
2. Press ▼arrow button until Adu shows on screen.
3. Press Ebutton once to go into auto-zero mode
4. Press Ebutton again and AUTO will be blinking on screen
5. Press Ebutton a third time to complete the zeroing process.
6. Press MENU button two times to get back to the pressure reading.
7. Pressure should be reading zero or within +/- 0.02 in.wg. If not, repeat steps.

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Cobra Tester User Manual © Copyright 2021
Avoiding Over-Pressurization
Prior to starting the blower, shut the inlet slide gate on models without the speed controller
option. For models with the VFD speed controller, rotate speed control knob counter-
clockwise until the readout shows 10.00 (the lowest speed setting). See Figures 11.
Figure 11 –Avoid Over-Pressurizing by Minimizing Air Delivery upon Startup
(inlet slide model on left, VFD speed control model on right)
Obtaining System Test Pressure
Turn the blower on and slowly open the inlet slide gate if your tester has an inlet slide gate. If
your tester has the VFD speed controller, press the RUN button, and then rotate the speed
control knob clockwise to increase fan speed which will increase test pressure. The faster you
rotate the knob, the more quickly the speed will increase. See Figures 12.
Figure 12 –Obtaining System Test Pressure (inlet slide model on left, VFD
speed control model on right)

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Cobra Tester User Manual © Copyright 2021
Obtaining System Test Pressure (continued)
Pay attention to the DUCT SYSTEM gauge while increasing airflow (Figures 13). When you
have reached the required system static pressure, tighten the setscrew on the inlet damper (or
STOP rotating the speed control knob).
Figure 13 –Duct System Test Pressure (analog on left, digital on right)
Determining the Leakage Rate
Now that you have obtained the system test pressure, note the pressure drop of the ORIFICE
PLATE gauge (Figures 14). [Note: Ideally, the pressure drop across the orifice plate should be
over 1.0 in.wg. to reduce the amount of error introduced into the reported leakage rate.Use
next smaller orifice plate so the pressure drop reading will increase for a given leakage rate.]
Refer to your calibration certificate to determine the leakage rate that corresponds to the
gauge reading. An example of a calibration certificate is shown in Figure 15; it is for
informational purposes only and used in the example shown on the next page. Always refer
to the calibration certificate(s) that came with your calibrated orifice plate(s).
Figure 14 –Orifice Plate Pressure Drop (analog on left, digital on right)

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Cobra Tester User Manual © Copyright 2021
SAMPLE CALIBRATION CERTIFICATE
USE YOUR CERTIFICATE
Figure 15 –Example Calibration Certificate. Use the calibration certificate that came with your orifice
plate
Example (refer to Figures 14 and 15)
For an ORIFICE PLATE pressure drop (gauge reading) of 2.46 in.wg. (Figure 14), the leakage
rate is approximately 210 cfm using the calibration certificate shown in Figure 15.
For an exact value, use the equation that comes with every calibration certificate. For the
certificate shown in Figure 15:
Leakage = 134.42 x ,
where the value of “134.42” is the “Leakage Coefficient”and will be specific to the orifice plate
used (every plate has its own value; yours will be different).
Using a calculator, take the square root of the ORIFICE PLATE gauge reading first, and then
multiply by the constant for your orifice plate (for this example, the constant is "134.42"). The
exact leakage is 134.42 x (square root of 2.46) = 210.8 cfm. Better yet, download Oriflow’s
test summary sheet described on the bottom of page 5 of this manual.

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Cobra Tester User Manual © Copyright 2021
Troubleshooting
Can’t obtain system test pressure (DUCT PRESSURE TOO LOW)
This typically happens when the system is leaking too much air. Make sure all outlets are
sealed. Check corners of rectangular duct for excessive leakage. Inspect all duct and fitting
joints for leakage. Make sure you seal all suspect joints and allow to cure 24 to 48 hours.
Always refer to duct sealant manufacturer’s instructions.
Perform troubleshooting steps in the order shown in the Table 8 below.
Table 8 –Troubleshooting steps when DUCT SYSTEM test pressure is too low
Step
Scenario
What to do
1
Allowable Leakage is
greater than capacity of
tester.
Refer to top of page 4, “Are you using the correct tester.”
2
Inlet damper was left shut,
cutting off air to the system.
Open inlet damper slowly.
3
Pressure tubing connected
to gauge incorrectly
Look at the P1 and P2 stickers that are located on the orifice
tube (airflow meter) and gauges. Make sure tubing from P1
tap is connected to the P1 tap on the ORIFICE PLATE
gauge.
4
Plugged pressure port on
orifice tube
Remove pressure tubing from the P1 and P2 ports on the
ORIFICE PLATE gauge. Blow through each tubing end. You
should be able to blow air freely through both ports. If
plugged, use paper clip or 1/16”drill bit to clear hole.
5
Malfunctioning gauge.
Attach pressure tubing to the port labeled “SUPPLY
SYSTEM.”Gently blow through other end of pressure
tubing. The pressure reading should increase.
6
System is leaking
too much air.
Check for these other sources of leakage:
•Rectangular duct joints (check and seal corners),
•Fire or smoke dampers,
•Duct joints (pay particular attention to flex-duct
joints if they are part of the leak test),
•VAV boxes (pay particular attention to parallel box
back draft dampers),
•Built-up air handlers,
•Plenums,
•Uncured duct sealant blow-thru (follow
manufacturer instructions for cure time),
•Improperly sealed or un-sealed joints,
•Hot water coils and electric heaters,
•Open duct end that was supposed to be
sealed/capped-off for the leak test.
A non-toxic smoke machine is an excellent tool for locating significant sources of leakage.
Call ORIFLOW at 727-400-4881 or to our website at www.oriflow.com for more information.

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Cobra Tester User Manual © Copyright 2021
Can’t obtain system test pressure (DUCT PRESSURE TOO HIGH)
This typically happens on small or tight systems when using a duct tester without the VFD
speed controller. Testers equipped with the inlet slide gate damper always run at about 3600
rpm and are so powerful, air pressure is generated even with the inlet damper is completely
shut and sealed.
•Use a smaller orifice plate. If using the 1-inch plate, install the ½-inch plate which is
used to measure flow rates from 1 to 10 cfm.
•Remove the end of the flex-duct where it connects to the duct system (typically, a 6-
inch round tap). Using duct tape, completely cover the tap, and then poke a hole(s) in
it with a screwdriver or pen. Then install the flex-duct as usual. This will act as an
outlet damper or restriction. Now you can use the inlet damper to regulate flow.
ORIFICE PLATE gauge reading maxed out
•Scenario 1: The system is leaking too much air. Make sure all outlets are sealed.
Check corners of rectangular duct for excessive leakage. Inspect all duct and fitting
joints for leakage. Make sure you seal all suspect joints and allow curing time of 24 to
48 hours. Always refer to duct sealant manufacturer’s instructions.
•Scenario 2: orifice plate bore could be too small, causing a high pressure-drop at low
to moderate flows. Use the next larger sized orifice.
GFI/GFCI trips
This happens when using a Cobra duct leakage tester with the variable speed option. The
supply wiring has ground wired to neutral which causes the GFI to activate when the tester is
operating.
Possible solutions:
1) Utilize a correctly wired GFI outlet that has separate neutral and true ground,
2) Use a non-GFI outlet to power the tester,
3) Use a non-VFD model tester.
Error Codes
Error Code
Description
What to do
Undervoltage error. Too much
voltage drop between power
source and duct leakage
tester.
Use power cord with thicker gauge wire.
See Table 2 for power requirements and
Table 3 for minimum wire gauge for
extension cords.
Undervoltage error. Too much
voltage drop between power
source and duct leakage
tester.
Use power cord with thicker gauge wire.
See Table 2 for power requirements and
Table 3 for minimum wire gauge for
extension cords.