Statement of Methodology for Inspection and Leakage Testing (Pressure Test) of Air Duct

TITLE: METHOD STATEMENT FOR INSPECTION AND LEAKAGE TESTING (PRESSURE TEST) OF AIR DUCT

1. Purpose

This method statement describes the detailed inspection and leakage testing plan (pressure test) for the air duct.

2. Scope

This method statement covers all scope of works related to air duct leakage testing (presure test).

3. Testing Procedures

Leakage Testing of G.I. Air Duct:

* The conventional leak testing of air duct is based on a positive pressure mode analysis. It

involves using temporay plugs / seals (plates, sheets, balloons, bags, etc.) in openings of the

duct to be tested. At the duct opening on one end of the specimen to be tested, connect the

blower and other test instruments/equipment as shown in illustrations 1 and 2 below.

* Select a test pressure not to exceed the pressure class rating of the duct.

* Calculate the allowable leakage using the leakage factors applicable to the duct area.

* Select and calculate a duct section to be tested for which the estimated leakage will not

exceed the capacity of the test equipment/apparatus.

* Connect the blower and flow meter to the duct section and provide temporary plugs/seals

at the end of the ducts.

* Start the blower with a variable inlet damper to prevent over pressurization of the duct.

Then, adjust / set the pressure to the required test pressure value.

* Read the flowmeter and compare with the allowable leakage value in CFM/100 S.F.

If the reading is within the allowable leakage value, complete the test reports/forms then

signed by both the contractor's and the Owner's representatives who witnessed the test.

However, if the reading is more than the allowable leakage value, do the following:

a. Inspect the pressurized duct under test for leaks.

b. Depressurize the duct, then perform the necessary repairs for leaks found.

c. After curing of the seals, repeat the test.

In case that during inspection of the pressurized duct, which failed the allowable leakage

value, no leaks were discovered, divide the section being tested into smaller segments and/or

use larger test apparatus/equipment then repeat the test process until it passed.

* Remove the plugs / blanks and seals.

* Clean the area.

1. Leakage classes in table 1 apply when the designer does not designate other limits and has

specified seal class C for 1/2" and 1" W.G.

2. Unsealed rectangular metal duct may follow leakage class 48.

3. Fibrous glass duct may follow leakage class 6 (at 2"W.G. or less).

4. Although seal class A or B might be assigned for lower pressures, the leakage class achieved

may not conform to those associated with high pressure. Other construction details

influence results.

5. Leakage class (CL) is defined as being the leakage rate (CFM/100S.F.) divided by P0.65 where

P is the static pressure (in W.G.). When P is numerically equal to 1" the leakage rate is CL.

6. The duct pressure classification is neither the fan static pressure or the external static pressure

(on an HVAC unit) unless the system designer has made such an assignment in his contract

documents. Unless constrcution class is otherwise specified it means a static pressure classification

in SMACNA HVAC-DCS. Those classifications pertain to maximum operating pressure in the

duct as follows:

0.5" w.g. maximum 3.1" to 4" w.g. maximum

0.6" to 2" w.g. maximum 4.1" to 6" w.g. maximum

1.1" to 2" w.g. maximum 6.1" to 10" w.g. maximum

Precautions to befollowed for the test apparatus.

1. Start the blower with blocked suction or discharge to avoid over pressurizing the ductwork.

2. Use clean manometers.

3. Heat manometers to avoid freezing fluid during cold weather.

4. If manometer fuid is blown out, refill with the appropriate fluid. For convenience in reading,

add a drop of soluble dye to water-filled manometers.

5. Level position sensitive instruments and set them to zero scale reading.

6. Read liquid levels by viewing them horizontally.

4. Testing Material, Tools and Equipment

* Red Oil
* Flexible Duct
* Duct Temporary Plugs / Seals.
* Blower
* Inclined Manometer (Calibrated / with calibration certificate)
* Flow meter (Calibrated / with calibration certificate)
* Hand tools