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Qualliry matters: Kitchen extractor ducting manufacturing and installation (Part 3)

Qualliry matters: Kitchen extractor ducting manufacturing and installation (Part 3)

By Charel Marais

In this edition, we continue looking at the particulars of a kitchen extractor ducting installation.

Quality matters: Kitchen extractive ducting manufacturing and installation (Part 1)
Quality matters: Kitchen extractive ducting manufacturing and installation (Part 2)

JOINTS

Referring to SANS 1850, item 4.7 – Joints:
Joints, metal flanges, and corners shall be folded sheet metal flanges and corners. Suitable gaskets and seals for all connections, including access panels, which are non-porous, non-combustible, impervious to grease or cooking oils, and capable of withstanding elevated temperatures, should be provided. It shall be the contractor’s responsibility to ensure that joints are grease tight.


Webbing tape has been found to be practical and safe for use on gasket material between kitchen extractor duct joints.


Option 1 indicates a folded sheet metal flange. In most cases, duct manufacturers only bend over ±10mm of either 1mm or 1.2mm sheeting. Practically, this method is not recommended, as it interferes with the gasket by pushing it outwards and causing leakages.

Metal sheeting bending outwards MMOption 1: Metal sheeting bending outwards.

Charel001Metal sheeting bent 90 degreesoutwards.

Option 2 is to extend the 10mm over-bend as mentioned in option 1 to the same height as the angle flange, ensuring a smooth flat surface for the gasket.

Extending the bendOption 2: Extending the bend.

Option 3 is to weld the 1mm or 1.2mm sheeting to the angle flange, leaving a smooth flat surface for the gasket material and ensuring a leak-free joint.

Sheeting welded to angle flangeOption 3: Sheeting welded to angle flange.

Charel002Metal sheeting welded to angle flange.

LEAK TESTING OF KITCHEN EXTRACTOR DUCTING

Kitchen oil, liquids, and grease leaking from the kitchen extractor ducting must be avoided. There are three ways of testing for leaks. First is by pressurising the ducting with air and calculating the presence of air leaking from the ducting.

Referring to SANS 10173, item 4.3 – Leakage:
The leakage rate of any section of the system must not exceed the values as indicated in SANS 10173.

The standard indicates that the air leakage rate for low-pressure duct systems is 8%, 4% for medium-pressure duct systems, and 2% for high-pressure duct systems. What SANS 10173 and SANS 1850 do not indicate, is the leakage rate for kitchen extractor ducting.

SANS 1850 does however indicate that all joints must be ‘grease tight’: a condition that does not permit the passage of any liquid at any temperature.

Due to the information in the standards (SANS 10173 and SANS 1850), it is recommended that the leakage rate for kitchen extractor ducting must be 0%. I am suggesting this not only for practical reasons, but for the health and safety of all.

The second method for testing for leaks is adding a smoke bomb into the ducting during pressure testing. This is a very effective way of looking for leaks, as the smoke leaking from the joints makes it quite easy to see.

The third method that can be used, is to pour cooking oil on the joints inside the ducting during the installation process. If a leak exists, one or more oil droplets will then be evident on the outside of the ducting on the joints of the installed duct sections. Access to the inside of the ducting is through the access panels on the side of the ducting.

Charel003Cooking oil poured on duct joint.

Charel004Cooking oil evident on duct joint during leak test.

What not to do! Do not try to cover duct joints of kitchen extractor ducting with membrane and paste, as the oil will leak through.

Charel005 Membrane applied over duct joints.

Charel006Oil leaking through membrane applied over duct joints.

GASKETS FOR KITCHEN EXTRACTOR DUCTING JOINTS
Referring to SANS 1850 item 4.2.5 – Joints and Seams:

4.2.5.1             All internal components shall be adequately sealed against grease and liquid.
4.2.5.2             All external corners shall be adequately sealed against grease and liquid.
4.2.5.3             All joints over which air will flow shall be made as smooth as possible to prevent grease build-up and to enhance cleaning.
4.2.5.4             Recesses where grease can accumulate shall be avoided.

Prestik or ordinary silicon-type sealants must not be used between joints for kitchen extractor ducting. It is practically incorrect, and how it will react under high temperatures, fire, explosions, cleaning chemicals, and oil must still be tested 

High heat-resistant silicon sealant can be used to seal ducting corners and joints external to the ducting.

Charel007Prestik used on duct joint.

Webbing tape has been found to be practical and safe for use on gasket material between kitchen extractor duct joints.

Charel008Example of webbing tape.


DUCT JOINTS NOT DONE CORRECTLY

Charel009Gap on angle flanges.

Charel010Access panel installed on bottom of ducting.

Charel011Incorrect bolt position – oil leak evident.

Charel012Webbing tape incorrectly installed.

Photos by Charel Marais


Click below to read the February 2018 issue of RACA Journal

RACA FEB2018

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06 Jun 2018
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FRIGAIR Expo 2018 - Day1
07 Jun 2018
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FRIGAIR Expo 2018 - Day2
08 Jun 2018
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FRIGAIR Expo 2018 - Day3

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