Manual

7
Collar & Adjustable Duct Connections
The collar and the adjustable length duct have two major
functions: (1) Make up odd lengths of duct as needed in short
runs as in termination of the duct at the exhaust fan. (2) Serve as
an expansion joint for thermal expansion in larger runs of duct.
When used in systems of any orientation, it can perform both
functions simultaneously. The adjustable duct section is overlapped
to allow grease to drain back to the hood in both vertical and
horizontal installations See Fig.10. The adjustable duct is flanged
at one end only. The collar is constructed of the same material as
the duct, and is also designed with a ½” flange that is connected to
the standard duct section using the joint assembly method listed
above See Fig.1. Collars are also sealed using high temperature
silicone that compresses around the adjustable duct when the collar
hardware is tightened. The collar is designed to securely hold the
adjustable duct, while allowing for thermal expansion.
Collar & Adjustable Duct Vertical Installation
When the adjustable length duct and collar are installed in the vertical position between two fixed points,
such as the beginning support and the ending support, it should be installed just below the higher support. To
ensure proper axial alignment, wall guide support assemblies must be installed below the duct joint
immediately below the adjustable duct. This combination of parts will force the sliding inner and outer parts
of the adjustable duct to overcome collar friction allowing movement along the axis of the duct and thus
relieving expansion stresses which would otherwise develop between the fixed points of the heated vertical
duct.
1. Slide the adjustable collar over the adjustable duct. Flanges
should be opposite.
2. Slide the adjustable duct into the standard duct to the point
that the collar flange and the standard duct flange meet.
3. The adjustable collar and standard duct are joined and
sealed using the method listed above in Fig.1.
4. Slide the adjustable duct into the standard duct to the
desired length. The minimum overlap dimension depends
on the duct diameter. See Table 2. for proper overlap
dimensions.
5. The collar is sealed to duct using high temperature silicone.
6. Once the desired overlap has been met, tighten the ¼-20
hardware on the “V” clamp and the outside of the adjustable
collar to 85 in-lbs.
7. Inspect the connection for gaps in silicone.
Fig. 2a – Adjustable Duct Overlap
Fig. 2 – Adjustable Duct Overlap
Table 2 – Minimum Overlap
DIAMETER
MIN OVERLAP FOR
ADJUSTABLE DUCT
8" 4”
10" 5”
12" 6”
14" 6”
16" 6”
18" 6”
20" 6”
24" 6”
Standard duct
Adjustable collar
Adjustable duct
See table 2
Adjustable
duct
Collar
See Table 2
min overlap
Adapter plate
Main duct
"V" clamp
Vented curb
per NFPA96