TAB Journal Summer 2020 - 18

"The advantage of an air valve is its ability to react immediately to a
signal requirement, as it uses a direct volume/cubic feet per-minute
(CFM) chart to move instantly rather than a flow ring."

There are four basic styles of return systems which have
increasingly higher static pressure requirements:
1.	 Low pressure (approx. 0.00 in. water column (WC) to 1.00
in. WC) - open-end duct for plenum ceiling.
2.	Low/medium pressure (approx. 0.75 in. WC to 2.00 in. WC)
- return-ducted with flex and grilles.
3.	Medium/high pressure (approx. 1.50 in. WC to 3.00 in. WC)
- return-ducted with VAVs, flex, and grilles.
4.	High pressure (approx. 2.50 in. WC to 5.00 in. WC) -
return-ducted with spring-actuated valves, flex, and grilles.
Unfortunately, we had a higher-end system to pressurize, with
the added challenge that the ductwork was oversized and the
systems had manual volume damper constant volume grilles
installed as well.
The advantage of an air valve is its ability to react
immediately to a signal requirement, as it uses a direct
volume/cubic feet per-minute (CFM) chart to move instantly
rather than a flow ring. A flow ring actually reads flow and
then must react in its program and adhere to a proportional
integral derivative loop, which takes time.

18

The disadvantage of an air valve is the extra system pressure
required to activate the internal spring cartridge, which the
valve must float on to stay calibrated at +/- 5 percent.
This means the system not only needs pressure to overcome all
of the loss from duct, flex, grilles, hoods, etc., it also requires
added pressure to satisfy the spring range of the air valve.
Each Phoenix Valve has factory-installed test ports that are
used to measure the pressure drop (ΔP) across the spring and
must be between the minimum and maximum of the spring
range.
In this case, the range was 0.30 in. to 3.00 in. If the ΔP is
within range the variations in the main duct static will not
affect the CFM total at the grilles.
If the ΔP goes below or above the spring range, the grilles
CFM is no longer being controlled by the spring. (see graphic
below)
All valves must remain above minimum springe range at all
times, or the CFM to the grille or equipment will change.
Systems should be set up adhering to the following concerns.
Not too high as to go over spring range and not too low as to
have no room for slight fluctuation or filter loading.

TAB Journal Summer 2020



TAB Journal Summer 2020

Table of Contents for the Digital Edition of TAB Journal Summer 2020

TAB Journal Summer 2020 - Cover1
TAB Journal Summer 2020 - Cover2
TAB Journal Summer 2020 - 1
TAB Journal Summer 2020 - 2
TAB Journal Summer 2020 - 3
TAB Journal Summer 2020 - 4
TAB Journal Summer 2020 - 5
TAB Journal Summer 2020 - 6
TAB Journal Summer 2020 - 7
TAB Journal Summer 2020 - 8
TAB Journal Summer 2020 - 9
TAB Journal Summer 2020 - 10
TAB Journal Summer 2020 - 11
TAB Journal Summer 2020 - 12
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TAB Journal Summer 2020 - 14
TAB Journal Summer 2020 - 15
TAB Journal Summer 2020 - 16
TAB Journal Summer 2020 - 17
TAB Journal Summer 2020 - 18
TAB Journal Summer 2020 - 19
TAB Journal Summer 2020 - 20
TAB Journal Summer 2020 - Cover3
TAB Journal Summer 2020 - Cover4
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https://www.nxtbook.com/ygsreprints/AABC/tab-journal-winter-2021
https://www.nxtbook.com/ygsreprints/AABC/G122399AABC_Fall2020
https://www.nxtbook.com/ygsreprints/AABC/G120138AABC_Summer2020
https://www.nxtbook.com/ygsreprints/AABC/G118248AABC_Spring2020
https://www.nxtbook.com/ygsreprints/AABC/G116302AABC_Winter2020
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