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Halton PLL – Plenum for linear slot diffuser

Plenum for Halton SLL and SLN diffusers

  • Ensures proper function of the supply air diffuser
  • Access for ductwork cleaning
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  • Plenum for connecting Halton SLL and SLN linear slot diffuser supply/exhaust unit to ductwork
  • Ensures proper function of the supply air diffuser
  • Access for ductwork cleaning

Product models and accessories

  • Model with sound attenuation, mineral wool or polyester fibre
  • Detachable airflow rate measurement and balancing module available.


Slots H K K1  ØD
1 235 *) 117 47 160 or 125
2 275 *) 155 85  200, 160 or 125
3 275 *) 193 123  200, 160 or 125
4 325 *) 231 161  250, 200, 160 or 125
5 325 *) 269 199 250, 200, 160 or 125
6 325 *) 307 237 250, 200, 160 or 125

*) When reduced plenum height option (PH=R) is selected, H=D+65 mm

Standard dimensions for linear slot diffusers

Diffuser active
length (mm)
572 872 1172 1472 1772
L (mm) 571 871 1171 1471 1771
L1 (mm) 286 436 586 368 443
Duct connections
1 1 1 2 2

In addition to standard linear slot diffuser sizes, other sizes can be ordered.
The maximum active length of one piece is 2000 mm. The minimun is 372 mm.

Continuous plenums with modular design are also available for installation lengths greater than 2000 mm.


Part Material Note
Plenum box/spigot Galvanised steel
Sound attenuation
Mineral wool or
polyester fibre
The mineral wool
is fixed with nails


Accessory Code Description
Sound attenuation material 2W Mineral wool on 2 sides
Sound attenuation material 5W Mineral wool on 5 sides
Sound attenuation material 2P Polyester fibre on 2 sides
Sound attenuation material 5P Polyester fibre 5 sides
Airflow measurement and
adjustment unit
OM For supply installation


The duct pressure and air velocity are reduced inside the Halton PLL plenum box.
Air is supplied into the space through the diffuser, improving the air distribution quality.
The airflow rate can be adjusted using the optional measurement and adjustment module MSM.


1.  Plenum
2.  Measurement and adjustment module

The Halton PLL is installed into the suspended ceiling with M8 drop rods (not supplied in the delivery) and connected to the ductwork with a spigot equipped with an integral rubber gasket.

When equipped with a measurement and adjustment module, the recommended safety distance upstream of the device is at least 3D, in order to ensure a reliable airflow rate measurement.

The unit s control spindle must not be excessively bent.


In order to enable airflow adjustment and measurement of airflow rate, it is recommended that the diffuser be connected to the plenum equipped with the MSM module.

The supply flow rate is determined by using the measurement and adjustment module MSM.

Detach the diffuser and pass the tubes and control spindle through the diffuser.
Replace the diffuser.

Measure the differential pressure using a manometer. The flow rate is calculated using the formula below:

∆pm      Measured pressure [Pa]
k           The k factor given as a function of mounting and diameter
qv         Airflow rate [l/s]

The k-factor for installations with different safety distances
(D= duct diameter):

PLL > 6xD min. 3xD
160 19 22
200 49 32
250 51 51

Adjust the airflow rate by rotating the control spindle until the desired setting is achieved.
Lock the damper position with a screw.

Replace the tubes and spindle into the plenum and replace the diffuser.


Remove the measurement and adjustment module by gently pulling the shaft (not the control spindle).
Wipe the parts with a damp cloth, instead of immersing in water.

Reassemble the measurement and adjustment module by pushing the shaft back into place until the module meets the stopper.


The plenum is made of galvanised steel.

The plenum comprises an airflow measurement and adjustment module.

The diffuser is detachable in order to provide access to the measurement and adjustment module in the plenum.

The plenum comprises sound attenuation material made of mineral wool or polyester fibre.

The plenum reduces duct pressure and air velocity in order to supply air throughout the entire face area of the linear diffuser and improve the air distribution quality.

Order code


S = Number of slots
1, 2, 3, 4, 5, 6

L = Active length (mm)
372, +1, .., 49972

D = Duct connection size (mm)
125, 160, 200, 250

N = Number of duct connections
1, +1, …, 322

Other options and accessories

PH  = Plenum height
S        Standard
R        Reduced (D+65 mm)

IN = Sound attenuation
N         No
2W     2 sides, mineral wool
5W     5 sides, mineral wool
2P       2 sides, polyester fibre
5P       5 sides, polyester fibre

ST  = Spigot type
G        With gasket (standard)
W       Without gasket

OM = Measurement/adjustment module (MSM)
N        No
Y        Yes (in each connection)

ID  = Diffuser assembled with plenum
N          No
Y          Yes

ZT = Tailored product
N       No
Y       Yes (ETO)

Code example

PLL/1-400-125-1, PH=S, IN=2W, ST=G, OM=Y, ID=N, ZT=N


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