Air distributor with automatically closable damper

A reciprocating pneumatic actuator moves the damper of an air diffuser between open and closed positions and is automatically vented to atmosphere if fire or high heat occurs in the vicinity of the diffuser. When the actuator is vented, the return spring of the actuator snaps the damper to its closed position. A heat responsive latch automatically holds the damper in its closed position and prevents the damper from dropping open in the event the return spring is weakened by heat.

BACKGROUND OF THE INVENTION 
This invention relates generally to an air distribution unit. While the 
invention is applicable to various types of air distribution units, it is 
particularly useful in conjunction with a unit adapted to be mounted in 
the ceiling of a room and adapted to admit air into the room from the 
outlet of an air duct located above the ceiling. 
In a more specific sense, the invention relates to an air diffuser in which 
a reciprocating pneumatic actuator moves a valve element or damper between 
open and closed positions relative to the outlet of the air duct. The flow 
of pressure fluid to the actuator preferably is controlled so as to enable 
the actuator to move the damper to various positions between its fully 
open position and its fully closed position and thus effect regulation of 
the volume of conditioned air delivered to the room. A typical pneumatic 
actuator includes slidably telescoped piston and cylinder members with one 
of the members being advanced by pressure fluid to open the damper and 
being retracted by a spring to close the damper. 
In the case of fire, it is desirable to close the outlet of the duct in 
order to cut off the flow of air from the duct, to prevent smoke from 
entering the room by way of the duct and to retard heat flow from the room 
to the structural members above the ceiling. Automatically closable fire 
dampers for air ducts have existed previously. To the best of my 
knowledge, however, those dampers are normally held in a fully open 
position and are closed only in the event of fire. Such a damper is not, 
therefore, capable of regulating the flow of air into the room under 
normal conditions. 
SUMMARY OF THE INVENTION 
The general aim of the present invention is to provide a new and improved 
air distribution unit having a valve element or damper which is adapted to 
be moved between open and closed positions under normal conditions and 
which is automatically shifted to its fully closed position if fire or 
heat causes the temperature in the room or in the vicinity of the damper 
to exceed a predetermined value. 
A further object of the invention is to provide a variable air volume 
diffuser in which a pneumatic actuator is capable of moving the damper to 
various open positions to modulate the air flow and serves to close the 
damper automatically in the case of fire or extreme heat. 
A more detailed object is to achieve the foregoing by providing a unit in 
which heat responsive means automatically vent the actuator to atmosphere 
under high heat conditions so as to enable the spring of the actuator to 
snap the damper closed. 
Still another object is to latch the damper securely in its closed position 
independently of the actuator spring but to effect such latching only if 
the damper has been moved to its closed position as a result of a high 
heat condition. 
The invention also resides in the relative simple and inexpensive apparatus 
which is used to vent the actuator and to latch the damper. 
These and other objects and advantages of the invention will become more 
apparent from the following detailed description when taken in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the drawings for purposes of illustration, the invention is 
embodied in an air distribution unit 10 which, in this particular 
instance, is adapted to be mounted in an opening in the ceiling 11 of a 
room and is adapted to diffuse conditioned air flowing into the room from 
a heating and/or cooling passage or duct 12 located above the ceiling. The 
ceiling which has been illustrated is of the suspended type and is located 
below the structural members of the building. A cavity or plenum is 
located between the ceiling and the structural members and defines a space 
which accommodates the duct, electrical conduits and the like. 
Herein, the unit 10 includes a downwardly opening box 13 having a square 
and horizontally disposed top wall 14 (FIG. 2) and having four downwardly 
extending side walls 15. A circular opening 16 is formed through the 
center portion of the top wall 14 and is adapted to communicate with the 
duct 12 in order to admit a downward flow of air into the box 13. A 
downwardly flaring skirt 17 extends around the opening 16 and is secured 
to the top wall 14. 
To connect the duct 12 and the box 13, an upstanding cylindrical pipe 18 
(FIG. 2) is concentric with the outlet opening 16 and its lower end is 
fixed to the top wall 14. A grille 19 in the form of a louvered plate, a 
perforated screen or the like is connected to the lower margins of the 
side walls 15 and covers the lower end of the box 13 to effect a patterned 
distribution of the air flowing downwardly into the room. Secured to the 
center portion of the grille on the upper side thereof is a circular steel 
disc 19a which serves as a baffle to cause the air to flow horizontally 
and then downwardly through the grille rather than flowing in a direct 
downward stream. 
Located within the box 13 adjacent the lower end of the pipe 18 is a valve 
element which herein is in the form of a damper 20 (FIG. 2) adapted to 
open and close the outlet 16. In the present instance, the damper is 
formed by a comparatively thick circular top disc 21 made of sheet rock or 
the like and by a sheet metal bottom plate 22 whose margins extend 
outwardly beyond the margins of the disc and define a flange 23. When the 
damper 20 is in its fully closed position, the disc 21 telescopes into the 
pipe 18 while the flange 23 abuts the underside of the top wall 14 around 
the margins of the outlet 16 (see FIG. 3). 
To move the damper 20 between its open and closed positions, a 
reciprocating pneumatic actuator 25 is supported by the box 13 and is 
operably connected to the damper. Herein, the actuator 25 comprises an 
upright cylinder member 26 whose lower end is secured to the central 
portion of a spider 27 (FIG. 2) having three radiating arms which are 
connected to the inside of the pipe 18. Telescoped slidably within the 
cylinder 26 is a piston member 28 (FIG. 3) carrying a depending rod 29 
which is slidably guided by an externally threaded tubular fitting 30 
connected to the lower end of the cylinder. A jam nut 31 is threaded onto 
the fitting and clamps the cylinder to the spider. Another nut 32 fastens 
the damper 20 to the lower end portion of the rod 29 with the damper being 
spaced downwardly from the nut 31. 
A flexible diaphragm 33 (FIG. 3) is secured within the upper end portion of 
the cylinder 26 and extends across the upper end of the piston 28 so as to 
divide the cylinder into upper and lower chambers. When pressure fluid 
such as pressurized air from an air source 34 (FIG. 2) is admitted into 
the upper chamber, the piston 28 and the rod 29 are forced downwardly to 
move the damper 20 toward its open position. When air is exhausted from 
the upper chamber to relieve the pressure, the damper is moved toward its 
closed position by a coil spring 35. The spring is telescoped over the rod 
29 and is compressed between the lower end of the piston and the bottom of 
the cylinder. 
While the actuator 25 could be operated simply to move the damper 20 either 
to its fully open position or to its fully closed position, the damper 
herein is preferably adapted to be moved to any position between those two 
extreme positions so that the damper may act to vary the volume of air 
flowing into the room. For this purpose, the pressure of the air supplied 
to the actuator is regulated, for example, as a function of room 
temperature so as to cause the actuator to position the damper as required 
to effect delivery of an air volume sufficient to maintain a given 
temperature. As shown in FIG. 2, a temperature responsive control 36 is 
interposed between the actuator 25 and the air source 34 and regulates the 
pressure of the air supplied to the cylinder 26 so as to increase the 
pressure and effect opening of the damper 20 when a greater volume of 
conditioned air is required. Conversely, the control 36 allows pressurized 
air to exhaust from the cylinder at a controlled rate when closing of the 
damper is necessary to reduce the volume of conditioned air. A flexible 
tube 37 extends from the control 36 to a fitting 38 on the top of the 
cylinder and establishes communication between the air source and the 
cylinder by way of the control. 
In accordance with the present invention, the cylinder 26 of the actuator 
25 is automatically vented to atmosphere if fire or extreme heat causes 
the temperature adjacent the distribution unit 10 to exceed a 
predetermined value. As an incident to venting of the cylinder, the spring 
35 automatically snaps the damper 20 to its closed position so as to shut 
off the flow of air and smoke into the room and to retard the flow of heat 
from the room to the ceiling plenum by way of the pipe 18. 
More specifically, the cylinder 26 preferably is adapted to be vented under 
high heat conditions by means of a flexible sensing tube 40 (FIG. 2). One 
end of the tube is connected to the fitting 38 and communicates with the 
upper chamber of the cylinder 26. The other end of the sensing tube herein 
is connected to the outer end of a tubular fitting 41 (FIG. 7) which is 
secured to a support bracket 42. The bracket 42 is welded to the underside 
of the jam nut 31 and is formed with an enlarged hole 43 (FIG. 6) which 
receives the rod 29 of the actuator 25 with substantial radial clearance. 
In carrying out the invention, the inner end of the tubular fitting 41 is 
closed by a plug 45 (FIG. 7) of fusible or meltable material such as 
solder. Thus, the plug normally keeps the sensing tube 40 in a 
pressure-tight condition so as to enable pressurization of the cylinder 
26. In the event of fire or extreme heat, however, the plug melts to open 
up the inner end of the tubular fitting 41 and vent the sensing tube 40 to 
atmosphere. As a result, the pressurized air in the upper chamber of the 
cylinder 26 is rapidly exhausted to atmosphere by way of the open tube and 
thus the spring 35 acts to snap the damper 20 upwardly to its closed 
position to close off the opening 16. The disc 21 of the damper preferably 
is made of sheet rock or other heat resistant material to help retard the 
flow of heat through the opening 16. 
According to another feature of the invention, means are provided for 
positively latching the damper 20 in its closed position if the damper is 
moved to that position as a result of a high heat condition. By virtue of 
the positive latching, the damper is prevented from opening even if the 
temperature is sufficiently high to weaken the spring 35 and cause the 
spring to lose its resiliency. 
In the present invention, the latching means comprise a detent in the form 
of a plate 47 (FIGS. 3 to 6) which is pivotally mounted on the lower side 
of the bracket 42 by a vertical rivet 48. The rivet supports the plate 47 
for pivoting between unlatched and latched positions (FIGS. 5 and 6) with 
the plate being urged toward its latched position by a contractile spring 
49 which is stretched between an ear 50 on the plate and an ear 51 on the 
bracket 42. An arcuate slot 52 (FIG. 6) is formed in the plate and 
receives a rivet 53 on the bracket to guide the plate for pivoting on the 
bracket. 
A vertical hole 55 (FIGS. 3 and 6) is formed through the center of the 
plate 47 and, when the plate is in its unlatched position shown in FIG. 5, 
the rod 29 of the actuator 25 may freely move upwardly and downwardly 
within the hole. When the plate pivots clockwise to its latched position 
shown in FIG. 6, the edge of the hole 55 moves into an annular groove 56 
(FIG. 3) formed around the rod 29 and catches against a downwardly facing 
shoulder defined by the upper side of the groove. 
Pursuant to the invention, heat responsive means normally hold the latching 
plate 47 in its unlatched position against the action of the spring 49 but 
release the plate to move to its latched position in the event of fire. In 
this instance, the heat responsive means comprise a fusible link 60 (FIGS. 
4 and 5) formed with holes which receive a tab 61 on the bracket 42 and a 
tab 62 on the plate 47. The link normally is rigid and prevents the spring 
49 from pivoting the plate to its latched position. Thus, the rod 29 
normally may freely move up and down within the opening 55 and may shift 
the damper 20 between its fully open and fully closed positions without 
interference from the latching plate. When fire or high heat occur, 
however, the link 60 melts so as to permit the spring 49 to move the plate 
47 to its latched position. If the damper 20 already has been moved to its 
closed position by the spring 35, the edge of the hole 55 in the plate 47 
immediately moves into the groove 56 in the rod 29 and catches the upper 
side of the groove to positively latch the damper. If the link 60 melts 
before the sensing tube 40 has been vented, the plate 47 pivots until the 
edge of the hole 55 engages the side of the rod 29 and then pivots further 
to move the edge of the hole into the groove 56 once the rod has been 
fully retracted. In either case, the damper is securely latched against 
returning to its open position if the heat reduces or destroys the 
effectiveness of the spring 35. 
From the foregoing, it will be apparent that the present invention brings 
to the art an air distribution unit 10 with a new and improved actuator 25 
for automatically closing the damper 20 under high heat conditions. While 
the actuator has been specifically shown and described in conjunction with 
a variable air volume diffuser, those familiar with the art will 
appreciate that the actuator could be used equally well with other air 
distribution units (e.g., terminal units, mixing units, side wall 
diffusers and the like) for automatically closing a damper or other valve 
element with respect to an air outlet or passage.