Counterweight static pressure-air flow damper assembly

A barometric damper includes a swingably mounted damper blade having a first adjustable counterweight assembly lying in a common plane with the damper blade and mounted for rotation therewith. The torque arm mass loading can be varied. A second adjustable counterweight assembly coupled to the damper shaft adjusts the static control point of the damper.

FIELD OF THE INVENTION 
The present invention relates to dampers, and more particularly, to static 
pressure control dampers for operation over a wide range of static 
pressure. 
BRIEF DESCRIPTION OF THE PRIOR ART 
Energy conservation systems are widely used throughout many industries for 
a variety of applications. One application is the use of preheated air 
streams as make-up air and as a heat source for industrial drying systems. 
Since most dryers incorporate recirculation loops at each zone, the use of 
preheated air as a heat source mandates both temperature and flow control. 
This is usually accomplished with an automated damper system to control 
both temperature and flow rate. Noting FIG. 1, the recirculation flow path 
for oven 10 comprises a recirculation duct 11, a return duct 12 and a 
first blower 14. A burner 25 heats the air in the return duct 12 before 
the air is delivered to the oven 10. An exhaust path including exhaust 
duct 18 and second blower 16 is also provided for exhausting steam, 
particulate matter, and the like. The direction of air flow through the 
system is indicated by the arrows. A first branch duct 20 is connected to 
a hot air source (not shown) to introduce heated air into the return duct 
12 through temperature regulating controls, including a temperature 
instrument controller TIC, a temperature operator TZ and a temperature 
sensor or thermocouple TE. The temperature operator TZ controls valve 
means positioned within the first branch duct 20 to control the flow of 
recirculated air therethrough under the control of temperature instrument 
controller TIC in response to the signal generated by the thermocouple TE 
positioned in the return duct 12. A second branch duct 22 introduces 
ambient air into the return duct 12 under control of a pressure instrument 
controller PIC, a pressure controller PZ, and a pressure sensor PDT, to 
control the static pressure or flow in the return duct 12. 
It can be thus seen that the prior art arrangement of FIG. 1 requires both 
a temperature control loop and flow or static pressure control loop. 
Another system to accomplish the same results is shown in FIG. 2, which 
incorporates a barometric damper and a temperature control loop. Like 
elements are designated by like numerals in FIGS. 1 and 2. The arrangement 
of FIG. 2 eliminates the barometric control loop comprised of elements 
PIC, PZ and PDT, which are replaced by the barometric damper 24. 
Although this second approach eliminates the need for a flow or static 
pressure control loop, the barometric damper 24 provides control only at a 
predetermined set point or flow rate. Thus, in applications that require 
control of temperature over a wide range, the barometric damper is unable 
to maintain proper static or flow balance in oven 10, which is related to 
the gravitational effect of the damper blade, as the temperature control 
point is varied. 
SUMMARY OF THE INVENTION 
The present invention overcomes the limitations of the barometric damper 
approach shown in FIG. 2 while eliminating the static pressure control 
loop of FIG. 1 through the employment of an improved barometric damper 
having an adjustable weight assembly mounted on a torque arm which is 
preferably also adjustable. A counterweight attached to the torque arm 
counteracts the gravitational and frictional effects of the damper blade 
so that the blade is substantially weightless. The improved barometric 
damper also includes a disc and a cooperating adjustable disc/linkage 
counterweight assembly for adjusting the static pressure control of the 
damper. Weights of an appropriate amount are attached to the linkage 
coupled to the disc/linkage assembly to obtain the desired static pressure 
control point. The weight utilized in the disc/linkage assembly provides 
the desired static pressure control by enabling the damper to assume 
openings over a wide range of angles at the same static pressure. 
Preferably, the counter-torque exerted by the disc/linkage assembly is 
independent of the angular orientation of the damper blade. 
It is therefore one object of the present invention to provide a barometric 
damper having a counterweight assembly which renders the damper blade 
substantially weightless and provides an adjustable static control 
counterweight assembly for adjusting the static pressure control point for 
the damper. 
Another object of the present invention is to provide a barometric damper 
assembly providing a first adjustable weight means for rendering the 
damper blade substantially weightless and a second adjustable weight means 
for selecting the damper static pressure control point.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 3 shows a system 30 in which a static control damper 100 of the 
present invention can be employed. The system 30 includes an oven 10 
having a housing 32 and a driver (nozzle) supply 33 for providing heat 
within the housing 32. Such ovens can be used for drying articles conveyed 
therethrough on conveyor means (not shown) and the like. 
The air to be recirculated is obtained from the oven 10 through a 
recirculation duct 11 and returned to the oven 10 through return duct 12 
aided by a first blower 14. The air delivered to the oven 10 is heated by 
burner 25. Air which is not to be recirculated can be exhausted from 
housing through an exhaust duct 18 aided by a second blower 16. 
Preheated air can be introduced through a first branch duct 20. The amount 
of preheated air introduced into the return duct 12 is controlled by a 
thermocouple TE positioned in the return duct 12, a temperature instrument 
controller TIC, and a temperature controlled operator TZ for operating a 
damper 24 in the first branch duct 20. A static control damper 100 
introduces fresh air into the return duct 12 through a second branch duct 
22. 
FIG. 4 shows a simplified perspective view of the damper blade assembly 100 
of a first embodiment of the present invention which comprises a damper 
blade 102 mounted proximate one edge thereof on a shaft 104 for rotation 
with the shaft 104 (best seen in FIG. 5a). Alternatively, the damper blade 
102 can include integrally formed pivots (not shown). At rest, the damper 
blade 102 is preferably oriented at an acute angle relative to the 
vertical; in the preferred embodiment this angle is of the order 20 to 25 
degrees. The damper blade 102 is swingably mounted for rotation about an 
axis of rotation adjacent an open end of a duct for controlling the flow 
of gas into the duct. 
A torque arm 106 is secured to one end of the shaft 104 and is aligned so 
as to lie in a common plane but oriented in a direction substantially 
opposite to that of the damper blade 102 with respect to the shaft 104 
(i.e., forming a 180.degree. angle with the damper blade 102). The free 
end 106a of the torque arm 106 is coupled to a first weight 110 through a 
flexible coupling member or rope 108. The magnitude of the first weight 
110 placed upon the flexible member 108 is selected to counterbalance the 
weight of the damper blade 102 and associated frictional forces to render 
the damper blade 102 substantially "weightless." The length of the torque 
arm 106 is preferably variable to provide an additional degree of freedom 
in balancing the damper blade 102 (not shown). 
The static pressure in the return duct 12 is regulated by the disc 112 
mounted to the opposite end of the shaft 104 and rotatable therewith (FIG. 
4). A flexible linking member or chain 114 is coupled to a point along the 
circumference of the disc 112 and is adapted to receive and mount a second 
weight 116, the magnitude of the weight being selected to adjust the 
static pressure control point within the return duct 12. The chain 114 is 
received in a groove 113 formed in the outer periphery of its disc 112. 
Thus, the torque exerted by the second weight 116 on the shaft 104 is 
advantageously constant and independent of the extent to which the damper 
blade assembly 100 is open and the angular orientation of the damper blade 
102 when it is open. The flexible linking member 114 mounted with the disc 
112 is thus similar to a line passing over a pulley and having one end 
fixed to the pulley proximate the outer perimeter of the pulley. 
In operation, the static pressure causes the damper blade 102 to be lifted 
when the negative pressure within the return duct 12 is less than 
atmospheric or set point (generally negative) pressure, the angle through 
which damper blade 102 rotates in the counterclockwise direction (with 
respect to FIG. 4) being a function of the pressure differentials and the 
magnitude of the second weight 116 coupled to linkage 114. Stops 118 are 
arranged along the floor of the second branch duct 22 in which damper 
blade 102 is mounted to limit the movement of damper blade 102 in the 
clockwise direction (with respect to FIG. 4). Preferably, the stops 118 
are placed to give the damper blade 102 an angle of about 25.degree. with 
respect to the vertical when the damper blade assembly 100 is closed. 
Thus, when the damper blade assembly 100 first opens, laminar flow through 
the damper is promoted and turbulence and additional forces resulting from 
velocity pressure of air flow are minimized. 
The lower end of damper blade 102 is preferably provided with a resilient 
flexible rubber of rubber-like strip 20a to improve the seal between the 
floor of the second branch duct 22 and the damper blade 102. The damper 
blade 102 is thus only lifted to open the second branch duct 22 to the 
atmosphere when the negative pressure in the return duct 12 exceeds the 
set point pressure. 
FIGS. 5a through 5e show detailed views of a second embodiment of the 
damper assembly. It can be seen from FIGS. 5a, 5b and 5c that the disc 112 
and the lever arm 106 can both be mounted on the same end of the shaft 
104, which is preferably mounted to the second branch duct 22 by means of 
a pair of flange bearings 120. In the embodiment shown in FIGS. 5a through 
5e, and specifically in FIGS. 5b and 5c, linking member 114 is a 
double-pitched chain comprised of a plurality of pairs of links 114a 
coupled together end-to-end by pins 114b. The bottom-most link 121 is 
coupled to a block 122 having a threaded rod 124 at its lower end for 
threadedly engaging a suitable weight (not shown). 
In this embodiment, as best seen in FIGS. 5b and 5c, the double-pitched 
chain 114 is fixed at one end 115 to the disc 112. A first portion 117 of 
the chain 114 is carried on the upper portion of the outer periphery of 
the disc 112 as the disc 112 rotates when the damper blade 102 
simultaneously rotates from a closed (FIG. 5b) to a fully open position 
(FIG. 5c). A second portion 119 of the chain 114 extends vertically 
downward from the disc 112. Thus, the torque exerted by the weight 
attached to the threaded rod 124 is constant and independent of the 
orientation of the damper blade 102 over this range of damper blade 
orientations. 
In operation, a first weight 110 is selected for coupling to the torque arm 
106 to counterbalance the weight of damper blade 102 as well as any 
friction encountered in the swingable mounting (e.g., between the flange 
bearings 120 and the shaft 104). The second weight 116, which threadedly 
engages the threaded member 124, is then selected to have a magnitude 
which fixes the static control point for operation of damper blade 102. 
The blade 102 is thus effectively weightless while the second weight 116 
threadedly mounted upon threaded member 124 increases the pressure 
required to move the damper blade 102 from its closed position as the 
second weight 116 is increased. With the present invention, damper 
openings from about 25 to 70 degrees are possible at the same static 
pressure, for example one-half inch of water. 
As will be recognized by those skilled in the art, latitude of 
modification, change and substitution is intended in the foregoing 
disclosure, and in some instances, some feature of the invention will be 
employed without a corresponding use of other features. For example, while 
ducts having rectangular cross-sections are illustrated, ducts with 
circular or other cross-sections can also be used with the apparatus of 
the present invention. Accordingly, it is appropriate that the appended 
claims be construed broadly and in a manner consistent with the spirit and 
scope of the invention herein.