[0001] The present invention comprises improvements relating to ventilators and concerns
controllable ventilators comprising an outwardly opening hinged flap which when closed
covers over and closes or assists in closing a ventilation opening of the ventilator.
[0002] Such ventilators are often used as fire ventilators and, to ensure a failsafe operation,
are provided with a flap opening spring or springs. For normal day-to-day ventilation
the flap is opened by its spring and closed against the action of its opening spring
by means of a fluid pressure operable piston and cylinder unit or an electric motor,
for example.
[0003] Since the opening spring is required to open the flap in all circumstances it is
usual to make proper allowance for the weight of the flap, any snow load on the flap
and the frictional forces of the mechanism which need to be overcome when moving the
flap from its closed, e.g. horizontal, position to its open, e.g. vertical, position,
when choosing the power of the opening spring.
[0004] It will be understood that the horizontal closed and vertical open position of the
flap are chosen to represent the worst example concerning the opening force requirements
for the flap and that the ventilator might well be mounted at some inclined angle
or even vertically in practice instead of horizontal.
[0005] However, in any orientation of the ventilator, an equal and opposite power is, in
general, required to be exerted on the flap to move the flap from its, e.g. vertical
open position to its horizontal closed position ignoring the self weight of the flap.
The closing force determines the stress regime to which the ventilator frame is subjected
during the closing of the flap and any reduction of this stress is of benefit to the
design and functioning of the ventilator as a whole.
[0006] Taking a single hinged flap ventilator mounted in a horizontal position as an example
and referring to Fig. 2 of the accompanying drawings, it may be seen that the torque
required to open the flap is W cos α

where W is the weight of the flap, H is the length of the flap and α is the opening
angle which changes from 0° to 90°. This torque is at a maximum when the flap is horizontal
and a minimum when the flap is vertical, as indicated by the curve d in Fig. 3 of
the accompanying drawings. To this must be added the snow load and friction load allowance.
The expected torque to open the flap is as indicated by the curve e shown in Fig.
3.
[0007] The opening torque characteristic due to the force exerted by the opening spring
must start above this curve e. If the opening spring is to be in the form of a linearly
extendable strut housed generally within the depth of the ventilator frame, however,
then as may be seen from Fig. 2 the effective radius of action about the flap hinge
axis at which the spring operates on the flap increases from b to e as the flap is
moved from its closed to its open position. The opening torque characteristic thus
rises with the opening angle α, generally as indicated at g in Fig. 3 and the torque
required to close the flap, taking into account the assistance of the flap self weight,
is indicated at f in Fig. 3.
[0008] The present invention aims to reduce the maximum closing torque requirement in a
sprung-to-open hinged flap ventilator having an opening spring in the form of a linearly
extendible strut the effective radius of action of which increases as the flap is
moved from its closed to its fully open position.
[0009] To this end the present invention provides that the strut is composed of a series
of springs of different linear spring rates.
[0010] A specific embodiment of the present invention will now be described by way of example
with reference to the accompanying drawings in which:
FIG. 1 is a cross section of a single flap ventilator of the present invention in
a closed position;
FIG. 2 is a cross section of the ventilator in an open position; and
FIGS. 3 and 4 are diagrams.
[0011] With reference now to the accompanying drawings, the ventilator comprises a frame
10 defining a ventilation opening 11 and a single, glazed ventilation flap 13 hinged
to the frame and angularly movable about its hinge axis 15 to open and close the ventilator.
[0012] Mechanism generally indicated at 20 is provided for opening and closing the ventilator
and one such menchanism is housed in each longitudinally extending internal side channel
21 of the frame. The mechanisms 20 are identical and one only of them will be described.
[0013] The mechanism 20 comprises a pneumatic piston and cylinder unit 22 having its cylinder
25 mounted to the frame 10 with its cylinder inner end positioned in the side channel
22 adjacent the flap hinge axis 15 and its cylinder axis 26 extending longitudinally
of the side channel 21. Rotatably mounted towards the opposite end of the side channel
21 is an integral pair of drums 30, 31 of different diameter. The smaller diameter
drum 31 receives a wound-on end portion of a flat high tensile flexible steel strip
34 connected at its other end to the piston rod 23 of the piston of the piston and
cylinder unit 22. The larger diameter drum winds on one end of a wire rope or a further
flexible steel strip 36, the other end of which is connected to the flap 13 as at
38.
[0014] A pair of linearly operable gas springs 40 are fixed together in parallel, side-by-side,
so as to overlap their linearly operable extents. The gas springs 40 have their piston
rods 42 extending in opposite directions and hingeably connected at their outer ends
respectively to the flap 13, as at 43, and the frame 10, as at 44, in this case by
means of ball joints 45. Instead of side-by-side gas springs 40 a pair of telescoping
gas springs, one housed within the other, could be used. Again, cylinder guided, coiled
wire torsion springs could be substituted. However, linearly operable gas springs
are preferred.
[0015] The gas springs 40 operate as linearly extendible struts to open the ventilator and
the ventilator is closed by fluid pressure supplied to the piston and cylinder units
22.
[0016] As will be appreciated, the overall length of the cylinders 25 is dependent upon
their stroke length and a fixed dimension for internal seals, piston and end mountings.
Thus, the overall outstroked length of the piston and cylinder units 22 is at least
twice their stroke length. By using the different diameter drums 30, 31, the stroke
length of the units 22 is magnified to an extent sufficient to close the ventilator
flap whilst positioning the connection points 38 of the flexible connection members
36 at a location close to the connection points 43 of the gas springs 40 and close
to the free transverse edge of the flap 13.
[0017] The arrangement thus achieved gives rise to a favourably low stress distribution
in an otherwise compact mechanism. Further, this outcome is assisted by the use of
the back-to-back gas springs 40 which have an increased outstroked to instroked length
ratio enabling them to be accommodated, in their instroked condition, in front of
the units 22 in the side channels 21 and between the units 22 and the drums 30, 31
as clearly seen in Fig. 3
[0018] Also, by use of high tensile flexible steel strip 34, 36, the acceptable diameter
of winding and, therefore, the acceptable diameter(s) of the drum(s) 30, 31 is/are
reduced.
[0019] The gas springs 40 of each pair are pressurised with gas to provide the springs of
each pair with different spring rates. In particular, the lowest force of the higher
pressure spring of the pair is selected to be above the highest force of the lower
pressure spring of the pair. As a result, the higher pressure spring of the pair outstrokes
first to move the flap 13 from its closed to a partly open position indicated at α₁
in Fig. 4 and then the lower pressure spring of the pair outstrokes to move the flap
13 from is α₁ position to its α₂ position is indicated in Fig. 4.
[0020] Conveniently the struts formed by the pairs of springs 40 are arranged to extend
symmetrically, the springs 40 anchored to the frame 10 being the higher pressure springs
and extending first.
[0021] The torque required to overcome the weight of the flap 13 and open the flap 13 is
W cos α

where W is the weight of the flap 13, H is the length of the flap 13 and α is the
opening angle of the flap 13. This torque is at a maximum when the flap 13 is horizontal
and at a minimum when the flap is vertical as indicated by the curve d in Fig. 4.
To this must be added a snow load and friction load allowance which increases the
opening torque requirement to e indicated in Fig. 4.
[0022] The maximum torque required to be exerted by the piston and cylinder unit 22 during
closing of the flap 13 is indicated at f₁ in Fig. 4. This maximum occurs at the angle
α = α₁.
[0023] Examination of Fig. 4 will show that this maximum torque requirement is substantially
reduced.
[0024] Fig. 4 is drawn for the case of a ventilator mounted with its flap 13 disposed at
an angle of 15° to the horizontal when closed and 55° to the horizontal when open,
i.e. α₂ = 55°. For the more general case with a flap 13 required to open from 0° to
90° the curve g in Fig. 4 would commence as shown in Fig. 3 and drop down vertically
at the α₁ angle of opening.
[0025] Clearly, using a multispring arrangement of opening springs employing a series of
more than two springs, the curve g would step down in more than one step but would
still remain always above the curve e.
[0026] Instead of providing two mechanisms 20 one only may be used, housed as illustrated
in one of the longitudinally extending internal side channels 21 of the frame. In
order to ensure a symmetrical pull on the flap 13 the connection point at 38 of the
other end of the wire rope or steel strip 36 is shifted to a point close to the mid
point of the free edge of the flap 13. The wire rope is then led from the larger diameter
drum 30 over a pulley on the frame, the axis of rotation of the drums 30, 31 extending
at right angles and the drums being drivingly interconnected by means of a pair of
bevel gears.
1. A sprung-to-open hinged flap ventilator having an opening spring in the form of a
linearly extendible strut the effective radius of action of which increases as the
flap is moved from its closed to its fully open position, the strut being composed
of a series of springs of different linear spring rates.
2. A ventilator as claimed in claim 1 in which the springs are gas springs, the pressure
of gas in one of which, when fully outstroked, is higher than the pressure of gas
in another of the springs when fully instroked.
3. A sprung-to-open hinged flap ventilator substantially as hereinbefore described with
reference to, and as illustrated in, Figs. 1 and 2 of the accompanying drawings.