[0001] The present invention relates to pneumatic actuators.
[0002] Pneumatic actuators are conveniently employed for performing controlled functions
in sequence. One example is the selective or automatic closing of a hinged flap, and
the subsequent engagement of a catch for holding the flap closed. Thus a first pneumatic
actuator may be operated to close the flap and a second pneumatic operator then operated
to engage the catch.
[0003] In a particular example, the flap may be movable to open and close the ventilation
opening of a fire ventilator in which case it is desirable to locate the pneumatic
actuators in a position which does not obstruct the ventilation opening. Furthermore,
for aesthetic reasons, it may be desirable to locate the pneumatic actuators in a
confined space, for example within a hollow frame member of the ventilator defining
the ventilation opening so that the actuators are hidden from view.
[0004] The object of the present invention is to provide a pneumatic actuator unit for performing
two controlled functions in a predetermined sequence, the unit being compact and having
a single compressed airline connection.
[0005] According to the present invention such a unit comprises a pair of pneumatic pistons
and cylinders of which the cylinders have a common head having a single compressed
air inlet which serves also as an exhaust outlet in communication with one of the
cylinders on one side of the piston therein, said piston in said one of said cylinders,
after performing a predetermined movement in said one of said cylinders under the
action of compressed air supplied through said inlet, uncovering a port for the supply
of compressed air from said one of said cylinders on said one side of the piston therein
to the other of said cylinders on one side of the piston therein for displacing the
piston in said other of said cylinders, there being a non-return valve in said head
for communicating said other of said cylinders on said one side of the piston therein
with said exhaust outlet for exhausting air from said other of said cylinders on said
one side of the piston therein.
[0006] A specific embodiment of the present invention will now be described by way of example
and not by way of limitation with reference to the accompanying drawing which is a
cross sectional elevation of an pneumatic actuator unit in accordance with the present
invention.
[0007] With reference to the accompanying drawing, the actuator unit comprises a pair of
in line cylinders 7 and 21 having respective outer end plugs 3 and 27 forming the
cylinder outer.end walls and defining bores 4 in the cylinder outer end walls for
the piston rods 5 and 20 of pistons 9 and 18 associated with the cylinders 7 and 21
respectively, the cylinders having a common head 15 disposed between them having a
single compressed air inlet 30 which serves also as an exhaust outlet through which
air under pressure may be supplied to or air exhausted from the unit under the control
of a conventional two way valve (not shown).
[0008] A non-return valve 23, 25, 26 is housed in an enlarged end portion 23 of a bore 31
in the head 15 which communicates with the compressed air inlet and exhaust air outlet
30 and the cylinder 7 space on the inside of the piston 9 that is to say, the side
adjacent the head 15.
[0009] The head carries a central tubular spiggot 8 which aligns with the common axis of
the cylinders 7 and 21 and which slides in a bore in the piston 9 and its piston rod
5. The spiggot 8 has slot-like ports 32 at its outer end which admit compressed air
from the cylinder 7 space on the inside of the piston 9 to the cylinder 21 space on
the inside of the piston 18 via the hollow interior of the sriggot 8 when the piston
9 uncovers the ports 32 at the end of its outstroke.
[0010] The piston 9 has a reduced diameter inner portion 34 which enters a bore 14 of the
head 15 which communicates in turn with the bore 31. A pair of piston ring seals 10
and 12 are carried respectively by the piston 9 and in the wall of the bore 14 of
the head 15 to entrap between them cushioning air over a last portion of the instroke
of the piston 9 the cushioning air exhausting through bores 36, 37 of the head, along
the clearance between the portion 34 of the piston 9 and the wall of the bore 14 and
the bore 31 to reach the exhaust outlet 30. A screw plug 13 adjusts the restriction
in the bore 37.
[0011] The piston 9 has a frusto-conical outer end portion to enter a foreshortened return
spring 6 which is mounted on, and centered by,a boss of the outer end plug 27, the
return spring 6 being compressed between the plug 27 and the piston 9 proper on the
full outstroke of the piston 9.
[0012] The piston 18 has a conventional return spring 19.
[0013] Air bleed holes 1 in the cylinder end plugs 3 and 27 allow the flow of air into and
out of the outside cylinder spaces on stroking of the pistons.
[0014] Screw threaded mounting holes seen in the head 15 are used to mount the unit.. One
such further mounting hole may be provided in the end plug 27 and is seen in the drawing.
[0015] The operation of the unit will now be described by way of further example and not
by way of limitation with reference to the opening and closing of a fire ventilator
flap and the movement of a catch to retain the flap in its closed position and thereafter
to release the catch to allow the flap to be opened.
[0016] The unit is mounted within a side frame member of the ventilator defining the opening
controlled by the flap, the flap being hinged for opening and closing movement along
its lower edge and having a substantially vertical closed position.
[0017] Extension of the piston 9 and the piston rod 5 under the action of air under pressure
supplied through the compressed air inlet 30 moves a slide block (not shovm) which
pivots a flap stay hinged to the flap and to the slide block to move the flap from
its open to its closed position. Towards the end of the outstroke of the piston 9
the piston uncovers the ports 32 and air under pressure is supplied to the inside
of the piston 18 to extend the piston rod 20 thereby rotating the catch to lock the
flap closed.
[0018] When the control valve supplying compressed air to the inlet 30 is adjusted to connect
the inlet with atmosphere, the inlet 30 then serving as an exhaust outlet, air is
exhausted from the inside of the piston 18 through the non-return valve 23, 25, 26
and the spring 19 returns the piston 18 through its instroke and the catch is rotated
to release the flap. The piston 9 is accelerated by the spring 6 through an initial
portion of its instroke to force the flap open and the resulting gravitational opening
movement of the flap is finally arrested by the act on of the cushioning air bled
through the re -iction at 37 to the exhaust outlet 30.
[0019] The two-position control valve supplying compressed air to the inlet 30 will be placed
at a convenient remote location.
[0020] The ventilator just described may be as described in detail in GB-85 14571 or EP-A-85
304499.8 with reference to Fig. 22 of its specification, the piston rod 5 of the pneumatic
unit described herein and forming the unit 175 in the specifications referred to being
connected to operate the slider 172 and the piston rod 20 of the pneumatic unit described
herein being connected to operate the latch hook 173 in the specifications referred
to.
1. A pneumatic actuator unit comprising a pair of pneumatic pistons and cylinders
of which the cylinders have a common head having a single compressed air inlet which
serves also as an exhaust outlet in communication with one of the cylinders on one
side of the piston therein, said piston in said one of said cylinders, after performing
a predetermined movement in said one of said cylinders under the action of compressed
air supplied through said inlet, uncovering a port for the supply of compressed air
from said one of said cylinders on said one side of the piston therein to the other
of said cylinders on one side of the piston therein for displacing the piston in said
other of said cylinders, there being a non-return valve in said head for communicating
said other of said cylinders on said one side of the piston therein with said exhaust
outlet for exhausting air from said other of said cylinders on said one side of the
piston therein.
2. A pneumatic unit as claimed in claim 1 in which said pneumatic pistons and cylinders
are in line.
3. A pneumatic unit as claimed in claim 2 in which the head carries a tubular spiggot
which aligns with the common axis of the cylinders and which slides in a bore in said
piston in said one of said . cylinders, said port being formed at the outer end of
said spiggot and opening into the hollow interior of the spiggot to communicate said
one of said cylinders on said one side of the piston therein with the other of said
cylinders on said one side of the piston therein.
4. A pneumatic unit as claimed in claim 2 in which said port is formed as an open-ended
slot in the wall of the spiggot.
5. A pneumatic unit as claimed in any preceding claim in which said piston in said
one of said cylinders has a reduced diameter inner portion to enter a bore of the
head over a terminal portion of its instroke thereby to entrap cushioning air at the
inner end of said one of said cylinders, the cushioning air exhausting through exhaust
bores of the head and said exhaust outlet.
6. A pneumatic unit as claimed in claim 5 in which said exhaust bores of said head
include the bore which receives the reduced diameter inner portion of said piston
in said one of said cylinders, the cushioning air exhausting along the clearance between
the reduced diameter inner portion of the piston and that bore.
7. A pneumatic unit as claimed in claim 5 or 6 in which said exhaust Dores include an adjustable restriction.
8. A ventilator comprising a frame, a flap hinged to the frame along its lower edge
and movable to open and close a ventilation opening defined by the frame, the flap
having a substantially vertical closed position closing said opening, a releasable
catch engageable with the flap to retain the flap in its closed position and a pneumatic
unit as claimed in any preceding claim carried by the frame and operable by compressed
air supplied to said single compressed air inlet to close the flap and then engage
said catch.
9. A ventilator as claimed in claim 8 in which said pneumatic unit is a unit as claimed
in claim 5 and said piston in said one of said cylinders has a foreshortened return
spring, housed in the outer end of said one of said cylinders, and operable to move
the flap from its closed position towards its open position during its initial opening
movement, the flap being moved to its fully open position by gravitational action
and being arrested in its final opening movement by the action of cushioning air exhausted
through said exhaust outlet.
10. A ventilator as claimed in claim 8 or 9 including a two position control valve
for supplying compressed air to said inlet and for connecting said inlet with atmosphere
respectively.