Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a turntable mounted
elevatable member having personnel support means such as a
turntable ladder suitable for use on a fire figh~ing and
rescue vehicle or a man carrying platform.
Fire fighting and rescue vehicles are usually
provided with a ladder mounted on a turntable which-can be
extended to bring the head of the ladder to a desired
position either to enable a fireman to direct a jet of
water on to the fire or to provide an escape route for
10 persons trapped by the fire. It is a safety requirement
of turntable ladders that where the elevation of the ladder
is performed by hydraulic-rams a~ hydraulic lock must be
provided at the base of each ram to prevent uncontrolled
depression of the ladder. ~In addition, a mechanical
15 lock should also preferably be provided in the case o~
two or more rams and must be provided where a single r~m
only is used. These requirements are clearly sensible,
but they give rise to difficulties in enabling the ladder
to be trained in all required directions. I* the vehicle
20 is standing on a level site, such as a road; orlthe turn-
table axis is movable~so that the plane of the turntable
is horizontal, there is no problem, but if it is necess~ry
to provide for plumbing of the ladder so that the rungs of
tha ladder are horizontal even though the vehicle and the
25 plane of the turntable are not horizontal, then the rotation
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of the ladder axis to permit the plumbing of the ladder is
complicated by the safety requirements described above.
If the ladder is elevated by means of two hydraulic rams,
then all that is required by the safety legislation is that
30 these rams have hydraulic locks, but the plumbing of the~
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ladder wilI mean that the two rams must have different
lengths and also must be provided with universal
joints for connecting them to the ladder and the
mounting. As a result the control of the rams and the
construction of the ladder is complicated. Other and
similarly complicated methods involve the use of an
additional turntable or a multiple slew ring having
two opposed wedges to effect the plumbing. On the
other hand, if a single elevation ram is provided,
10 with self-aligning bearings at both ends, then the
plumbing movement of the ladder would be allowed i
for and the overall system would be relatively
straightforward. However, the safety legislation
requires that a single elevation ram must be fitted
15 with a mechanical lock which is not only expensive
and introduces complication but also prevents the
ram from being simply constructed as double acting,
which feature would be useful for stabilising the
ladder against wind pressure and water jet reaction.
Although the safety requirements for man carrying
platforms are not as stringent as those for fire
escape ladders, it would be clearly desirable to -~
make such plat~orms as safe as reasonably possible.
It is an object of the present invention to
provide a turntable mounted elevatable member in which
the difficulties described above are substantially
overcome.
~ccordi.ng to the present invention there is
provided a turntable mounted elevatable ladder suitable
for mounting on a vehicle, in which the ladder is
mounted on an elevation axis parallel to rungs of the
ladder, which axis is pivoted at its centre on the
turntable and hydraulic ram means are provided to tilt
the axis about its centre relative to the turntable
thereby to raise and lower the ends of the axis about
its centre so as to permit the axis and therefore also the
rungs to be made horizontal when the turntable is
inclined to the horizontal, wherein there is provided a
single dual concentric hydraulic ram extending between
self-aligning bearings on the turntable and on the
ladder for elevating the ladder by rotating it about
the elevation axis.
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The dual concentric ram may have cylinder diameters
close to the ratio 1 : v~2 so that the effective piston
areas of the two expansion cylinders of the ram are
substa~tially equal. The cylinder diameters may be of i~
suitably related standard sizes, such as 6" and ~
160 mm and 110 mm or 1~0 mm and 100 mm, so that manufac~uring
and s~rvicing costs can be kept down. The ram may also
include a retracting chamber to enable hydraulic pre~sure ¦~
therein to oppose lifting of the member by wind pressure
10 or water jet reaction~
For ~afety reasons, the -two expan~ion-cylinders
of the dual ram may have individual hydraulic lock vlaves
which may be load control valves instead of pilot-operated
check valves to giv~ smoother operation of the ram and
15 therefore also smoother elevation of the member. In order
to prevent the ram extending due to external influences
such as wind pressure or water jet reaction, a further load
control val~e m~y-be ~onnected to the inlet to the
retracting ch~m~er~.- T~e-t~ree valves may ~e built int~
20 ~he~base of the ram.
III order that the invention may be fully understood
and carried out into effect it will now be described with
reference to an exa~ple shown in the accompanying drawings,
of which:-
FIGURE 1 is a diagram illustrating the di~ferent
movements required of a turntable ladder,
FIGURE 2 shows in detail the mounting of a turntable
ladder in accordance with one example of the invention'
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FIGURE 3 shows the cross-section of a dual concentric
ram suitable for use in the present invention, and
FIGURE ~ is an hydraulic circuit diagram showing how
the dual concentric ram might be controlled.
Referring now to Figure 1, a turntable ladder A has
four degrees of freedom. It is rotatable about a vertical
axis B by rotation of the turntable, it is extendible
along its length by means which will not be described in
this specification since they form no part of the present
invention, it can be raised to a required elevation, and
it can be plumbed by rotation about an axis which may be
either horizontal or extend alongthe length of the ladder
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or about some line lying between them or approximating either
of them. As explained above, the purpose of the plumbing
15 movements is to keep the rungs of the ladder horizontal
despite departure of the rotation axis B from the ve~tical.
Similar~ considerations apply to the plumbing of a turntable
mounted man-carrying platform on an articulated arm.
Figure 2 shows a part of a ladder 1 mounted on a turn-
20 table 2. The turntable 2 has a built-up bracket (3) supporting
a substantially horizontal bearing ~ on which the ladder 1
is mounted on an elevation bearing 5. Two plumbing rams
6A and 6B are provided mounted on the bracket 3 and
attached to the ends of the elevation bearing 5 to adjust
25 the attitude of the bearing 5 about the generally
horizontal axis defined by the bearing 4 so as to effect
the plumbing of the ladder. The elevation of the ladder
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is effected by a dual concentric ram 7 extending from a self-
aligning bearing 8 on the bracket 3 to a self-aligning
bearing 9 on the ladder 1. It will be apparent ~hat extension
of the ram 7 will result in elevation of the ladder 1 about
the bearing 5. ~he ladder 1 is shown in the fully lowered
position. The bearing a may be arranged to ke substantially
horizontal. ' I
Figure 3 shows in cxoss-section one form of construction
of the dual concentric hydraulic ram 7 shown in Figure 2.
10 In Figure 3, the ram which,extends from the self-aligning
bearing 8 to the self-aligning bearing 9 has an external
cylinder 11 in which moves a.piston 12 mounted on an
internal cylinder 13 which is attachPd to the bearing 9.
Within the internal cylinder 13 there is provided a piston
lS la which is fixed within the external cylinder 11, so that
as the piston 12 moves within the cylinder 11, so the
piston la moves within the cylinder 13. The piston la is
mounted on a tubular support 150 A seal 16 is provid~d
between the cylinders 11 and 13, is fixed to the cylinder'
11 and allows sliding movement of the cylinder 13. The ram 7
has 'three volumes. A first volume 17 is between the external
cylinder 11 and the tubular support 15 and bounded by the
pistons 12 and 1~. A second volume 18 is contained within
the internal cylinder 13 and is bounded by the piston 1~.
25 A third vo~lume 19 is fonmed between the external cylinder 11,
the internal cylinder 13 and-is bounded by the piston 12
and thei`,seal 16. On extension of the ram koth volumes
17 and 18 increase and the volume 19 decreases, ana on
retraction of the ram the volumes 17 and 18 decrease and
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volume 19 ~increases. Built into the base of the ram are
valves~2~ 22 and 3~3 which are used to sontrol the
ingress and egress of hydraulic ~luid in the three
volumes of the ram. The operation of the valves 20, 21, 22
5 and 33 will be described later with reference to Figure a. 1.
The use of a single concentric ram satisfies the
safety requirements in that it provides two hydraulically
separate pressure c~ambers, and since these are placed
concentrically one about the other, they not only avoid
10 the problems of offset constructional loading in the event
of failure of one of the hydraulic systems, but also they
permit the freedom of movement required by the plumbing
movement of the ladder without ~he need to alter the
volumes of the two pressure chambers differentially as would
15 be required if two separate rams were employed. Preferably,
the effec~ive areas of the pistons 12 and 1~ should be
the same so that the load is shared equally between the
hydraulic systems feeding the volume 17 and the volume 18,
and in the event of failure of either system the working
20 system is then subjected to just double its normal load. If any
other relationship between the areas of the rams is employed,
then the failure of the larger system would give rise to more
than double the pressure in the smaller system. Since the
piston 12 is annular and the piston la is circular, it
25 follows that to achieve the equal piston areas the internal
diameter P of the external cylinder 11 should be ~2 x the
internal diameter Q of the internal cyllnder 13. In order
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to simplify servicing and reduce costs, it is preferable 1,
that standard sizes of cylinder material and seals be
employed and suitable combinations for the values of
P and Q are:
P 6" 160 mm 1~0 mm
Q ~" 110 mm 100 mm
Figure ~, which is a hydraulic circuit diagram for
controlling the dual concentric ram, shows the three volumes
17, 18 and 19 referred to in Figure 3, and the valves 20,
10 21, 22. and 33 shown in the base of the ram 7 in Figure 3.,
The valves 20 and 21 are load control valves and are
connected to permit the flow of oil from the volumes 17 and
18 respectively when opened by a pilot signal supplied
along a line 23. The valves 20 and 21 are by-passed by
15 one-way valves 2~ and 25 respectively which are arranged
to allow fluid to enter the volumes 17 and 1~3. The fluid
under pressure for extending ~he ram 7 is produced by an
hydraulic pump 26 and applied to the valves 2~ and 25 through
a three-position control valve 27 and a line 28. The line 28
20 is also connected to the load'co~trol valve 22 to open
this valve and permit oil to escape from the volume 19 whilst
the ram 7 is being exte~d.ed~.:~h'e~'return oil from the volume
19 passing through the load.co~l~.valv~'22'flows along-a
line 29 and through the control valve 27 to a reservoir 30.
25 A fluid pressure control valve 31 is provided to limit the
output pressure of the pump 26. The valve 33 is connected
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between the volume 19 and the reservoir 30 to relieve excess
pressure due to thermal expansion or certain combinations of
seal and cylinder failure. The valves 22 and 33 are
combined in a single cartridge (Fig.3).
In order to extend the ram 7 thé control valve 27 is
moved to the left permitting oil to flow from the pump 26 ~.
through the line 28 and the valves 2~ and 25 into the
volumes 17 and 18~ Oil ejected from the volume 19 is
returned through the load control valve 22 held open by the
10 pressure in the line 28, which oil flows through the line 29
back through the control valve 27 to the reservoir 30.
Retraction of the ram 7 is effected by m~ving the control
valve 27 to the right so that fluid pressure from the pump 26
flows along the line 29 through the valve 22 into the
15 volume 19. This fluid pressure is also applied via the
line 23 to open the lo~d control valves 20 and 21 and permit
the oil to be released from the volumes 17 and 18. Fluid
pressure connections are also provided from the volumes 17
and 18 to control the load control valves 20 and 21 so that
20 any *endency for the ladder to depress too rapidly w.ill
result in closure of the valves 20 and 21 as a result of the
reduction in pressure. It has been found in practice that
the valves 20 and 21 operate smoothly to contxol the
pressure in the volumes 17 and 18.
2~ In order to prevent the ram 7 from being extended due
to an external influence, such as wind pressure or water
jet reaction, the valve 22 is provided to prevent oil from
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leaving the volume 19 except when required to do soO Relief
valve 33 is provided to limit induced pressure to a safe
level.
For convenience and safety, by avoiding external
connections the valves 20, 21, 22, 2~, 25 and 33 are all
built into the base of the ram 7, as indicated by the ¦~
broken rectangle 32 in Figure ~. Conventional bleed nipples
should be provided where necessary-in the hydraulic system
to permit air to be forced out of the system which otherwise
10 would interfere with the effectiveness of the hydraulic
control. This also provides a safe means of checking the
correct individual operation of valves 20 and 21.
The invention can also be applied to an elevatable
man~carrying platform to keep the platform level despite
15 inclination of the turntable carrying the platform. The
use of a dual-concentric ram for elevating the arm carrying
the platform would permit the plumbing of the platform
to be carried out in a straightforward way whilst enabling
the provision of the additional safety resulting from the
use of independent hydraulic circuits to elevate the
platform.
