GB2105298A

GB2105298A - Turntable mounted elevatable member

Info

Publication number: GB2105298A
Application number: GB08127094A
Authority: GB
Inventors: Anthony Clubley Armstrong
Original assignee: Merryweather & Sons
Current assignee: Merryweather & Sons
Priority date: 1981-09-08
Filing date: 1981-09-08
Publication date: 1983-03-23
Also published as: IT8249084A0; DE3232597A1; GB2105298B; IT1155232B; CA1209550A

Abstract

A turntable mounted elevatable member such as a ladder 1 uses a dual concentric ram 7 for elevation thereby providing two independent hydraulic circuits for safety and avoiding the need for mechanical Sons locks. The single point mounting at each end of the ram 7 by self- aligning bearings 8, 9 permits the state movement required for plumbing the ladder of elevation bearing 5 by rams 6A, 6B without the need for the complexity required to control two separate elevation rams during plumbing. The dual ram 7 has a retraction chamber to enable the ladder 1 to be held against lifting due to external influences. Lock valves for the separate chambers of the ram 7 are built into its base. The invention can also be embodied in a turntable mounted elevatable man-carrying platform. <IMAGE>

Description

SPECIFICATION Turntable mounted elevatable member This invention relates to a turntable mounted elevatable member having personnel support means such as a turntable ladder suitable for use on a fire fighting and rescue vehicle or a man carrying platform.

Fire fighting and rescue vehicles are usually provided with a ladder mounted on a turn table 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 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 an hydraulic lock must be provided at the base of each ram to prevent uncontrolled depression of the ladder. In addition, a mechanical lock should also preferably be provided in the case of two or more rams and must be provided where a single ram only is ued. These requirements are clearly sensible, but they give rise to difficulties in enabling the ladder to be trained in all required directions.If the vehicle is standing on a level site, such as a road, or the turntable axis is movable so that the plane of the turntable is horizontal, there is no problem, but if it is necessary to provide for plumbing of the ladder so that the rungs of the ladder are horizontal even though the vehicle and the plane of the turntable are not horizontal, then the rotation 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 these rams have hydraulic locks, but the plumbing of the ladder will 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, with self-aligning bearings at both ends, then the plumbing movement ladder would be allowed for and the overall system would be relatively straightforward. However, the safety legislation requires that a single elevation ram must be fitted 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 platforms as safe as reasonably possibie.

It is an object of the present invention to provide a turntable mounted elevatable member in which the difficulties described above are substantially overcome.

According to the present invention there is provided a turntable mounted elevatable member having personnel support means, in which the elevatable member is mounted on an elevation axis, which axis is supported at its centre on a turntable and is rotatable by hydraulic ram means to raise and lower the ends of the axis relative to its centre so as to permit plumbing of the member, whereinthere is provided a dual concentric ram extending between self-aligning bearings on the turntable and on the member for elevating the member. The elevatable member may be a ladder or a man-carrying platform, for example.

The dual concentric ram may have cylinder diameters close to the ratio 1: o/2 so that the effective piston areas of the two expansion cylinders of the ram are substantially equal.

The cylinder diameters may be of suitably related standard sizes, such as 6" and 44", 160 mm and 110 mm or 140 mm and 100 mm, so that manufacturing and servicing costs can be kept down. The ram may also include a retracting chamber to enable hydraulic pressure therein to oppose lifting of the member by wind pressure or water jet reaction.

For safety reasons, the two expansion cylinders of the dual ram may have individual hydraulic lock vlaves which may be load control valves instead of pilot-operated check valves to give smoother operation of the ram and 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 valve may be connected to the inlet to the retracting chamber. The three valves may be built into the base of the ram.

In order that the invention may be fully understood and carried out into effect it will now be described with reference to an example shown in the accompanying drawings, of which: Figure 1 is a diagram illustrating the different 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; Figure 3 shows the cross-section of a dual concentric ram suitable for use in the present invention; and Figure 4 is an hydraulic circuit diagram showing how the dual concentric ram might be controlled.

Referring now to Fig. 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 along the length of the ladder or about some line lying between them or approximating either of them. As explained above, the purpose of the plumbing movements is to keep the rungs of the ladder horizontal despite departure of the rotation axis B from the vertical. Similar considerations apply to the plumbing of a turntable mounted man-carryinga platform on an articulated arm.

Fig. 2 shows a part of a ladder 1 mounted on a turntable 2. The turntable 2 has a builtup bracket (3) supporting a substantially horizontal bearing 4 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 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 is effected by a dual concentric ram 7 extending from a selfaligning bearing 8 on the bracket 3 to a selfaligning bearing 9 on the ladder 1. It will be apparent that extension of the ram 7 will result in elevation of the ladder 1 about the bearing 5. The ladder 1 is shown in the fully lowered position. The bearing 4 may be arranged to be substantially horizontal.

Fig. 3 shows in cross-section one form of construction of the dual concentric hydraulic ram 7 shown in Fig. 2. In Fig. 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 1 2 mounted on an internal cylinder 1 3 which is attached to the bearing 9. Within the internal cylinder 1 3 there is provided a piston 1 4 which is fixed within the external cylinder 11, so that as the piston 1 2 moves within the cylinder 11, so the piston 14 moves within the cylinder 13.The piston 14 is mounted on a tubular support 1 5. A seal 1 6 is provided between the cylinders 11 and 1 3, is fixed to the cylinder 11 and allows sliding movement of the cylinder 1 3. The ram 7 has three volumes. A first volume 1 7 is between the external cylinder 11 and the tubular support 1 5 and bounded by the pistons 1 2 and 1 4. A second volume 1 8 is contained within the internal cylinder 1 3 and is bounded by the piston 14.A third volume 1 9 is formed between the external cylinder 11, the internal cylinder 1 3 and is bounded by the piston 1 2 and the seal 1 6. On extension of the ram both volumes 1 7 and 18 increase and the volume 1 9 decreases, and on retraction of the ram the volumes 1 7 and 18 decrease and volume 1 9 increases. Built into the base of the ram are valves 20, 21, 22 and 33 which are used to control the ingress and egress of hydraulic fluid in the three volumes of the ram. The operation of the valves 20, 21, 22 and 33 will be described later with reference to Fig.

4.

The use of a single concentric ram satisfies the safety requirements in that it provides two hydraulically separate pressure chambers, and since these are placed concentrically one about the other, they not only avoid 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 the need to alter the volumes of the two pressure chambers differentially as would be required if two separate rams were employed.Preferably, the effective areas of the pistons 1 2 and 14 should be the same so that the load is shared equally between the hydraulic systems feeding the volume 1 7 and the volume 18, and in the event of failure of either system the working 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 1 2 is annular and the piston 1 4 is ciruclar, it follows that to achieve the equal piston areas the internal diameter P of the external cylinder 11 should be aX the internal diameter 0 of the internal cylinder 1 3. In order to simplify servicing and reduce costs, it is preferable 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 140 mm Q 44" 110 mm 100 mm Fig. 4, which is a hydraulic circuit diagram for controlling the dual concentric ram, shows the three volumes 17, 1 8 and 1 9 referred to in Fig. 3, and the valves 20, 21, 22 and 33 shown in the base of the ram 7 in Fig. 3. The valves 20 and 21 are load control valves and are connected to permit the flow of oil from the volumes 1 7 and 1 8 respectively when opened by a pilot signal supplied along a line 23. The valves 20 and 21 are by-passed by one-way valves 24 and 25 respectively which are arranged to allow fluid to enter the volumes 1 7 and 1 8. The fluid under pressure for extending the ram 7 is produced by an hydraulic pump 26 and applied to the valves 24 and 25 through a three-position control valve 27 and a line 28. The line 28 is also connected to the load control valve 22 to open this valve and permit oil to escape from the volume 1 9 whilst the ram 7 is being extended.The return oil from the volume 19 passing through the load control valve 22 flows along a line 29 and through the control valve 27 to a reservoir 30. A fluid pressure control valve 31 is provided to limit the output pressure of the pump 26. The valve 33 is connected between the volume 1 9 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 the control valve 27 is moved to the left permitting oil to flow from the pump 26 through the line 28 and the valves 24 and 25 into the volumes 1 7 and 1 8. Oil ejected from the volume 1 9 is returned through the load control valve 22 held open by the 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 moving 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 volume 1 9. This fluid pressure is also applied via the line 23 to open the load control valves 20 and 21 and permit the oil to be released from the volumes 1 7 and 1 8.

Fluid pressure connections are also provided from the volumes 1 7 and 1 8 to control valves 20 and 21 so that any tendency for the ladder to depress too rapidly will 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 control the pressure in the volumes 17 and 18.

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 leaving the volume 1 9 except when required to do so.

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, 24, 25 and 33 are all built into the base of the ram 7, as indicated by the broken rectangle 32 in Fig. 4. Conventional bleed nipples should be provided where necessary in the hydraulic system to permit air to be forced out of the system which otherwise 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 inclination of the turn table carrying the platform. The use of a dualconcentric 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.

Claims

1. A turntable mounted elevatable member having personnel support means, in which the elevatable member is mounted on an elevation axis, which axis is supported at its centre on a turntable and is rotatable by hydraulic ram means to raise and lower the ends of the axis relative to its centre so as to permit plumbing of the member, wherein there is provided a dual concentric ram extending between self-aligning bearings on the turntable and on the member for elevating the member.

2. A member according to claim 1 wherein the member is a ladder.

3. A member according to claim 1 wherein the member is a man-carrying platform.

4. A member according to claim 1, 2 or 3 wherein the dual concentric ram has two expansion cylinders, one outside the other, with diameters close to the ratio 1: VTso that the piston areas of the two cylinders are substantially equal.

5. A member according to claim 4 wherein the two expansion cylinders of the dual concentric ram have individual lock valves for preventing undesired egress of oil from the expansion cylinders.

6. A member according to claim 5 wherein the lock valves are load control valves, controlled by a control pressure balanced against the pressure in the respective expansion cylinder.

7. A member according to claim 4, 5 or 6 wherein the dual concentric ram also includes a retraction volume.

8. A member according to claim 7 including a load control valve for preventing undesired egress of oil from the retraction volume due to external influences.

9. A member according to claim 8 further including a relief valve to limit the pressure induced within the volumes of the dual-concentric ram.

1 0. A member according to claim 5 or 6 or claim 8 when dependent on claim 5 or 6, wherein the valves are built into the base of the dual-concentric ram.

11. A turntable ladder substantially as described herein with reference to the accompanying drawings.