GB2206929A

GB2206929A - Improvements in or relating to hydraulically operated telescopic devices

Info

Publication number: GB2206929A
Application number: GB08815942A
Authority: GB
Inventors: Pietro Pagliero
Original assignee: OP PAGLIERO SpA
Current assignee: OP PAGLIERO SpA
Priority date: 1987-07-10
Filing date: 1988-07-05
Publication date: 1989-01-18
Also published as: IT8767589A0; IT1211191B; FR2617915B1; FR2617915A1; GB8815942D0; NL8801732A; ES2011101A6

Abstract

In a telescopic device comprising a plurality of piston and cylinder elements (3, 4, 5, 6) having passages 8 for enabling a hydraulic fluid to flow between the elements, each element is provided with a valve (A) mechanically opened when the element nears its retracted position. When the device is extending, the valves (A) open under the pressure of the hydraulic fluid but are closed when the device is retracting. Known devices have been unable to assume the fully retracted position due to the hydraulic pump not being able to remove the residual hydraulic fluid. Because the valves (A) are opened as the device approaches the retracted position, the residual hydraulic fluid can be discharged to enable the device to fully retract. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO TELESCOPIC DEVICES The present invention relates to telescopic devices and in particular, but not exclusively, to multistage, coaxial, hydraulic jacks. Such jacks are simultaneously actuated telescopically utilzing one-way valves having two purposes: a) allowing the passage of fluid under pressure from one telescopic element to another, which act as a piston for the cylinder under it and as a cylinder for the piston above it; b) allowing the complete outflow of hydraulic fluid in the final stage of retraction of the various stages of the jack. Each cylinder/piston is fitted with a valve (except the first cylinder) that opens owing to the pressure exerted on the inner surface of the base of the corresponding cylinder (FIG.1).

A known telescopic jack disclosed in Italian patent No 1,000,659 is structured so that the various hydraulic stages can be activated and deactivated at the same time requiring a minimum amount of time for the extension and/or retraction of the complex. These telescopic jack complexes, mounted on vehicles, enable rapid manoeuvres to be performed at considerable heights, which can be reached by a platform attached to the terminal telescopic element. Said platform can support one or two operators and pertinent equipment for repairs, rescue operations and/or various other procedures where similar devices cannot be utilized because of their larger size and the time required to actuate them.

Said hydraulic jacks have a drawback in that during the retraction phase the telescopic elements of the cylinder/pistons constituting the device are not always able to reach the fully retracted position.

It has been found that a limited amount of hydraulic fluid remains between the outer base of each piston and inner base of the corresponding cylinder owing to the leakage of oil past the sealing rings occurring when the operating pressure of the pump or pumps is low as the complex is approaching the fully retracted position.

This phenomenon does not impede the operation of the device, but a variation in the overall length of said device could create transport problems assuming the unit has been mounted on a vehicle having a bed length calculated based on the length said device should have when all its elements are fully retracted.

An -object of the present invention is to eliminate the aforementioned shortcoming.

According to the present invention there is provided a telescopic device as defined in the appended claim 1.

Embodiments of the present invention are defined in any one of the appended claims 2 to 13.

An embodiment of the present invention provides each cylinder/piston with a one-way valve. Said one-way valves are opened by the pressure of the hydraulic fluid when the cylinders are in the process of extending: said valves are closed during the retraction phase, but when the cylinders have almost reached the fully retracted position the valve fitted on each cylinder is automatically opened owing to the interference of a projection integral with the surface of the inner base of the corresponding cylinder causing the fluid contained in each cylinder to be completely expelled.

Said fluid is conveyed to the reservoir allowing all the telescopic elements to return to the correct, fully retracted position.

An embodiment of the present invention will be described further, by way of example, with reference to the accompanying drawing in which: Figure 1 is a schematic partial cross-section of the embodiment with the telescopic elements in the fully retracted position; Figure 2 is a schematic partial cross-section illustrating the embodiment in an intermediate position of extension or retraction: Figure 3 is an enlarged schematic partial cross-section of one of the one-way valves that govern the passage of hydraulic fluid during the extension phase of the jack, and are automatically opened during the final retraction phase to expel any remaining fluid; Figure 4 schematically illustrates a diminished cross-section of the embodiment having five hydraulic stages.

Given that the shape, length and number of elements may vary in each version of the hydraulic jack complex depending on the purpose for which said complex will be used, the drawing hereinunder described only has the purpose of clarifying the operation of the device and the improvement.

Referring to figures 1, 2 and 3, arrows -X- indicate the direction of flow of the hydraulic fluid under pressure, which is pumped through a series of valves reaching cylinder 2 (fig.2). The various cylinder/pistons making up the complex - indicated respectively by numbers 3, 4, 5 and 6 - are fitted with sealing rings 7 and at least one one-way valve -A-. shown in detail in figure 3. The pressurized fluid arriving from -X- enters cylinder 2 causing valve -A- to open (position shown by the dashed lines in figure 3). Said fluid also flows by radial passages 8 entering the various telescopic elements 2...6.The jack complex moves from the position illustrated in figure 1 to the intermediate positions one of which is shown in figure 2 - until reaching the fully extended position illustrated schematically in figure 4; a check valve is located in the position indicated by -Y-, and is coupled to the pumping system (not illustrated).

When, from the fully extended position shown in figure 4, or any other position between the fully extended and fully retracted positions, the jack complex has to be placed in the fully retracted position, the direction of the hydraulic fluid is inverted. Said fluid passes through orifice 9 and passages 8 following the path indicated by arrows -Y- which, in this stage, serve as passages for the discharge of hydraulic fluid being conveyed back to the system reservoir. During this operative phase one-way valves -A- remain closed.

When the jack complex arrives at the almost fully retracted position (example shown in figure 2) a portion of the fluid may tend to remain in the chambers indicated by -B- in figure 2 owing to changes in the operating conditions of said jack complex.

In order to eliminate this drawback during the last phase of retraction (see position illustrated in figure 2), the various cylinder/pistons bring the projecting shafts 10 (figure 3) of each valve -A- associated with the base of the various elements into contact with bases 11 of the underlying elements, thereby causing valves -A- to open allowing the complete elimination of hydraulic fluid from the inside of chambers -B-. Under these conditions the retraction of the various stages of the telescoping jack complex is complete and the various elements have returned to the position illustrated schematically in figure 1.

Referring to figure 3, springs 12 and 13 contrast the movement of ball 14. Said springs 12, 13 are appropriately calibrated to suit the operating pressure utilized.

Furthermore, assuming valve 10 can always be opened automatically as described above, it may have any structure different from that shown as an example.

In the attached drawing valves -A- are shown axially aligned, and each valve has a slight upper projection intended to interfere with appendix 10 of the valve above it. The present invention may, of course, comprise valves having different positions and structures from that shown in figure 3.

Claims

1. A telescopic device comprising a plurality of elements, at least one of which is provided with a valve which opens when the or at least one element approaches a fully retracted position.

2. A telescopic device as claimed in Claim 1, in which each element is provided with means for enabling a fluid to flow between adjacent elements and a first and a further element are each provided with an aperture for enabling the device to be coupled to a hydraulic circuit.

3. A telescopic device as claimed in Claim 1 or Claim 2, in which said valve is open during extension of the device and is closed during retraction of the device except when the element approaches the fully retracted position.

4. A telescopic device as claimed in any one of Claims 1 to 3, in which each element is provided with said valve.

5. A telescopic device as claimed in any one of the preceding claims, in which said valve is provided with an appendix such that when the element approaches the fully retracted position the appendix enables the valve to be open.

6. A telescopic device as claimed in Claim 5; in which at least one element is provided with a projection for engaging with the appendix.

7. A telescopic device as claimed in any one of the preceding claims, in which said valve comprises a ball valve.

8. A telescopic device as claimed in any one of the preceding claims, in which the hydraulic circuit includes a control unit and a reversible pump.

9. A multistage coaxial hydraulic jack extendible telescopically comprising a number of cylinders intercommunicating by means of internal radial passages (8); a base cylinder (2) and a terminal cylinder (6), said base cylinder and said terminal cylinder being fitted with orifices (1) for connecting to a hydraulic circuit, the hydraulic circuit being governed by a control unit and a reversible pump: each cylinder, except the base cylinder (2), is fitted with at least one one-way valve (A), said valve being opened automatically during extension of the jack, characterized in that said valve is closed initially during the retraction, and said valve is equipped with an appendix1 (10) such that during a final phase of retraction, said valve is opened automatically allowing the complete discharge of hydraulic fluid thereby enabling the jack to return to a minimum retracted height.

10. A hydraulic jack in accordance with claim 9 characterized in that said valve is positioned in each cylinder and said valve (A) has on appendix projection from the lower surface of the base said appendix (10) engages the base of the corresponding cylinder during the final phase of retraction opening said valve against the reaction of elastic devices allowing the residual hydraulic fluid to be completely discharged.

11. A hydraulic jack in accordance with claim 9 characterized in that said valve (A) is a ball valve comprising a shaft (10) projecting from the valve with respect to the base of the corresponding cylinder.

12. A hydraulic jack intended to allow the complete retraction of the cylinders when the jack is being retracted as described and illustrated in accordance with the purposes specified.

13. A telescopic device as hereinbefore described with reference to the accompanying figures.