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GB2335905A - Pallet truck - Google Patents

Pallet truck Download PDF

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Publication number
GB2335905A
GB2335905A GB9807067A GB9807067A GB2335905A GB 2335905 A GB2335905 A GB 2335905A GB 9807067 A GB9807067 A GB 9807067A GB 9807067 A GB9807067 A GB 9807067A GB 2335905 A GB2335905 A GB 2335905A
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Patent type
Prior art keywords
forks
reservoir
pumping
lifting
during
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9807067A
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GB9807067D0 (en )
Inventor
Thomas Henry Chadwick
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Thomas Henry Chadwick
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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B62LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62BHAND-PROPELLED VEHICLES, e.g. HAND CARTS, PERAMBULATORS; SLEDGES
    • B62B3/00Hand carts having more than one axis carrying transport wheels; Steering devices therefor; Equipment therefor
    • B62B3/04Hand carts having more than one axis carrying transport wheels; Steering devices therefor; Equipment therefor involving means for grappling or securing in place objects to be carried; Loading or unloading equipment
    • B62B3/06Hand carts having more than one axis carrying transport wheels; Steering devices therefor; Equipment therefor involving means for grappling or securing in place objects to be carried; Loading or unloading equipment for simply clearing the load from the ground
    • B62B3/0618Hand carts having more than one axis carrying transport wheels; Steering devices therefor; Equipment therefor involving means for grappling or securing in place objects to be carried; Loading or unloading equipment for simply clearing the load from the ground using fluid lifting mechanisms

Abstract

A hand operated pallet truck includes lifting forks 3 raisable by pumping a hydraulic fluid with a pumping handle 2. The hydraulic arrangement is such that during an initial phase of pumping with the pumping handle 2 the amount by 0 which the lifting forks 3 are raised is greater than during a subsequent phase. The transition from the initial phase to the subsequent phase takes place after a predetermined distance of raising of the forks. A reservoir 11 for the hydraulic fluid is provided with a one way air valve 25 to 5 allow air to flow into the top of the reservoir while obstructing air flow in the opposite direction. Preferably, a piston 13 raising the forks 3 has a small area initially acted on by the fluid to cause the initial lifting and thereafter a greater area on which the fluid acts (Figs 5a to 5e). Preferably, the initial lift is 38 mm and 10 mm a time thereafter, each achieved with one stroke of the handle. Valves 17, 21 control flow through the pump and reservoir.

Description

Pallet Truck 2335905 This invention relates to hand-operated pallet

trucks. Hand-operated pallet trucks are well known pieces of equipment used for the movement of loads. Such loads may be conveniently arranged on a pallet and the pallet is lifted. In some cases, the load is not arranged on a pallet but the load incorporates an arrangement for the forks of the pallet truck to enter.

The forks of the pallet truck are manoeuvred beneath the load to be lifted and the pumping handle of the truck is pumped up and down to raise the forks. The forks are raised to lift the pallet a sufficient distance above the ground so that the pallet may be moved on the truck. Conventionally, the pallet is lifted between 75 to 85mm off the ground. The truck is provided with wheels and the pumping handle is used to pull, push and steer the load into the desired position.

The carrying capacity of the trucks can range between 1000kg to 3000kg. The usual capacity of the trucks is about 2000kg.

In the usual operating procedure, the forks of the truck begin at a rest height above the ground of about 85mm. The forks at that height are pushed under the load to be lifted and the handle is pumped to raise the forks. For the forks to be easily located under the load, the base of the load to be lifted is a few centimetres above the rest height of the forks and the forks are usually lifted from their rest height - 2 of about 85mm to a height of about 123mm before the forks begin to lift the load from the ground. The pumping of the forks during that first stage of lifting takes little effort. In the second stage of lifting, the forks are raised to a height of approximately 20Omm from the ground. During the second stage of lifting, the load is being raised from the ground and the pumping requires a much greater effort.

Ideally, the forks would be lifted quickly during a first stage, for example using only one pumping stroke to raise the forks from their rest height of 85mm to a height at which the load begins to be lifted from the ground (a height of about 123mm). Once the forks have begun to lift the load, it would be desirable for the forks to be lifted at a slower lifting speed so that several pump strokes are required to lift the load.

In an attempt to overcome the problem indicated above, one known type of pallet truck includes a "quick lift" system. The quick lift pallet truck operates by a back pressure system. When the forks are pushed under the load and the pumping is commenced, the forks rise quickly because there is little resistance to movement of the forks. Once a load on the forks is detected, for example when the forks first touch the underside of the load, the ratio of the fork elevation to the pump strokes is decreased and the forks rise more slowly as the pumping is continued. The change in the ratio is effected by the use of an overload valve which redirects hydraulic fluid in the pumping system. The valve is activated as soon as an increased resistance to movement of the forks is detected, for example as the forks touch the base of the load.

While the quick-lift truck improves the pallet truck by decreasing the time taken to lift the load, it has been identified that there are several problems that can occur with the quicklift system.

a. The load required to activate the valve and to switch the pumping from fast to slow pumping is low. Any resistance to movement detected on the forks, such as even an empty pallet, can cause the slow lifting to be engaged.

b. Lack of control when the forks first come into contact with the load. Even once the forks have contacted the load, there is still approximately 10 to 15mm through which the forks may relatively easily be moved by pumping while the forks take up the flexing of the pallet and the load and before the load is lifted fully from the ground.

Using the quick-lift system, that distance is moved using the slow pumping. Lifting of the load would be quicker if the forks could be pumped quickly through that distance.

The fixed weight setting prevents any very light loads, or even empty pallets from being quick-lifted throughout the operation.

c.

d.

e.

- 4 Any stiffness in the moving parts of the pallet truck may be misinterpreted by the quick-lift truck as being an increased weight as the forks touch.the load and therefore the slow lifting may be activated prematurely, leading to slower lifting times. Any overhanging load to the rear of the pallet to be lifted may also cause the slow lift to be activated, therefore increasing lifting time. f. The valve system of the quick-lift truck is complicated and is susceptible to failure in operation and mechanical breakdown. g. The weight setting at which the slow lifting is activated is not easily adjustable, and for some quick-lift trucks is not adjustable at all.

h. The change to low speed may take place at any fork height and may occur during the middle of a pumping stroke. That is detrimental to the efficient lifting of the load.

It is an object of the first aspect of the invention to avoid or mitigate at least one of those problems.

According to a first aspect of the invention, there is provided a hand operated pallet truck including lifting forks raisable by pumping a hydraulic fluid with a pumping handle, wherein the hydraulic arrangement is such that during an initial phase of pumping with the pumping handle the amount by which the lifting forks are raised is greater than during 5 a subsequent phase and the transition from the initial phase to the subsequent phase takes place after a predetermined distance of raising of the forks.

In accordance with the first aspect of the invention, the moment of transition from an initial fast lifting mode to an ordinary mode is determined by the height by which the forks have been raised rather than, for example, the force required to raise the forks.

The height at which the transition occurs can be selected by a designer and indeed it is possible for a user to be able to adjust the set up of the truck to adjust the height. Current pallets are, however, almost all designed to the same standard so that if the forks are initially at a height of 85mm above the ground, as is customary, the transition from the initial phase to the subsequent phase of pumping preferably takes place after lifting through a distance of the order of 40mm, preferably about 38mm.

It is convenient for the initial phase of pumping to end approximately at the end of a stroke of the pumping handle and preferably the raising of the forks through the predetermined distance is arranged to be accomplished within one full stroke of the pumping handle. Conveniently, the pumping handle is operated by moving it through an arc. 25 During the subsequent phase of pumping, one stroke of the pumping handle is arranged to raise the forks about 1Omm.

- 6 In a conventional truck a raising of 9 or 1Omm per stroke is a common arrangement.

Preferably the lifting forks are raisable by a total height of approximately 115mm in the course of both the initial and subsequent phases of pumping. Such a total lift is conventional and sufficient to lift a standard pallet well clear of the floor.

Preferably the hydraulic arrangement includes a piston and cylinder assembly arranged such that during the initial phase of pumping the crosssectional area of the cylinder space over which hydraulic pressure is applied to generate the lifting force on the forks is a first relatively small area and during the subsequent phase of pumping said crosssectional area is a second relatively large area. It will be appreciated that for a given volume of fluid supplied during pumping, the amount of lift generated by the hydraulic arrangement is inversely proportional to the cross-sectional area of the space being filled by the fluid. Thus by selecting appropriate values for the cross-sectional areas that apply during the initial and the subsequent phases of pumping the desired rate of lift and lifting force can be selected and the desired change in rate of lift and lifting force obtained without any change to the pumping conditions. Preferably the relatively large cross-sectional area is more than three times the relatively small cross-sectional area; thus during the initial phase of lifting the rate of lifting - 7 is more than three times as fast as during the subsequent phase but the lifting force generated is less than one third of the force generated during the subsequent phase.

Preferably the cylindrical spaces having the first and second crosssectional areas are respective portions of a common space. As will be clear from the description of different embodiments of the invention below, there are a variety of ways in which the change in cross-sectional area can be accomplished.

Preferably the truck includes a reservoir for hydraulic fluid, from which fluid is arranged to be pumped during raising of the forks and to which fluid is arranged to be returned during lowering of the forks. In accordance with an especially advantageous feature of the invention the reservoir includes a one way air valve for allowing flow of air into the reservoir when fluid is pumped out of the reservoir and for preventing flow of air out of the reservoir when fluid is returned to the reservoir, whereby in use the reservoir becomes pressurised by a volume of pressurised air in the reservoir. The automatic pressurisation of the reservoir when the lifting arrangement is first used (when fluid is returned to the reservoir) is especially advantageous because it facilitates the supply of fluid from the reservoir when required and enables the reservoir to be sealed such that there is no likelihood of fluid leaking from the reservoir. Whilst the air valve allows flow of air into the reservoir when fluid is pumped out, it will be appreciated that such flow will take place only if the pressure in the reservoir drops below ambient pressure; thus the pressurisation of the reservoir can be self-regulating.

Preferably the truck includes a fluid passageway connecting the reservoir to a main lifting chamber which is operative during the subsequent phase of pumping, the passageway including a one way valve for allowing fluid to flow along the passageway from the reservoir into the main lifting chamber during the initial phase of pumping but not in the reverse direction. Such an arrangement prevents a vacuum developing in the main lifting chamber during the initial phase of pumping when, in embodiments of the invention described below, the main lifting chamber although inoperative is expanding.

Preferably the truck includes a fluid passageway connecting the pump to a main lifting chamber which is operative during the subsequent phase of pumping, the passageway including a one way valve for allowing fluid to flow along the passageway from the main lifting chamber during a lowering step but not in the reverse direction. Such an arrangement enables the main lifting chamber to be emptied when, in embodiments of the invention described below, during the final phase of lowering the main lifting chamber would otherwise be sealed and resisting further lowering.

While the provision of a one way air valve is of particular advantage in a truck according to the first aspect of the invention as defined above, it is also of wider relevance and may therefore be employed even when the hydraulic arrangement does not switch from an initial fast lifting phase to a subsequent slower lifting phase at a predetermined height or indeed at any other stage. Thus according to a second aspect of the invention there is provided a hand operated pallet truck including lifting forks raisable by pumping a hydraulic fluid with a pumping handle, a reservoir for hydraulic fluid, from which fluid is arranged to be pumped during raising of the forks and to which fluid is arranged to be returned during lowering of the forks, the reservoir including a one way air valve for allowing flow of air into the reservoir when fluid is drawn out of the reservoir during pumping to raise the lifting forks and for preventing flow of air out of the reservoir when fluid is returned to the reservoir.

It should be understood that whilst in the embodiments of the invention illustrated in the drawings, the one way air valve is physically positioned in the top of the reservoir housing, other arrangements are also within the scope of the invention; for example the air valve may be provided in a conduit connected at one end to the top of the reservoir and at the other end to atmosphere. Also, the one way valve may take any suitable form that enables air to be drawn into the - 10 reservoir during at least an initial pumping cycle, and that is able to prevent air leaving the reservoir whereby the reservoir becomes pressurised.

The pallet truck according to the second aspect of the invention may incorporate any of the features of the truck according to the first aspect of the invention.

The invention further provides a method of operating a hand-operated pallet truck in accordance with the first and/or second aspect of the invention.

Embodiments of the invention will now be described, by way of example, having reference to the drawings of which:

Figure 1 is a side view of part of a hand pallet truck and shows the handle of the truck Figure 2 Figure 3 Figure 4 Figures 5a to 5e Figure 6 in the starting position; shows the truck of Figure 1 with the handle in the lowered position; is a schematic sectional view of the main lifting cylinder of the pump in accordance with the present invention; shows in section a detail of the pump depicted in Figure 3; show schematically in successive views the pumping operation shows in section an alternative embodiment of the pump shown in Figures 3 and 4; and Figures 7A and 7B show schematically in section a detail of a pump designed according to the principles of the pump depicted in Figure 6, the pump being shown in two successive positions in Figs. 7A and 7B.

Figure 1 shows a hand pallet truck 1 having a handle 2 and a raisable forks frame including forks 3, a pump piston 4 and a lift piston 5. Figure 1 shows the truck with the handle 2 in an upright starting position. The lifting forks 3 are lowered and are positioned beneath a load to be lifted. The handle 2 can be depressed to a lower position (shown in Figure 2) and the lifting forks 3 thereby raised. The handle 2 is pumped up and down between the upright and the lower position to raise the forks 3.

The general operation of the pumping mechanism including the pump piston 4 is of a known type. Each downward stroke of the handle 2 causes a cam on the fulcrum of the handle to depress the pump piston 4. When the downward stroke of the handle 2 is complete, the handle 2 is allowed to return to the upright position aided by a return spring (not shown) and the pump piston 4 is urged upwards by the return spring. The movement of the pump piston 4 draws oil from an oil reservoir located in the pump assembly. The downward strokes of the handle 2 force hydraulic fluid into a lifting chamber (not visible in Figs. 1 and 2) which causes the lift piston 5 to 12 - i rise. The rising of the lift piston causes the forks 3 to rise.

In a conventional known hand pallet truck, each full downward movement of the handle 2 causes the forks to be lifted about 9mm. In order to raise the forks 3 from a height of 85mm to a height of 20Omm, some 14 full strokes of the pumping handle may be required. An initial 38mm movement of the forks 3 will require minimum pumping effort whilst the subsequent movement of the forks 3 which involves lifting of the load (not shown) will require much greater effort.

In accordance with the first aspect of the invention, the hydraulics are arranged in this example so that one first full pump stroke of the handle 2 will cause the forks 3 to be raised about 38mm, after which the conventional arrangement resumes and each further full pump stroke of the handle 2 causes the forks 3 to be raised about 9mm. In this way pallet load movement can be speeded up tremendously. Furthermore, conventional hydraulic systems can be modified in a simple described.

and inexpensive manner to operate as just To demonstrate this, reference will now be made to Figures 3, 4 and 5a to 5e.

Figure 3 shows the lifting arrangement. A pump housing 8 is formed with conduits 9 and 10. During a lifting operation oil is passed from a reservoir 11 through the conduit 10 into the pump operated by the handle 2 (the pump and handle not being visible in Figure 3) and delivered - 13 through the conduit 9; during a lowering operation oil is passed back through the conduit 9, a control valve (not shown), through the conduit 10 and into the reservoir 11.

Such an arrangement per se is conventional.

The pump housing 8 has a central main cylinder 12 in which a main piston 13 is slidably mounted. The oil reservoir 11 is defined by the space within the housing 8 and outside the main cylinder 12.

The arrangement of the main cylinder 12 and the main piston 13 at the bottom of the housing 8 is special and will now be described referring also to Figure 4. A primary piston 14 of smaller diameter than the main piston 13 is formed at the bottom of the main piston 13 and a primary cylinder 15 whose internal diameter is smaller than the internal diameter of the main cylinder 12 is inserted at the bottom of the main cylinder 12. The primary piston 14 is a snug fit inside the primary cylinder 15 whilst the main piston 13 is a snug fit inside the main cylinder 12. As will be clear from the description below, the piston 13 is shown in Fig 4 well above its lowermost position. In the lowermost position the bottom of the main piston 13 is adjacent to the top of the primary cylinder 15 and the primary piston 14 is almost wholly within the primary cylinder 15. An '0' ring 16 received in a recess in the central base of the primary cylinder 15 seals its interface with the primary piston 14 - 14 and a similar 101 ring (not shown) seals the interface of the main cylinder 12, at its top, with the main piston 13.

Two one way ball valves are also provided: a ball valve assembly 17 with a ball 18, a valve seat 19 and a roll pin 20 is provided in the primary cylinder 15, allowing oil to flow downwards through the cylinder 15 past the ball 18, but not a ball valve assembly 21 with a ball 22, a valve a roll pin 24 is provided in the wall of the main upwards; and seat 23 and cylinder 12 just above the primary cylinder 15, allowing oil to flow out of the main cylinder 12, past the ball 22 into the reservoir 11, but not from the reservoir into the cylinder 12.

A one way air valve 25 is provided in the top of the housing 8 to allow air to flow into the top of the reservoir 11 from the ambient surroundings whilst obstructing air flow in the opposite direction.

The operation of the lifting arrangement will now be described with reference also to Figures 5a to 5e. Fig. 5a shows the arrangement when the forks 3 are in their lowermost position and before any pumping has begun. It can be seen that the primary piston 14 is fully inserted into the primary cylinder 15. As the handle 2 is pulled down for a first time oil is driven from the reservoir 11 along the conduit 10 to the pump and back along the conduit 9 into the primary cylinder 15. The ball 18 of the valve assembly 17 is pressed against its seat 19 closing that valve and the oil pressure j - 15 is therefore operative over the face of the primary piston 14 only and the assembly of the main piston and primary piston is raised as shown in Fig. 5b. Oil from the reservoir 11 passes freely into the main cylinder past the ball 22 of the valve assembly 21 to fill the space created between the main piston 13 and the primary cylinder 15. As a result air is drawn into the top of the reservoir 11 through the air valve 25.

It will be understood that during this initial pumping phase a small volume of oil generates a relatively large linear displacement of the piston, with less lifting force being applied to the piston for a given oil pressure. The bottom of the primary piston 14 is arranged to clear the '0' ring 16 after the piston has risen 38mm and that rise is arranged to occur before the end of one full pumping stroke of the handle 2 by a user. As the piston 14 clears the '0' ring 16 the oil pressure from the pump is applied in the main cylinder causing the ball 22 of the valve assembly 21 to be pressed against its seat 23. The arrangement is now as shown in Fig. 5c and it can be seen that as pumping continues the piston will be raised at a much slower rate and with much greater force for a given oil pressure than before.

When it is desired to lower the piston the pump is caused to operate in the opposite direction (Fig. 5d) so that oil returns along the conduit 9, through the control valve (not shown) and along the conduit 10 to the reservoir 11.

- 16 once the primary piston 14 reaches the '0' ring 16 (Fig. 5e) the oil between the main piston 13 and the primary cylinder 15 is removed via the valve assembly 17, the ball 18 dropping down to rest on the roll pin 20; it should be noted that this oil, when returned to the reservoir 11 creates an excess pressure in the reservoir. Thus assuming no leakage, when the cycle is repeated, during the initial raising of the forks 3 (Fig. 5b) oil from the reservoir entering through the valve assembly 21 does so with the aid of the excess pressure in the reservoir 11 and therefore no further air passes through the air valve 25.

In the particular example illustrated in Figs. 3 and 4 the diameter of the main piston is 30mm and the diameter of the primary piston is 5mm.

Figs. 6, 7A and 7B illustrate a modified version of the arrangement shown in Figs. 3 and 4 and corresponding parts are referenced by the same reference numerals. In this case the primary piston 14 is formed as a part of the base of the main cylinder 12 and the main piston 13 is bored from its bottom face to a depth of a little over 38mm to form a primary cylinder 15. It will be appreciated that such an arrangement operates in a similar manner to the arrangement described in Figs. 3 and 4 with appropriate one way oil flow valves and a pressurised oil reservoir with a one way air valve. Fig. 7A shows the piston and cylinder arrangement during a first fast-lifting phase, and Fig. 7B shows the r - 17 arrangement during a second slower lifting phase. It will be seen that, during the first fast-lifting phase shown in Fig. 7A, oil entering through conduit 9 exerts a pressure on an outer portion only of the piston 13 and that the space between the inner portion of the piston 13 and the top of the primary piston 14, which during this initial phase is nonoperative, is filled from the oil reservoir via a one way spring valve 21 (air being drawn into the reservoir as before). During the final stage of lowering, oil trapped between the primary piston 14 and the primary cylinder 15 is returned to the conduit 9 through a passageway having a one way valve 17, which allows flow out of the cylinder, but not in the reverse direction; the connection of the passageway to the conduit 9 is not shown in Figs. 7A and 7B. Also marked in Figs. 7A and 7B is a main oil seal 26 between the main piston 13 and the main cylinder 12. In Figs. 7A and 7B the oil is shown by hatching.

It will be seen that in the embodiments of the invention described above, there is an automatic switching from an initial fast lift mode to a slower lift mode at a predetermined height of lift, regardless of the load being lifted. By adjusting the geometry of the pistons and cylinders and/or the positions of the seals the height at which the automatic switching takes place can be selected and the ratio of the speeds of lifting can be varied.

18 The provision of a one way air valve in the oil reservoir is an especially important and advantageous feature that is of value also in an otherwise conventional handoperated pallet truck, which would usually have a vented reservoir. In such a conventional design oil in the reservoir has to be drawn from the reservoir when required by using ambient pressure only, whereas in accordance with the second aspect of the invention the reservoir becomes pressurised so that removal of oil from the reservoir is 10 facilitated.

19 -

Claims (21)

Claims
1. A hand operated pallet truck including lifting forks raisable by pumping a hydraulic fluid with a pumping handle, wherein the hydraulic arrangement is such that during an initial phase of pumping with the pumping handle the amount by which the lifting forks are raised is greater than during a subsequent phase and the transition from the initial phase to the subsequent phase takes place after a predetermined distance of raising of the forks.
2. A pallet truck as claimed in claim 1, in which the predetermined distance is of the order of 40mm.
3. A pallet truck as claimed in claim 2, in which the predetermined distance is about 38mm.
4. A pallet truck as claimed in any preceding claim, in which the raising of the forks through the predetermined distance is arranged to be accomplished within one full stroke of the pumping handle.
5. A pallet truck as claimed in any preceding claim, in which the pumping handle is operated by moving it through an
6. A pallet truck as claimed in any preceding claim, in which during the subsequent phase of pumping, one stroke of the pumping handle is arranged to raise the forks by about 1Omm.
- 20
7. A pallet truck as claimed in any preceding claim, in which the lifting forks are raisable by a total height of approximately 115mm in the course of both the initial and subsequent phases of pumping.
8. A pallet truck as claimed in any preceding claim, which the hydraulic arrangement includes a piston and cylinder assembly arranged such that during the initial phase of pumping the cross-sectional area of the cylinder space over which hydraulic pressure is applied to generate the lifting force on the forks is a first relatively small area and during the subsequent phase of pumping said crosssectional area is a second relatively large area.
9. A pallet truck as claimed in claim 8, in which the relatively large cross-sectional area is more than three times the relatively small cross-sectional area.
10. A pallet truck as claimed in claim 8 or 9, in which the cylindrical spaces having the first and second crosssectional areas are respective portions of a common space.
11. A pallet truck as claimed in any preceding claim, further including a reservoir for hydraulic fluid, from which fluid is arranged to be pumped during raising of the forks and to which fluid is arranged to be returned during lowering of the forks.
12. A pallet truck as claimed in claim 11, in which the reservoir includes a one way air valve for allowing flow of air into the reservoir when fluid is pumped out of the 1 21 reservoir and for preventing flow of air out of the reservoir when fluid is returned to the reservoir, whereby in use the reservoir becomes pressurised by a volume of pressurised air in the reservoir.
13. A pallet truck as claimed in claim 11 or 12, including a fluid passageway connecting the reservoir to a main lifting chamber which is operative during the subsequent phase of pumping, the passageway including a one way valve for allowing fluid to flow along the passageway from the reservoir into the main lifting chamber during the initial phase of pumping but not in the reverse direction.
14. A pallet truck as claimed in claims 11 to 13, including a fluid passageway connecting the pump to a main lifting chamber which is operative during the subsequent phase of pumping, the passageway including a one way valve for allowing fluid to flow along the passageway from the main lifting chamber during a lowering step but not in the reverse direction.
15. A hand operated pallet truck including lifting forks raisable by pumping a hydraulic fluid with a pumping handle, a reservoir for hydraulic fluid, from which fluid is arranged to be pumped during raising of the forks and to which fluid is arranged to be returned during lowering of the forks, the reservoir including a one way air valve for allowing flow of air into the reservoir when fluid is pumped out of the - 22 reservoir and for preventing flow of air out of the reservoi when fluid is returned to the reservoir.
16. A pallet truck as claimed in claim 15, in which the hydraulic arrangement includes a piston and cylinder assembly arranged such that during an initial phase of pumping the cross-sectional area of the cylindrical space over which hydraulic pressure is applied to generate the lifting force on the forks is a first relatively small area and during a subsequent phase of pumping the cross- sectional area is a second relatively large area.
17. A pallet truck as claimed in claim 16, in which the relatively large area is more than three times the relatively small area.
18. A pallet truck as claimed in claim 16 or 17, in which the cylindrical spaces having the first and second crosssectional areas are respective portions of a common space.
19. A pallet truck as claimed in any of claims 16 to 18, including a fluid passageway connecting the reservoir to a main lifting chamber which is operative during the subsequent phase of pumping, the passageway including a one way valve for allowing fluid to flow along the passageway from the reservoir into the main lifting chamber during the initial phase of pumping but not in the reverse direction.
20. A pallet truck as claimed in any of claims 16 to 19, including a fluid passageway connecting the pump to a main lifting chamber which is operative during the subsequent - 23 phase of pumping, the passageway including a one way valve for allowing fluid to flow along the passageway from the main lifting chamber to the pump during a lowering step but not in the reverse direction.
21. A hand operated pallet truck substantially as herein described with reference to and as illustrated by the accompanying drawings.
GB9807067A 1998-04-01 1998-04-01 Pallet Truck Withdrawn GB9807067D0 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9807067A GB9807067D0 (en) 1998-04-01 1998-04-01 Pallet Truck

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Application Number Priority Date Filing Date Title
GB9807067A GB9807067D0 (en) 1998-04-01 1998-04-01 Pallet Truck

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Publication Number Publication Date
GB9807067D0 GB9807067D0 (en) 1998-06-03
GB2335905A true true GB2335905A (en) 1999-10-06

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2350402A (en) * 1999-05-24 2000-11-29 Flight Refueling Ltd Stores ejection system

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB865834A (en) * 1957-12-24 1961-04-19 Savoisienne De Verins Hydrauli Hydraulic traction jack and method of employing it
GB1462621A (en) * 1973-01-24 1977-01-26 Tangye Epco Ltd Hydraulic units
GB2095332A (en) * 1977-10-11 1982-09-29 Conway John P Fluid operated piston device
US4567911A (en) * 1981-10-26 1986-02-04 Equipment Company Of America Cartridge type directional control valve
US4641815A (en) * 1986-06-12 1987-02-10 Fu-Chi Metalic Engineering Co. Ltd. Hydraulic jack

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB865834A (en) * 1957-12-24 1961-04-19 Savoisienne De Verins Hydrauli Hydraulic traction jack and method of employing it
GB1462621A (en) * 1973-01-24 1977-01-26 Tangye Epco Ltd Hydraulic units
GB2095332A (en) * 1977-10-11 1982-09-29 Conway John P Fluid operated piston device
US4567911A (en) * 1981-10-26 1986-02-04 Equipment Company Of America Cartridge type directional control valve
US4641815A (en) * 1986-06-12 1987-02-10 Fu-Chi Metalic Engineering Co. Ltd. Hydraulic jack

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2350402A (en) * 1999-05-24 2000-11-29 Flight Refueling Ltd Stores ejection system
US6481669B1 (en) 1999-05-24 2002-11-19 Flight Refuelling Limited Pneumatic actuator for a stores carriage and ejection system

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Publication number Publication date Type
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