Background of the Invention Reciprocable hand pumps comprising multiple c-axial cylinder arrangements have been known for at least 90 years. Such pumps, sold under Applicant's"Nesthill" trade mark basically consisted of a base plate comprising a valved, ambient air inlet aperture, and a valved compressed air outlet aperture, with an innermost tube secured at its lower end to the base plate, a reciprocable tube coaxially surrounding the innermost tube to define an annular chamber and provided at an upper end with an operating handle to achieve recriprocable movement, and finally an outermost tube also secured at its lower end to the base plate and defining another annular air chamber, with successive chambers of decreasing volume, and with valve means to control air transfer from one chamber to the next, principally being developed for motor vehicle type inflation and capable of delivering at say 10-20 bar. In more recent times there has been a demand for higher pressures, and there exists proposals for hand operable multiple co-axial cylinder air pumps, such as SE 463732, EP 0832359 and WO 01/57400.

Object of the Invention A basic object of the invention is the provision of an improved, multi-stage, reciprocable hand pump capable of delivering 100-150 bar or higher pressure.

Summary of the Invention According to the present invention, there is provided a multi-stage, reciprocable hand operable air pump comprising: (i) a first and inner static cylinder ; (ii) a piston reciprocable within the inner cylinder and carried by a piston rod extending to a handle, the piston incorporating a valve to control transfer of air, during reciprocation from the annulus side of the piston to the full bore side of the piston, with a valved delivery aperture at a first end of the inner cylinder, and (iii) a second and outer reciprocable cylinder co-axially surrounding the inner cylinder having one closed end connected to the handle for simultaneous reciprocation with the piston rod and piston, and together with the piston rod defining a first annular chamber for receipt of a change of air at atmospheric pressure upon reciprocation in a first direction, and for effecting a first compression upon reciprocation in the opposite direction, characterised in that (iv) a static tube located co-axially between the first static cylinder and the reciprocable cylinder, being spaced from both so as to define, between the external periphery of the static tube, and the internal periphery of the reciprocable cylinder a second annular chamber, of smaller volume than the first annular chamber, with at least one transfer port provided in the second end of the static cylinder for the transfer of air from the second annular chamber to the annulus side of the piston, and also between the internal periphery of the static tube, and the external periphery of the static inner cylinder an annular air admittance and transfer passage, with at least one air ingress aperture in the wall of the static tube at a first end of the static tube and connecting the annular air admittance and transfer passage to atmosphere, the static tube being located within the reciprocable cylinder, and (v) a one-way valve assembly provided at a second end of the static tube, and comprising valve means operable, on an induction stroke of the pump, to permit air at ambient pressure to flow through the annular air admittance and transfer passage and in to the first annular chamber, and operable, upon a compression stroke of the pump, to transfer air changed to a first pressure from the first chamber to a second, downstream chamber of smaller volume than the first annular chamber.

Operation Thus, with the pump arranged vertically, or generally so, then from a contracted position, an upstroke firstly draws a change of ambient air through the annular air admittance and transfer passage, via the then open internal valve of the one-way valve means, into the first annular chamber. Simultaneously, a partially compressed change of air is swept from the second annular chamber through the transfer port to the annulus side of the piston.

On a downstroke, the internal valve means of the one way valve assembly closes, and the external valve member opens permitting air transfer from the first annular chamber to the second annular chamber, and simultaneously increasing the pressure in the fuel bore side of the piston until the valve of the delivery aperture opens at the required delivery pressure.

Preferred or Optional Features The first end of the static cylinder is sealingly engaged in a fitting eg by being screwed into a tapped bore of the fitting.

The fitting houses a spring-loaded, one-way valve.

The fitting is retained in a body member provided with a delivery bore leading to a tapped hole for connection of one end of a flexible delivery tube.

The body member carries an air pressure gauge, in communication with the delivery bore.

The body member is provided with a base plate, adapted to be engaged by a foot of a user.

The second end of the static cylinder sealingly engages a portion of the one-way valve assembly eg by being screwed into a tapped hole of a component, which assembly sealingly engages the internal periphery of the static tube, and the external periphery of the piston rod.

The one-way valve assembly is also provided with an external displaceable valve member eg an'O'-ring to permit, or to prevent, air flow between the first and second annular chambers.

The internal one-way valve assembly comprises at least one ball as a valve member.

The closed end of the reciprocable cylinder is provided with a closure plug attached both to an end of the piston rod, and to a transverse, operating handle.

The other, open end of the reciprocable cylinder sealingly engages the external periphery of the static tube.

Brief Description of the Drawings By way of example only, a pump in accordance with the invention is shown at various operational stages in the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of a pump in accordance with the invention; Figure 1A is an enlargement of a portion of Figure 1 as indicated by the arrow A ; Figure 1 B is an enlargement of another portion of Figure 1 as indicated by the arrow B; Figures 2 and 2B correspond to Figures 1 and 1 B respectively, but show different operational positions in the pumping cycle ; Figure 3 corresponds to Figures 1 and 2 but shows yet different operational positions in the pumping cycle ; Figure 3B corresponds to Figures 1 B and 2B but shows yet different operational positions in the pumping cycle ; Figure 4 is an enlargement of a portion of Figure 3 as indicated by the arrow C; and Figures 5 and 5A correspond to Figures 1 and 1A but show yet different operational positions in the pumping cycle.

In the drawings is illustrated a multi-stage, reciprocable hand operable air pump 1.

The pump 1 comprises at its lower end a foot plate 2 adapted in use, to seat on the ground and to be stabilized by a foot of the user, and at its upper end is provided a transversely extending operating handle 3 adapted to be gripped by the hands of the user.

The pump 1 comprises a first, and inner, static cylinder 4 in which is located a reciprocable piston 5 carried by a piston rod 6 extending to the handle 3, and hence reciprocable by the handle.

As best seen in Figure 4, the piston 5 is provided with a circumferential groove 7 which receives a valve in the form of an'O'-ring 8 which is displaceable between flow and no-flow positions dependent upon the direction of reciprocation of the piston 5 the 'O'-ring 8 therefore controlling the flow of air between annulus side/chamber 9 of the piston 5, and full bore side/chamber 10 of the piston 5. At its lower end, the cylinder 4 is screwed into a fitting 11 in turn screwed into a base member 12 to which the foot plate 2 is attached. As best seen in Figure 1A and Figure 5A, the fitting 11 provides a delivery aperture 13 normally closed by a spring loaded valve member 14. The aperture 13 is in air flow communication via a bore 15 in the base member 12 to a flexible conduit 16 having an end fitting 17 appropriate to the article, such as an air gun, to receive a charge of compressed air. The base member 12 is provided with a further bore 18 to which is connected a pressure gauge 19 so that the user can see what air pressure is being created by the pump 1, and discharged via the delivery aperture 13 and fitting 17.

The first static cylinder 4 is co-axially surrounded by a second and outer reciprocable cylinder 20 having an upper, closed end 21 connected to the handle 3 for simultaneous reciprocation with the piston 5. The cylinder 4 defines, with the piston rod 6, a first stage, annular chamber 22.

In accordance with the invention, a static tube 23 is located co-axially between the first static cylinder 4 and the reciprocable cylinder 20, and is spaced from both so as to define between the external periphery 24 of the static tube 23 and the internal periphery 25 of the reciprocable cylinder 20, a second stage annular chamber 26 of smaller volume than the first stage annular chamber 22. At least one transfer port 27 (Figure 1A) is provided in the second and lower end of the static tube 23, and between the internal periphery 28 of the static tube 23 and the external periphery 29 of the static inner cylinder 4, an annular air admittance and transfer passage 30 is provided. At least one air ingress passage 31 is provided in the wall of the static tube 23 at a first, lower end 32 of the static tube 23 connecting the annular air admittance and transfer passage 30 to atmosphere, and the static tube 23 being located within the reciprocable cylinder 20.

Finally, a valve assembly 33 is provided at a second and upper end of the static tube 23. In detail, the valve assembly 33 comprises a fitting 34 having a c-axial bore 35 partially threaded so that the fitting 34 may be screwed onto the externally threaded terminal end of the static cylinder 4, with an annular skirt 36 projecting into the annular space between the external periphery of the piston rod 6, and the internal periphery of the static tube 23. The valve assembly comprises a first seal in the form of an'O'-ring 37 to seal against the external periphery of the reciprocable piston rod 6, a second'O'- ring 38 located in an oversize groove so as to constitute a one-way valve member by being displaceable between flow (Figure 1B) and no-flow (Figure 2B) positions and serving to seal against the internal periphery 25 of the reciprocable cylinder 20, and a third'O'-ring 39 to seal against the internal periphery 28 of the static tube 23. At least one radial transfer passage 40 is provided in the fitting 34. The valve assembly 33 also comprises a further one-way valve means comprising a plurality of balls 41 each to seat in a no-flow position (Figure 2B) under gravity on an individual valve seat 42 of an ambient air admittance aperture 43 during a downstroke of the handle 3 but during an upstroke of the handle 3 being lifted from their valve seats (Figure 3B) to permit ambient air flow.

In operation, from a pump start position in which the pump 1 has been fully telescoped to a minimum length condition, the user grips the handle 3 and with a foot on the foot plate 2 commences an initial upward stroke, which is illustrated in Figure 1.

During this stroke, ambient air enters the air admittance and transfer passage 30 via ports 27 as indicated by arrows 43, and is drawn into the first stage chamber 22 through the lifted balls 41.

After the initial upstroke, with the chamber 22 at maximum volume and containing air at ambient pressure, the user performs an initial downstroke, as illustrated in Figure 2.

As the air pressure within the diminishing volume first stage chamber 22 increases, first stage chamber air is forced, as indicated by arrows 44 (Figure 2B), between the external periphery 45 of the valve assembly 33, and the internal periphery 25 of the reciprocable cylinder 20 to displace the second'O'-ring 38 downwardly, to permit air flow into second stage chamber 26, as best seen in Figure 2B, air transfer from first stage to second stage continuing until the downstroke has been completed.

At the second upstroke illustrated in Figures 3,3B and 4, the pump 1, in addition to introducing a second charge of ambient air as already discussed regarding Figure 1, simultaneously effects a transfer from second stage annular chamber 26, to a third stage annular chamber 9 which is of smaller volume than the second stage chamber 26, as shown by arrows 46 via the radial transfer passages 40. As shown by arrows 47, air is forced firstly between the exterior 48 of the piston rod 6 and internal periphery 40 of the static cylinder 4 and then, as indicated by arrows 50, between the exterior 51 of the piston 5, and the internal periphery 49 of the static cylinder 4, displacing the'O'-ring 8 downwardly, to permit air flow into the full bore side/chamber 10 of the cylinder 4, the air pressure within the full bore side/chamber 10 being such that it is unable to defeat the spring loading valve member 14.

However, upon the second downstroke of the pump 1 illustrated in Figures 5 and 5A, the arrangement is such that downward movement of the piston 5 and hence progressive diminution of the full bore side/chamber 10 eventually creates an air pressure to unseat the valve member 14 to cause delivery of a charge of high pressure air to the end fitting 17.

Clearly, the stroke of the pump and the volumes of the chambers 22,26 and 10 need to be so selected as to provide at the fitting 17 a charge of compressed air at the required pressure.