GB2342125A

GB2342125A - :Manually operated pump

Info

Publication number: GB2342125A
Application number: GB9821411A
Authority: GB
Inventors: Julian Claude Peck
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-10-01
Filing date: 1998-10-01
Publication date: 2000-04-05
Also published as: GB9821411D0

Abstract

The pump is operated by a pull-cord 3 wound around a main shaft 12 which drives a reciprocating piston in cylinder 19 via a crank. Tension is maintained in the tailing end 3a of the cord by a pulley 9 on a slave shaft (7 Fig. 3) biased to tension the chord by a spring 10. When the handle is pulled, there is grip between the cord and the shaft which is then driven. Upon release, the cord slips around the shaft and is pulled back by the tension on the tailing end. The main shaft need not rely on friction and may have circular or polygonal cross section, a rotary cleat (Figs 4a-f) or a second shaft (Fig. 5). Pump types include cam driven reciprocating, roots, scroll, gear and 'rotary tooth'. Cord tension may alternatively be maintained by hand or weights.

Description

2342125 Manually Operated Pump This invention relates to a manually

operated pump, suitable for use in inflating bicycle tyres and other applications involving the compression or movement of compressible fluids or the movement of incompressible fluids.

Many manually operated pumps suitable for the above applications are already known in prior art. In particular, many portable bicycle pumps are positive displacement reciprocating action pumps in which a single piston reciprocates inside a single cylinder and this is achieved by the operator using the strength of his/her arms directly on the piston in the cylinder. I shall term such devices 'conventional bicycle pumps'.

Conventional bicycle pumps have a number of disadvantages. In particular, the selection of both bore and stroke for the piston necessitate design compromises. The pump will be quick to use if it has a large bore and a long stroke, but the large bore may mean that the compressive force required on the piston will become excessive at high pressures and a long stroke will make the pump less portable.

A further disadvantage of conventional bicycle pumps is that they use only the arm and shoulder muscles. which are not the body's strongest muscles.

The present invention seeks to mitigate these problems by employing a novel means of transmitting power from the operator to the pump itself. The present invention relates to the power transmission system as applied to a manually operated pump, and as such can operate with a wide range of pumps, including both reciprocating pumps or compressors and rotary pumps or compressors.

LikeNNise the application of the present invention is not limited to bicycle pumps as it may also be used for other inflation or air movement applications, orMth incompressible fluids such as water in a bilge-pump or similar application. In particular, the present invention may be used as a pump for compressing air for use in spraying systems, such as domestic or commercial garden spraying systems.

Some of the disadvantages of conventional bicycle pumps have been overcome by another class of pumps which I shall term rope driven pumps. Rope driven pumps typically comprise a body, held down usually by the user's foot, and one or more ropes on which the user pulls to drive the pump. The present invention is a rope driven PUMP- Two main kinds of rope driven pumps are known. The first kind comprises two handles and is operated with two hands, driving the pump in both directions. An example is US 5,180,283. Such pumps suffer several disadvantages. Firstly, it is important that the length of rope is correct for each user - and since some people are taller than others, the length of rope should be made adjustable. Secondly, after use the rope is left outside the body of the pump. It is usually best to coil the rope around a part of the apparatus, but this is somewhat 2 inelegant. Thirdly. since the arrangement is substantially symmetrical, it is desirable for the user to place both feet on the apparatus to stabilise it against the tensile forces applied to it by the ropes - but this can make the user lose his / her balance and may require the body of the apparatus to be larger than would otherwise be necessary. Fourthly, the pulleys used to coil each rope can be co-axial but cannot be co- planar, which causes the forces on the pump to be out of balance. This problem is avoided with certain embodiments of the present invention. The present invention can also incorporate fewer components than pumps manufactured according to US 5,180,283 (only one cord is required, and only one pulley).

In the second kind of rope driven pump, the pump is driven only in one direction. The rope is pulled off a pulley and the pulley drives the pump, then as the handle is released a coiled spring recoils the rope onto the pulley and the pulley is disengaged from the pump by some sort of clutch or ratchet means. An example is EP 0806568.

The present invention may be applied to either of these two kinds of rope driven pump, but the preferred embodiment is an example of the second kind of rope driven pump because this avoids the disadvantages of the first kind of rope driven pumps described above.

The present invention provides an apparatus for movement or compression of a fluid comprising: pump or compressor means arranged to receive a mechanical rotational drive input, and drive means arranged to provide said drive input, said drive means comprising a rotary part and pull-cord means passing round said rotary part, a first end of said pull-cord means being arranged to have a first tensile force applied to it and a second end of said pull-cord means being arranged to have a second tensile force applied to it by a user. whereby application of said second force bv a user causes movement of said cord means in a first direction and corresponding rotation of said rotanpart, said rotation being used to pro%ide said mechanical rotational input.

The pull-cord means may pass round said rotary part to a degree of more than one complete turn. or to a degree of one complete turn, or to a degree of less than one complete turn. The pull-cord means may comprise one of a cable, rope, cord, string, chain and belt.

In one preferred embodiment the apparatus ftirther comprises a take-up means separate from said rotary part arranged to apply. said first force to said first end of said pull-cord means and to retract said pull-cord means in the absence of said second force. Preferably the take-up means comprises a winding means arranged to have said pull-cord means wound thereon and spring means associated with said winding means in order to apply said first force to said pull-cord means.

In an alternative embodiment the first end of said pull-cord means is arranged to have said first force applied to it by said or another user- 3 In the preferred embodiments, in the absence of said second force, said first force causes movement of said cord means in a second direction opposite to said first direction and further preferably this movement causes substantially no corresponding rotation of said rotary part.

This is facilitated in the preferred embodiments in which force is transferred from said pull-cord means to said rotary part to cause said rotation by way of frictional contact.

The pull-cord means may be arranged to pass round a portion of said rotary part having a circular or polygonal cross-section. In some embodiments the cross-section of the portion of the rotary part round which the pull-cord passes is configured to partially deform said pull- cord means whereby to increase grip. In a further alternative the cross- section is not symmetrical whereby grip in one rotational direction is greater than in the other. In a further alternative the portion of the rotary part round which the pull-cord means passes comprises gripping means arranged to grip said pull-cord means when it is pulled in said first direction and to release said pull-cord means when it is pulled in said second direction. In this latter arrangement the gripping means may comprise a clam cleat.

Additionally, the rotary part may comprise portions of different crosssectionMth said pull-cord means being arranged to pass selectively round one of said portions. In particular one of said portions may be of larger cross section than another.

Preferably the rotary part is a rotary shaft extending from and arranged to provide said drive input to said pump or compressor means.

The reciprocating piston embodiment of the present invention will now be describedwith reference to the accompanying drawings in which:

Figure I shows the fully assembled apparatus.

Figure 2 shows the assembled apparatus with the lid removed to show the main elements of the invention.

Figure 3 shows the assembled apparatus removed from the housing.

Figure 4 shows cross sections through round, polygonal and asymmetric shafts.

Figure 5 shows a free shaft parallel to a main shaft.

Figure 6 shows an example of the cam embodiment of the present invention.

4 The reciprocating piston embodiment of the present invention will now be described by reference to figures I to 3.

Figure I shows that the apparatus is substantially inside a 'housing' I contained by a 'lid' 2. A 'cord' 3 is shown coming out through a 'hole' 4 in the lid 2 and the external end of the cord 3 is attached to a 'handle' 5. The lid 2 is designed with a 'footplate' 6 to enable an operator to hold it in place on the ground with his foot, against the forces that will be applied to it as a result of tension being applied to the cord 3 by means of the handle 5.

Figures 2 and 3 show the rest of the apparatus, including a system for tensioning the cord 3, comprising a fixed 'slave shaft' 7 mounted on 'mounting blocks' 8, with a pulley' 9 rotatably mounted on the slave shaft 7 and a 'coiled spring' 10 creating a torque between the slave shaft 7 and pulley, 9.

The coiled spring 10 is reverse coiled inside a recess' I I and the outer end of the coiled spring 10 is attached to the inside of the recess I I in the pulley 9. The inner end of the coiled spring 10 is attached to the slave shaft 7.

The internal end of the cord 3 is attached to the pulley 9. The cord 3 is then wound a number of times around a 'main shaft' 12, (shown in the figures with one and three quarters turns) before passing out through the hole 4 in the lid 2 and being attached to the handle 5. The number of turns of the cord 3 around the main shaft 12 should be sufficient that the cord 3 can impart enough torque to the main shaft 12 to drive it when there is tension in both the 'tailing part' 3A and the 'working part' 3B of the cord 3, but few enough that the cord 3 can slide around the main shaft 12 when there is tension only in the tailing part 3A of the cord 3. The number of turns required will depend on many factors including the design of the cord 3. the design of the main shaft 12 and the tension in the tailing part 3A of the cord 3. In certain circumstances. the number of turns required may be less than one.

Underneath the main shaft 12, the two turns of the cord 3 are separated by a 'cord guide' 13 which passes close to the main shaft 12 and prevents the cord 3 from travelling along the main shaft 12.

The main shaft 12 is rotatably mounted in 'bearings' 14, and on one end of the main shaft 12 is mounted an offcentre 'spigoC 15. A 'connecting rod' 16 is rotatably mounted both on the spigot 15 and on a 'piston bearing' 17 which is mounted on the bottom of a piston' 18, and the piston 18 is free to slide inside a 'cylinder' 19. A seal (not shown) forms an air-tight seal between the piston 18 and the cylinder 19.

At the top end 19A of the cylinder 19 there is an 'inlet valve' 20 arranged to draw air into the cylinder 19 from the atmosphere and an 'outlet valve' 21 arranged to deliver compressed air into a hose (not shown) from the cylinder 19. The other end of the hose is fitted with an appropriate coupling (not showi) to enable it to be attached with an airtight seal to an appropriate valve. In the context of bicycle tyres, this is likely to be a Schrader or Presta valve.

The operation of this embodiment, used to inflate a bicycle tyre will now be described with reference to figures 2 and 3.

The apparatus is placed on the ground near to the tyre which is to be inflated and the coupling is attached to the tyre valve. The apparatus should be close enough to the tyre for the hose not to be unduly stressed. The operator places his/her foot on the footplate to hold the apparatus in place and then grasps the handle in his/her hand.

The operator then repeatedly pulls on the handle causing the cord to unwind from the pulley, then releases the handle and lets the coiled spring recoil the cord back on to the pulley- When the operator is pulling the handle, the cord grips the main shaft and drives the pump but when the operator releases the handle. the cord slips on the main shaft and recoils easily onto the pulley. This is described in detail in the paragraphs below.

As the operator pulls on the handle, the cord unvinds from the pulley and the pulley rotates against the torque from the coiled spring. Let us assume that the tension in the tailing part 3 A is TT,,d,,, and that the tension in the working part 3B is Tw,,rkng. These two opposing tensions will cause the cord to grip the main shaft, by friction or possibly other means as described below. When the operator pulls on the handle. Tw.,k. becomes greater than TTajj, and will cause the main shaft to rotate because there is sufficient grip between the cord and the main shaft.

The rotation of the main shaft will cause the spigot to rotate about the axis of the main shafL which will in turn cause the connecting rod and piston to reciprocate inside the cylinder. As the piston moves towards the main shafL air is drawn into the cylinder via the inlet valve, then as the piston moves back away from the main shaft, air is compressed inside the cylinder then discharged through the outlet valve into the hose and thence via the coupling and the Schrader or Presta valve into the tvre itself.

The cord is prevented from moving along the main shaft by means of the cord guide, which also prevents the cord wrapping over itself and affecting the smooth operation of the apparatus.

When the operator stops pulling the handle, the Schrader or Presta valve and the outlet valve will close. There may be some partially compressed air in the cylinder which may cause the piston to be pushed slightly back towards the main shaft. This does not affect the successful operation of the apparatus.

When the operator releases the handle, there will no longer be any tension Tw.,k. in the working part of the cord. The tension TTajg from the coiled spring will tend to pull the cord back onto the pulley. Importantly, since there is no longer any tension Tw,,kig, the cord will no longer grip the main shaft so the cord will now slip over the main shaft and run easily back onto the pulley without having to drive the main shaft and the pump.

6 Again. the cord is prevented from moving along the main shaft by means of the cord guide, which also prevents the cord wrapping over itself and affecting the smooth operation of the apparatus.

Once the operator is satisfied that there is enough air in the tyre (a pressure gauge may be fitted to the apparatus), the handle can be released altogether and will retract into the housing under the action of the coiled spring. The coupling can then be detached from the Schrader or Presta valve and the tyre inflation process is complete.

It is not necessary to dwell upon the design of the crankshaft, connecting rod, piston. cylinder, valves. hose and coupling here as this is merely one example of a pump or compressor and such pumps are well known already. Equally, it is not necessary to dwell upon the design of the slave shaft, pulley and coiled spring as such systems are also well known, being used in tape measures. retractable dog leads and cable retractors for vacuum cleaners. Since the core of the present invention is the interface between the cord and the main shaft, this will now be described in greater detail.

One means by. which the cord may grip the main shaft is friction. There are established engineering equations governing the limiting friction (F) between a cord and a shaft. Firstly. the limiting friction F is simply the difference between the tension at one end of the cord Ti and the tension at the other end T,. For T2 greater than TI:

F = T - T1 But also:

T2=TI e fa where 'e' is the base of Napierian logarithms (roughly 2.718), 'f is the coefficient of friction and 'a' is the angle of contact between the cord and the shaft (measured in radians).

Let us first consider the case where T2 is T&,,,k.,,. the pulling force applied by the operator and T1 is Tr., the tailing force applied by the coiled spring. The ratio T,: T1 equals the ratio Tw.,ki,. TTailing which equals J' and is highly sensitive to f and a due to the exponential function. In other words, for a fairly small TTaJmg the system can be designed to accommodate a large Ti,,,,k,,,g before slipping.

Next let us consider the case where the operator releases the handle. Now. Tw.,idlg is zero and must be T1 (since T, > T1). T, is therefore TTading and F cannot exceed T:, so the cord will recoil easily.

7 In pure theory, since T2= T, e fa and T, is zero, T, should also be zero. However, the theory above ignores several real world factors, notably the weight, stiffness and deformability of the cord. These factors combine to mean that there is some friction between the cord and the shaft even in the absence of any Tw.rk,,,g.

However, friction is not the only means by which the cord may grip the shaft. If the shaft is manufactured with polygonal (rather than round) cross section as shown in Figures 4B and 4C then another principle starts to have an effect. It has been established in the design of winches that a rope is more resistant to pulling about a polygonal cross section than about a round cross section (see US patent 4,688,765 Jesus Guangorena). Guangorena says that this is caused not by friction but by the vertices of the polygons causing the rope to deform (flatten), and that there is a resistance to the propagation of this deformation along the length of the rope.

In practice, for a polished stainless steel shaft having a circular cross section, five or six turns of cord around the shaft may be required to achieve adequate grip to drive the pump - but for a polished stainless steel shaft having a hexagonal or octagonal section. two turns may be sufficient. The vertices of the polygonal section do not have to be sharp to cause the deformation in the cord, and a small radius on each vertex helps to reduce wear on the cord. Likewise., the cord will suffer less wear if there are fewer turns about the shaft and therefore fewer cord guides for it to rub against.

A third way in which the cord may grip the shaft is to design either the cord or the shaft or both to have an asynunetric surface, i.e. one which exerts more ffiction in one direction than in the other. A simple version of this is shown in Figure 4D. Such a profile might enable the cord to grip the shaft very well in one direction despite having only a very small number of turns about the shaft (eg less than one turn), but still to slip easily in the other direction. It would also be possible to design an asymmetric cord (perhaps more like a kind of chain or a belt) having a set of teeth that enable it to grip in one direction but to slide in the opposite direction. Ultimately, such teeth might be designed to mate with asymmetric features on the profile of the shaft, effectively transforming the cord and shaft into a ratchet like system.

The same effect may also be achieved without using an asymmetric cord by designing the shaft to operate in the manner of a clam cleat. An example of this is shown in Figures 4E and 4F. The rotary claiin cleat system is mounted on the main shaft so that when the user pulls the cord, the cord jams between the 'splines' 24 of the cleat system and drives the pump. The cord cannot slip around the shaft, because any increase in the working tension Tw.,kmgwill simply cause the cord to be gripped more firmly between the splines of the cleat system. However, when the user releases the handle the line of action of the tailing tension TT".. Will tend to pull the cord out from between the splines of the cleat system and the cord will be pulled freely under the action of TTaai,,,. Figures 4E and 4F show straight splines, but the splines could form arcs of circles or be part of spirals or some other form. In particular, they could have an involute form (the path traced by the end of a cord being unwound off a circular shaft).

8 However, for conventional shafts the other parameter affecting the number of turns required is the tailing tension TTzding. The effect of increasing this tension (by strengthening the spring) is both to increase the friction between the cord and the shaft (so that it grips more when the handle is pulled) and to increase the recoiling tension (so that the cord recoils more easily onto the pulley). However, the spring should not be made too strong as the work that is put into the spring while pulling on the handle is not being used to drive the pump and is not recovered.

Figures 2. 3 and 6 show a small number of turns (1.75 turns) for the sake of clarity. This assumes either a high friction main shaft, or a polygonal main shaft, or a strong coiled spring.

One problem that can arise in implementations of the present invention is that the cord can tend to travel along the main shaft, ultimately wrapping over itself and affecting the smooth operation of the apparatus. The apparatus may be designed with a shaft long enough to allow this to happen, or this may be prevented as indicated above by means of a cord guide. The use of a cord guide is not ideal. as this causes friction between the cord and the shaft as the cord is pushed axially along the shaft by the cord guides.

There are many design details that can be used singly or in combination to prevent the cord wrapping over itself and to prevent excessive friction between the shaft and the cord. Winches are often designed with an hourglass or dumbbell form or with angled ends, allowing the cord to move along the shaft between limits and preventing itwrapping over itself at the ends. A tapered shaft would work in a similar way. Alternatively, the working end and tailing end of the cord may be led away from the main shaft at angles that will prevent the wrapping over problem, either preventing or allowing a certain amount of axial movement along the shaft.

The problem can also be prevented if the cord can drive the shaft with a number of turns that is less than one. as then it may operate in a groove in the shaft without having any tendency to propagate along the shaft. This may be easier to achieve using a belt rather than a cord. so that the surface area in contact with the shaft may be large even though the number of turns used is less than one.

A similar effect using a larger number of turns may be achieved by mounting two shafts parallel to each other, as shown in figure 5, either one or both of which may be driven by the cord. In the case shown. the main shaft 12 is driven by the cord and a 'free shaft" 22 is simply free to rotate in bearings (not shown). The cord 3 operates in a series of 'grooves' 23 in both shafts. The effective number of turns is therefore quite large, but the cord has no tendency to move axially along either shaft and there is no rubbing between the cord and the shaft.

There are two main reasons why the preferred embodiments of the present invention are superior to EP 0806568. Firstly. the present invention requires no freewheel or overrunning clutch, which is an expensive component. The freewheel or overrunning clutch is also potentially an unreliable component. as bicycle pumps may be subjected to dirt and damp which could affect the reliable operation of such a component. Secondly, the use of a main shaft and a slave shaft enables the number of rotations of the pulley to be different from the 9 number of rotations of the pump, without the use of any additional transmission system such as a system of gears. This is important, because coiled springs cannot generally provide much more than about 3040 turns, which limits the number of turns of cord on the pulley to the same number. In order to supply a sufficient quantity of air, this requires the use of larger cylinders than might otherwise be chosen, or the use of multiple cylinders, all of which adds cost. The same effect can be achieved with preferred embodiments of the present invention simply by reducing the diameter of the main shaft.

Other example embodiments of the present invention are described below.

Firstly, the tailing tension TTaAmgcould be supplied by means other than those described above. A simple change would be to make the slave shaft rotate with the pulley and the spring act between the shaft and the housing. More fundamentally, TTailmgcould come from other sources entirely, such as a weight being suspended from the tailing end of the cord. Alternatively, the tailing end of the cord could be led back out of the housing to another handle, and the user could provide the tailing force themselves with their other hand. There are. of course. many other possibilities too.

In the multi-cylinder embodiment, a plurality of pistons may be operated by a plurality of connecting rods being driven by a crankshaft attached to the main shaft.

Another way of driving a reciprocating piston in a cylinder is by use of cams. This is the principle of the cam embodiment, an example of which is illustrated in figure 6. The drive mechanism described earlier is substantially unchanged, except that the main shaft 12 now passes through the beanngs 14 and drives a 'cam 25. This cam lies inside a 'reciprocating shaft' 26, between two parallel faces which behave as flat followers on the cam. The reciprocating shaft is free to slide through 'slide bearings' 27 held in a 'bracket' 28. Each end of the reciprocating shaft terminates in a piston 18, free to reciprocate inside a cylinder 19.

The profile of the cam is designed to smooth out the jerkiness that would arise if a simple crankshaft and connecting rod system were used to drive the pump.

In the spring assisted embodiment, one or more springs may be used to help to smooth out variations in the torque at the pulley that occurs naturally each cycle. This variation is most pronounced in the single- cylinder reciprocating piston embodiment (without cams), in which no work is done during at least half the cycle as the piston is drawing air into the cylinder. A system of springs may be devised in which the springs will absorb energy during the parts of the cycle in which less work is done on the air, and be allowed to relax (releasing some of their stored energy) during the parts of the cycle in which more work is done on the air.

In the twin screw embodiment, Roots blower embodiment, gear pump embodiment and rotan- tooth embodiment of the present invention, the output shaft is connected to one shaft of the compressor and the other shaft of the compressor is driven by a set of timing gears or similar mechanism operating between the two shafts.

In the scroll embodiment of the present invention, the output shaft is connected to the shaft of a scroll compressor.

There are also several multi-speed embodiments. In the first multi-speed embodiment, the main shaft would have a smaller cross section and a larger cross section, separated axially along the main shaft, such that the main shaft could be driven either by the cord gripping the smaller cross section or by the cord gripping the larger cross section. The cord guide could be movable both axWly along the main shaft and radially (towards the axis of the main shaft when the smaller cross section is in use). Alternatively, the main shaft could be movable axially and the cord guide could be movable radially.

In the second multi-speed embodiment, there is a sleeve around part of the main shaft, which has a larger cross section than the main shaft itself. With the tension in the cord slackened off. the sleeve can be moved along the main shaft, then the cord will grip the surface of the sleeve rather than the surface of the shaft.

Claims

1. Apparatus for movement or compression of a fluid comprising: pump or compressor means arranged to receive a mechanical rotational drive input-, and drive means arranged to provide said drive input; said drive means comprising a rotary part and pull-cord means passing round said rotary part, a first end of said pull-cord means being arranged to have a first tensile force applied to it and a second end of said pullcord means being arranged to have a second tensile force applied to it by a user, whereby application of said second force by a user causes movement of said cord means in a first direction and corresponding rotation of said rotary part, said rotation being used to provide said mechanical rotational input.

2. Apparatus according to claim I in which said pull-cord means passes round said rotary part to a degree of more than one complete turn.

3. Apparatus according to claim I in which said pull-cord means passes round said rotary part to a degree of one complete turn.

4. Apparatus according to claim I in which said pull-cord means passes round said rotary part to a degree of less than one complete turn.

5. Apparatus according to any of claims 1-4 in which said pull-cord means comprises one of a cable, rope, cord, string, chain and belt.

6. Apparatus according to any of claims 1-5 further comprising a take-up means separate from said rotary part arranged to apply said first force to said first end of said pull-cord means and to retract said pull-cord means in the absence of said second force.

7. Apparatus according to claim 6 in which said take-up means comprises a winding means arranged to have said pull-cord means wound thereon and spring means associated with said winding means in order to appIN said first force to said pull-cord means.

8. Apparatus according to any of claims 1-5 in which said first end of said pull-cord means is arranged to have said first force applied to it by said or another user.

9. Apparatus according to any of claims 1-8 in which, in the absence of said second force, said first force causes movement of said cord means in a second direction opposite to said first direction.

12

10. Apparatus according to claim 9 in which said movement in said second direction causes substantially no corresponding rotation of said rotary part-

11. Apparatus according to an), of claims 1-10 in which force is transferred from said pull-cord means to said rotaii. part to cause said rotation by way of frictional contact.

12. Apparatus according to any of claims I - 11 in which said pull-cord means passes around a portion of said rotary part having a circular crosssection.

13. Apparatus according to any of claims 1-11 in which said pull-cord means passes around a portion of said rotary part having a polygonal cross-section.

14. Apparatus according to any of claims 1 - 11 in which the crosssection of the portion of the rotary part around which the pull-cord passes is configured to partially deform said pull-cord means whereby to increase grip.

15. Apparatus according to claim 14 wherein said cross-section is not symmetrical whereby grip in one rotational direction is greater than in the other.

16. Apparatus according to any, of claims I -I I in which the portion of the rotary part round which the pull-cord means passes comprises gripping means arranged to grip said pull-cord means when it is pulled in said first direction and to release said pull-cord means when it is pulled in the other direction.

17. Apparatus according to claim 16 in which said gripping means comprises a clam cleat.

18. Apparatus according to any of claims 1- 15 in which said rotary part comprises portions of different crosssection and said pull-cord means is arranged to pass selectively round one of said portions.

19. Apparatus according to claim 18 in which one of said portions is of larger cross section than another.

20. Apparatus according to any of claims 1-19 in which said rotary part is a rotary, shaft extending from and arranged to provide said drive input to said pump or compressor means.