GB2354057A - A valve and a marine propulsion unit incorporating a valve - Google Patents

Abstract

A valve 15 has one or more fluid inputs 21 and an output 23, communication between the inputs 21 and output 23 is determined by the fluid pressure at a control input 17. Preferably the valve 15 has a closure member 18 slidingly disposed within a valve body 16. The body 16 may be closed at one end and the closure member 18 make a fluid-tight seal with the body 16. The member 18 may be biassed towards a closed end 16' of the body 16 by bias means 20. In this position the inputs 21 are in communication with the output 23. If a sufficiently large pressure occurs at the input 17 the bias means 20 are overcome and the member 18 moves away from the closed end 16' preventing communication between the inputs 21 and the output 23. The closure member 18 is preferably a hollow cylinder, closed at one end. Through-holes 22 may be located in annular grooves 22a around the member and spaced circumferentially. The grooves 22a allow a high flow rate to reach all through-holes 22. The grooves 22a may alternatively be provided on the interior of the body 16. The body 16 and member 18 may be of non-circular cross-section and the through-holes may consist of an elongate aperture (figure 5, 26) and the grooves combined to form one large groove.

Description

2354057 A valve, and a marine propulsion unit incorporating a valve The

present invention relates to a valve, and more particularly to a valve that controls a flow of fluid on the basis of the pressure of a control fluid. The invention also relates to a marine propulsion unit having such a valve.

One particular application of a valve of the present invention is in relation to a postimmersion restart system for a marine propulsion unit. When a boat capsizes the propulsion unit is submerged and it will flood with water. Even in the case of a vessel provided with a self-righting capability, the engine is generally flooded with water by the time the vessel has righted itself In order to restart the engine it is necessary to drain each cylinder of water, and also to drain the carburettor or carburettors. A post immersion restart system for draining a carburettor is described in European Patent EPB-0 219 278, and a post immersion restart system incorporating crankcase drainage is described in co-pending UK Patent Application No. 9909947.5. The contents of these two documents are hereby incorporated by reference.

The basic principle of operation of the post-immersion restart system of UK Patent Application No. 9909947.5 is illustrated in Figure 1.

The marine propulsion unit shown in Figure I is a two-stroke internal combustion engine. Only one cylinder I is shown in Figure I for clarity and ease of explanation, although the propulsion unit will in general have two or more cylinders.

A combustion chamber 2 is disposed at a first end of the cylinder 1, and a crank-ease 3 is disposed at a second end of the cylinder 1. The engine is a crank-case scavenged engine, and a transfer passage 4 connects the crank-case 3 to the combustion chamber 2.

A piston 5 is disposed within the cylinder, and can move reciprocably within the cylinder. A crank-shaft 6 is disposed within the crank-case 3, and the piston 5 is connected to the crank-shaft 6 by a connecting rod 7, so that reciprocating motion of the piston 5 is converted into rotary motion of the crank-shaft 6.

2 In use, fuel and air are introduced into the crank-case from the carburettor I I by inlet means (not shown). One or more spark plugs 8 are provided in the combustion chamber to ignite the compressed air/fuel mixture at the completion of the compression stroke, and the resultant combustion of the fuel/air mixture drives the piston 5 away from the combustion chamber 2. An exhaust port E allows the combustion products to exhaust from the cylinder when it is uncovered by the piston.

The post-immersion restart system shown in Figure 1 essentially consists of two ports provided in the cylinder. A first port, or purge port, 9 is provided in the combustion chamber and a second port, or drain port, 10 is provided at the lowest effective drainage point of the propulsion unit. In the propulsion unit of Figure 1, the drain port 10 is located in the transfer passage 4. These ports are additional to the exhaust port E, and they are selectively and independently openable regardless of the position of the piston 5 in the cylinder 1. The ports 9,10 are shown in their open states in Figure 1, but in normal operation of the propulsion unit both ports will be closed since operation of the engine would be adversely affected if one or both of the ports 9, 10 were open.

When the vessel fitted with the marine propulsion unit of Figure 1 capsizes, water will enter the propulsion unit through, for example, the air intake or the exhaust. Thus, when the vessel is righted after a capsize, the propulsion unit will typically be flooded with water. If the unit has stopped with the piston 5 blocking the exhaust port E, it will not be possible for the water to leave the cylinder so that the piston 5 is hydraulically locked and so cannot move within the cylinder 1. In a multi-cylinder propulsion unit it is possible that the unit will stop with the crank-shaft in a position such that the exhaust port in one cylinder is uncovered. However, if just one cylinder in the unit is hydraulically locked this will lock the entire unit and will prevent it from being restarted.

The first step in the purging process is to open the drain port 10 so that the interior of the cylinder is vented to atmosphere. Water can then drain out of the unit as a result of the action of gravity, through the transfer passage 4 and the drain port 10. Subsequent 3 opening of the purge port 9 enables release of hydraulic pressure above the piston (that is, from the combustion chamber 2). It is then possible to rotate the crank-shaft 6 and so reciprocate the piston 5 within the cylinder 1, and such movement of the piston 5 will cause water within the propulsion unit to be expelled through the drain port 10. The crank-shaft can be rotated either manually or, if the propulsion unit is fitted with a starter motor, using the starter motor.

Once the engine has been restarted, the purge port 9 and drain port 10 are closed and the engine operates in -a conventional manner.

In principle, the drain port 10 can be fort-ned by any suitable valve. However, the crew member attempting to restart the engine will have been flung into the sea when his vessel capsized and will have had to scramble back into the vessel, and so may well be shocked and disoriented and, moreover, the restarting operation is likely to be carried out in heavy seas and possibly at night. It is thus desirable for the restart operation to be made as simple as possible.

Furthermore, until the engine is completely drained of water, turning the engine over will tend to drive any water remaining in the engine through the transfer passage 4 to the combustion chamber, from where it will be have to leave the engine through the purge port 9. Thus, it is desirable to ensure that the drain port 10 is open as soon as possible after rerighting after a capsize, since this will minimise the time taken to drain and restart the engine.

For the above reasons, it would be desirable for the port to open automatically such that draining the engine commences as soon as the vessel has been re-righted after a capsize. It would also be desirable for it to close automatically once the engine is restarted.

A first aspect of the present invention provides a valve having a first fluid input; a fluid output; and a second fluid input; wherein fluid communication between the first fluid input and the fluid output is determined by the fluid pressure at the second fluid input, 4 Water-cooled marine propulsion units are in widespread use. The cooling system of a water-cooled propulsion unit is provided with a water intake below water level. Means for drawing water into the cooling system, such as a pump or impeller, is located at or near the input, and this is driven by the engine so as to draw water into the cooling system. An output of the cooling system is located above the water level so that, after passing through the cooling system, at least part of the water is discharged through what is known as the "tell-tale" so as to provide a visual indication that water is passing through the cooling system. Where a valve of the present invention is used in a purging system for a water- cooled engine, a flow of water in the cooling system such as, for example, the flow of used cooling water discharged through the t6ll-tale, can be used to control the valve so that the cylinder drain port opens as soon as the engine stops and the flow of water in the cooling system ceases.

A second aspect of the present invention provides a marine propulsion unit comprising a valve as described above.

In a preferred embodiment, the propulsion unit is a water-cooled propulsion unit, and the fluid pressure at the input for control fluid is derived from the flow of water in the cooling system of the propulsion unit.

Preferred features of the invention are set out in the dependent claims.

Preferred embodiments of the present invention will now be described, by way of illustrative example, with reference to the accompanying drawings in which:

Figure I is a schematic view of a marine propulsion unit fitted with a drain port; Figure 2(a) is a schematic view of a valve according to an embodiment of the present invention in a first state; Figure 2(b) is a schematic view of the valve of Figure 2(a) in a second state; Figure 2(c) is a schematic cross-sectional view of the valve of Figures 2(a) and 2(b); Figure 3 is a schematic view of valve according to another embodiment of the present invention; Figure 4 is a schematic view of valve according to another embodiment of the present invention; and Figure 5 is a schematic view of valve according to another embodiment of the present invention.

Like reference numerals denote like components throughout the drawings.

A valve according to an embodiment of the invention is illustrated in Figure 2(a), which shows the valve in a first position, and Figure 2(b), which shows the valve in a second position.

The valve 15 has a valve body 16 which is generally cylindrical in shape. The valve body 16 is hollow and is closed at one end 16'. It is provided with an input 17 for fluid at its closed end 16'. This will be referred to as an input 17 for control fluid, for reasons that will become apparent.

A closure member 18 is disposed within the valve body 16. The exterior cross-section of the closure member 18 is complementary to the interior cross-section of the valve body, and the closure member is dimensioned so as to be a substantially fluid-tight, sliding fit in the hollow interior of the valve body 16. The closure member is generally hollow, and is closed at one end 18'. The closure member 18 is inserted into the interior of the valve body 16 so that its closed end 18' is towards the closed end 16' of the valve body 16.

An end cap 19 is fitted over the open end of the valve body 16 so as to retain the closure member 18 within the interior of the valve body 16. It is desirable that the end cap 19 6 can be removed from the valve body 16 for maintenance purposes. For example, a screw thread (not shown) could be provided on the exterior of the reduced-diameter end portion of the valve body 16, and a complementary screw thread (also not shown) could be provided on the interior of the end cap.

A bias means is provided within the interior of the valve body, to bias the closure member 18 towards the closed end of the valve body 16. In the embodiment of Figure 2(a), the bias means is a coil spring 20 that extends within the interior of the closure member and one end of the coil spring bears against the inside of the closed end 18' of the closure member. The other end of the coil spring is retained in position by, and bears against the interior of, the end cap 19. The coil spring is in compression, and so tends to urge the closure ember 18 towards the closed end 16' of the valve body (that is, to the left in Figure 2(a)).

The valve body 16 is provided with one or more fluid inputs 21. Three fluid inputs 21 are shown in Figure 2(a) and Figure 2(b), but the invention is not limited to a valve having three such fluid inputs.

The closure member 18 is provided with one or more apertures 22 for each of the fluid inputs. In the embodiment of Figures 2(a) to 2(c), four apertures 22 are provided for each of the fluid inputs 22. As shown in Figure 2 (c) these are arranged at 90' intervals around the circumference of the closure member 18. The invention is not however limited to a valve where four apertures are provided for each input port. Furthermore, although the apertures 22 are shown with a circular cross-section in Figure 2(a) the apertures could have a non-circular cross-section.

Providing more than one aperture for each of the fluid inputs 21 has the advantage that the total area of the apertures 22 corresponding to one of the fluid inputs 21 can be made greater than the cross-sectional area of the fluid input 21. This assures that there is no unnecessary restriction to flow of fluid when the valve is in the state shown in Figure 2(a). The diameter of each aperture is preferably substantially equal to the diameter of the fluid inputs 21. Since the valve shown in Figures 2(a) and 2(b) has 7 three fluid inputs, its closure member is provided with three sets of four apertures 22, one set of four apertures for each fluid input. The spacing between neighbouring sets of apertures is substantially equal to the spacing between neighbouring fluid inputs 21.

In the embodiment shown in Figure 2(a) three circumferential groves 22a are provided in the closure member 18, one each at a position corresponding to one of the sets of apertures 22. This feature has two advantages. Firstly, fluid entering the fluid input 21 is able to pass through the groove 22a and so can reach each of the four apertures 22 provided for that fluid input 2 1. This maximises the through area of the valve, thereby preventing unnecessary restrictions to fluid flow. Secondly, in a case where the closure member 18 can rotate relative to the valve body 16 providing the groove 22a ensures that operation of the valve is not affected if the closure member 18 should rotate relative to the valve body 16, since fluid entering one of the input ports 21 will be able to flow around the corresponding annular grove 22 to the apertures 22.

The apertures 22 and the grooves 22a are so positioned such that, when the closed end 18' of the closure member 18 is pushed against the closed end of the valve body 16 by the coil spring, each groove in the closure member is aligned with a respective input port 2 1. With the closure member in this position, fluid entering one of the input ports 21 is able to pass through the corresponding groove 22a in the valve body, flow around the groove to the corresponding apertures 22 in the valve body 18, and pass into the interior of the valve body. The fluid is then able to pass out of the valve body through the outlet port 23 provided in the end cap 19.

If the cross-section of the closure member is such that the closure member cannot rotate relative to the valve body, it would be possible not to provide the grooves 22a. It would, however, still be desirable to provide the grooves, since this would allow fluid entering a fluid input 21 to pass around a groove and thereby reach a number of apertures 22 in the closure member, thereby ensuring that there is no unnecessary restriction to the flow of fluid through the valve.

8 In the state shown in Figure 2(a), the pressure at the input 17 for control fluid is around atmospheric pressure. This is not sufficient to displace the closure member against the force exerted by the bias means, so that the grooves 22a are aligned with their respective input ports 21. Fluid entering one of the input ports is therefore able to flow around the respective grove 22a to the corresponding apertures 22, pass into the interior of the valve body 18, and subsequently pass out of the valve 15 through the outlet port 23.

In order to prevent fluid communication between the input ports 21 and the outlet port 23, it is necessary to apply to the input 17 for control fluid a fluid pressure that is sufficient to overcome the force exerted by the bias means 20. The results of doing this are shown in Figure 2(b). It will be seen that the effect of applying such a fluid pressure at the input 17 for control fluid is to force the closure member 18 away from the closed end 16' of the valve body 16, against the force exerted by the bias means (i.e., the coil spring 20). Because the closure member 18 has moved in the longitudinal direction of the valve relative to the valve body 16, the groves 22a and apertures 22 are no longer aligned with their respective input port 21. The input ports 21 are therefore closed by the valve body 18 which, as noted above, makes a fluid-tight fit against the valve body 16, so that fluid flowing into one of the fluid inputs 21 is blocked by the valve body 18. Thus, by applying a suitable fluid pressure at the input 17 for control fluid, it is possible to prevent fluid communication between the fluid inputs 21 and the fluid output 23.

The valve body 16 is provided with an output 24 for fluid entering the input 17 for control fluid. The output 24 for control fluid is positioned such that, when sufficient fluid pressure is applied to the input 17 for control fluid to displace the closure member against the force of the bias means, the output 24 for the control fluid is then opened. If the input 17 for control fluid is connected in the tell-tale of an engine, provision of the output 24 for control fluid ensures that the usual flow of used cooling water from the tell-tale will still be visible during normal operation of the engine.

When the valve of Figures 2(a) to 2(c) is used in connection with a postimmersion restart system of the type shown schematically in Figure 1, the valve 15 would be positioned at a lower level than the drain port(s) 10 of the engine to allow gravity 9 drainage from the drain port(s) 10 to the valve 15. The drain port 10 of each cylinder of the marine propulsion unit would be connected to one of the input ports 21. The number of input ports of the valve is preferably at least equal to the number of cylinders of the engine, since this enables the drain port of each cylinder to be connected to a separate input port of the valve. An engine having two cylinders would require a valve having at least two fluid input ports. A valve according to the invention having two input ports could be used, or a valve having three input ports could be used with one input port blanked-off. As a further example, an engine having six cylinders would require a valve having at least six fluid input ports or, as an alternative, two valves each with three input ports could be used with a six cylinder engine. While this means that two valves are needed for the engine, it does allow one valve to be used across a range of engines, rather than needing a large number of valves having different numbers of input ports.

Where a valve having three input ports 21 is used with a three cylinder engine, the drain port of one cylinder would be connected to one input port of the valve, the drain port of the second cylinder would be connected to a second input port of the valve, and the drain port of the third cylinder would be connected to the third input port of the valve.

The output of used cooling water from the tell-tale of the propulsion unit would be connected to the input 17 for control fluid. The strength of the bias means is chosen such that, when the engine is running normally, the flow of used cooling water into the input 17 for control fluid provides sufficient fluid pressure to displace the closure member 18 against the force of the bias means so as to close the input ports 21. That is, when the engine is running normally the valve would be in the state shown in Figure 2(b).

If the vessel were to capsize or submerge, and the engine fill with water as a result, the engine would stop running as a result of hydraulic locking. When the engine stops, the impeller or pump of the cooling system stops thereby stopping the flow of cooling water through the engine. As a result, the discharge of used cooling water through the telltale, and the flow of this water into the input 17 for control fluid, cease. As the fluid pressure exerted by the flow of used cooling water falls off, the bias means displaces the closure member 18 towards the closed end 16' of the valve body 16, thereby aligning the groves 22a with their respective input ports 21 and so opening communication between the input ports 21 and the outlet port 23. Once the boat had been righted, water trapped in the cylinders below the piston would then be able to drain out of the cylinder under gravity, through the drain port 10 of Figure 1, the input ports 21 of the valve 15, and the output port 23 of the valve.

Once the engine had been drained and restarted, the discharge of used cooling water through the tell-tale would re-commence. This would again displace the closure member against the bias means, thereby closing the ports 21 and so closing off the drain ports 10 of the engine.

The valve 15 of the present invention accordingly allows automatic draining of a marine propulsion unit to be accomplished.

The closure member can be displaced by applying a fluid - that is, a gas or liquid, pressure to the input 17 for control fluid. The end face 18a of the closed end 18' of the closure member is preferably concave as shown in Figures 2(a) and 2(b), since this increases the area over which the liquid pressure is initially exerted, and so increased the force that the liquid exerts on the closure member. If the end face 18a of the closed end 18' of the closure member were flat, when a fluid pressure was applied at the input 17 for control fluid, it would initially only be able to apply a pressure against an area of the end face 18a that was equal to the cross-section area of the input 17 for control fluid.

Figure 2(c) is a cross-section of the valve 15 in the state shown in Figure 2(a) along the line CC shown in Figure 2(a). This figure is a cross-section through the valve and through one of the input ports 21, when the input port 21 is open. Fluid entering the input port 21 can flow through the grove 22a around the circumference of the closure member 18, until it reaches the apertures 22. The fluid can then pass into the interior of the closure member through the apertures 22, and leave the valve through the output port 23.

11 In places where the groves 22a are not provided, the outer circumference of the closure member 18 is approximately equal to the inside diameter of the valve body 16. This is shown in broken lines in Figure 2(c). For clarity of the drawing, a gap is shown between the exterior of the closure member and the interior of the valve body 16. In reality, however, the exterior diameter of the closure member 18 is substantially equal to the interior diameter of the valve body so that the closure member 18 makes a fluidtight sliding seal with the valve body 16.

It is possible that some leakage of control fluid will occur between the valve body 16 and the closure member 18, particularly if a high pressure source of control fluid is used. The closure member 18 is therefore preferably provided with a further set of one or more apertures 25 which connects with a corresponding circumferential grove 25a provided in the exterior of the valve body 18. The grove 25a and the aperture(s) 25 are provided towards the closed end of the valve body 18. If any control fluid should leak between the valve body 16 and the closure member 18, it will be able to pass into the grove 25a and through the aperture(s) 25 into the interior of the closure member 18, and will subsequently pass out of the valve through the output 23 rather than back feeding through the fluid input ports 21.

The valve body 16, closure member 18 and end cap 19 can be made of any materials having the required strength and corrosion resistance. Suitable materials include, for example, brasses, bronzes, gun-metal, stainless steel or high strength plastics materials. It is not necessary for the valve body 16 and the closure member 18 to made of the same material, since the valve will generally operate over a limited temperature range so that differential thermal expansion/contraction of the valve body 16 and the closure member 18 is unlikely to be significant.

The invention has been described above with reference to one preferred embodiment. It will be understood, however, that the invention can be embodied in any other ways.

12 For example, in Figures 2(a) to 2(c) the valve bodies 16 and the closure member 18 both have the general form of a hollow cylinder. While this allows for easy manufacture of these components, it is in principle possible for the components to have other shapes. For example, the exterior cross-section of the valve body 18 could be rectangular, triangular, polygonal etc., with the valve body 16 having a complementary interior cross-section.

In the embodiment described above, the groves 22a, 25a are provided on the exterior of the closure member 18. It would, however, be possible for these groves to be provided instead on the interior of the valve body 16, as shown schematically in Figure 3. Alternatively, some of the groves 22a, 25a could be provided on the exterior of the closure member 18, with others being provided on the interior of the valve body 16.

In the embodiments described above a coil spring 20 is used to bias the closure member 18 towards the closed end of the valve body 16. The invention is not limited to a coil spring as the bias means, and any suitable bias means can be used.

Where a coil spring is used as the bias means, it is not necessary for it to bear against the closed end of the valve body 16 in the manner shown in Figure 2(a). It would alternatively be possible to use a larger diameter coil spring that was positioned between the valve body 18 and the end cap 19 as shown in Figure 4.

It is not necessary to provide an end cap 19 of the form shown in Figures 2(a), 2(b), 3 and 4. All that is necessary is to provide a means for retaining the bias member 20 and the closure member 18 within the valve body 16.

Where an end cap of the type shown in Figure 2(a) is provided, the end cap 19 can be secured to the valve body 18 by any suitable means. For example, in Figure 3 a screw thread is provided on the exterior of the reduced-diameter end portion 16a of the valve body. A complementary screw thread is provided on the inside of the end cap 19, so that the end cap 19 can simply be screwed onto the valve body 16.

13 In the embodiments described above, a separate set of one or more apertures 22 is provided for each of the fluid inputs 2 1. In an alternative embodiment, however, the closure member 18 is provided with one set of elongate apertures 26, with each elongate aperture being sufficiently long for it to be able to allow fluid entering any of the fluid inputs 22 to pass into the interior of the closure member 18. This embodiment is shown schematically in Figure 5. In this embodiment, a greater travel of the closure member 18 within the valve body'16 is required before the closure member 18 will seal off all the fluid inputs 22.

In Figure 5 a separate groove 22a for each fluid input 21 is provided in the exterior of the closure member 18. It would alternatively be possible to provide one groove having a length substantially equal to the length of the elongate aperture 26, and this is indicated in broken lines in Figure 5.

It will be seen that where a valve of the invention is used as a cylinder drain port 10 in a post-immersion restart system for a marine propulsion unit, the drain port 10 is not closed at the cylinder but is rather closed at the valve 15. It is therefore preferable for the valve 15 to be mounted as close as possible to the cylinders (subject to there being sufficient vertical drop between the drain port(s) 10 and the valve 15 to provide good gravity drainage), to minimise the dead space between the drain port 10 of the cylinder and the input port 21 of the valve.

Although the invention has been described with reference to preferred embodiments, the invention is not limited to the embodiments described above. For example, although the valve has been described with particular reference to operating the drain ports in a postimmersion restart system the invention is not limited to this application. If necessary for other applications, it would be possible to arrange the valve so that the fluid inputs 21 are closed when no fluid pressure (that is, no fluid pressure in excess of normal atmospheric pressure) is applied to the input for control fluid, and are opened if a sufficiently large fluid pressure is applied to the input for control fluid.

14

Claims (17)

CLAIMS:

1. A valve having a first fluid input; a fluid output; and a second fluid input; wherein fluid communication between the first fluid input and the fluid output is deten-nined by the fluid pressure at the second fluid input.

2. A valve as claimed in claim I wherein fluid communication between the first fluid input and the fluid output is established when the fluid pressure at the second fluid input is substantially atmospheric pressure, and wherein fluid communication between the first fluid input and the fluid output is substantially prevented when the fluid pressure at the second fluid input exceeds a predetermined value.

3. A valve as claimed in claim I or 2 and further comprising a control member movable between a first position in which it allows fluid communication between the first fluid input and the fluid output and a second position in which it substantially prevents fluid communication between the first fluid input and the fluid output, the fluid pressure at the second fluid input determining whether the control member is in the first or second position.

4. A valve as claimed in claim 3 and further comprising bias means for biasing the control member towards one of its first and second positions.

5. A valve as claimed in claim 4 wherein the bias means biases the control member towards its first position.

A valve as claimed in claim 3, 4 or 5 wherein the control member is disposed within a valve body, the first fluid input and the fluid output being provided in the valve body.

7. A valve as claimed in claim 6 wherein the control member is slidingly disposed within the valve body.

8. A valve as claimed in claim 6 or 7 wherein the control member makes a substantially fluid-tight seal against the valve body.

9. A valve as claimed in claim 6, 7 or 8 wherein the control member has a hollow interior and comprises at least one through-hole, the through-hole being so positioned that fluid entering the first fluid input is able to pass into the hollow interior of the control member via the through-hole when the control member is in its first position.

10. A valve as claimed in claim 9 and further comprising a circumferential groove disposed on the exterior of the control member, the groove communicating with the through-hole.

11. A valve as claimed in any of claims 3 to 10 wherein a fluid pressure at the second fluid input is exerted on a part of the control member that is concave.

12. A valve as claimed in any preceding claim and comprising an outlet for fluid entering the second fluid input, the outlet for fluid entering the second fluid input being open when fluid communication between the first fluid input and the fluid output is substantially prevented

13. A valve substantially as described herein with reference to Figures 2(a) to 2(c) of the accompanying drawings, to Figure 3 of the accompanying drawings, to Figure 4 of the accompanying drawings, or to Figure 5 of the accompanying drawings.

14. A marine propulsion unit comprising a valve as defined in any of claims 1 to 13.

15. A marine propulsion unit as claimed in claim 14, wherein the propulsion unit is a water-cooled propulsion unit, and wherein the fluid pressure at the second fluid input is derived from the flow of water in the cooling system of the propulsion unit.

16 16. A marine propulsion unit as claimed in claim 15 wherein the output from the cooling system of the propulsion unit is connected to the second fluid input of the valve.

17. A marine propulsion unit as claimed in any of claims 14 to 16 wherein the cylinder or at least one cylinder of the propulsion unit is provided with a drain port, the drain port being connected to the first fluid input of the valve.