Field of the Invention

The present invention concerns hydraulic manifolds.

Background of the Invention

Hydraulic manifolds are devices which regulate the flow of fluid in a hydraulic system, between source components such as pumps and accumulators, and output power devices such as motors and actuators.

Hydraulic manifolds usually have a monolithic metallic structure which is either machined from billet, cast or forged. Typically, they contain one or more of valves and fluid pathways connecting the valves to an outside pressure source. The fluid pathways are provided either by material removal during machining, or by creation of voids, during casting.

A common problem in use, is failure of the hydraulic manifold through repeated pressure cycling. A fatigue crack in the hydraulic manifold can propagate, providing a pathway between high pressure galleries and atmosphere. High pressure fluid exiting a cracked manifold can form an atomised spray. This can pose a risk to operators because the spray is highly flammable. In addition, the atomised spray can penetrate skin, with serious medical consequences .

To reduce the risk of harm to the operator in the event of failure, secondary protection is often provided in the form of personal protective equipment. In

addition, there may be a separate barrier provided between the hydraulic manifold and the operator. Such personal protective equipment is, however, cumbersome and difficult to use, and providing a separate barrier requires an additional component to be provided, increasing the weight and cost of the product.

The present invention seeks to mitigate the above- mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved hydraulic manifold.

Summary of the Invention

The present invention provides, according to a first aspect, a hydraulic manifold formed in one piece and comprising an exterior wall defining an inner space within which there is at least one flow gallery for conveying hydraulic fluid, the flow gallery providing a fluid flow path and being bounded by a boundary wall, the boundary wall being spaced inwardly from the exterior wall .

The invention recognises that an exterior wall may be provided integrally with a hydraulic manifold, to minimise the risk of atomised fluid being expelled from the hydraulic manifold in a damaging way in the event of structural failure of the hydraulic manifold. Compared to hydraulic manifolds of the prior art, the hydraulic manifold of the present invention may be used safely without separate components such as a separate barrier wall or personal protective equipment. The present invention therefore provides a simple and effective solution for safeguarding operators in the event of failure of the hydraulic manifold.

There may be a plurality of flow galleries within the hydraulic manifold. The flow galleries may

interconnect, for example adjoining other flow galleries and/or branching into further flow galleries. Some of the flow galleries may contain hydraulic fluid at high pressure, for example in excess of 25 bar. Some of the flow galleries may contain hydraulic fluid at high pressure, for example in excess of 50 bar. Some of the flow galleries may contain hydraulic fluid at low

pressure, for example, less than 25 bar. Some of the flow galleries may connect with a high pressure fluid inlet to the hydraulic manifold, and some of the flow galleries may connect with a low pressure fluid outlet from the hydraulic manifold. Some of the flow galleries may connect with a control valve within the hydraulic manifold.

The exterior wall may be a wall which extends around the periphery of the hydraulic manifold. When it is oriented in an upright position (although it could feasibly have any orientation in use) , the hydraulic manifold may have identifiable sides and a top and bottom. The exterior wall may extend around

substantially all of the sides of the hydraulic manifold. The exterior wall may extend over the top of the

hydraulic manifold, or alternatively may not extend over the top of the hydraulic manifold. The hydraulic

manifold may be substantially open (i.e. exposed) across its top. The exterior wall may extend over substantially all of the bottom of the hydraulic manifold, or

alternatively may not extend over substantially all of the bottom of the hydraulic manifold.

The hydraulic manifold may be configured to attach to a lid. For example, the exterior wall may be shaped to provide a rim onto which a lid may be fitted. When the lid is attached to the hydraulic manifold, the inner space may be at least partially enclosed, and may be fully enclosed by a combination of the lid and the exterior wall, apart from inlet or outlet ports.

The exterior wall may have a flat outer face, for example a flat bottom face. The manifold may be

configured to be mounted on a flat interface plate of an external component. For example, the hydraulic manifold may include bolt holes, for example passing through the manifold and surrounded by the exterior wall, through which bolts may be fitted to attach the hydraulic

manifold to the interface plate. One or more flow galleries may enter/exit the manifold at the flat outer face of the exterior wall.

When the lid is attached to the hydraulic manifold and the hydraulic manifold is attached to the interface plate of the external component, the inner space may be at least partially enclosed, and may be fully enclosed by a combination of the lid and the exterior wall and the interface plate. Fully enclosed in this context should be understood to mean that in use, there is a secondary layer provided on all sides of the hydraulic manifold, whether by the exterior wall or by the lid or interface plate so as to retain hydraulic fluid in the event of failure of the primary containment. Thus the term "fully enclosed" still allows for there to be fluid flow paths defined by flow galleries between the interior and exterior of the manifold. In use, any open ports for example fluid inlet and/or outlet conduits would be connected as appropriate to a hydraulic fluid source, sink or service.

The exterior wall may have a thickness of less than 5 mm, for example less than 2 mm over the majority of its external surface area. The exterior wall may have a thickness of less than 1 mm or less than 0.7 mm, for example between 0.3 and 0.6 mm over the majority of its external surface area. The exterior wall may therefore provide the advantage of providing a safety barrier in the event of failure, whilst adding relatively little additional weight and cost to the hydraulic manifold.

The thickness of the exterior wall may vary or may be constant over the majority of its external surface area.

The boundary wall may extend along the majority of the length of the flow gallery. The length of the flow gallery may be defined as the uninterrupted part between the beginning of the gallery where it adjoins a part for example a further flow gallery or inlet port, and the end of the gallery where it adjoins another part for example a further flow gallery, outlet port or valve port. The majority of its length may be more than 50% of its length, for example more than 70% of its length. The majority of its length may be more than 90% of its length .

The boundary wall may provide a primary containment for the hydraulic fluid in the flow gallery. The

boundary wall, along with any further boundary walls and other internal structures of the hydraulic manifold may provide a primary containment for the hydraulic fluid in the hydraulic manifold. The exterior wall may provide a secondary containment for the hydraulic fluid in the hydraulic manifold.

The boundary wall may have a thickness of less than 2 mm along the majority of its length. The boundary wall may have a thickness of less than 0.2 mm along the majority of its length, for example for a hydraulic fluid pressure of up to 70 bar. The length of the boundary wall may be defined as the length corresponding to the length of the flow gallery. The majority of its length may be more than 50% of its length, for example more than more than 90% of its length. The thickness of the boundary wall may be constant along the majority of its length. The thickness of the boundary wall may vary along the majority of its length.

At least half of the inner space may be hollow.

At least 70% of the inner space may be hollow. Such hollow space includes the flow galleries within the boundary walls.

In the event of failure of the hydraulic manifold structure (for example in the event of a crack forming in a boundary wall), the inner space which is hollow may fill with hydraulic fluid, thereby acting as a reservoir to temporarily store the leaked hydraulic fluid. The exterior wall may therefore substantially contain the leaked fluid in the hydraulic manifold for a temporary period. The exterior wall may prevent the expelling of a damaging spray of hydraulic fluid (which might be at high pressure) from the hydraulic manifold, instead allowing the controlled release of the leaked hydraulic fluid.

The boundary wall, along the majority of its length, may be spaced inwardly from the exterior wall. The boundary wall may be spaced inwardly from the exterior wall along its entire length. The boundary wall may be spaced apart from the exterior wall by more than 5 mm along the majority of its length. Spacing apart the boundary wall (from the exterior wall) along the majority of its length may reduce the risk of any crack which has formed in the boundary wall extending to the exterior wall, thereby providing double containment over the majority of the external surface area of the hydraulic manifold. In use, for example when the hydraulic

manifold is fitted to a lid and/or an interface plate, double containment may be provided over the entire external surface area of the hydraulic manifold (because in regions where the exterior wall is not provided, or in regions where the boundary walls are joined to the exterior wall such that there is no spacing apart, there is additional protection provided by the adjoining lid and/or interface plate) .

The boundary wall, along the majority of its length, may extend around the whole circumference of the flow gallery. The boundary wall, along a short part of its length, may extend around part of the circumference of the flow gallery, for example at a point of connection to an internal component of the hydraulic manifold, or at a point of connection to a port, for example a fluid inlet or outlet, or in the region of a branching of a flow gallery .

The boundary wall may be joined along part of its length to the exterior wall. Such joining portions may provide structural support to the components inside the hydraulic manifold. Such joining portions may typically be provided in regions of low pressure (e.g. around a low pressure gallery) and/or in regions which would

ordinarily be covered by a lid or interface plate in use. The risk of an atomised spray exiting the hydraulic manifold may therefore be small, even if there is no "second skin" in certain regions where the boundary wall is joined to the exterior wall. There may be very few or zero joining portions provided around the sides of the hydraulic manifold, where the risk of an atomised spray exiting the hydraulic manifold may be higher (due to the absence of any protection provided by a further component such as a lid or interface plate) . In other words, there may be a separation between the exterior wall of the hydraulic manifold and the inner components of the hydraulic manifold around substantially all of the sides of the hydraulic manifold. There may be at least one port into the hydraulic manifold, and the hydraulic manifold may be configured to be attached to a connecting part of an external component at the port. The ports may be located on any of the top, bottom or sides of the hydraulic manifold. Preferably the ports are confined to the top and bottom of the hydraulic manifold.

A port may for example be an access port allowing access to the interior of the manifold, for example to enable a valve to be installed in the manifold. Such a port may be closed by a plug, cap or other closure member

A port may for example be a fluid inlet or outlet. One or more fluid inlets and outlets may be located on the bottom (i.e. on the underside) of the hydraulic manifold.

The hydraulic manifold may be configured to form a screw-thread seal with an external component. The screw- thread seal may provide a fluid-restrictive (i.e. a tortuous or labyrinth) path to fluid exiting the

hydraulic manifold. A fluid-restrictive path may be a path through which hydraulic fluid is forced to travel slowly and suffers a substantial pressure reduction along the path. Fluid exiting the hydraulic manifold via the fluid-restrictive path may be in liquid drops, and therefore may provide a visual indication of failure to the operator.

The fluid-restrictive path may begin at a point inside the external surface of the hydraulic manifold (e.g. at the innermost point where the external component is inserted within the hydraulic manifold) and end at a point outside the external surface of the hydraulic manifold. The helical length of the fluid-restrictive path may be more than ten times greater than the width of the gap through which the fluid must pass. The helical length of the fluid-restrictive path may be more than twenty times greater than the width of the gap through which the fluid must pass. If the fluid-restrictive path is wider, then the path must also be longer to produce the same pressure reduction effect. The screw-thread seal may comprise a sealing member, for example an O-ring seal .

The hydraulic manifold may be configured to form a face seal with the external component. An interface between an outer surface of the hydraulic manifold and an adjoining surface of the external component may provide a fluid-restrictive path to fluid exiting the hydraulic manifold. The interface may be an interface of two plain surfaces. The length of the fluid-restrictive path may be more than ten times greater than the width of the gap between the surfaces through which the fluid must pass. The length of the fluid-restrictive path may be more than twenty times greater than the width of the gap between the surfaces through which the fluid must pass.

The hydraulic manifold may be configured to form a diameter seal with the external component. An interface between an outer surface of the hydraulic manifold and an adjoining surface of the external component may provide a fluid-restrictive path to fluid exiting the hydraulic manifold. The length of the fluid-restrictive path may be more than ten times greater than the width of the gap between the surfaces through which the fluid must pass. The length of the fluid-restrictive path may be more than twenty times greater than the width of the gap between the surfaces through which the fluid must pass. The fluid-restrictive path may begin at a point inside the hydraulic manifold and end at a point outside the outer surface of the exterior wall of the hydraulic manifold. There may be a plurality of flow galleries for conveying hydraulic fluid, the flow galleries having boundary walls. Some of the flow galleries may be high pressure galleries. Some of the flow galleries may be low pressure galleries. Each of the flow galleries may have any of the features described in relation to a single flow gallery.

The hydraulic manifold may have been made by

additive manufacturing. Forming a hydraulic manifold by additive manufacturing may be a convenient way of forming the hydraulic manifold in one piece, with an exterior wall. Such a technique may overcome problems associated with traditional manufacturing techniques. Forming a hydraulic manifold by additive manufacturing may enable significant scaling down of the component sizes. Some of the interior components of the hydraulic manifold may be formed by alternative manufacturing techniques, for example machining, or the hydraulic manifold and its internal components may be entirely formed by additive manufacturing .

The present invention provides, according to a second aspect, use of a hydraulic manifold as described, containing hydraulic fluid at a pressure of more than 25 bar .

The present invention provides, according to a third aspect, a method of making a hydraulic manifold as described, wherein the hydraulic manifold is made in one piece by additive manufacturing.

The present invention provides according to a fourth aspect, a kit of parts comprising: a hydraulic manifold formed in one piece and comprising an exterior wall defining an inner space within which there is at least one flow gallery for conveying hydraulic fluid, the flow gallery providing a fluid flow path and being bounded by a boundary wall, the boundary wall being spaced apart from the exterior wall; and a lid.

The present invention provides according to a fifth aspect, a hydraulic manifold assembly comprising: a hydraulic manifold formed in one piece and comprising an exterior wall defining an inner space within which there is at least one flow gallery for conveying hydraulic fluid, the flow gallery providing a fluid flow path and being bounded by a boundary wall, the boundary wall being spaced apart from the exterior wall; a lid fitted to the hydraulic manifold thereby enclosing the inner space.

The inner space may be fully enclosed by a

combination of the exterior wall and the lid. The inner space may be partially enclosed by a combination of the exterior wall and the lid, and the hydraulic manifold may be configured to be attached to an interface plate of a separate component, and the inner space may be fully enclosed when the hydraulic manifold is attached to the interface plate.

The present invention provides according to a sixth aspect, a hydraulic manifold comprising: a cover defining an enclosed space within which there is at least one flow gallery for conveying hydraulic fluid, the flow gallery providing a fluid flow path and being bounded by a boundary wall, the boundary wall being spaced inwardly from the cover along the majority of its length. The cover may be an aluminium cover. The cover may be formed of several panels, or may be formed of one piece. The cover may extend around the sides of the hydraulic manifold, or may extend around the sides and the top and/or bottom of the hydraulic manifold. The cover may be between 1 to 1.5 mm thick over the majority of its external surface area. The present invention provides according to a seventh aspect, a computer-readable medium having

computer-executable instructions adapted to cause a 3D printer to print a hydraulic manifold suitable for use as the hydraulic manifold described above.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the features described with reference to the apparatus of the invention may incorporate any of the features described with reference to the method of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 is a cross-sectional top view of a hydraulic manifold according to a first embodiment of the invention;

Figure 2 is a perspective view of the cross-section of the hydraulic manifold of Figure 1;

Figure 3 is a different cross-sectional top view of the hydraulic manifold of the first embodiment of the invention;

Figure 4a is a cross-sectional view of a screw-thread join between the hydraulic manifold of the first embodiment of the invention and another part, at a fluid inlet/outlet;

Figure 4b is a cross-sectional view of a screw-thread join between the hydraulic manifold of the first embodiment of the invention and another part, at an access port;

Figure 5 is a cross-sectional view of a face seal join between the hydraulic manifold of the first embodiment of the invention and another part, at a fluid inlet/outlet ;

Figure 6 is a cross-sectional view of a diameter seal join between the hydraulic manifold of the first embodiment of the invention and another part, at a fluid inlet/outlet;

Figure 7 is a cross-sectional side view of the

hydraulic manifold of the first embodiment of the invention, with a lid fitted;

Figure 8 is a perspective view of the cross-section of the hydraulic manifold of Figure 7;

Figure 9 is a perspective view of the hydraulic

manifold of the first embodiment of the invention;

Figure 10 is a bottom view of the hydraulic manifold of the first embodiment of the invention;

Figure 11 is a cross-sectional top view of a hydraulic manifold according to a second embodiment of the invention; and

Figure 12 is a perspective view of the cross-section of the hydraulic manifold of Figure 11.

Detailed Description

A hydraulic manifold 1 according to a first example embodiment of the invention (Figures 1 and 2) has been formed using additive manufacturing techniques. It has a homogeneous steel structure, but in alternative

embodiments may be formed from other metals, such as aluminium, or brass. The hydraulic manifold 1 is

suitable for deployment in a wide range of applications such as in injection moulding and seismology testing systems. Outside of the hydraulic manifold 1 is

atmosphere "A".

The hydraulic manifold 1 is formed of a number of galleries 11 in fluid connection with a rotary-linear valve (not visible in Figures 1 and 2) . The valve comprises a rotary electric motor (not visible in Figures 1 and 2) which powers a linear hydraulic control valve (not visible in Figures 1 and 2) . The valve has four control ports (6a, 6b, 6c, 6d) supplying pressure (6a), return (6b) and first and second service (6c, 6d) connections. In use, high pressure fluid enters the hydraulic manifold 1 from an external pressure source such as a pump or accumulator (not shown) , through an input gallery (not visible in Figures 1 and 2) and flows via the input port (6a) to the valve. The relative position of the valve spool (not shown) within the sleeve (not visible in Figures 1 and 2) controls the flow of fluid through the valve to the first service port (6c), through a first service gallery (not visible in Figures 1 and 2) and out of the hydraulic manifold 1 to an end component such as a motor or actuator (not shown) . Upon returning, metered fluid enters the hydraulic manifold 1 through a second service gallery (not visible in Figures 1 and 2) through the second service port (6d) and through the valve to the return port (6b) . Ultimately, the fluid exits the hydraulic manifold 1 through a return gallery (not visible in Figures 1 and 2) .

The flow galleries 11 are bounded by thin boundary walls, approximately 0.8 mm thick, which provide primary containment of the hydraulic fluid within the flow galleries 11 (and therefore within the hydraulic manifold 1) ·

The cavity 3 within the hydraulic manifold 1 which is not occupied by galleries 11 or other physical components of the valve or motor, is hollow. At the outer surface of the hydraulic manifold 1, is an outer skin 9. The outer skin 9 encloses the physical

components of the hydraulic manifold 1 within the cavity 3. The hydraulic manifold 1 of the first example

embodiment is approximately 73% hollow.

The outer skin 9 has an average thickness of approximately 0.5 mm, and is formed in one piece with the inner portions of the hydraulic manifold 1. Whereas the boundary walls 7 of the flow galleries 11 provide primary containment to the hydraulic fluid, the outer skin 9 provides secondary containment. In the event of a fatigue crack occurring within the hydraulic manifold 1 causing hydraulic fluid to leak from one of the flow galleries 11, the hydraulic fluid floods the cavity 3 and is retained by the outer skin 9. If the failure occurs in a region of high pressure, any fluid spray is

contained within the outer skin 9 and does not exit the hydraulic manifold 1. Such a feature contrasts with manifold designs of the prior art, which require

additional protective measures to deal with such high pressure spray formation.

The outer skin 9 is joined to the inner components of the hydraulic manifold 1 only at certain designated low-pressure regions (for example around low pressure galleries) of the hydraulic manifold 1. Thus, the risk associated with failure in regions of high pressure is always mitigated by the double containment. The low pressure fluid does not present a vaporised fluid fire risk, or skin penetration risk, and therefore low pressure fluid return galleries do not necessarily require a second barrier structure. As such, they may be used as connection points to provide structural support within the hydraulic manifold 1. In any case, the design of the hydraulic manifold 1 of the first example

embodiment of the invention is such that any joining portions (i.e. regions where there is no "second skin" because the gallery boundary wall is attached to the outer skin) are confined to the lower surface of the manifold 1 which would tend to be attached to an

interface plate during use. Therefore, secondary

containment is provided by the external component, where it is not provided by the outer skin.

The hydraulic manifold 1 is fixed on top of an interface plate (not shown) by bolts in bolt holes 4. Further bolts in bolt holes 5 enable a lid (not shown) to be attached to the top of the hydraulic manifold 1. Thus when in situ, on the upper and lower surfaces (i.e. the top and the bottom respectively) of the hydraulic

manifold 1, there is containment provided by other external structures. The outer skin 9 therefore is of primary importance around the sides of the hydraulic manifold 1.

In the particular cross-section shown, the hydraulic manifold 1 includes a housing for a bearing 12, and support structures 10 which are used for supporting the formation of galleries 11 during the additive

manufacturing process. In the particular cross-section shown, the hydraulic manifold 1 also includes a solid structure 8 protruding into the hydraulic manifold 1 interior from the outer skin 9. The solid structure 8 provides a connection point between the outer skin 9 and the inner components of the hydraulic manifold 1, in a region of low pressure. Figure 3 shows a cross-sectional slice of the hydraulic manifold 1 of the first example embodiment taken on a different plane from that of Figure 1. In Figure 3, a linear hydraulic control valve 13 is visible centrally within the hydraulic manifold 1. A control bore 14 of the valve 13 contains control ports 16 into which hydraulic fluid flows through galleries 11. An access port 19 is provided for assembly of parts during manufacture (i.e. enabling the valve components to be fitted within the hydraulic manifold 1) . The access port 19 is filled with a plug 15, fitted after additive manufacturing and assembly. The plug 15 is sealed to the hydraulic manifold by an O-ring 17. In the region of the access port 19, the outer skin 9 thus extends into the interior of the hydraulic manifold 1, where it joins the inner manifold components. Such region is low pressure, being comparatively distant from any high pressure galleries. Thus in the event of a leakage through the seal occurring, only low pressure fluid would be exposed to atmosphere. The plug/ manifold interface is, however, designed to cope with high pressure fluid, providing a tortuous path to fluid exiting the hydraulic manifold via the interface between the parts. Thus, in the event of leakage of high pressure fluid through the seal, or failure of the seal entirely, high pressure fluid would not exit the hydraulic manifold 1 in a spray, but rather in a controlled form in liquid drops.

The hydraulic manifold 1 contains several access ports 19 (only one visible in Figure 3) to facilitate access to the hydraulic manifold interior during

assembly, or maintenance. The hydraulic manifold 1 also contains several inlet and outlet ports (not visible in Figure 3) for transporting hydraulic fluid into and out of the hydraulic manifold 1. Figure 4a shows a screw-thread join 21 between an external component 23 in a fluid inlet/outlet, and the outer skin 9. The component 23 is open-ended to permit fluid to flow in and out of the hydraulic manifold. The join 21 is sealed by a rubber O-ring 25. The seal is designed so that the risk of high pressure spray

formation in the event of leakage or structural failure is reduced. For example, high pressure fluid leaking into the join between the outer skin 9 and component 23, would follow a tortuous path along the interface between the respective parts (9, 23) to reach atmosphere. In the present example, the tortuous path is provided by the relatively long screw-thread. Consequently, any

hydraulic fluid exiting the hydraulic manifold would be sufficiently low in pressure so as to form liquid drops (rather than an atomised spray) . Similarly, in the event of failure of the O-ring 25, fluid would follow a

tortuous path, and be prevented from exiting the

hydraulic manifold quickly. Finally, in the event of failure within the hydraulic manifold causing fluid to flood into the cavity provided by the outer skin 9, the fluid would again be prevented from exiting the hydraulic manifold in a spray in the region of the sealed component 23.

Figure 4b shows a screw-thread join 21a between an external component 23a in an access port, and the outer skin 9. The external component 23a is capped to close the fluid path out of the hydraulic manifold. The join 21a is sealed by a rubber O-ring 25a. Whilst such access ports provided for access or maintenance are typically located in regions of low pressure so that any leakage does not form a high pressure spray, the join 21a is designed so that, even if the access port is located in a region of high pressure, there can be no high pressure spray formation. For example, high pressure fluid leaking into the join 21a between the outer skin 9 and the component 23a, would follow a tortuous path along the interface between the respective parts (9, 23a) to reach atmosphere. In the present example, the tortuous path is provided by the relatively long screw-thread join.

Consequently, any fluid exiting the hydraulic manifold would be sufficiently low in pressure so as to form drops of fluid. Similarly, in the event of failure of the 0- ring 25a, fluid would follow a tortuous path, and be prevented from exiting the hydraulic manifold quickly. Finally, in the event of failure within the hydraulic manifold causing fluid to flood into the cavity provided by the outer skin 9, the fluid would again be prevented from exiting the hydraulic manifold in a spray in the region of the sealed component 23a.

Figure 5 shows a face seal join 21' between an external component 23' providing an inlet/outlet, and the outer skin 9' . The join 21' is sealed by a rubber O-ring 25'. Similar to the screw-thread joins 21, 21a of

Figures 4a, 4b, any fluid leaking into the join 21' will follow a long path between the outer surface of the outer skin 9' and the adjacent surface of the component 23' before reaching atmosphere, thereby forming drops rather than a spray. In the present example, the long path is provided by the relatively wide interface between the joining faces of the outer skin 9' and the component 23' . Such fluid leakage may be low-level leakage in use, or may be as a result of failure of the seal 25' , or failure of an internal component within the hydraulic manifold (causing the hydraulic manifold cavity to flood) .

Figure 6 shows a diameter seal join 21'' between an external component 23' ' providing an inlet/outlet, and the outer skin 9''. The join 21'' is sealed by a rubber O-ring 25' ' . Similar to the screw-thread joins 21, 21a, of Figures 4a, 4b, any fluid leaking into the join 21'' will follow a long path between the outer surface of the outer skin 9'' and the adjacent surface of the component 23' ' before reaching atmosphere, thereby forming drops rather than a spray. In the present example, the long path is provided by the relatively wide interface between the joining faces on the outside of the hydraulic

manifold 1, coupled with the relatively long interface between the joining faces extending into the hydraulic manifold 1. Such fluid leakage may be low-level leakage in use, or may be as a result of failure of the seal 25' ' , or failure of an internal component within the hydraulic manifold (causing the hydraulic manifold cavity to flood) .

Figure 7 is a cross-sectional side view of the hydraulic manifold 1 of the first example embodiment. Eight control ports 16 are shown in diametrically opposed pairs, surrounding the central control bore 14 (the control bore having five layers of control ports in an axial direction, as shown in Figure 3) . Various

galleries 11 are provided within the hydraulic manifold 1 amongst regions of empty space. A lid 18 is fitted above the hydraulic manifold 1, attached at a rim 28 on the upper edge of the side walls 30 of the hydraulic manifold 1. The lid 18 and outer skin 9 together provide an enclosed space inside the hydraulic manifold 1 (although there are various ports into the underside of the

hydraulic manifold which are not visible) . The bottom face 32 (i.e. the underside) of the hydraulic manifold 1 is flat, being substantially covered by the outer skin 9 (which may be broken only to allow for fluid inlet/outlet ports into the manifold 1) . The bottom face 32 of the hydraulic manifold 1 is suitable for being attached to an interface plate (not shown) of a further component, having bolt holes (not visible in Figure 7) matching bolt holes in the further component. In order that the various ports (not visible in Figure 7) into the

hydraulic manifold 1 on the underside 32 of the hydraulic manifold 1 do not present a risk of allowing a high pressure spray to be ejected from the hydraulic manifold 1, the interface plate is typically at least as wide and as deep as the underside of the hydraulic manifold 1.

An advantageous function provided by the outer skin 9 is secondary containment in regions where there is no protection afforded by external structures i.e. around the sides of the hydraulic manifold 1. Whilst at the bottom of the hydraulic manifold 1, the outer skin 9 is joined to the boundary walls 7 of the inner galleries 11 in several locations by physical structures 27, around the sides of the hydraulic manifold 1, the outer skin 9 is separated from the boundary walls 7 by empty space 3, thereby providing distinct and separate containment (i.e. if a high pressure gallery boundary wall fails, the crack will not propagate through to any exposed part of the manifold) .

Figure 8 shows a perspective view of the cross- section of the hydraulic manifold 1 of Figure 7. A piston bore 29 is shown. Physical stops 31 are provided to prevent extremes of travel of the piston spool in use (in addition to electronically controlled soft stops) . A rim 28 extends around the circumference of the upper edge of the sides walls 30 of the hydraulic manifold 1.

Figure 9 shows a perspective view of the exterior of the hydraulic manifold 1 of the first embodiment of the invention. The side walls 30 extend fully around the sides of the hydraulic manifold 1. As described above in relation to Figure 7, the underside 32 of the hydraulic manifold 1 is flat, suitable for mounting on a flat interface plate of a separate component. The top 34 of the hydraulic manifold 1 is open, having no outer skin.

In the example embodiment, the outer skin 9 extends around the sides 30 and bottom 32 of the hydraulic manifold 1 but does not extend across the top 34 of the hydraulic manifold 1. The upper edge of the sides 30 of the hydraulic manifold is shaped to provide a rim 28 onto which a lid (not shown) may be fitted. In use, a second skin is provided on all sides of the hydraulic manifold, whether by the outer skin 9 or by the lid.

Figure 10 shows the underside 32 of the hydraulic manifold 1 of the first example embodiment of the

invention. The underside 32 is a flat face of the outer skin 9, and has four bolt holes 4 for attaching the hydraulic manifold 1 to a flat interface plate of an external component (not shown) . Further bolt holes 5 are provided for attaching a lid (not visible in Figure 10) to the hydraulic manifold 1. Four inlet/outlets ports 36 are provided for connecting a high pressure source and sink, and a service to the hydraulic manifold 1. In the example embodiment, the inlets and outlets 36 are sealed by a face seal (as shown in Figure 5) or a diameter seal (as shown in Figure 6) . The fluid restrictive path to atmosphere "A" is provided by the relatively long path between the closely adjoining surfaces of the underside 32 of the hydraulic manifold 1 and the interface plate 9 (not shown in Figure 10) . The interface plate therefore corresponds with the external component (23' , 23' ' ) of either Figure 5 or Figure 6.

Figure 11 shows a hydraulic manifold 101 according to a second example embodiment, also formed by additive manufacturing. Like components are provided with similar reference numerals, but increased by 100. The hydraulic manifold 101 is a bespoke subsystem provided for an integrated actuator design. The hydraulic manifold 101 has two control valves 113, separated across the

hydraulic manifold 101 by empty space 103 (i.e. having no crack propagation path between the valves 113) . The valves 113 have separate hydraulic supplies, with no hydraulic components in common. The valves are sealed by rubber O-ring seals 125. The hydraulic manifold 101 is fixed within the integrated actuator (not shown) by bolts in bolt holes 104. The hydraulic manifold 101 has various flow galleries 111 surrounding a central piston bore 129, the flow galleries 111 having boundary walls 107.

Figure 12 shows a perspective view of the cross- section of the hydraulic manifold of Figure 11, and shows for example, the recess 126 in which the seal 125 is located .

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different

variations not specifically illustrated herein.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable,

advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.