Technical Field

The present disclosure relates generally to hydraulic cylinder systems which include pre-fill valves.

Background

Pre-fiU valves are used to control the flow of hydraulic fluid into and out of a cylinder bore of a main hydraulic cylinder, such as a press cylinder. The pre-fill valve is typically mounted at a base end of the main hydraulic cylinder and controls the flow of hydraulic fluid between the cylinder bore of the main hydraulic cylinder and a hydraulic fluid reservoir. When a piston of the main hydraulic cylinder is extended, the pre-fill valve opens to allow hydraulic fluid to rapidly flow from the reservoir into the cylinder bore of the main hydraulic cylinder. Typically, the piston of the main hydraulic cylinder is rather quickly extended from a retracted position to a given staging position (e.g., a press position). When the piston reaches the intermediate position, the pre-fill valve is closed. With the pre-fill valve closed, the region of the cylinder bore of the main hydraulic cylinder axially between the piston head of the main hydraulic cylinder and the pre-fill valve is pressurized by a separate pressurization source to force the main piston further in the extension direction for high pressure pressing or other purpose. After the high pressure pressing or other function has taken place, the piston of the main hydraulic cylinder is retracted. During retraction the pre-fill valve is opened to allow hydraulic fluid to rapidly flow from the cylinder bore of the main hydraulic cylinder back into the reservoir.

A typical pre-fill valve includes a poppet that engages a valve seat when in a closed position. The poppet is offset from the valve seat when in an open position. The poppet is moved by a pre-fill hydraulic cylinder mounted at least partially within the hydraulic fluid reservoir. Alignment errors between the piston of the pre-fill hydraulic cylinder and a central axis of the valve seat, alignment errors between the mounting surface of the pre-fill hydraulic cylinder and a corresponding mounting surface of the end cap, and/or alignment errors between a piston of the pre-fill hydraulic cylinder and a sleeve of the pre-fill hydraulic cylinder can result in improper seating of the poppet on the valve seat, thereby resulting in leakage. Improvements are needed in this area.

Summary'

One aspect of the present disclosure relates to a pre-fill hydraulic cylinder for moving a poppet of a pre-fill valve relative to a valve seat. The pre-fill valve can be configured to open and close fluid communication between a main hydraulic cylinder and a hydraulic fluid reservoir. The pre-fill hydraulic cylinder has selected clearances between a piston of the pre-fill hydraulic cylinder and a cylinder body of the pre-fill hydraulic cylinder. The clearances are adapted to facilitate establishing proper alignment between the piston of the pre-fill hydraulic cylinder and the valve seat. In certain examples, alignment between the pre-fill cylinder piston and a central axis of the valve seat is established by a close running clearance fit between the piston rod of the pre-fill hydraulic cylinder and a piston locating bore defined by an end cap of the main hydraulic cylinder. Preferably, the pre-fill hydraulic cylinder is designed with tolerances and clearances designed to be compatible with the alignment established by the piston locating bore of the main cylinder end cap. For example, the pre-fill hydraulic cylinder can be designed with a hydraulic cylinder body having an enlarged cylinder bore and an enlarged opening through the cylinder head which are configured to eliminate contact between the piston of the hydraulic pre-fill cylinder and the hydraulic cylinder body of the pre-fill hydraulic cylinder. Elimination of contact points helps reduce the risk of concentricity errors as the piston of the pre-fill hydraulic cylinder strokes within the hydraulic cylinder body of the pre-fill hydraulic cylinder. Additionally, the pre-fill hydraulic cylinder can be mounted to the end cap of the main hydraulic cylinder by a fastening configuration that allows the mounting location of the pre-fill hydraulic cylinder to be radially adjusted. Another aspect of the present disclosure relates to a pre-fill hydraulic cylinder having a piston adapted to be coupled to a pre-fill valve poppet. The piston of the pre-fill hydraulic cylinder is movable between an extended position and a retracted position. In one example, the pre-fill valve poppet is moved to an open position when the piston is extended and is moved to a closed position when the piston is retracted. In one example, the pre-fill hydraulic cylinder is a single acting cylinder, and at least one spring is used to move the piston from the extended position to the retracted position.

Another aspect of the present disclosure relates to a pre-fill valve hydraulic cylinder that mounts to an end cap of a main cylinder by a fastening arrangement that allows for radial adjustment of the pre-fill valve hydraulic cylinder relative to the end cap of the main cylinder. In certain examples, the radial adjustment of the pre-fill valve hydraulic cylinder assists in providing effective alignment between the pre-fill valve hydraulic cylinder and a piston locating bore defined by the main cylinder end cap. The piston locating bore of the main cylinder end cap can be configured to locate a piston rod of the pre-fill valve hydraulic cylinder along an axis of a valve seat defined by the end cap of the main cylinder.

Another aspect of the present disclosure relates to a pre-fill valve hydraulic cylinder having a pre-fill valve cylinder body including a pre-fill valve cylinder head defining an oversized piston rod opening through which a piston rod of the pre-fill valve hydraulic cylinder extends.

Still another aspect of the present disclosure relates to a pre-fill valve hydraulic cylinder having a pre-fill valve cylinder body including a pre-fill valve cylinder sleeve in which a pre-fill valve piston reciprocates. The pre-fill valve piston includes a piston rod and a piston head. The pre-fill valve cylinder sleeve defines a cylinder bore that is oversized relative to the piston head of the pre-fill valve piston. In certain examples, because the cylinder bore of the pre-fill valve cylinder sleeve is oversized relative to the piston head of the pre-fill valve piston, honing of the interior of the pre-fill valve cylinder sleeve is not required thereby reducing manufacturing costs.

Still another aspect of the present disclosure relates to a pre-fill valve cylinder including a pre-fill valve piston configured to reciprocate with respect to a pre- fill valve cylinder body. The pre-fill valve cylinder body includes a pre-fill valve cylinder sleeve and a pre-fill valve cylinder head. The pre-fill valve cylinder head defines fastener openings for receiving fasteners for securing the pre-fill cylinder body to a main cylinder end cap. The pre-fill valve piston includes a pre-fill valve piston rod and including first and second ends. The first end of the pre-fill valve piston rod is adapted for connection to a pre-fill valve poppet. The pre-fill valve piston also includes a piston head at the second end of the pre-fill valve piston. The piston head is positioned within a cylinder bore defined by the pre-fill valve cylinder sleeve. The pre- fill valve cylinder head defines a piston rod opening through which the pre-fill valve piston rod extends. In one example, the fastener openings are radially oversized in diameter by at least 1mm with respect to the fasteners. In one example, the piston rod opening defined by the pre-fill valve cylinder head is radially oversized in diameter by at least .5mm with respect to a corresponding diameter of the pre-fill valve piston rod. In one example, the cylinder bore of the pre-fill valve cylinder sleeve is oversized by at least lmm in diameter with respect to a corresponding diameter of the piston head of the pre-fill valve piston.

Another aspect of the present disclosure relates to a cylinder assembly including a main cylinder including a main piston that reciprocates within a main cylinder body. The main cylinder body includes a main cylinder sleeve and a main cylinder end cap. The main cylinder end cap has a first side and an opposite second side. The first side of the main cylinder end cap is coupled to the main cylinder sleeve. The second side of the main cylinder end cap is coupled to a hydraulic fluid reservoir. The main cylinder end cap includes a pre-fill valve seat. The pre-fill valve seat defines a central valve axis. The main cylinder end cap also defines a flow passage that extends from the hydraulic fluid reservoir at the second side of the main cylinder end cap to the valve seat. The main cylinder end cap also defines a piston locating bore that extends through the main cylinder end cap from the first side to the second side. The piston locating bore is coaxially aligned with the central valve seat axis. The cylinder assembly also includes a pre-fill valve poppet movable between an open position and a closed position. The pre-fill valve poppet contacts the pre-fill valve seat when in the closed position to block the flow passage to prevent fluid communication between the hydraulic fluid reservoir and an interior of the main cylinder body. The pre-fill valve poppet is displaced from the pre-fill valve seat when in the open position to open the flow passage thereby allowing fluid communication between the hydraulic fluid reservoir and the interior of the main cylinder. The cylinder assembly also includes a pre-fill valve cylinder for moving the pre-fill valve poppet between the open and closed positions. The pre-fill valve cylinder includes a pre-fill valve piston configured to reciprocate with respect to a pre-fill valve cylinder body. The pre-fill valve cylinder body includes a pre-fill valve cylinder sleeve and a pre-fill valve cylinder head. The pre-fill valve cylinder head defines fastener openings for receiving fasteners for securing the pre-fill valve cylinder body to the second side of the main cylinder end cap within the hydraulic fluid reservoir. The pre-fill valve piston includes a pre-fill valve piston rod including first and second ends. The first end of the pre-fill valve piston rod is connected to the pre-fill valve poppet. The pre-fill valve piston also includes a piston head at the second end of the pre-fill valve piston. The piston head is positioned within a bore defined by the pre-fill valve cylinder sleeve. The pre-fill valve cylinder head defines a piston rod opening through which the pre-fill valve piston rod extends. In one example, the pre-fill valve piston rod extends through and is coaxially aligned with the central valve seat axis by the piston locating bore of the main cylinder end cap. In one example, the piston locating bore has a tighter clearance with respect to the pre-fill valve piston rod than the piston rod opening defined by the pre-fill valve cylinder head. In one example, fastener openings are oversized with respect to the fasteners to allow the position of pre-fill valve cylinder to be radially adjusted relative to the central valve seat axis. In one example, the cylinder bore defined by the pre-fill cylinder sleeve is oversized with respect to the piston head.

A variety of additional aspects will be set forth in the description that follows. The aspects can relate to individual features and to combinations of features. It is to be understood that both the forgoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the examples disclosed herein are based. Brief Description of the Drawings

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate aspects of the present disclosure and together with the description, serve to explain the principles of the disclosure. A brief description of the drawings is as follows:

Figure 1 depicts a cylinder assembly in accordance with the principles of the present disclosure including a main hydraulic cylinder and pre-fill valve, the main hydraulic cylinder is shown in the process of being extended and the pre-fill valve is open to allow hydraulic fluid to flow from a reservoir to the main hydraulic cylinder;

Figure 2 illustrates the cylinder assembly of Figure 1 with the pre-fill valve closed to hold a piston of the main hydraulic cylinder in a staging position relative to a cylinder body of the main hydraulic cylinder;

Figure 3 depicts the cylinder assembly of Figure 1 with the main hydraulic cylinder in the process of being retracted and the pre-fill valve open to allow hydraulic fluid to flow from the main hydraulic cylinder back to the reservoir and; and

Figure 4 is a cross-sectional view showing the pre-fill valve mounted to a cylinder end cap of the main hydraulic cylinder.

Figure 4A is an enlarged view of a portion of Figure 4;

Figure 4B is an enlarged view of a portion of Figure 4 with the shape of the mating surface of the poppet modified to have a radius instead of a chamfer; and

Figure 5 is a cross-sectional view showing an alternative pre-fill valve mounted to a cylinder end cap of the main hydraulic cylinder.

Detailed Description

Figures 1-3 illustrate a cylinder assembly 20 in accordance with the principles of the present disclosure. The cylinder assembly 20 includes a main hydraulic cylinder 22 including a main piston 24 configured to reciprocate within (i.e., move back and forth within) a main cylinder body 26. The main piston 24 has a piston head 50 that separates the interior 30 of the main cylinder body 26 into first and second sections. The cylinder assembly 20 also includes a pre-fill valve 28 for opening and closing fluid communication between an interior 30 of the main cylinder body 26 and a hydraulic fluid reservoir 32 (i.e., a tank). The pre-fill valve 28 includes a poppet 34 that engages a valve seat 36 to close fluid communication between the interior 30 of the main cylinder body 26 and the hydraulic fluid reservoir 32. The poppet 34 is displaced from the valve seat 36 to open fluid communication between the interior 30 of the main cylinder body 26 and the hydraulic fluid reservoir 32. The poppet 34 is moved between open and closed positions by a pre-fill cylinder 38.

In accordance with some aspects of the disclosure, the cylinder assembly 20 functions to apply a pressing load to one or more objects. The pre-fill valve 28 fills the first section of the interior 30 of the main cylinder body 26 sufficient to extend the main piston 24 to a staging position (e.g., contacting the object to be pressed). Once at the staging position, the pre-fill valve 28 is closed and high pressure fluid is introduced into the first section of the interior 30 to apply pressure to the main piston 24 in the extension direction. To retract the main piston 24, the pre-fill valve 28 is opened and fluid is introduced to the second section of the interior 30 of the main cylinder body 26.

Figures 1-3 depict different operating states of the cylinder assembly 20. Figure 1 shows the cylinder assembly 20 in a state where the main piston 24 is being extended relative to the main hydraulic cylinder 22. In this state, the pre-fill valve 28 is open to allow low pressure hydraulic fluid to flow from the hydraulic fluid reservoir 32 into the interior 30 of the main cylinder body 26 as the main piston 24 is extended. Fluid at the opposite side of the main cylinder body 26 exits the body 26 through the second port 43. The first port 41 is closed.

In some implementations, the main piston 24 is mounted vertically so that gravity will pull the main piston 24 into the extended position (e.g., via the weight of the main piston 24 or a weight of a load attached to the main piston 24). In other implementations, a separate actuator can be disposed external of the main cylinder 26 and attached to the main piston 24 to extend the main piston 24 relative to the main cylinder body 26. In certain examples, the low pressure fluid from the reservoir does not apply a driving force to the piston 24 during extension, but rather merely functions to fill the main cylinder body 26. Figure 2 depicts a state of the cylinder assembly 20 in which the main piston 24 is disposed in a staging position relative to the main hydraulic cylinder 22. In this state, the pre-fill valve 28 is closed such that fluid communication is blocked between the hydraulic fluid reservoir 32 and the interior 30 of the main cylinder body 26. High pressure can be applied to the first section of the interior 30 of the main cylinder body 26 via the first port 41 (e.g., from a source of pressurized fluid) to apply a high pressure load to the main piston 24 in the extension direction. The second port 43 is open to enable fluid to exit the second section of the interior 30.

Figure 3 illustrates a state of the cylinder assembly 20 in which the main piston 24 is being retracted relative to the main hydraulic cylinder 22. In this state, the first port 41 is closed. The pre-fill valve 28 is open to permit hydraulic fluid to flow from the first section of the interior 30 of the main cylinder body 26 into the hydraulic fluid reservoir 32 as the main piston 24 is retracted. Fluid is introduced into the second section of the interior 30 to drive retraction of the main piston 24. It will be appreciated that the pre-fill cylinder 38 functions to move the pre-fill valve 28 between the open and closed positions.

It is desirable for the poppet 34 to properly seat on the valve seat 36 to prevent leakage when the pre-fill valve 28 is closed to ensure proper operation of the device. For proper seating, the poppet 34 is desirably centered (e.g., coaxially aligned) with respect to the valve seat 36, and preferably the poppet 34 is not tilted relative to the valve seat 36 such that full circumferential contact is maintained between the poppet 34 and the valve seat 36 when the poppet 34 is in the closed position. Aspects of the present disclosure relate to features of the pre-fill cylinder 38 that allow for proper alignment and seating of the poppet 34 relative to the valve seat 36.

The main cylinder body 26 of the main hydraulic cylinder 22 includes a main cylinder sleeve 40 that extends between opposite first and second ends 42, 44. A main cylinder head 46 is located at the first end 42 and a main cylinder base end cap 48 is located at the second end 44 of the main cylinder sleeve 40. The main piston 24 includes a main piston head 50 positioned within the main cylinder sleeve 40 and a main piston rod 52 coupled to the main piston head 50. The main piston rod 52 extends through the main cylinder head 46. The main cylinder sleeve 40 defines a first port 41 and a second port 43. The first port 41 is selectively fluidly coupled to a high pressure source. The second port 43 is alternatingly fluidly coupled to a reservoir and a pressure source.

The base end cap 48 of the main cylinder body 26 includes a first side 54 and an opposite second side 56 (see Figure 4). The main cylinder sleeve 40 couples to the first side 54 of the base end cap 48 and the hydraulic fluid reservoir 32 couples to the second side 56 of the base end cap 48. The base end cap 48 defines the valve seat 36 which is radially centered with respect to a central valve seat axis 58 (Figure 4). The base end cap 48 defines a flow passage 60 that extends from the hydraulic fluid reservoir 32 at the second side 56 of the base end cap 48 to the valve seat 36.

When the pre-fill valve 28 is in the open position (as shown at Figures 1 and 3), the flow passage 60 provides fluid communication between the hydraulic fluid reservoir 32 and the interior 30 of the main cylinder body 26. When the pre-fill valve 28 is in the closed position (as shown at Figure 2), the poppet 34 engages the valve seat 36 to block the flow passage 60 such that fluid communication is prevented between the hydraulic fluid reservoir 32 and the interior 30 of the main cylinder body 26. The base end cap 48 of the main cylinder body 26 also defines a piston locating bore 62 that extends through the base end cap 48 and is preferably co-axially aligned with the central valve seat axis 58.

Figure 4 A shows an example of an engagement between the valve seat 36 and the poppet 34 shown in Figure 4. The poppet 34 has a chamfered surface 35 A that engages the valve seat 36 along a face of the chamfered surface 35 A. Figure 4B shows another example of an engagement between the valve seat 36 and an alternative embodiment of the poppet 34. The alternative poppet 34 has an engagement surface 35B defining a radius instead of a chamfer. Using a poppet 34 having a surface radius instead of a chamfer to engage the valve seat 36 provides line contact with the valve seat 36 instead of face-to-face contact. The line contact can enhance alignment between the poppet 34 and the valve seat 36. Referring to Figure 4, the pre-fill valve cylinder 38 includes a pre-fiU valve piston 64 configured to reciprocate with respect to a pre-fill valve cylinder body 66. The pre-fill valve cylinder body 66 includes a pre-fill valve cylinder sleeve 67 having a first end 68 positioned opposite from a second end 70. The pre-fill valve cylinder body 66 includes a pre-fill valve cylinder head 72 positioned at the first end 68 of the pre-fill valve sleeve 67 and a pre-fill valve cylinder base 74 positioned at the second end 70 of the pre-fill valve sleeve 67. The pre-fill valve cylinder head 72 includes fastener openings 76 for receiving fasteners 78 for securing the pre-fill valve cylinder body 66 to the second side 56 of the base end cap 48 of the main hydraulic cylinder 22. The pre-fill valve cylinder 66 is positioned within an interior of the hydraulic fluid reservoir 32. The pre-fill valve cylinder base 74 defines a port 80 for coupling an interior of the pre-fill valve cylinder body 66 to a source of pressurized hydraulic fluid such as a pump. By pressurizing the interior of the pre-fill valve cylinder body 66 through the port 80, the pre-fill valve piston 64 is extended relative to the pre-fill valve cylinder body 66 by the fluid pressure within the pre-fill valve cylinder body 66. By extending the pre-fill valve piston 64 relative to the pre-fill valve cylinder body 66, the poppet 34 is moved from the closed position to the open position.

The pre-fill valve piston 64 includes a pre-fill valve piston rod 82 having a first end 84 positioned opposite from a second end 86. The first end 84 of the pre-fill valve piston rod 82 is coupled to the pre-fill valve poppet 34 via a nut 33. The pre-fill valve piston 64 also includes a piston head 88 coupled to the second end 86 of the pre- fill valve piston 64. In one example, the pre-fill valve piston rod 82 and the pre-fill valve piston head 88 have a metal construction. The piston head 88 is positioned within a cylinder bore 90 defined by the pre-fill valve cylinder sleeve 67. The pre-fill valve cylinder head 72 defines a piston rod opening 92 through which the pre-fill valve piston rod 82 extends.

The pre-fill valve piston rod 82 also extends through the piston locating bore 62 of the base end cap 48 of the main cylinder body 26. It will be appreciated that it is preferred for the piston locating bore 62 to be the primary feature for positioning and aligning the pre-fill valve piston rod 82. The piston locating bore 62 can be configured to maintain the pre-fill valve piston rod 82 in an orientation that is concentric with the valve seat and coaxially aligned with the central valve seat axis 58. The piston locating bore 62 can also maintain perpendicularity between the pre-fill valve piston rod 82 and the base end cap 48 such that the poppet 34 is prevented from tilting or angling relative to the valve seat 36 in such a way that leakage may occur due to improper valve seating. In certain examples, a close running clearance fit (H8/17) as defined by the International Organization for Standardization (ISO) is defined between the piston locating bore 62 and the pre-fill valve piston rod 82. In certain examples, the piston locating bore 62 has a diameter that is no more than .08 millimeters (mm), or .07mm, or .06mm, or .05mm, or .04mm, or .03mm larger than an outer diameter of the pre-fill valve piston rod 82. In one example, the piston locating bore 62 has a diameter that is in the range of .08mm to .03mm larger than the outer diameter of the pre-fill valve piston rod 82. In other examples, other tight tolerance fits can be used depending on the application need.

As indicated above, precise alignment and positioning of the pre-fill valve piston rod 82 is determined (e.g., set, established, controlled, etc.) by the piston locating bore 62. In this regard, it is desirable for the structure of the pre-fill valve cylinder body 66 to be configured to not compromise or otherwise negatively affect the alignment provided by the piston locating bore 62. In this regard, the pre-fill valve cylinder body 66 is configured with tolerances and features that allow the pre-fill valve cylinder body 66 to be positioned relative to the piston locating bore 62 and the central valve seat axis 58 without compromising alignment provided by the piston locating bore 62. In one example, the pre-fill valve cylinder body 66 is constructed with clearances and tolerances relative to the pre-fill valve piston rod 82 so as to prevent contact points with the pre-fill valve piston rod 82 that could induce concentricity errors as the pre-fill valve piston rod 82 strokes relative to the pre-fill valve cylinder body 66. Concentricity errors can be the result of angular misalignment and other perpendicularity issues. To prevent undesirable contact between the pre-fill valve piston rod 82 and the pre-fill valve cylinder body 66, the piston rod opening 92 of the pre-fill valve cylinder head 72 is enlarged relative to the pre-fill valve piston rod 82 and the cylinder bore 90 of the pre-fill valve cylinder sleeve 67 is enlarged relative to the pre-fill valve piston head 88. The degree of enlargement is selected to prevent undesired contact between the pre-fill valve piston rod 92 and the pre-fill valve cylinder body 66 that could cause

misalignment of the pre-fill valve piston rod 82. In one example, the piston rod locating bore 62 has a tighter clearance with respect to the pre-fill valve piston rod 82 than the piston rod opening 92. In one example, the piston rod opening 92 is radially oversized in diameter by at least .5mm, or .6 mm, or .7mm, or .8 mm with respect to a diameter of the pre-fill valve piston rod 82. In certain examples, the cylinder bore 90 of the pre-fill cylinder sleeve 67 is oversized by at least 1mm, or 2mm, or 3mm, or 4mm, or 5 mm in diameter with respect to a corresponding diameter of the piston head 88 of the pre-fill valve piston 64.

In certain examples, the piston head 88 of the pre-fill valve piston 64 (including the rod and the head) has a metal construction and the pre-fill valve cylinder 66 also has a metal construction. When determining the degree to which the cylinder bore 90 is oversized with respect to the piston head 88, the relevant diameters at issue include the outer diameter piston head 88 not including any seal (e.g., an elastomeric seal) that may circumferentially surround the body of the piston head, and the diameter defined by the cylinder bore 90.

In other examples, a sealing element such as an elastomeric sealing element may be positioned between the piston head 88 and the pre-fill valve sleeve 67 within the cylinder bore 90. This type of seal can provide for sealing between separate chambers within the interior of the pre-fill valve cylinder body 66. Additionally, because such a seal can be elastomeric in nature, the seal can allow for radial adjustment or movement between the main body of the piston head 88 and the pre-fill valve cylinder body 66 to prevent misalignment issues.

A seal 94 can also be provided between the pre-fill valve cylinder head 72 and the second side 56 of the base end cap 48 of the main cylinder body 26. The seal 94 can circumferentially engage an outer circumference of the pre-fill valve piston rod 82 and can provide sealing for preventing pressurized fluid from within the interior of the pre-fill valve cylinder body 66 from leaking from the interior of the pre-fill valve cylinder body 66. The seal 94 can also engage the pre-fill valve cylinder head 72and the second side of the end cap 48 of the main hydraulic cylinder. The seals disclosed herein are preferably extrusion resistant seals. In certain examples, the seals can be elastomeric seals. In certain examples, the seals can include gaskets such as O-ring seals or annular seals having other cross-sectional profiles (e.g.. square shaped cross- sectional profiles). In certain examples, the seals can be constructed of materials such as thermoset polymers, thermoplastic polymers, rubbers, or other materials.

The extrusion resistant seals are designed to provide effective sealing while still allowing the pre-fill valve piston rod 82 to move laterally or radially relative to the pre-fill valve cylinder body 66 so as not to interfere with the precise alignment of the pre-fill valve piston rod 82 established by the piston locating bore 62.

It will be appreciated that the pre-fill valve cylinder body 66 also includes mounting structure for allowing the pre-fill valve hydraulic cylinder 38 to be mounted to the second side 56 of the base end cap 48 in general alignment with the central valve seat axis 58 and the axis defined by the piston locating bore 62. In certain examples, the pre-fill valve cylinder head 72 has an end face 96 that is preferably fiat (e.g., planar) so as to make surface-to-surface contact with a corresponding planar surface 98 at the second side 56 of the base end cap 48 (see Figure 4). Additionally, a relatively large clearance is provided between the fasteners 78 (e.g., bolts) and the corresponding fastener openings 76 defined by the pre-fill valve cylinder head 72. By making the fastener openings 76 oversized with respect to the fasteners 78, the pre-fill valve cylinder body 66 can be radially/laterally adjusted into general alignment with the central valve seat axis 58 without causing angular misalignment. In certain examples, the fastener openings 76 are radially oversized by at least .5mm, or .75mm, or 1mm, or 1.5mm, or 2mm with respect to the corresponding fasteners 78. Once the pre-fill valve cylinder body 66 has been adjusted to the proper position relative to the central valve seat axis 58, the fasteners 78 can be fully tightened to clamp the pre-fill valve cylinder body 66 in position.

In the depicted example, the cylinder bore 90 is oversized with respect to the piston head 88 of the pre-fill cylinder 38. Thus, a radial clearance C is defined between the piston head 88 and the cylinder bore 90. In the depicted example, no seal is provided in the clearance region so that hydraulic fluid can flow past the piston head 88 as the piston rod 82 is extended. Additionally, because the piston head 88 is not designed to contact the interior surface of the pre-fill valve sleeve 67, it is not necessary to hone or otherwise precisely process the cylinder bore 90 thereby reducing

manufacturing costs. The pre-fill valve cylinder 38 includes at least one spring 100 (more than one spring can be used as well) for biasing the pre-fill valve piston rod 82 toward a retracted position corresponding to the pre-fill valve 28 being closed. The spring is shown axially captured between the piston head 88 and the pre-fill valve cylinder head 72. The spring 100 retains the pre-fill valve 28 in a closed position in which the poppet 34 seats against the valve seat 36. The spring 100 ensures the poppet 34 seats properly on the valve seat 36 and absorbs any alignment issues.

To move the pre-fill valve 28 from the closed position of Figure 2 to the open position of Figures 1 or 3, hydraulic pressure is applied to the port 80 of the pre- fill valve cylinder body 66 to pressurize the interior of the pre-fill valve cylinder body 66. The pressurized fluid within the pre-fill valve cylinder body 66 acts on an axial end face 102 of the piston head 88 thereby causing the piston 64 to be driven from a retracted position toward an extended position. As the pre-fill valve piston 64 extends, the spring 100 is compressed. The pre-fill valve piston 64 continues to extend relative to the pre-fill valve cylinder body 66 until the force applied on the end face 102 by fluid pressure from the source of pressurized fluid equals the spring force applied to the piston head by the spring 100. When the pre-fill valve piston 64 is extended, the poppet 34 is displaced from the valve seat 36 and the pre-fill valve 28 is in the open position. It will be appreciated that the pre-fill valve cylinder 38 is a single-acting cylinder with only one pressure port 80. As the pre-fill valve piston 64 extends relative to the pre-fill valve cylinder body 66, the radial clearance between the piston head 88 and the interior of the pre-fill valve sleeve 67 allows hydraulic fluid to flow across the piston head 88 from a first side 104 of the interior of the pre-fill valve sleeve 67 to a second side 106 of the interior of the pre-fill valve sleeve 67. When it is desired to close the pre-fill valve 28, the source of pressurized fluid is no longer coupled to the port 80 thereby allowing the spring 100 to push the pre-fill valve piston rod 82 from the extended position toward the retracted position. As the pre-fill valve piston rod 82 retracts, hydraulic fluid within the interior of the pre-fill valve sleeve 67 can flow across the piston head 88 through the clearance gap from the second side 106 to the first side 104 of the interior of the pre-fill valve sleeve 67.

It is preferred for the pre-fill valve cylinder 38 to be a single acting cylinder. In other examples, a double acting cylinder 38 can be used in which fluid pressure ports 69, 80 are provided on opposite sides of the piston head 88 for supplying and removing hydraulic fluid from opposite sides of the piston head 88 as the piston rod 82 is extended and retracted. In this type of example, a seal 89 such as an elastonieric seal can be provided radially between the outer circumference of the piston head 88 and the cylinder bore 90 to prevent hydraulic fluid from flowing across the piston head 88. Preferably, the seal 89 is elastonieric in nature and is extrusion resistant. The elastomeric nature of the seal 89 can provide effective sealing and can concurrently allow for radial movement between the piston head 88 and the pre-fill valve

sleeve 67 to prevent misalignment issues.