REMOVABLE TANK PORTAL COVER

Abstract

A hatch cover includes spring-loaded exhaust and suction valves to regulate internal tank pressure with respect to outside pressure. The valves are disposed in a ring housing. The cover further includes a spring-loaded locking bolt configured to engage the hatch base and thereby provide a retaining force between the housing and the hatch base. The exhaust-valve springs may be selectively preloaded to establish a target exhaust pressure. The locking-bolt spring may be selectively disengaged or overcome to release engagement of the bolt from the hatch base.

Claims

1. A hatch cover comprising: (a) a substantially cylindrical housing comprising: (i) a first sealing surface, (ii) a radial axis; (b) a pressure assembly comprising: (i) an exhaust valve having an exhaust-valve spring, an exhaust-valve plate having second and third sealing surfaces, and an exhaust-valve-spring loader, and (ii) a suction valve having a suction-valve spring, a suction-valve plate having a fourth sealing surface, and a suction-valve-spring loader, (iii) wherein the exhaust-valve spring is positioned to provide a pushing force between the exhaust-valve-spring loader and the exhaust-valve plate, (iv) wherein the suction-valve spring is positioned to provide a pulling force between the suction-valve-spring loader and the suction-valve plate, (v) wherein the housing and exhaust-valve plate are configured to provide a first interface between the first sealing surface and the second sealing surface, (vi) wherein the exhaust-valve plate and the suction-valve plate are configured to provide a second interface between the third sealing surface and the fourth sealing surface; and (c) a locking assembly comprising: (i) a bolt, and (ii) a bolt-loading spring; (iii) wherein the bolt-loading spring is positioned to provide a pushing force on the bolt directed along the radial axis.

2. The hatch cover of claim 1 further comprising a means for selectively reducing the pushing force on the bolt.

3. The hatch cover of claim 1 wherein the bolt includes a first end configured to engage a hatch base and a second end configured as a first member of a first sliding joint and wherein the bolt-loading spring includes a first post-engaging end and a second post-engaging end, the cover further comprising: (a) a track ring comprising: (i) a first spring-retaining post engaged with the first post-engaging end of the bolt-loading spring, and (ii) a second member of the first sliding joint engaged with the first member to form the first sliding joint; (b) a second spring-retaining post connected to the housing and engaged with the second post-engaging end of the bolt-loading spring; and (c) a channel ring comprising a channel directed along the radial axis and within which the bolt is positioned; (d) wherein the track ring is circumferentially nested within the channel ring; (e) wherein the first sliding joint has a first joint position placing the bolt at a first point along the radial axis and a second joint position placing the bolt at a second point along the radial axis; (f) wherein the bolt-loading spring provides a biasing force pushing the bolt toward the second joint position; (g) wherein the first joint position corresponds to a first rotational position of the track ring relative to the channel ring; and (h) where the second joint position corresponds to a second rotational position of the track ring relative to the channel ring.

4. The hatch cover of claim 3 wherein the channel ring is connected to the housing.

5. The hatch cover of claim 3 wherein the channel ring is integral with the housing.

6. The hatch cover of claim 3 wherein the track ring is joined to the channel ring through a second sliding joint configured to enable rotational motion between the track ring and channel ring.

7. The hatch cover of claim 6 wherein the track ring provides a circumferential groove as a slide guide.

8. The hatch cover of claim 1 further comprising a means for selectively preloading the exhaust-valve spring to control the pushing force between the exhaust-valve-spring loader and the exhaust-valve plate.

9. The hatch cover of claim 1 further comprising a valve-assembly retaining ring, wherein the exhaust-valve-spring loader includes a spring-loader ring threadedly engaged within the valve-assembly retaining ring and wherein rotation of the valve-assembly retaining ring relative to the spring-loader ring varies preloading of the exhaust-valve spring.

10. The hatch cover of claim 9 wherein the valve-assembly retaining ring is connected to the housing via a third sliding joint.

11. The hatch cover of claim 10 wherein the valve-assembly retaining ring provides a circumferential groove as a slide guide.

12. The hatch cover of claim 10 further comprising a scale reflecting a rotational position of the valve-assembly retaining ring relative to the spring-loader ring.

13. The hatch cover of claim 12 wherein the scale is calibrated to the force provided by the exhaust-valve spring to the exhaust-valve plate.

14. The hatch cover of claim 12 wherein the scale reflects an operational exhaust pressure.

15. The hatch cover of claim 3 further comprising a valve-assembly retaining ring, wherein the exhaust-valve-spring loader includes a spring-loader ring threadedly engaged within the valve-assembly retaining ring and wherein rotation of the valve-assembly retaining ring relative to the spring-loader ring varies preloading of the exhaust-valve spring.

16. The hatch cover of claim 3 wherein the housing is an assembly of a bottom component, a top component, and the channel ring, and wherein the bottom component includes the first sealing surface.

17. The hatch cover of claim 15 wherein the housing is an assembly of a bottom component, a top component, and the channel ring, and wherein the bottom component includes the first sealing surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings where:

[0011] FIG. 1 is a perspective view illustrating an exemplary tank and open hatch according to an aspect of the invention.

[0012] FIG. 2 is a perspective view illustrating an exemplary tank and closed hatch according to an aspect of the invention.

[0013] FIG. 3 is a perspective view illustrating an exemplary hatch cover secured in a hatch base according to an aspect of the invention.

[0014] FIG. 4 is a side sectional view illustrating an exemplary hatch cover secured in a hatch base according to an aspect of the invention.

[0015] FIG. 5 is a perspective exploded view of an exemplary hatch cover according to an aspect of the invention.

[0016] FIGS. 6A-6G are various views illustrating an exemplary hatch cover according to an aspect of the invention.

[0017] FIGS. 7A-7E are various views illustrating an exemplary internal locking mechanism for securing a hatch cover in a hatch base.

[0018] FIG. 8A is a top sectional view illustrating an exemplary valve assembly and an exemplary internal locking mechanism for securing a hatch cover in a hatch base.

[0019] FIG. 8B is a side sectional view illustrating an exemplary valve assembly and an exemplary internal locking mechanism for securing a hatch cover in a hatch base.

[0020] FIGS. 9A-9D are various views illustrating an exemplary internal locking mechanism for securing a hatch cover in a hatch base.

[0021] FIGS. 10A-10C are various views illustrating an exemplary valve assembly of a hatch cover.

[0022] FIG. 11 is a side sectional view of an exemplary relative valve-seat position for a tank-over-pressure exhaust event.

[0023] FIG. 12 is a side sectional view of an exemplary relative valve-seat position for a tank-under-pressure suction event.

DETAILED DESCRIPTION

[0024] In the summary above, and in the description below, reference is made to particular features of the invention in the context of exemplary embodiments of the invention. The features are described in the context of the exemplary embodiments to facilitate understanding. But the invention is not limited to the exemplary embodiments. And the features are not limited to the embodiments by which they are described. The invention provides a number of inventive features which can be combined in many ways, and the invention can be embodied in a wide variety of contexts. Unless expressly set forth as an essential feature of the invention, a feature of a particular embodiment should not be read into the claims unless expressly recited in a claim.

[0025] Except as explicitly defined otherwise, the words and phrases used herein, including terms used in the claims, carry the same meaning they carry to one of ordinary skill in the art as ordinarily used in the art.

[0026] Because one of ordinary skill in the art may best understand the structure of the invention by the function of various structural features of the invention, certain structural features may be explained or claimed with reference to the function of a feature. Unless used in the context of describing or claiming a particular inventive function (e.g., a process), reference to the function of a structural feature refers to the capability of the structural feature, not to an instance of use of the invention.

[0027] Except for claims that include language introducing a function with means for or step for, the claims are not recited in so-called means-plus-function or step-plus-function format governed by 35 U.S.C. 112(f). Claims that include the means for [function] language but also recite the structure for performing the function are not means-plus-function claims governed by 112(f). Claims that include the step for [function] language but also recite an act for performing the function are not step-plus-function claims governed by 112(f).

[0028] Except as otherwise stated herein or as is otherwise clear from context, the inventive methods comprising or consisting of more than one step may be carried out without concern for the order of the steps.

[0029] The terms comprising, comprises, including, includes, having, haves, and their grammatical equivalents are used herein to mean that other components or steps are optionally present. For example, an article comprising A, B, and C includes an article having only A, B, and C as well as articles having A, B, C, and other components. And a method comprising the steps A, B, and C includes methods having only the steps A, B, and C as well as methods having the steps A, B, C, and other steps.

[0030] Terms of degree, such as substantially, about, and roughly are used herein to denote features that satisfy their technological purpose equivalently to a feature that is exact. For example, a component A is substantially perpendicular to a second component B if A and B are at an angle such as to equivalently satisfy the technological purpose of A being perpendicular to B.

[0031] Except as otherwise stated herein, or as is otherwise clear from context, the term or is used herein in its inclusive sense. For example, A or B means A or B, or both A and B.

[0032] FIGS. 1 and 2 are perspective views illustrating an exemplary tank 10 with an exemplary thieves hatch 11 comprising a hatch base 14 and a hatch cover 12. FIG. 1 depicts the tank with the cover 12 removed from the base 14 enabling access to the interior of the tank 10 through a hatch portal 16. FIG. 2 depicts the tank 10 with the cover 12 secured in the base 14, closing the portal 16 and thereby preventing (or limiting) unwanted ingress into the tank or egress from the tank through the portal 16.

[0033] FIGS. 3 and 4 illustrate the exemplary cover 12 secured within the base 14 so as to seal the portal. (The tank has been omitted from the drawings for sake of clarity.) FIG. 3 is a perspective view, FIG. 4 is a side sectional view of section A-A of FIG. 3. The cover 12 includes an exhaust valve comprising an exhaust-valve plate 30 with a spring housing bottom 28 containing one end of an exhaust-valve spring 24 connected to a top support 18 with a spring housing top 26 containing the other end of the exhaust-valve spring 24. The cover 12 also includes a suction valve comprising a suction-valve plate 32 connected to a suction-valve guide rod 38/guide-rod cap 36 and biased with a suction-valve spring 40. The exhaust and suction valve are positioned in a valve housing 42 which in turn is secured in a ring base 20 via a valve ledge 34 in the ring base 20. The ring base 20 is secured in the hatch base 14 using one or more retaining springs 22. Mating surfaces (e.g., valve housing 42 to ring base 20, ring base 20 to hatch base 14) are sealed as appropriate with, e.g., nitrile gaskets.

[0034] The exhaust and suction valves work to regulate the internal tank pressure: when the internal tank pressure exceeds the pressure outside the tank by a predetermined amount, the exhaust-valve spring 24 compresses, opening a path for tank contents to vent; when the pressure outside the tank exceeds the internal tank pressure by a predetermined amount, the suction-valve spring 40 compresses, opening a path into the tank allowing, e.g., atmosphere into the tank. Thus, the exhaust and suction valves work in concert to keep the internal tank pressure within a predetermined range of the pressure outside the tank. In operation, the exhaust-valve spring 24 and the suction-valve spring 40 are tuned (e.g., to a specific spring constant) to the predetermined pressure range for the particular tank/environment.

[0035] The retaining springs 22 that secure the cover 12 in the closed position in the hatch base 14 enable quick insertion and removal of the cover 12 to close and open the tank hatch. The retaining springs 22 are tuned (e.g., spring constant, number of springs) to provide a retaining force sufficient to hold the cover in place when internal tank pressure exceeds to the pressure outside the tank by greater than the amount the required to open the exhaust valve.

[0036] FIG. 5 is an exploded perspective view illustrating the exemplary components of the exemplary hatch cover.

[0037] FIGS. 6A-6G are various views illustrating an exemplary hatch cover 600 according to an aspect of the invention. FIGS. 6A and 6B are 3D perspective views illustrating the cover 600 in high-pressure and low-pressure states respectively. FIGS. 6C and 6F are sectional views of the cover 600 in a low-pressure state. FIG. 6D is a side view of the cover 600. FIG. 6E is a top view of the cover 600. The exemplary hatch cover 600 includes an internal-locking mechanism 700 configured to selectively lock the cover 600 in a hatch base and a valve assembly 800 configured to manage exhaust and intake of fluids to regulate the pressure in a tank.

[0038] The internal lock 700 includes a loading bracket 702 and a plurality of bolts 704. The bracket 702 includes a channel ring 702a, configured with radial channels 714 to hold the bolts 704, and a track ring 702b, configured with tracks 708 to engage and guide the bolts. The channel ring 702a and track ring 702b are circumferentially nested together, with the track ring 702b inside the circumference of the channel ring 702b. The inside edge of the channel ring 702a engages a outside groove on the track ring 702b such that the track ring 702b and channel ring 702a may rotate relative to each other but may not translate relative to each other (they are substantially static translationally). The bolts 704 are selectively positionable within the bracket 702 to radially protrude to engage the hatch base (as illustrated in FIG. 7D) or to radially retract to release from the hatch base (as illustrated in FIGS. 6A-6E, 7D) for insertion or removal of the cover 600. The bolts 704 engage a curved track 708 within the bracket 702 such that: (1) rotation of the bracket 702 in a first direction will cause the bolts 704 to radially retract and (2) rotation in the second direction will cause the bolts 704 to radially protrude. The bolts 704 are biased by a plurality of springs 706 to protrude. The bracket 702 may include one or more locating features 710 to allow an operator to rotate the bracket to engage/disengage the bolts 704 with the hatch base. (The rotation direction and extents are indicated by curved dashed arrows 710a in FIG. 6E.)

[0039] The valve assembly 800 includes: (1) an exhaust valve comprising a number of exhaust-valve springs 806 positioned about exhaust-valve guide rods 808 and between an exhaust-valve plate 810 and an exhaust-valve-spring loader 804 (in this embodiment, a compression plate); and (2) a suction valve comprising a number of suction-valve springs 812 positioned about suction-valve guide rods 814 and between a suction-valve guide-rod head 814a and a suction-valve-spring loader 818 (in this instance, a compression plate). The exhaust-valve springs 806 are configured to push the exhaust-valve plate 810 toward the tank when the cover 600 is installed in a tank hatch, providing a force of F.sub.ES. The suction-valve springs 812 are configured to pull the suction-valve plate 816 away from the tank when the cover 600 is installed in a tank hatch, providing a force of F.sub.SS.

[0040] In operation, the cover 600 is oriented such that the bottom surface 810a of the exhaust-valve plate 810 and the bottom surface 816a of the suction-valve plate 816 face the fluid in the tank (thus, the bottom surface of each is the valve plate's tank-side surface and the opposite surface of the plate is the atmospheric-side surface). The tank-side surface of the exhaust-valve plate 810 will experience a force toward the atmospheric-side surface due to tank-fluid pressure. The atmospheric-side surface of the exhaust-valve plate 810 will experience a force toward the tank-side surface due to atmospheric pressure and compressive loading of the exhaust-valve springs 806. The tank-side surface of the suction-valve plate 816 will experience a force toward the atmospheric-side surface due to tank-fluid pressure. The atmospheric-side surface of the suction-valve plate 816 will experience: (1) a force toward the tank-side surface due to atmospheric pressure and (2) a force away from the atmospheric-side surface due to compressive loading of the suction-valve springs 812 (pulling the suction-valve plate 816 out toward the atmospheric side).

[0041] As described in more detail below, the exhaust-valve assembly and the suction valve assembly are nested such that edge surfaces of the suction-valve plate 816 seat with edge surfaces of the exhaust-valve plate 810. Edge surfaces of the exhaust-valve plate 810 seat with surfaces of a bottom cover housing 606. When the force on the exhaust plate 810 due to the tank-fluid pressure exceeds the force due to the combination of atmospheric pressure and the loading of the exhaust-springs 806, the exhaust-plate 810 will move away from the tank, unseating from its sealing surfaces and allowing tank fluid to exhaust into atmosphere until the tank-fluid pressure drops below the level needed to compress the exhaust-valve springs 806. When the force on the suction plate 816 due to atmospheric pressure exceeds the force due to the combination of tank-fluid pressure and the loading of the suction-springs 812, the suction-plate 816 will move into the tank, unseating from its sealing surfaces and allowing atmospheric fluid to enter the tank until the tank-fluid pressure rises above the level needed to overcome the combination of atmospheric pressure and exhaust-valve springs 812.

[0042] In summary: (1) the exhaust valve opens when the force provided by tank fluid (F.sub.TF) is greater than the combined force provided by the atmosphere (F.sub.atm) and the exhaust-valve springs 806 (F.sub.ES)if F.sub.TF>F.sub.atm+F.sub.ES, then open the exhaust valve and (2) the suction valve opens when the force provided by the atmosphere (F.sub.atm) is greater than the combined force provided by the tank fluid (F.sub.TF) and suction-valve springs 812 (F.sub.SS)if F.sub.TF<F.sub.atmF.sub.SS, then open the suction valve. In this way, tank pressure is automatically regulated.

[0043] The valve assembly 800 can be tuned for a particular application by changing the compressive loading on the exhaust-valve springs 806 or suction-valve springs 812. In the exemplary hatch cover 600, the exhaust valve springs 806 can be selectively loaded by changing the position of the exhaust-valve-spring loader 804 relative to the exhaust-valve plate 810: (1) narrowing the distance between the exhaust-valve-spring-compression plate 804 and the exhaust-valve plate 810 increases the compressive loading force of the exhaust valve springs (F.sub.ES), thus increasing the tank-fluid pressure at which the exhaust valve opens, (2) increasing the distance between the exhaust-valve-spring-compression plate 804 and the exhaust-valve plate 810 decreases the loading force of the exhaust-valve springs (F.sub.ES), thus decreasing the tank-fluid pressure at which the exhaust valve opens.

[0044] In the exemplary valve assembly 800, the exhaust-valve-spring compression plate 804 is placed in threaded engagement with a valve-assembly retaining ring 802 such that: (1) rotation of the exhaust-valve-spring compression plate 804 relative to the valve-assembly retaining ring 802 in a first direction moves the spring loader 804 toward the exhaust plate 810 and thereby increases the loading force of the exhaust-valve springs (F.sub.ES), and (2) rotation of the exhaust-valve-spring compression plate 804 relative to the valve-assembly retaining ring 802 in a second direction moves the spring loader 804 away from exhaust plate 810 and thereby decreases the loading force of the exhaust-valve springs (FES). (The rotation direction and extents are indicated by a curved dashed arrow 804a in FIG. 6E. Counterclockwise rotation increases F.sub.ES and clockwise rotation decreases F.sub.ES.) The rotation may be calibrated such that a given rotational position corresponds to a known F.sub.ES (or pressure equivalent). Thus, a scale 602 may be provided to enable the operator to configure the F.sub.ES as appropriate. As illustrated in FIGS. 6A and 6B, the valve-assembly retaining ring 802 may include a spring-pressure indicator 802a that corresponds to the scale 602. Rotating the retaining ring 802 to place the indicator 802a at the desired location on the scale 602a moves the exhaust-valve-spring compression plate 804 relative to the exhaust-valve plate 810 to place it in a position that corresponds to the F.sub.ES pressure indicated on the scale 602. In FIG. 6A, the indicator 802a is positioned at 24 oz/in.sup.2 which moves the exhaust-valve-spring compression plate 804 down toward the exhaust-valve plate 810 to load the exhaust-valve springs 806 to provide an Fes pressure of 24 oz/in.sup.2. (The internal threads 802b of the retaining ring 802 are visible in FIG. 6A. The exhaust-valve-spring compression plate 804 has corresponding outer threads.) In FIG. 6B, the indicator 802a is positioned at 6.3 oz/in.sup.2 which moves the exhaust-valve-spring compression plate 804 back away from the exhaust-valve plate 810 to load the exhaust-valve springs 806 to provide an F.sub.ES pressure of 6.3 oz/in.sup.2.

[0045] In the exemplary valve assembly 800, the force F.sub.SS provided by the suction-valve springs 812 is controlled by positioning the suction-valve guide-rod heads 814a relative to the guide rods 814. Each suction-valve spring 812 is positioned between a guide-rod head 814a and the suction-valve-spring loader 818 such that the compressive load on the spring 812 may be set by adjusting the position of the guide-rod head 814a relative to the suction-valve-spring loader 818. In this embodiment, the guide-rod heads 814a are threaded into the guide rods 814. Threading the heads 814a further into the guide rods 814 will increase the amount by which atmospheric pressure must exceed tank pressure before the suction valve opens.

[0046] FIGS. 7A-7E, 8A-8B, and 9A-9D illustrate further details of the exemplary hatch-cover locking assembly 700. FIG. 7A is a 3D perspective of an exemplary bolt-loading bracket ring 702 with multiple hatch-base-engagement bolts 704 positioned in radial channels 714 dispersed circumferentially about the channel ring 702a. Locating features 710 and spring-retaining posts 712 extend longitudinally up from the track ring 702b. FIG. 7B is a top view. FIG. 7C is a side view. FIG. 7D is a top sectional view of section C2-C2 of FIG. 7C. FIG. 7E is a side sectional view of section C1-C1 of FIG. 7B. In FIG. 7D, the bolts 704 (with angled hatching) are illustrated in a fully retracted position. The figure is overlayed with a second set of bolts 704 (with cross-hatching and broken lines) illustrating the fully extended position. As the track ring 702b is rotated circumferentially (as illustrated in FIG. 6E with the dashed curved arrows 710a) the track 708 travels along the bolt 704 between a fully retracted position at a first end of the track 708a to a fully extended position at a second end of the track 708b. The bolt 704 may be configured with a T-shaped feature 704a engaging a T-shaped slot forming the track 708. The track 708 is curved such that the first end 708a is farther from the perimeter of the ring 702 than is the second end 708b.

[0047] FIG. 8A is a top sectional view of section C3-C3 of FIG. 6G, illustrating the engagement of the bolts 704 with the tracks 708 for the exemplary hatch cover 600. FIG. 8B is a side sectional view of section D-D of FIG. 8A. Multiple lateral bolt-loading springs 706 are disposed roughly tangentially near the circumference of the cover 600. A first end of each bolt-loading spring 706 connects to a spring-retaining post 712 of the bolt-loading carrier ring 702 and a second end of each bolt-loading spring 706 connects to a spring-retaining post 604a of a top cover housing 604. The bolt-load springs 706 bias the bolt-loading ring 702 toward the position to cause the bolts 704 to protrude to engage a hatch base.

[0048] FIG. 9A is a 3D perspective illustrating the engagement between the top cover housing 604, bolt-loading ring 702, and bolt-loading springs 706. FIG. 9B is a side view. FIG. 9C is a top view. FIG. 9D is sectional view of section E-E of FIG. 9B. The top cover housing 604 includes: (1) slots 604b through which the locating features 710 of the track ring 702b may protrude and (2) reference features 604c that may be engaged by the operator to help rotate the track ring 702b relative to the housing 604 and channel ring 702a to move the bolt 704 radially in or out. For example, the operator may place a finger on a reference feature 604c and a thumb on a locating feature 710 and squeeze them together to rotate the track ring 702b to cause the bolts 704 to retract, allowing the cover 600 to be removed from the hatch. In this embodiment, four bolt-loading springs 706 are distributed at roughly 90-degree intervals near the circumference of the housing 604 and track ring 702b.

[0049] FIGS. 10A-10C illustrate further details of the exemplary valve assembly 800. FIG. 10A is a 3D perspective illustrating the valve assembly 800. FIG. 10B is a top view of the assembly 800. FIG. 10C is a sectional view of section F-F of FIG. 10B. In this embodiment, the valve assembly includes: (1) six sets of exhaust-valve rods 808 and springs 806 uniformly distributed about the ring-shaped exhaust-valve plate 810 and (2) three sets of suction-valve rod 814 and spring 812 uniformly distributed about the disc shaped suction-valve plate 816. The suction-valve plate 816 seats within the exhaust-valve plate 810, sealing at surface-interface 822. The exhaust-valve plate 810 seats within the bottom cover housing 606, sealing at the surface-interface 820.

[0050] FIGS. 11 and 12 are sectional views analogous to the view of FIG. 10C, but showing the state of the surface-interfaces in certain pressure conditions. In FIG. 11, a tank-pressure force 904 on the exhaust-valve plate 810 exceeds the combined force of the atmosphere and exhaust-valve springs 902. This causes the exhaust-valve plate 810 to move up out of its seat with the bottom cover housing 606 and suction-valve plate 816. The surface-interfaces 822 and 820 are broken and tank fluid may exhaust through the opening. In FIG. 12, an atmospheric-pressure force 906 on the suction-valve plate 816 exceeds the combined force of the tank-fluid pressure and suction-valve springs 908. This causes the suction-valve plate 816 to move down out of its seat with the exhaust-valve plate 810. The surface-interface 822 is broken and atmospheric fluid may enter the tank through the opening.

[0051] While the foregoing description is directed to the preferred embodiments of the invention, other and further embodiments of the invention will be apparent to those skilled in the art and may be made without departing from the basic scope of the invention. And features described with reference to one embodiment may be combined with other embodiments, even if not explicitly stated above, without departing from the scope of the invention. The scope of the invention is defined by the claims which follow.