Patent Application
20240133375
The present invention relates to the field of high pressure reciprocating pumps and, in particular, to securing a fluid end component to a fluid end casing of a high pressure reciprocating pumps.
High pressure reciprocating pumps are often used to deliver high pressure fluids during earth drilling operations. Generally, a reciprocating pump includes a power end and a fluid end. The power end can generate forces sufficient to cause the fluid end to deliver high pressure fluids to earth drilling operations. The fluid end may include a casing that defines one or more internal pumping chambers and conduits that define pathways between one or more internal pumping chambers and external surfaces of the fluid end casing.
Elements are secured to the fluid end casing, and the joints between the elements and the fluid end casing encounter high levels of cyclical stress. Common fluid cylinder designs utilize large threaded retainers to secure elements to the fluid end casing of a fluid end of a reciprocating pump. The threaded retainers engage with threads machined into the fluid cylinder or fluid end casing to load a joint. Those threads are often subject to high levels of cyclical stress, and are typically not pre-loaded correctly in operation, thereby creating opportunity for fatigue failure.
Thus, there is a need for an improved joint between an element and a fluid end casing of a reciprocating pump, and in particular, for a joint between an element and a fluid end casing of a reciprocating pump that can be pre-loaded to improve the performance and lifetime of the joint. There is also a need for a less complex, and more easily serviceable joint.
The present application relates to techniques for securing one or more fluid end components, such as a stuffing box, against a fluid end casing of a fluid end of a high pressure reciprocating pump and/or against a seal of the fluid end. The techniques may be embodied as a retaining or clamping assembly. Additionally, the techniques may be embodied as one or more methods for securing one or more fluid components to a fluid end casing of a high pressure reciprocating pump.
More specifically, in accordance with at least one embodiment, the present application is directed to a reciprocating pump including a power end and a fluid end. The power end is configured to generate pumping power and the fluid end is configured to deliver a fluid from an inlet bore to an outlet bore as the power end generates the pumping power.
In some embodiments, one or more fluid end components are coupled to the fluid end casing by a retaining or clamping assembly. The invention relates to a retaining assembly for a positive displacement, reciprocating pump that utilizes a particular geometry to secure elements together. The retaining assembly includes a clamp that secures elements together, such as an external fluid end element or component and the fluid end casing of the pump.
In one embodiment, the retaining assembly includes a clamp with a wedge-shaped geometry. A benefit of the wedge-shaped geometry is that it allows the clamp to be pre-loaded to a stress level that is close or similar to the stress level that the joint will experience during operation of the pump. The pre-load stress increases the fatigue life of the parts of a joint significantly. In the present invention, the retaining feature or clamp utilizes a minimal number of connectors due to the mechanical advantage provided by the wedge geometry.
The present invention accomplishes the issue of pre-loading a joint for a fluid end component without threads at the interface of the fluid end component and the casing. The wedge-shaped geometry allows the joint between the elements and the clamp to be pre-loaded to the desired stress.
In one embodiment, the fluid end element or component is a stuffing box that is coupled or secured to the fluid end casing of a reciprocating pump. In particular, the element is coupled to a flange that is formed integrally with a body/casing of the fluid end. In an alternative embodiment, a flange may be bolted to the body/casing of the fluid end, and the element is secured to the bolted flange. The present invention can be used with fluid cylinders in high pressure reciprocating pumps in fracking, drilling, well service, or similar applications.
In one embodiment, a reciprocating pump includes a power end configured to generate pumping power, a fluid end casing having an inlet bore and an outlet bore, the fluid end being configured to deliver a fluid from the inlet bore to the outlet bore as the power end generates the pumping power, the fluid end casing including a first mounting portion, a fluid end component configured to engage the fluid end casing, the fluid end component including a second mounting portion, and a retainer assembly engageable with the first mounting portion and the second mounting portion, the retainer assembly applying a force to each of the first mounting portion and the second mounting portion to press the first mounting portion and the second mounting portion toward each other, the retainer assembly including a pair of spaced apart rails, the pair of spaced apart rails defining a wedge-shaped groove that increases the pressure on the first mounting portion and on the second mounting portion as the retainer assembly is tightened.
In an alternative embodiment, the retainer assembly includes a first clamp member and a second clamp member, the first clamp member includes a body having an inner surface and an outer surface opposite to the inner surface, the inner surface includes the pair of spaced apart rails, the pair of spaced apart rails includes a first rail with a first end and a second rail with a second end, and the first clamp member includes a groove formed between the first rail and the second rail. In another embodiment, the first rail includes a first angled surface, the second rail includes a second angled surface, the groove is located between the first angled surface and the second angled surface, the first angled surface and the second angled surface applying an increasing force to the first mounting portion and to the second mounting portion as the retainer assembly is tightened.
In one embodiment, the first mounting portion of the fluid end casing includes a first flange, the second mounting portion of the fluid end component includes a second flange, and the retainer assembly includes a first clamp member and a second clamp member, each of the first clamp member and the second clamp member includes a first rail and a second rail defining a groove therebetween, the grooves receiving the first flange and the second flange when the clamp members are coupled together, and each of the first clamp member and the second clamp member has a wedge-shaped geometry defining the corresponding groove. In addition, the wedge-shaped geometry of the first clamp member is symmetrical about a longitudinal center plane of the first clamp member, and the wedge-shaped geometry of the second clamp member is symmetrical about the longitudinal center plane of the second clamp member.
In another embodiment, the retainer assembly includes a first clamp member and a second clamp member, the first clamp member has a first rail with a first angled surface and a first curved surface and a second rail with a second angled surface and a second curved surface, and the first angled surface, the first curved surface, the second angled surface, and the second curved surface collectively defining a groove therebetween. In addition, the groove has a lower surface, the lower surface, the first curved surface and the second curved surface collectively defining a lower portion of the groove. Also, the first curved surface of the first rail engages the first mounting portion of the fluid end casing, the second curved surface of the second rail engages the second mounting portion of the fluid end component, and the first curved surface and the second curved surface collectively apply a continuously increasing force on both of the first mounting portion and the second mounting portion as the retainer assembly is tightened. Moreover, an angle of orientation of the first curved surface relative to the lower surface is different than an angle of orientation of the first angled surface relative to the lower surface. In yet another embodiment, the second curved surface is oriented at a same angle relative to the lower surface as the first curved surface, the second angled surface is oriented at a same angle relative to the lower surface as the first angled surface, and the first curved surface and the second curved surface collectively apply more force to the first mounting portion and the second mounting portion than the first angled surface and the second angled surface.
In an alternative embodiment, the fluid end component is a flanged stuffing box, a portion of the stuffing box is locatable in the fluid end casing and the first mounting portion is a first flange coupled to the fluid end housing/casing, the second mounting portion is a second flange extending from the stuffing box, and the retainer assembly couples the first flange to the second flange. In another embodiment, the fluid end casing includes a third mounting portion, the fluid end component is a first fluid end component, and the reciprocating pump includes a second fluid end component configured to engage the fluid end casing, the second fluid end component including a fourth mounting portion, wherein the retainer assembly is engageable with the third mounting portion and the fourth mounting portion simultaneously when the retainer assembly engages the first mounting portion and the second mounting portion, and the retainer assembly applies a force to each of the first mounting portion and the second mounting portion to force the first mounting portion and the second mounting portion together, and applies a force to each of the third mounting portion and the fourth mounting portion to force the third mounting portion and the fourth mounting portion together. The retainer assembly can be placed in a first orientation in which the retainer assembly couples the fluid end component to the fluid end casing, and in a second orientation in which the retainer assembly is tightened to apply a pre-load force to the fluid end casing and the fluid end component.
In another embodiment, a fluid end of a reciprocating pump includes a casing (also referred to herein as a housing and/or main body) defining a fluid cylinder and including a first mounting portion, a fluid end component configured to engage the fluid cylinder, the fluid end component including a second mounting portion, the first mounting portion and the second mounting portion collectively forming a joint, and a coupling assembly that engages the first mounting portion and the second mounting portion, the coupling assembly including a first curved surface portion and a second curved surface portion opposing the first curved surface portion, the first curved surface portion engages the first mounting portion, the second curved surface portion engages the second mounting portion, the first curved surface portion and the second curved surface portion along with a curved lower surface collectively forming a wedge-shaped groove therebetween, and both of the first curved surface portion and the second curved surface portion applying an increasing pre-load compression to the joint formed by the first mounting portion and the second mounting portion as the coupling assembly is tightened from a coupling position to a pre-load applying position.
In an alternative embodiment, the coupling assembly includes a first rail with the first curved surface portion and an opposing second rail with the second curved surface portion, the wedge-shaped groove has a lower point, the distance between the first curved surface portion and the second curved surface portion at a first distance from the lower point is greater than the distance between the first curved surface portion and the second curved surface portion at a second distance from the lower point when the first distance is greater than the second distance. The first mounting portion is a first flange on the fluid end casing, the second mounting portion is a second flange on a removable stuffing box, and the coupling assembly is a pair of arcuate clamps that can be secured together about the first flange and the second flange.
In yet another embodiment, a fluid end of a reciprocating pump includes a casing defining a fluid cylinder and including a first flange extending therefrom, a fluid end component configured to engage the fluid cylinder and including a second flange extending therefrom, and a clamping assembly having a first clamp member and a second clamp member coupleable to the first clamp member, the first clamp member having a first clamp rail and a second clamp rail that define a first wedge-shaped groove therebetween configured to receive the first flange and the second flange, the first clamp rail and the second clamp rail being configured so that the wedge-shaped groove forces the first flange into engagement with the second flange to apply a pre-load force thereto, wherein the amount of pre-load force applied to the first flange and the second flange is determined by how far the first flange and the second flange extend into the wedge-shaped groove.
Alternatively, the first clamp rail includes a first end, a first angled surface and a first compression applying surface, the second clamp rail includes a second end, a second angled surface across the groove from the first angled surface, and a second compression applying surface across the groove from the first compression applying surface, the groove has a lower point, a first distance between the first angled surface and the second angled surface continuously decreases closer to the lower point, and a second distance between the first compression applying surface and the second compression applying surface continuously decreases closer to the lower point, the second distance being less than the first distance.
The first clamp member and the second clamp member are coupled together in a first configuration by at least one connector to secure the first flange and the second flange together, and the first clamp member and the second clamp member are tightened together in a second configuration different from the first configuration to apply a pre-load force to the first flange and the second flange. The fluid end component is a flanged stuffing box, a portion of the stuffing box is locatable in the casing, and the clamping assembly couples the first flange to the second flange.
The foregoing advantages and features will become evident in view of the drawings and detailed description.
To complete the description and in order to provide for a better understanding of the present application, a set of drawings is provided. The drawings form an integral part of the description and illustrate embodiments of the present application, which should not be interpreted as restricting the scope of the invention, but just as examples. The drawings comprise the following figures:
Like reference numerals have been used to identify like elements throughout this disclosure.
The following description is not to be taken in a limiting sense but is given solely for the purpose of describing the broad principles of the invention. Embodiments of the invention will be described by way of example, with reference to the above-mentioned drawings showing elements and results according to the present invention.
Generally, the present application is directed to techniques for securing one or more fluid end components, such as a stuffing box, against a fluid end casing of a high pressure reciprocating pump. The techniques may be embodied as a retaining or clamping assembly. Additionally, the techniques may be embodied as one or more methods for securing one or more fluid end components to a fluid end casing of a high pressure reciprocating pump.
The invention relates to a retaining assembly for a positive displacement, reciprocating pump that utilizes a particular geometry to secure elements together. The retaining assembly includes a clamp that secures elements together, such as an external fluid end element or component and the fluid end casing of the pump. In one embodiment, the retaining assembly includes a clamp with a wedge-shaped geometry. A benefit of the wedge-shaped geometry is that it allows the clamp to be pre-loaded to a stress level that is close or similar to the stress level that the joint will experience during operation of the pump. The pre-load stress increases the fatigue life of the parts of a joint significantly. In the present invention, the retaining feature or clamp utilizes a minimal number of connectors due to the mechanical advantage provided by the wedge geometry.
In one embodiment, the fluid end element or component is a stuffing box that is coupled or secured to the fluid end casing (also referred to as a housing, body, and/or main body) of a reciprocating pump. In particular, the element is coupled to a flange that is formed integrally with a casing of the fluid end. In an alternative embodiment, a flange may be bolted to the casing of the fluid end, and the element is secured to the bolted flange.
Referring to
In any case, often, the reciprocating pump 100 may be quite large and may, for example, be supported by a semi-tractor truck (“semi”) that can move the reciprocating pump 100 to and from a well. Specifically, in some instances, a semi may move the reciprocating pump 100 off a well when the reciprocating pump 100 requires maintenance. However, a reciprocating pump 100 is typically moved off a well only when a replacement pump (and an associated semi) is available to move into place at the well, which may be rare. Thus, often, the reciprocating pump is taken offline at a well and maintenance is performed while the reciprocating pump 100 remains on the well. If not for this maintenance, the reciprocating pump 100 could operate continuously to extract natural oil and gas (or conduct any other operation). Consequently, any improvements that extend the lifespan of components of the reciprocating pump 100, extend the time between maintenance operations (i.e., between downtime), and/or minimize the time needed to complete maintenance operations (minimizing downtime) are highly desirable.
Still referring to
In various embodiments, the fluid end 104, and specifically the fluid end casing 206, may be shaped differently and/or have different features, but may still generally perform the same functions, define similar structures, and house similar components. For example, while fluid end 104 includes a first bore 204 that intersects an inlet bore 212 and an outlet bore 222 at skewed angles, other fluid ends may include any number of bores arranged along any desired angle or angles, for example, to intersect bore 204 (and/or an access bore) substantially orthogonally and/or so that two or more bores are substantially coaxial. Generally, bores 212 and 222, as well as any other bores (i.e., segments, conduits, etc.), may intersect to form a pumping chamber 208, may be cylindrical or non-cylindrical, and may define openings at an external surface 210 of the casing 206. Additionally, bores 212 and 222, as well as any other bores (i.e., segments, conduits, etc.), may receive various components or structures, such as sealing assemblies or components thereof.
In the depicted embodiment, inlet bore 212 defines a fluid path through the fluid end 104 that connects the pumping chamber to a piping system 106 delivering fluid to the fluid end 104. Meanwhile, outlet bore 222 allows compressed fluid to exit the fluid end 104. Thus, in operation, bores 212 and 222 may include valve components 51 and 52, respectively, (e.g., one-way valves) that allow bores 212 and 222 to selectively open and deliver a fluid through the fluid end 104. Typically, valve components 51 in the inlet bore 212 may be secured therein by a piping system 106 (see
In operation, fluid may enter fluid end 104 via outer openings of inlet bores 212 and exit fluid end 104 via outer openings of outlet bores 222. More specifically, fluid may enter inlet bores 212 via pipes of piping system 106, flow through pumping chamber 208 (due to reciprocation of a reciprocating elements 202), and then flow through outlet bores 222 into a channel 108 (see
Meanwhile, each of bores 204 defines, at least in part, a cylinder for reciprocating elements 202, and/or connects the casing 206 to a cylinder for reciprocating elements 202. More specifically, in the illustrated embodiment, a casing segment 207 houses a packing assembly 36 configured to seal against a reciprocating element 202 disposed interiorly of the packing assembly 36 and prevent fluid from leaking through reciprocation or reciprocating bore 204. Reciprocation of a reciprocating element 202 in or adjacent to bore 204, which may be referred to as a reciprocation bore (or, for fracking applications, a plunger bore), draws fluid into the pumping chamber 208 via inlet bore 212 and pumps the fluid out of the pumping chamber 208 via outlet bore 222. However, over time, the packing assembly 36 will wear and/or fail, and thus, must be accessed for maintenance and/or replacement. Other components, such as valve components 51 and/or 52, or the fluid end casing 206 itself may also wear and/or fail and require repair or replacement over time. To help provide access to these parts and/or the pumping chamber, some fluid ends have access bores that are often aligned with (and sometimes coaxial with) the reciprocating bore 204. Other fluid ends needs not include access bore and, thus, such an access bore is not illustrated in
Regardless of whether the fluid end includes an access bore, the packing assembly 36 typically needs to be replaced from an outer opening of bore 204 (i.e., a side of bore 204 aligned with the external surface 210 of the casing 206). At the same time, to operate properly, the packing assembly 36 must be securely positioned around the reciprocating element 202, either in or proximate to the reciprocation bore 204. Thus, in many prior art embodiments, the reciprocation bore 204 defines a stuffing box 37, e.g., in the form of a stepped cavity wall. Then, a closure component 39, such as a sleeve or retaining nut, retains the packing assembly 36 (e.g., a set of packing rings) in the stuffing box 37. Alternatively, in some prior art embodiments, a removable stuffing box is removably coupled to a fluid end and defines, or at least partially defines, a stuffing box 37 for a packing assembly 36. However, since the packing assembly 36 often wears much faster than then removable stuffing box, the removably stuffing box must be openable to allow the packing assembly 36 to be replaced or repaired. Thus, removable stuffing boxes are often removably sealed by a component, such as a retaining nut (also referred to as a gland nut) that is removably attachable to the removable stuffing box.
In the former instances (e.g., where a closure component 39 retains the packing assembly 36 in a stuffing box 37 defined by the fluid end 104), the closure component 39 may experience a high load of forces (i.e., high stress). Thus, the closure component 39 must be tightly and securely coupled to the fluid end casing 206, e.g., with threads and/or bolts, and may wear out quickly over time. Meanwhile, in the latter instances (e.g., where a removable stuffing box is removably coupled to a fluid end casing), both the removably stuffing box and the closure component 39 (e.g., a retaining or gland nut) may experience a high load of forces. Thus, the removable stuffing box must be tightly and securely coupled to the fluid end casing 206, e.g., with threads and/or bolts, and the closure component 39 (e.g., a retaining or gland nut) must be tightly and securely coupled to the removable stuffing box. But, even with such connections, portions of the removable stuffing box and the closure component 39 may wear out quickly over time.
Now turning to
Coupled to housing 320 are several fluid end components 400, 500, and 600. In one embodiment, the fluid end components 400, 500, and 600 are flanged stuffing boxes, each of which is proximate to and associated with one of the reciprocating bores 330, 334, and 334. Several retaining members 450, 550, and 700 are used to couple respective ones of the fluid end components 400, 500, and 600 to the housing 320. In this embodiment, fluid end component 400 is coupled to housing 320 via retaining member 450, fluid end component 500 is coupled to housing 320 via retaining member 550, and fluid end component 600 is coupled to housing 320 via retaining member 700.
Referring to
Housing 320 includes a mounting flange or mounting portion 340 coupled thereto. In this embodiment, the mounting portion 340 is integrally formed with housing 320. The mounting portion 340 is aligned with a fluid cylinder 335. Similarly, the mounting flange or mounting portion 360 is coupled to the housing 320, and in this embodiment, is integrally formed with housing 320.
Fluid end component 600 is coupled to housing 320 via retainer assembly 700. The retainer assembly 700 is referred to alternatively as a coupler assembly. In this embodiment, retainer assembly 700 includes a pair of clamp members 710 and 810. Clamp member 710 can be referred to as an upper clamp member, and clamp member 810 can be referred to as a lower clamp member. The clamp members 710 and 810 are coupled to each other by several connectors, of which connectors 902, 904, and 906 are illustrated in
As described in greater detail below, each of the clamp members 710 and 810 has a configuration that enables the tightening of the connectors to initially couple the clamp members 710 and 810 together, and then as the connectors are further tightened, a pre-load force or tension is applied to the fluid end component 600 and a corresponding mounting portion on the housing 320. This feature allows a user to adjust the amount of pre-load or tension applied to the joint formed by the fluid end component and the fluid end housing.
Referring to
Fluid end housing 320 includes mounting flange or portion 350, which similar to mounting portions 340 and 360, is formed integrally with housing 320. As shown in
As shown in
Cross-sectional views of each of clamp member 710 and clamp member 810 are illustrated in
Clamp member 710 includes a first ridge or rail 730 and a second ridge or rail 740 that define a groove 765 therebetween. As illustrated, groove 765 is wedge-shaped. Similarly, clamp member 810 includes a first ridge or rail 830 and a second ridge or rail 840 that define a groove 865 therebetween. Groove 865 is also a wedge-shaped groove. First rails 730 and 830 are aligned with each other when the ends of clamp members 710 and 810 are placed in contact with each other. Similarly, second rails 740 and 840 are aligned with each other when the ends of clamp members 710 and 810 are placed in contact with each other. First rails 730 and 830 engage with an outer groove formed in the fluid end component 600. Second rails 740 and 840 engage with the groove 352 formed by the mounting flange 350.
As shown in
Turning to
Angled surface 736 is oriented at an angle (and angle of orientation) with respect to a longitudinal center plane 725 of the clamp member 710 as well as with respect to a lower surface of the groove. Angled surface 746 is also oriented at an angle with respect to plane 725, and in particular, at the same angle as angled surface 736. In other words, angled surface 746 is symmetrical about plane 725 with angled surface 736. When the flange 622 and the mounting portion 350 are placed proximate each other, the flange 622 engages angled surface 736 and mounting portion 350 engages angled surface 746. As the clamp members 710 and 810 are tightened, the angles of inclination of the angled surfaces 736 and 746 force or drive the flange 622 and mounting portion 350 together.
Clamp member 710 includes a curved surface 750 that has a portion 752 on rail 730 and an opposite portion 754 on rail 740. The curved surface 750 extends to end 756 proximate angled surface 736 and to end 758 proximate angled surface 746. As shown in
Turning to
Clamp member 1410 has a body 1420 that includes rails 1430 and 1440 and a groove 1465 between the rails 1430 and 1440. In this embodiment, the groove 1465 has a wedge-shape. Rail 1430 includes an end 1432 that has an outer angled surface 1434 on one side and an inner angled surface 1436 on another side. Similarly, rail 1440 includes an end 1442 that has an outer angled surface 1444 on one side and an inner angled surface 1446 on another side. As can be appreciated from
Angled surface 1436 is oriented at an angle (and angle of orientation) with respect to a longitudinal center plane 1425 of the clamp member 1410 as well as with respect to a lower surface 1460 of the groove 1465. Angled surface 1446 is also oriented at an angle with respect to the center plane, and in particular, at the same angle as angled surface 1436. Thus, angled surface 1446 is symmetrical about plane 1425 with angled surface 1436. When the flange 622 and the mounting portion 350 are placed proximate each other, the flange 622 engages angled surface 1436 and mounting portion 350 engages angled surface 1446. As the clamp members are tightened, the angles of inclination of the angled surfaces 1436 and 1446 force or drive the flange 622 and mounting portion 350 together.
As shown in
Referring to
Referring to
Referring to
Referring to
Referring to the cross-sectional view of clamp member 810 in
Referring to
Referring to
Referring to
Referring to
Referring to
In this embodiment, instead of separate retaining or clamping assemblies for each fluid end component, one retaining or clamping assembly is provided for all of the fluid end components. Retaining assembly 1225 includes a pair of clamp members 1230 and 1240, each of which includes several recesses 1232 and 1242 that are aligned with bores 1220, 1222, and 1224 and sized to receive fluid end components. The clamp members 1230 and 1240 are coupled together via several connectors 1250, such as screws or bolts. In a manner similar to previous embodiments of clamp members described herein, the increased tightening of the connectors 1250 that couple clamp members 1230 and 1240 together will force the flanges of the fluid end component and the fluid end housing together more and more.
As shown in
Referring to
Referring to
While the invention has been illustrated and described in detail and with reference to specific embodiments thereof, it is nevertheless not intended to be limited to the details shown, since it will be apparent that various modifications and structural changes may be made therein without departing from the scope of the inventions and within the scope and range of equivalents of the claims. In addition, various features from one of the embodiments may be incorporated into another of the embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure as set forth in the following claims.
Similarly, it is intended that the present invention cover the modifications and variations of this invention that come within the scope of the appended claims and their equivalents. For example, it is to be understood that terms such as “left,” “right,” “top,” “bottom,” “front,” “rear,” “side,” “height,” “length,” “width,” “upper,” “lower,” “interior,” “exterior,” “inner,” “outer” and the like as may be used herein, merely describe points of reference and do not limit the present invention to any particular orientation or configuration. Further, the term “exemplary” is used herein to describe an example or illustration. Any embodiment described herein as exemplary is not to be construed as a preferred or advantageous embodiment, but rather as one example or illustration of a possible embodiment of the invention.
Finally, when used herein, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc. Meanwhile, when used herein, the term “approximately” and terms of its family (such as “approximate,” etc.) should be understood as indicating values very near to those which accompany the aforementioned term. That is to say, a deviation within reasonable limits from an exact value should be accepted, because a skilled person in the art will understand that such a deviation from the values indicated is inevitable due to measurement inaccuracies, etc. The same applies to the terms “about” and “around” and “substantially.”
