Abstract:
Method and apparatus for raising a floating roof included in a storage tank whereby a first and a first opposite force are applied between a floor in the storage tank and an internal surface of the floating roof. An additional set of forces are also provided and are constrained according to the first and first opposite force, not only in magnitude, but in position. By constraining these forces to be applied orthogonally to the floating roof, horizontal shear forces can be resisted thus reducing the likelihood of failure of a cribbing unit. By increasing these forces, the roof is raised.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 15/003,714, entitled Method and Apparatus for Supporting a Floating Roof Disposed In A Storage Tank, by David L. Bush, filed on Jan. 21, 2016, the specification and figures of which are incorporated herein by reference in their entirety and the priority date of which is claimed herein to the maximum extent allowable. 
     
    
     BACKGROUND 
       [0002]    There are many situations where there is a need to support a planar structure at variable distances in height to different distances to lower some height above the ground. One such application is that of a storage tank that includes a floating roof disposed therein. This example use case can be best described with reference to  FIG. 1 . In  FIG. 1 , a floating roof structure  200  is typically used where a storage tank  205  is used to store a liquid, for example, jet fuel, gasoline, diesel, sour water and crude oil. It should be appreciated that there are merely examples of the type of liquids that can be stored in a tank. 
         [0003]    It is common place for such a storage tanks to include a floating roof structure for environmental protection purposes. Floating roofs substantially reduce the emission of flammable and/or hazardous vapor in to the environment. It should be appreciated that such a floating roof structure “floats” on top of the liquid product stored in the storage tank. As the level of the liquid product stored in the tank fluctuates, so does the height of the floating roof structure relative to a floor included in such a tank. 
         [0004]    Government regulations mandate that such storage tanks be inspected every ten years. Such an inspection is generally required to meet the requirements of API 653. The regulations require that all above ground storage tanks are to be inspected and repaired to API 653 standards in order to verify the structural integrity of the tank shell, the integrity of the floating roof vapor control integrity and the tank floor. One aim of such inspections is to detect and remedy any seepage of hazardous, toxic or flammable liquids into the ground. 
         [0005]    Undetected seepage is likely to cause environmental impact with wide reaching consequences, such as pollution of water tables. For example, more frequent inspection could have prevented a recent environmental crisis in West Virginia where a hazardous chemical leaked from a storage tank and contaminated the water table. Because such inspections are known to reveal the type and extent of repairs needed to remedy leaks and other environmental cataclysms, it is unlikely that any of these inspection requirements will ever be abated. And, there are also occasions when the storage tank must be cleaned in preparation for storing a different liquid produce or a different class of a liquid product relative to a former substance previously stored in the tank. The floating roof must be held above the floor of the storage tank so that personnel can freely and safely conduct themselves during all such inspection, repair and cleaning activities. 
         [0006]      FIG. 1  is a pictorial representation of a prior art apparatus for supporting a floating roof when a storage tank is devoid of liquid content. For years and years and years, the process of supporting a floating roof in the absence of a liquid product has been accomplished using substantially similar methods, each of which rely on the use of substantially identical support apparatus. As can be seen, the prior art has thus far relied on a basic support method using a “cribbing stack”, also known as a “vertical load backup”. 
         [0007]    A cribbing stack  210  is typically made up of alternating layers of wood members, wherein each wood member from a preceding layer is set orthogonal to a subsequent layer. Hence, the height of the cribbing stack could be adjusted by simply stacking up more of such alternating layers of wooden members. Up until now, this prior art technique has been used without much deviation from this basic concept, that being the use of alternating layers of wooden members. It should be noted that these wooden members are somewhat akin to common railroad ties that are readily available throughout the world. 
         [0008]      FIG. 1  also depicts one grave disadvantage associated with the use of a wooden, layered cribbing stack. It is well settled that a floating roof may exhibit rotational forces  215 . When the floating roof is first lowered and substantially all product is removed from the tank, a collection of “legs”, each of which penetrates the floating roof, are used to support the floating roof. These legs are very susceptible to horizontal forces that each leg experiences when the roof begins to rotate. This is true regardless of whether the storage tank is empty or of it has liquid content. 
         [0009]    Wind can induces such rotational movement of the floating roof. There are methods to retard such rotational movement, but these methods often fail. One such method is based on the use of “anti-rotation wedges”. These wedges are, by their very name, disposed between an outer perimeter of the floating roof and an internal wall of the storage tank. Such anti-rotational wedges are scarcely effective in the face of sever rotational movement of the floating roof. 
         [0010]    It is when the floating roof exhibits rotational movement that personnel working under a floating roof situated in a storage tank are most vulnerable to injury and death. When a floating roof begins to rotate, it begins to apply a moment force onto each leg. Now, as the legs begin to fail, the plurality of wooden cribbing stacks are intended to support the floating roof at some minimum height necessary to keep all personnel safe. Because the layers of a wooden cribbing stack are not fastened to each other, the cribbing stack simply falls apart when these horizontal forces go unopposed. The upper layers of the cribbing stack, from a force perspective, simply shear away from the lower layers of the cribbing stack. This, of course, results in the type of total failure of the support structure that has cost many lives and has resulted in extensive collateral, materiel damage and environmental impact. 
         [0011]    There are many serious environmental issues associated with the use of a wooden cribbing stack. In should be appreciated that the product ordinarily stored in a storage tank is a liquid and such liquids are typically hazardous materials. Such hazardous material may include petro chemical products, crude oil, flammable liquids and many other forms of extremely hazardous materials. Residual product in the storage tank will ordinarily permeate the wooden members. Hence, such contaminated wooden members cannot be reused and must be discarded as hazardous waste. And, each time a wooden member is discarded, new lumber must be used at the cost of many trees, harvested from our forests, further impacting global warming and greenhouse gas effects. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Several alternative embodiments will hereinafter be described in conjunction with the appended drawings and figures, wherein like numerals denote like elements, and in which: 
           [0013]      FIG. 1  is a pictorial representation of a prior art apparatus for supporting a floating roof when a storage tank is devoid of liquid content; 
           [0014]      FIG. 2  is a flow diagram that picks one example method for minimum of raising a first section of floating roof; 
           [0015]      FIG. 3  is a flow diagram that depicts one alternative example method for raising a first section of floating roof which relies upon a third set of forces; 
           [0016]      FIG. 4  is pictorial diagram that illustrates the usage of a Delta-P lifting unit together with a Delta-P cribbing unit; 
           [0017]      FIG. 5  is a flow diagram that depicts one alternative example method wherein raising a roof is accomplished with additional confidence through the use of a cribbing unit; 
           [0018]      FIG. 6  is a flow diagram that depicts one example method for adjusting the magnitude of the second and second opposite forces; 
           [0019]      FIG. 7  is a pictorial diagram that depicts the application of forces in order to raise different portions, or sections of a floating roof; 
           [0020]      FIG. 8  is a flow diagram for one alternative example method for lifting a second portion of a floating roof; 
           [0021]      FIG. 9  is a flow diagram that depicts alternative example method wherein a second portion of a roof is lifted by a force substantially similar to the forces applied in lifting a first section of a floating roof; 
           [0022]      FIGS. 10A and 10B  are pictorial diagrams that depict one alternative example embodiment of a multistage, extendable riser; 
           [0023]      FIG. 11  is a pictorial diagram that depicts a control structure for a Delta-P lifting unit; 
           [0024]      FIGS. 12A and 12B  are pictorial diagrams that illustrate a control structure for raising a floating roof in more than one section; and 
           [0025]      FIG. 13  is a pictorial diagram that depicts a hydraulic control structure for a Delta-P lifting unit. 
           [0026]      FIG. 14  is a pictorial diagram that depicts an alternative example of a control panel for use with Delta-P lifting units. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]      FIG. 2  is a flow diagram that picks one example method for minimum of raising a first section of floating roof. It should be appreciated that a storage tank, as already described in applicant&#39;s first disclosure referenced and incorporated herein, typically includes a floating roof. There are occasions where the floating roof may rotate and collapse and this can result in injury and death to personnel working under such roofs. According to one example method, raising a floating roof is accomplished by applying a first force to an internal surface of the roof (step  5 ). It should be appreciated that any reference to a method step by a reference to a figure, e.g. “(step  1 )”, is intended to include that method step in an open-ended enumeration of steps as provided in the method claims appended hereto. 
         [0028]    According to this example method, a first substantially opposite” linear forced is applied to the floor (step  10 ). Much akin to a method for supporting a floating roof described in the referenced application, the first forced and the first opposite force are typically provided by a vertically disposed mechanical member. In this example method, the vertically disposed mechanical member can be extended in order to effect raising of the floating roof. In contrast with the disclosure of a method for supporting a floating roof referenced herein, a method for supporting a floating roof is not provide for extension of such a vertically disposed mechanical member. 
         [0029]    This example method continues by applying a second forced to the internal surface of the roof (step  15 ). A second substantially opposite and linear forced to that (to the second force) is applied to the floor (step  20 ). In order to effect raising of the floating roof, the magnitude of the first substantially opposite first forced is increased (step  25 ). It should also be appreciated that the magnitudes of the second substantially opposite second force are adjusted according to the magnitude of the first substantially opposite first forced (step  30 ). These magnitudes are increased until the roof begins to lift (step  35 ). 
         [0030]    It should be appreciated that, according to various alternative example method, the magnitude of the second substantially opposite second forces are adjusted so that the force applied to a first section of a floating roof is substantially uniform, when considering that the first and first opposite force and the second and second opposite force are used conjunctively in raising such first portion of a floating roof. 
         [0031]      FIG. 3  is a flow diagram that depicts one alternative example method for raising a first section of floating roof which relies upon a third set of forces. In this alternative example method, a third forced is applied to the internal surface of the roof (step  40 ). A third substantially opposite and linear forced is applied to the floor (step  45 ). It should be appreciated that, according to the various alternative methods herein disclosed, a first forced and a first substantially opposite and linear forced are typically applied contemporaneously and are typically applied by a single vertical member that contacts the floor at one end and the floating roof at the other end. 
         [0032]    In this alternative example method, the magnitude of the third force and the substantially opposite linear force is adjusted according to at least one of the magnitude of the first forced (step  50 ), the magnitude of the first opposite force (step  60 ), the magnitude of the second force (step  55 ), and the magnitude of the second opposite force (step  65 ). 
         [0033]    It should be appreciated that any of the forces applied to either the internal surface of the floating roof or to the floor maybe uses references in order to adjust to the third force and its substantially equal and linear force. In this manner, the force applied to raise the floating roof is essentially uniform across a particular first section of a floating roof. 
         [0034]      FIG. 4  is pictorial diagram that illustrates the usage of a Delta-P lifting unit together with a Delta-P cribbing unit. It should be appreciated that, according to various alternative use cases, a Delta-P lifting unit  300  is used to raise a floating roof. However, to provide added safety for personnel, a Delta-P cribbing unit  200  may be used to reduce the risk of a catastrophic collapse of a floating roof as it is being lifted according to the teachings of the present method. In such situations, it should be appreciated that a Delta-P cribbing unit  200  includes vertical support members  220 , which are substantially disposed at the points of a triangle when viewed from a plan perspective. This is alternative embodiment of a cribbing unit is described in the incorporated reference. It should further be appreciated that one alternative method relies upon placement of the extendable vertical support members  310  included in a Delta-P lifting unit  300  proximate to the vertical support members  220  included in a Delta-P cribbing unit  220 . 
         [0035]    In a manner speaking, a Delta-P cribbing unit  200 , according to one example method, is placed coaxially with a Delta-P lifting unit  300 . Although  FIG. 8  depicts that a cribbing unit  200  is smaller than a lifting unit  300 , this is only one example of how a Delta-P lifting unit  300  can be used with a Delta-P cribbing unit  200 . It should be appreciated that a converse arrangement may be utilized where the Delta-P cribbing unit  200  is larger than the lifting unit  300 . 
         [0036]    What should be appreciated from this discussion is that vertical members in the Delta-P lifting unit  300  are, according to one alternative method, positioned proximate to vertical members  220  included in the Delta-P the cribbing unit  200 . Again, this is merely one illustrative use case which applicant believes is an effective means for using a cribbing unit  200  as a precautionary means for preventing a catastrophic collapse of a floating roof during a lifting procedure, as taught by the various alternative methods disclosed herein and by the cribbing techniques and methods taught in the incorporated reference. 
         [0037]      FIG. 5  is a flow diagram that depicts one alternative example method wherein raising a roof is accomplished with additional confidence through the use of a cribbing unit. As already discussed in relationship to  FIG. 8 , a Delta-P lifting unit  300 , according to one alternative method, is used in conjunction with a Delta-P cribbing unit  200 . Accordingly, in this alternative example method, the first and first opposite forces are positioned proximate to a first support member included in a Delta-P cribbing unit (step  70 ). Likewise, the second and second opposite force are positioned proximate to a second support member included in the Delta-P cribbing unit (step  75 ). 
         [0038]      FIG. 6  is a flow diagram that depicts one example method for adjusting the magnitude of the second and second opposite forces. It should be appreciated that the first force and a first opposite force, which is substantially collinear with and substantially equal in magnitude to the first force, maybe referred to as a force set. Accordingly, the magnitude of a first force set, which in this disclosure includes the first forced and its opposite force substantially opposite and collinear first force, is used as a reference for adjusting the second force set, which according to this disclosure includes the second and its substantially opposite and collinear second force. 
         [0039]    In this alternative example method, a first method step comprises determining the magnitude of the first force set by measuring, according to a pre-defined accuracy, of the magnitude of the first and the first opposite and substantially collinear force (step  80 ). Next, the magnitude of the second force set is determined by measuring, according to a pre-defined accuracy, the magnitude of the second and its substantially opposite and collinear second force (step  85 ). Once the magnitudes of the first and second forces sets are determined, a difference in these magnitudes is then calculated (step  90 ). The magnitude of the second and second opposite forces is then adjusted in order to reduce the difference between the first and second force sets (step  95 ). 
         [0040]      FIG. 7  is a pictorial diagram that depicts the application of forces in order to raise different portions, or sections of a floating roof. In this figure, a floating roof  107  is being raised in at least two different portions of the roof. In this illustrative use case, a set of forces is applied to a first section of a floating roof  122 . This is typically accomplished by a first Delta-P lifting unit  300 . 
         [0041]    A second Delta-P lifting unit  301  is utilized in order to apply lifting forces to a second section  123  of the floating roof  107 . Although not seen in this figure, the floating roof  107  includes an internal surface, upon which were forces are applied to raise the roof  107 . A storage tank itself includes a floor  111 , upon which are applied substantially equal forces that are collinear to the forces applied to the internal surface of the roof. 
         [0042]      FIG. 8  is a flow diagram for one alternative example method for lifting a second portion of a floating roof. According to this alternative example method, a second portion of the floating roof is lifted by applying a fourth force to the internal surface of the floating roof (step  100 ) along with a substantially opposite and substantially collinear force to the floor of the storage tank (step  105 ). In essentially a contemporaneous manner, a fifth force is applied to the internal surface of the roof (step  110 ) along with application to the floor of a fifth substantially opposite and substantially collinear force (step  115 ). In this example alternative method, a sixth force is applied to the internal surface of the roof (step  120 ) and a sixth substantially opposite and substantially collinear force is applied to the floor (step  125 ). 
         [0043]    It should be appreciated that according to this alternative example method, lifting a second portion of a floating roof is typically accomplished by a Delta-P lifting unit has already discussed relative to  FIG. 7 . Accordingly, an additional step of constraining the distance between the fourth and its opposite force, the fifth and its opposite force, and a sixth and its opposite force to a substantially similar value (step  130 ). 
         [0044]    It should be appreciated that this step for constraining the distances to a substantially equal value should typically result in a triangular pattern commensurate with Delta-P lifting technology disclosed herein. Applying these forces provides for lifting a second portion of a roof, but does not provide for a uniform application of force in said second portion of the roof. Accordingly, is typically necessary to adjust the magnitude of the fourth and its opposite force in the fifth and its opposite force and a sixth and its opposite force so is all of these forces are at the substantially similar magnitude (step  135 ). 
         [0045]      FIG. 9  is a flow diagram that depicts alternative example method wherein a second portion of a roof is lifted by a force substantially similar to the forces applied in lifting a first section of a floating roof. Just as the forces within a particular section of roof should be maintained at a substantially similar magnitude, has already described, one alternative example method provides for maintaining a substantially similar force across two or more section is of roof that are being lifted in accordance with the teachings presented herein. Accordingly, one such alternative example method provides for adjusting the magnitude of the fourth and its opposite force, the fifth and its opposite force, and a sixth and its opposite force so as the magnitude of these forces is substantially similar to the first in first opposite forces applied in a first section of the roof. 
         [0046]    In yet another alternative example employment, the forces in a second portion of the roof are adjusted so that their magnitude differs from forces applied in a first section of the roof by a pre-established value. This example alternative method recognizes that the force applied to a first section of the roof may need to be different and forces applied to a second section of the roof because of the mechanical dynamics involved in raising the roof. For example, once a particular section of roof is raised to particular level the total force at a particular section may be greater or less than forces involved in supporting and ultimately raising a second portion of the roof. 
         [0047]      FIG. 4  further illustrates one example embodiment of a lifting system that is useful in applying the methods taught herein. According to this one example employment, a lifting system  300  comprises a first base member  341  and a second base member  342 . Each such base member includes a vertical riser receptacle  315  and a receptacle for a horizontal span  344 . This example embodiment further includes a first camping member  301  and a second capping member  302 . It should be appreciated that each of these capping members includes a receptacle for a vertical riser  305  and a receptacle for a horizontal cap span  306 . This example embodiment further includes a horizontal base span  340  and a horizontal cap span  341 , which, upon assembly, are received by corresponding receptacles included in the base members and the capping members. 
         [0048]    Referring to the incorporated reference, it should be noted that vertical risers are used in order to hold the base span members and the capping span members at some vertical distance from each other. Typically, the base span members are placed upon a storage tank floor and then the vertical risers are used to hold the capping members, along with the capping span at some elevation above the storage tank floor. Again, it should be appreciated that, according to the incorporated reference and the teachings herein, the vertical risers are received by the vertical riser receptacles included in the capping members and the base members. 
         [0049]    According to one example embodiment of a lifting system, the vertical risers are not fixed in length as they are in a Delta-P cribbing unit, as described in the incorporated reference. Rather, a lifting system  300  includes a plurality of extendable risers  310 . The extendable risers  300  are received by the vertical riser receptacles included in the capping members and the base members. 
         [0050]    In order to fully appreciate the structure of this example embodiment of the lifting system  300 , we draw attention to a first extendable riser  310 , included in this example embodiment, which is received by the vertical riser receptacle included in the first base member  344  and is also received in a riser receptacle included in the first the cap member  301 . A second extendable riser  315  is also included in this example embodiment and is received by the vertical riser receptacle in the second base member  341  and the riser receptacle included in the second cap member  302 . 
         [0051]      FIG. 4  further illustrates that an extendable riser includes a length control function, which according to one alternative example embodiment is enabled by application of a working fluid to a first port  340 . When a pressurized working fluid is applied to the first port  340 , the length of the extendable riser increases according to the pressure of the working fluid. It should be appreciated that, according to one alternative example embodiment, an extendable riser comprises a pneumatic cylinder which extends in length when a hydraulic fluid, under pressure, is directed to such a first port  340 . 
         [0052]    It should likewise be appreciated that, according to yet another alternative example embodiment, the length control function is enabled by application of a working fluid to a second port  335 . In this alternative example embodiment, the second port  335  receives pressurized working fluid in order to shorten the length of the extendable riser. It should further be appreciated that, according to one alternative example embodiment, an extendable riser that can be shortened in this manner comprises a pneumatic cylinder that includes a dual action capability. Such “dual action” pneumatic cylinders extend the length of the cylinder upon application of a pressurized working fluid to the first port  340  and shorten the length of the cylinder upon application of a pressurized working fluid to the second port  335 . 
         [0053]      FIGS. 10A and 10B  are pictorial diagrams that depict one alternative example embodiment of a multistage, extendable riser. It should be appreciated that, according to one alternative example embodiment, an extendable riser  300  included in a lifting system comprises a dual acting, multistage pneumatic cylinder.  FIG. 10A  illustrates that, according to another alternative example embodiment, and extendable vertical riser  300  comprises a two-stage cylinder that includes a first stage  313 , a second stage  312  and a piston  311 . 
         [0054]    It should be appreciated that multistage, dual acting pneumatic cylinders are quite commonplace. The figures here are only intended to illustrate one example embodiment of such pneumatic cylinders and there is no need to teach the intricacies of this well-known technology. A very high-level summary reveals that the first stage  313  of the cylinder acts upon the second stage of the cylinder  312 . 
         [0055]    It should be appreciated that the second stage of the cylinder  312  acts as a piston within the first stage  313  of the pneumatic cylinder. Since the second stage of the cylinder  312  acts as a piston relative to the first stage  313 , application of a pressurized fluid at the first port  340  causes the second stage  312  to push upward away from the first port  340 . 
         [0056]    The pressurized working fluid is also channeled into the second stage  312  in order to cause of the piston  311  to move upward away from the first port  340 . Additional channeling is provided for the second port  335  in order to cause retraction of the piston  311  into the second stage  312  and retraction of the second stage  312  into the first stage  313  as shown in  FIG. 10B . Such a two stage cylinder is also depicted in  FIG. 4  where like reference numerals correspond to like stages and the piston  311  that the second stage  312  acts upon. 
         [0057]      FIG. 4  further illustrates that, according to yet another alternative example embodiment, the first and second base members  342 ,  341  further include second base span receptacles  792 ,  773 . Further, this alternative example embodiment includes capping members  301 ,  302  that include a second capping span receptacle  735 ,  736 . This alternative example embodiment provides for, and includes a third extendable riser  399 . This alternative example embodiment also includes a third base member  750 , and a third capping member  700 . It should be appreciated that the third base member  750  and the third capping member  700  include two base span receptacles  760 ,  770  and two cap span receptacles  705 ,  710 , respectively. 
         [0058]    It should be appreciated that, according to this alternative example embodiment, a lifting system comprises a Delta-P lifting unit  300 . It should be further appreciated that, according to one alternative example embodiment, the three extendable risers  310 ,  315  and  399 , when viewed from the top of the lifting unit, are situated at the vertices of a substantially equilateral triangle. As such, the base span receptacles, for example the base span receptacles  344  and  792  included in the first base member  342 , are set at an angle substantially equal to 60 degrees. This is true for all of the receptacles, except for the vertical riser receptacles, included in any particular base member or capping member. It should likewise be appreciated that the vertical riser receptacles are situated substantially orthogonal to the base span and cap span receptacles. 
         [0059]    Assembly of such a Delta-P lifting unit  300  is accomplished by receiving an included second base span  781  into the first base span receptacle  770  included in the third base member  750 . This second base span is also received in the second base span receptacle  792  of the first base member  342 . A third base span  780  is also included in this alternative example embodiment and is received in the second base span receptacle  760  of the third base member  750 . The other end of the third base span  780  is received by the second base span receptacle  773  included in the second base member  341 . 
         [0060]    This alternative embodiment also includes a second cap span  715  and a third cap span  720 . The second cap span  715  is received in the first cap span receptacle  705  in the third capping member  700 . This second cap span  715  is also received in the second cap span receptacle  735  included in the first capping member  301 . The third cap span  720  is received into the second cap span receptacles  710  included in the third capping member  700 . The second cap span receptacle  736  included in the second capping member  302  receives the other end of the third cap span  720 . Assembly of this alternative example embodiment also provides that the third extendable riser  399  is received from in the vertical riser receptacle  730  included in the third capping member  700  and the vertical riser receptacle  755  included in the third base member  750 . 
         [0061]      FIG. 11  is a pictorial diagram that depicts a control structure for a Delta-P lifting unit. For the sake of clarity, is helpful to visualize that the capping members held together by cap span can be referred to as a capping structure. It should be appreciated that, according to one alternative example embodiment, extendable risers, which are depicted here by reference numerals  370  and  380 , comprises dual acting pneumatic cylinders. It alternative example embodiment, a lifting unit also includes a third extendable riser  390 . In any such alternative embodiment, each extendable riser provides a load signal, which indicates the amount of force applied to that particular extendable riser. For example, one embodiment includes two extendable risers  370 ,  380  each of which generates an independent load signal  470 ,  475 . In embodiments that include a third extendable riser  380 , that extendable riser provides a third independent load signal  480 . 
         [0062]    Each extendable riser, according to one alternative example embodiment, is provided with at least one control valve, which is used to increase the length of a corresponding extendable riser. For example, in one alternative embodiment, a first valve  440  and a second valve  450  are included in a lifting system and are used to extend the length of a first extendable riser  370  and a second extendable riser  380 . It should be appreciated that, when any such valve is actuated, pressurized working fluid, which is obtained from a hydraulic stores  400 , is directed to a first port in a corresponding extendable riser. 
         [0063]    When the working fluid enters the first port included in the extendable riser, that riser will extend in length. As the riser extends in length, it applies an increasing force to the capping structure according to the pressure of the working fluid applied when a corresponding valve is actuated. Again, for the sake of clarity, an increasing force upon the capping structure causes the capping structure to move upward relative to a tank floor. As such, these valves are indicated as “UP” valves, (“U”). It should also be appreciated that, in those embodiments that include a third extendable riser, a third such “U” valve  460  is provided. When the third “U” vale is actuated, pressurized working fluid from the hydraulic source  400  is directed to the first port in the third cylinder  380 . Thus causes the extension of the third extendable riser  390 . 
         [0064]      FIG. 11  further illustrates that, at least according to some alternative example embodiments, the extendable risers comprises dual acting risers. In such embodiments, additional valves are provided for a downward movement (“D”) of the extendable vertical risers. Accordingly, in embodiments of a lifting system that include two extendable vertical risers  370 ,  380  a first down valve  445  and a second down valve  455  enable application of a pressurized fluid to a second port included in each such extendable riser. When the pressurized working fluid enters the second port included in the extendable riser, it causes the length of the extendable riser to be reduced. This reduces the force pushing upward on the capping structure included in a Delta-P the lifting unit, which causes the capping structure to move downward. The same is true for those embodiments that include a third extendable riser  390  and a third corresponding “D” valve  465 . 
         [0065]      FIGS. 12A and 12B  are pictorial diagrams that illustrate a control structure for raising a floating roof in more than one section. It should be appreciated that, as heretofore discussed, raising a floating roof, according to one illustrate use case, must be done by raising a floating roof according to sections. It should be appreciated that in such alternative example methods, it is necessary to utilize a first set of forces, which are applied to first section of the roof and a second set of forces which are applied to a second section of the roof. Accordingly, a first Delta-P lifting unit  420  is disposed underneath the floating roof at a first section ( 122  in  FIG. 7 ) and a second Delta P lifting unit is disposed under the floating roof at a second section ( 123  in  FIG. 7 ). 
         [0066]    It should be appreciated that, according to one alternative example embodiment, a Delta-P lifting unit includes an interface for receiving control signals that actuated valves in order to raise or lower a capping structure included in the Delta-P lifting unit. In this alternative example embodiment, the Delta-P lifting unit  420  includes an interface for raising or lowering any of three different extendable risers  370 ,  380 ,  390 , which are included in the Delta-P lifting unit  420 . A second Delta-P lifting unit  430  also includes such interfaces for its three separate extendable risers. According to this example embodiment, the interfaces for controlling valves in a Delta-P lifting unit  420  includes a first “UP” valve interface  440 , a first “DOWN” valve interface  445 , a second “UP” valve interface  450 , a second “DOWN” valve interface  455 , a third “UP” valve interface  460  and a third “DOWN” valve interface  465 . It should be appreciated that a Delta-P lifting unit is essentially a fungible item and a second Delta-P lifting unit  430  includes like interfaces to those included in the first Delta-P lifting unit  420 . 
         [0067]      FIG. 13  is a pictorial diagram that depicts a hydraulic control structure for a Delta-P lifting unit. It should be appreciated that each extendable riser  310  in a Delta-P lifting unit  420  is subject to at least two forces. One such force is a downward force  719  imparted upon the extendable riser as result of the weight of a floating roof applied upon the Delta-P lifting unit  420 . A substantially equal but opposite force is directed upward  717  against the extendable riser  300  and can in opposition to the downward force  719 . 
         [0068]    Notwithstanding the fact that the downward force  719  is imparted upon the extendable riser  310  by other mechanical members included in a Delta-P lifting unit  420 , for example a capping structure as heretofore described, forces imparted longitudinally upon the extendable riser  310  are, according to one alternative example embodiment, measured in at least one of two ways. In a first alternative embodiment, the force upon the extendable riser  310  is determined, or more properly measured by a strain gage  317  that is disposed upon the extendable riser  310  in order to measure the forces applied to longitudinally thereupon. 
         [0069]    In yet a second alternative embodiment, in the force imparted to the extendable riser  310  is determined by inference. For example, in this alternative embodiment, the pressure of a working fluid  319  applied to the extendable riser  310  is measured by a pressure transducer  313 . In either of these alternative example embodiments, a load signal is created in accordance with the forces applied to the extendable riser  310 . In the case where a strain gage  317  is disposed upon the extendable riser  310 , a strain gage generates a load signal  312 . Likewise, in those alternative embodiment set include a pressure transducer  313 , the pressure transducer  313  also generates a load signal  314 . 
         [0070]      FIG. 14  is a pictorial diagrams that depicts one alternative example embodiment of a control panel for use with the Delta-P lifting units in accordance with teachings of the present method. It should be appreciated that the hydraulic valves described above need to be controlled in order to safely and effectively raise a roof using the teachings set forth herein. In one alternative example embodiment, a control panel  900  includes a processor  900  a memory  915 . In this alternative example embodiment, the control panel  900  further includes a force acquisition system  920 . 
         [0071]    In yet another alternative example embodiment, the force acquisition system  920  comprises a signal multiplexer  925  and an analog digital converter  930 . Again, this is just one alternative example embodiment of a force acquisition system  920 . In other alternative example embodiments, the force acquisition system is a digital interface that receives force indications from force transducers that transmit force indications in digital form. In this alternative embodiment, a valve control system  950  is also included. A plurality of valve control outputs  955  are included in this alternative example embodiment. It should be appreciated that, according to one alternative embodiment, valve control outputs  955  are organized in pairs in order to control the upward valve (“UP”) and a downward valve (“DOWN”). It should also be further appreciated that three such pairs are needed to control each Delta-P lifting unit  420  has been used to raise a floating roof according to the techniques and teachings presented herein. 
         [0072]    In various alternative example embodiments, the processor  910  executes included instruction sequences that are stored in a memory  915 . These instruction sequences, when executed by the processor  910 , minimally cause the processor  910  to retrieve a force indicator from one of three force acquisition interfaces  970  included in the force acquisition unit  920 . The force acquisition interfaces  710  are typically organized in a grouping of three such interfaces, wherein each interface into grouping receives a force indicator, for example by way of a load signal, from each of three extendable risers included in a Delta-P lifting unit  420 . The instruction sequences, one further executed by the processor  910 , minimally cause the processor to adjust the forces experienced by each of the extendable risers in a Delta-P lifting unit  420  in accordance with the methods taught herein. In order to affect adjustment of the forces experienced by each of the extendable risers  310 , the instruction sequences further minimally cause the processor to actuate the upward and downward valves for each such extendable risers. 
         [0073]    It should be further appreciated that there are several further techniques described herein wherein the processor  910  as it executes instruction sequences stored in a memory  915  is further minimally caused to control three sets of control valves, wherein each set of three control valves control is extendable risers  310  in an individual Delta-P lifting unit. Accordingly, the processor  910  controls these valves in response to force signals from individual Delta-P lifting units  420  where the individual Delta-P lifting units are disposed underneath a floating roof in different sections of said roof. 
         [0074]    Accordingly, in these situations, the processor  910  not only seeks to normalize the forces experienced by each of the three extendable riser is in a particular Delta-P lifting unit  420 , but is also further minimally caused to maintain the forces experienced by the extendable risers in a first Delta-P lifting unit and the forces experienced by the extendable risers in a second Delta-P lifting unit so as to ensure that the forces experienced by extendable risers in the first Delta-P lifting unit are within some pre-established difference from the forces experienced by the extendable risers in the second Delta-P lifting unit. This is consistent with the teachings presented herein. It should further be appreciated that processor based control systems are well-known. However, the fact that processor based control systems are well-known is not intended to limit the scope of the claims appended hereto and a processor based control system that implements the methods and techniques for raising a floating roof as herein described is not heretofore known, either generally or in the field of raising floating roofs. 
         [0075]    While the present method and apparatus has been described in terms of several alternative and exemplary embodiments, it is contemplated that alternatives, modifications, permutations, and equivalents thereof will become apparent to those skilled in the art upon a reading of the specification and study of the drawings. It is therefore intended that the true spirit and scope of the claims appended hereto include all such alternatives, modifications, permutations, and equivalents.