Abstract:
A measurement gage includes a base having two scales at opposite site ends of the base for different ranges of measurement. A tapered feeler gage elements projects axially from each of the opposite ends, and a slide bar is movable along the base, with an indicator fixed thereto for each of the two different scales. Movement of the slide bar in each of two opposite axial directions is calibrated to respective thicknesses of the tapered feeler gage elements.

Description:
BACKGROUND OF INVENTION 
   This invention relates to steam turbines used for power generation and, more specifically, to a gage used for measuring turbine rotor and packing clearances. 
   The interpretation of the results of performance monitoring activities can be used to identify turbine internal problems that may cause a deterioration in performance, and to assist in planning maintenance required to address the problems. However, to restore performance during a turbine maintenance outage, the turbine components contributing to the performance loss need to be identified. This can best be done by conducting a turbine steam path evaluation. 
   A steam path evaluation generally includes a detailed visual inspection of the steam path components and clearance measurements of the pickings and bucket tip spill strips. The visual inspection is used to evaluate and quantify the performance impact of degradation effects such as erosion, deposits, damage, preening, etc. Clearance measurements at multiple circumferential positions of the diaphragm packings, tip radial spill strips, and end shaft packings are used to quantify the effect of increased clearances. With this information, decisions can be made based on the economics associated with the repair and replacement of turbine components, and the priority of necessary repair work. 
   Conventional gages used to make the required clearance measurements during steam path evaluations have not been completely satisfactory. One such gage indicates measurements in 0.005 inch (5 thousandths) increments. These gradations are not sufficiently precise and oftentimes result in the operator making a guess at the measurement, or taking additional measurements with a feeler gage and then using a micrometer to determine the final measurement. In addition, the gage is not flexible and does not always fit into (or cannot reach) the areas needing measurement. 
   SUMMARY OF INVENTION 
   In one exemplary embodiment, this invention includes a measurement gage having a pair of tapered, flexible feeler gage elements extending in opposite directions from an elongated, channel-shaped base (or base-channel). One feeler gage element includes a scale in a range from 5 to 25 thousandths while the other feeler gage portion includes a scale in the range of from 25 to 50 thousandths (both in one thousandth increments), thereby increasing both the preciseness and range of the gage. 
   A slide bar is located in the base channel and is constrained to axial sliding movement within the channel. Measurement indicators are attached to the slide bar, one for each of the two scales on the base channel. After calibration, the indicators are pinned to insure that they do not move thereby maintaining calibration and after insertion of one of the feeler gage portions into a gap to be measured to the extent permitted by the wedge-shape of the feeler gage element, the slide bar is moved axially into engagement with a support structure directly adjacent (above or below) the gap or clearance to be measured. Movement of the slide bar and the exact location of the indicator relative to the respective scale is calibrated to the thickness of the feeler gage element such that the indicator on the slide bar will accurately show the gap or clearance measurement. 
   Another feature of the invention includes the ability to lock the slide bar in its, extended position with a set screw acting on a leaf spring, or to simply rely on the friction generated by the leaf spring to hold the slide bar in any position along the channel. 
   Another feature of the invention relates to the use for a dowel pin projecting perpendicularly away from the slide bar to facilitate movement of that bar by the user in either of two opposite directions, depending on which scale is being used. 
   Accordingly, in its broader aspects, the invention relates to a measurement gage comprising a base having two scales at opposite ends of the base for different ranges of measurement; a tapered feeler gage element projecting axially from each of the opposite ends; and a slide bar movable along the base and having an indicator fixed thereto for each of the two different scales; wherein movement of the slide bar in each of two opposite axial directions is calibrated to respective thicknesses of the tapered feeler gage elements. 
   In another aspect, the invention relates to a measurement gage comprising a base having two scales at opposite ends and on opposite sides of the base for different ranges of measurement; a tapered gage element projecting axially from each of the opposite ends; and a slide bar movable along the base and having an indicator fixed thereto for each of the two different scales; wherein movement of the slide bar in each of two opposite axial directions is calibrated to respective thicknesses of the tapered gage elements; wherein the base is channel-shaped in cross section, and the slide bar is located within the base; and further wherein one of the two different scales is adapted to measure gaps between 5 and 25 thousandths and the other of the two different scales is adapted to measure gaps between 25 and 50 thousandths. 
   The invention will now be described in detail in connection with the drawings identified below. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a slightly tilted side elevation of the gage in accordance with an exemplary embodiment of the invention; 
       FIG. 2  is similar to  FIG. 1  but taken from the opposite side of the gage; 
       FIG. 3  is an exploded assembly drawing of the gage shown in  FIGS. 1 and 2 ; 
       FIG. 4  is a perspective view of the gage being used to measure a turbine rotor clearance between bucket tips and packing seals, but with the slide bar not yet engaged; and 
       FIG. 5  is a perspective view of the gage similar to  FIG. 4  but with the slide bar extended into engagement with the seal. 
   

   DETAILED DESCRIPTION 
   Referring to  FIGS. 1-3 , the clearance measurement gage  10  includes an elongated channel-shaped base  12  (or base channel) formed by a bottom wall  14  and a pair of perpendicular side walls  16 ,  18  that create a U-shaped cross-section. Side wall  18  is formed with an elongated, horizontally aligned slot  20 , located centrally along the length dimension of the base  12 . The function of slot  20  will be described in detail further below. Side wall  16  is provided with gradations for one scale  22  at one end of the gage corresponding to one range of rotor and packing clearances. Similarly, side wall  18  is provided at an opposite end of the gage with gradations for another scale  24  corresponding to a smaller range of rotor and packing clearances. This arrangement is for convenience and it will be understood that both scales could be located at opposite ends of one side of the base channel if desired, but this could cause some confusion reading the correct scale. 
   Note that the thickness of the bottom wall is reduced at opposite, exterior end portions  26 ,  28  (FIG.  3 ). A first spring tempered, tapered feeler gage element  30  is formed with a flat mounting portion  32  and a flexible tapered gage portion  34 . The flat mounting portion  32  of the gage element  30  is fixed to a flat surface  36  on end portion  26  of the base  12  via screws  38  that are passed through holes  40 ,  42  in the mounting portion  32  and threaded in aligned correspondingly threaded holes  44 ,  46  in the base channel  12 . A second tapered feeler gage element  48  also has a flat mounting portion  50  and a flexible tapered gage portion  52 . The flat mounting portion  50  of the gage element  48  is fixed to a flat surface  54  of the end portion  28  by screws  56  that are passed through holes  58 ,  60  in the mounting portion  50  and threaded in aligned correspondingly threaded holes  62 ,  64  in the base channel  12 . 
   A slide bar  66  ( FIG. 3 ) is received within the base channel  12  and is slidable on the bottom wall  14  in either of two opposite axial directions. U-shaped retainer clips  68 ,  70  are applied over the slide bar  66  and side walls  16 ,  18  and are secured to the base  12  by screws  72 ,  74 . These retainer clips confine the slide bar  66  to the base channel  12  so that only axial sliding movement of the slide bar is permitted. A threaded set screw  76  extends through a plate  78  fastened to the side wall  18  of the base channel  12  by screws  80 ,  82 . 
   A leaf spring  84  is located in the slot  20 , between the base side wall  18  and the slide bar  66 , generating sufficient friction to prevent free sliding of the slide bar in the channel. Nevertheless, a set screw  76  extends into the slot  20  and may be tightened against the spring  84  to effectively lock the slide bar  66  in place once a measurement is determined. This allows the user to remove the gage  10  and to read the results without accidental shifting of the slide bar  66  as will be explained in greater detail below. Thus, the user may rely on friction created by spring  84 , or the set screw  76  to generate additional tension so as to hold the slide bar  66  relative to the base channel  12 . 
   As already noted, the base channel  12  is provided with two sets of gradations, or scales, one at each end of the base. The scale  22  at one end permits measurements in the range of 5 to 25 thousandths, while the scale  24  at the other end, and on the opposite side of the base, permits measurements in the range of 25 to 50 thousandths. Measurement reading indicators  86 ,  88  are secured on top of the slide bar  64  by screw fasteners or the like, one for each of the scales  82 ,  84 . The indicator “points”  90 ,  92  face the respective scales  22 ,  24  on opposite side walls. Slots  94 ,  96  permit adjustment for purposes of calibrating the gage. In this regard, it will be appreciated that the degree of taper of the feeler gage elements  34 ,  52  is calibrated to the scales and to the movement of the slide bar  66  into engagement with a reference surface directly above the gap to be measured. In other words, since the measurement is determined by the extent of axial movement of the tapered feeler gage elements (e.g., element  34 ) into a particular gap, and since the scale  22  moves with the feeler gage element, the gap measurement can be read by the user when the slide bar  66  and indicator point  92  are moved along the scale until the slide bar  66  abuts a surface directly above or below the gap to be measured. A dowel pin  98  pressed into and projecting from the slide bar  66  facilitates movement of the slide bar  66  by the user relative to the channel base  12 . 
   In use, and with reference to  FIGS. 4 and 5 , one of the feeler gage portions, e.g., portion  52  of element  48 , is moved into a gap between the bucket spill strips  100  and seal insert  102 . When the tapered, flexible feeler gage portion  52  reaches its maximum travel, i.e., where the tapered surface of feeler gage portion  52  is engaged on both sides of the gap, the slide bar  66  is moved axially along the channel until the forward edge of the bar  66  engages the support structure  104  immediately above the clearance being measured. The indicator point  90  on indicator  86  will thus identify the clearance or gap dimension. The user may then either lock the slide bar  66  in place via set screw  76 , or simply rely on the friction generated by spring  84  to hold the bar  66  in place. 
   While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.