6.10. Scheme of Part Numbers for CT Darts
|The dart range has been substantially expanded to accommodate various customer requirements, as a result of which we re-numbered the range in 1994. Former part numbers are no longer given. Former 12mm versions with a cone tail added are now withdrawn as their function is better performed by 13mm or 16mm bore darts. Original variations of 12mm 1.25" types are not listed; now all have as standard a heavier-weight nose, which facilitates launch by encouraging the dart to keep head-down in some wider bore launch systems.|
|The first need was to have a wider range of bore sizes, especially the largest size that can be fitted within a given tubing diameter, in order to achieve greater volume flows and to enable the passage of trigger balls to lower tools in the string. This leads to the following general scheme of part numbers. Those shown in red are in existence; large bore sizes marked 'na' are not physically possible in the tubing; most smaller bore sizes are not wanted in larger tubing sizes; and the 12 are the re-numbered originals from which the range has been developed. As the need arises, others than those shown in red will be provided; this may also involve larger bore sizes.|
|Bore mm (top) or inch (below)|
|Max ball||7/16||1/2||9/16||11/16||7/8||1||1 1/8||1 3/8||1 5/8||2 1/4|
|The second requirement is to cope with tubing of different wall thickness. Ideally, it is desirable to make a dart with flexible enough lips to cope with all likely wall thicknesses, but, with only a few mm of rubber around the core, it is not easy to achieve flexibility with enough toughness; it has at present been found necessary to make slightly different dart diameters to allow the use of two or three wall thickness ranges eg. 098-109 & 125-156. Thus, in the detailed listings which follow, there may be more than one dart for a given CT diameter, a given bore and a given pressure, depending on wall thickness range. It is quite likely that different tapered strings will require variations to suit the particular string, so it is most important that the requirements are clearly understood when placing orders; we would prefer that you nominate the string details so we may check the suitability.|
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