Using dip tubes of the correct length is helpful by enabling the user to discharge essentially all the product from the dispenser, preventing the tube from becoming jammed into an incorrect position as a result of gassing, preventing the (non-dimpled) valve cup from excessively protruding from the can plug and perhaps causing production problems at the crimper or gasser/crimper, and preventing the tube from bottoming on the flat base of some aluminum cans in such a way that a seal is made that will act to limit or stop the entry of product into the tube when the valve is actuated.
Dip tubes that extend fully to the bottom of the dispenser, without excessive distortion, can also aid in retaining their connection to the valve body tailpiece, which may be important if the aerosol content exerts a very significant swelling action upon the dip tube plastic.
The choice of A-D dimension is influenced by a number of factors. These factors include:
Tube curvature, which may vary considerably between tubes.
Variation of valve cup and valve cup gasket thickness.
Elevation or suppression of the valve pedestal (thus top end of the dip tube) upon crimping.
Elevation of valve pedestal during hot-tanking, only partly diminished upon subsequent cooling.
Swelling (or shrinking) action of the product on the dip tube.
1.1 This practice covers the rapid determination of the A-D dimension defined as the centerline dimension from the top plane of the valve mounting cup curl to the far end of the dip tube. See Fig. 1.
1.2 This practice is limited to valves with 1-in. (25.4-mm) mounting cups.
1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
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