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6.4. Elastomer PU Scraper Pigs
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Function: based on a series of linked rubber discs, rather than the chevrons
of the wiper dart, these are harder to insert than the wiper darts, but
scrape tubing walls more thoroughly. They ought to be chosen for the
relevant wall thickness or they may not fit.
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Versions for 1.75" and above have not been requested: it is said that as
the wiper darts in these sizes have a thicker lip than their equivalents
in the smaller sizes, they give a good wiping action; this is a
rationalisation of a reluctance by operators to use them, not a proven
fact. Where tests have been done, in the 1.25" size, several extra
pounds of rubbish were removed by a scraper dart from a coil which had
just previously been pigged with a wiper dart.
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Material: polyurethane 75A one piece moulding. They could also be made
in harder grades to give an even firmer scrape.
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