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The KnolDp Polly-Spt'~re through the Outer .~<br />
COnSists of 0 horcI yet flex- oliow l::~ssure eq~<br />
tble polyurethone outer tK~n between hne I<br />
sphere with o high density and It~t of tt~e Sl~<br />
pOlyuretr~one loom core core. 11~us no inflot<br />
A ser,es of holes drilled required<br />
ex,ble but hard polyurethane outer sphere<br />
Fioure 7-6. Polly-Sphere pig. (Courtesy of Knapp Polly Pig, Inc.)<br />
criss-cross design imparts greater cleaning power,<br />
strength, and wearability. The nose is completely cov-<br />
ered <strong>to</strong> insure proper sealing. For extra-<strong>to</strong>ugh cleaning<br />
jobs, a coat of silicon carbide or abrasives can be added.<br />
Flame-hardened steel wires are bonded <strong>to</strong> the polyure-<br />
thane body of the pig (Figure 7-7) for use on long runs.<br />
The bristles are mounted at the specific angle that<br />
makes them self-sharpening. A simpler pig, the foam<br />
Sweege Pig, is made of extremely soft foam and is de-<br />
signed for temporary sweeping of lines <strong>to</strong> eliminate<br />
things such as oxides which cause red water. They are<br />
propelled by normal water pressure. A Polly-Pig of this<br />
type is shown in Figure 7-8.<br />
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