Pocket Guide to Flan..

The diameter of Polly-Pigs is usually one and a half
times the length. As a rule, ~/8" is added to the pig body
size for coating. Some pigs with diameters less than 6"
have mesh for internal reinforcement. Some are
equipped with a rope on one or both ends for ease in
handling and pulling. Dished ends add to the effective
fluid removal while pointed ends are used for bi-direc-
tional changes. The ends may be either shorter or longer
for extreme valves or launches. They also come in either
soft or hard for variations in density (Figure 7-9), which is
measured in pounds per cubic foot.
Some styles of Polly-Pigs made by Knapp are de-
scribed in Figure 7-10. They are color-coded by type of
cover for identification and some are criss-crossed.
S,ngle SID,rOI COOt~ng IDot-
tern allows greater flexlbd-
~,h,' O! the p,g for runn,ng
t~ght bends "T s." valves
0."~31 vOnohons ~n O~lOe I .D
Double sD=ral coating
po~ern Drov=des greater
number Of cleonmng edges
and makes the pig more
res:stont tO teonng Th~s de'-
s~gn ~s intended for longer
runs where less flexibility is
reclutred
Sdtcon corbtde ~mpreg-
noted coohng ~s ovodoble
~n both s,ngle and double
spiral patterns Th=s coot-
tr~:j =s advisable when re-
moving mill scale, weld
slog. calcite or carbonate
depos,ts, rust. or other hord
or abrasive delaOslts.
Figure 7-9. Coated polly pigs. (Courtesy of Knapp Polly Pig, Inc.)
143