Figure 3-30.Threading plastic pipe.
dries during the cool of the night, the thermal
contraction of the pipe could stress the joint and pull
the pipe apart due to the inadequate time to allow for
the cement to cure. See table 3-1 for a general guideline
on loop dimensions for various lengths of line and
TESTING.Testing should be done in two
1. The initial test should be a low-pressure
hydrostatic test. (Air or gas is NOT recommended.)
This test should never exceed 50 pounds per square inch
gauge (psig). When testing with a gauge, allow the pipe
to remain under pressure for a few hours; then check to
see if there is a pressure drop. When the pressure drops,
there is a leak. The pipeline should then be walked and
closely inspected, checking each joint closely. After
Table 3-1.Pipe Snaking Loop Offset
locating the leak, repair it, and pressurize it again using
2. After completion of the low-pressure test, place
the pipeline in the trench (if not tested in the ditch) and
backfill, leaving the joints exposed. The pipe should be
uniformly and constantly supported its entire length.
DO NOT SUPPORT WITH BLOCKS. The high-
pressure test should be conducted at 1 1/2 times the
working pressure and be held for at least 12 hours.
Leaks found on the pipe itself should be cut out
completely and replaced by using fittings (couplings).
Backfill in the early morning during hot weather. The
pipe should be covered 6 to 8 inches with backfill that is
free of rocks and debris. It is advisable to maintain a
pressure of 15 to 20 psig on the pipeline while
backfilling to keep from damaging it. Anchors, valves,
boxes, and so forth, should be supported separately to
prevent additional stress or bending from the pipe.
Piping, under roadways or railroads, should be done
with sleeving (metal or concrete). The pipe should be
isolated from direct contact with the concrete. When
concrete anchors are being poured, wrap the pipe with
rubber or other protective material. If the anchor is for
axial movement, use the solvent welding process to
weld a split collar to the pipe to provide the needed
protection. When solvent welding collars on the pipe,
allow 48 hours for drying time before pouring concrete.
Q3. What is the main purpose of a sanitary sewage