of hot water CPVC piping is more than 20′
long, it is a candidate for an expansion loop.
PVC runs of 50′ should also be considered for
expansion loops.
Measuring PVC and
CPVC Pipe
Most plastic water supply lines are mea-
sured using the face-to-face technique, with an
allowance for the depth of the fitting socket,
Figure 20-14. For example, if the face-to-face
measurement of a 3⁄4″ pipe is 4′-6″ and the pipe
must engage a fitting at both ends, the pipe
must be cut 4′-71⁄4″ long (4′-6″ + 5⁄8″ + 5⁄8″).
When it is necessary to make center-to-
center measurements, you must know the
laying length of the fitting(s) being installed.
Figure 20-15 gives the laying length for the
more common types of fittings. A local
plumbing supply house should have a
complete table of laying lengths for all the
fittings they sell.
Chapter 20 Installing Water Supply Piping
361
Figure 20-13. The dimensions of an expansion loop for
PVC or CPVC can be determined with this formula.
(NIBCO Inc.)
R(′) = 1.44 × Dia. of pipe (″) × Change in length (″)
The expansion of the 1⁄2″ (0.5″) PVC example from
Figure 20-11 was 1.08″. Therefore,
R = 1.44 × 0.5 × 1.08
= 1.55′ or 181⁄4″
and
1⁄2 R = 91⁄8″
The expansion of the 1⁄2″ CPVC example from
Figure 20-12 was 1.96″. Therefore,
R = 1.44 × 0.5 × 1.96
= 2.82′ or 34″
and
1⁄2 R = 17″
1⁄2 R
R
Figure 20-14. This chart gives the fitting allowance for
plastic pressure fittings.
Pipe Size Engagement
(in inches) (in inches)
1⁄2 1⁄2
3⁄4 5⁄8
1 3⁄4
11⁄4 11⁄16
11⁄2 11⁄16
2 3⁄4
3 11⁄2
4 13⁄4
6 3
Plastic Pipe
Depth of Engagement
Figure 20-15. The laying lengths for selected PVC
and CPVC fittings. (NIBCO Inc.)
45° ell
Coupling
90° ell
Tee
Laying length (A)
Fitting name Size PVC CPVC
1⁄2 3⁄32 1⁄8
3⁄4 3⁄32 1⁄8
1 3⁄32 1⁄8
1⁄2 1⁄4 3⁄16
3⁄4 5⁄16 1⁄4
1 11⁄32 5⁄16
1⁄2 13⁄32 13⁄32
3⁄4 9⁄16 17⁄32
1 11⁄16 21⁄32
1⁄2 1⁄2 13⁄32
3⁄4 9⁄16 17⁄32
1 11⁄16 21⁄32
A
A
A
A
A
A
A
A