Brochure

Thermoplastic Valves Product Guide & Engineering Specifictions
Threaded Connections
Page 831 Suitable for Oil-Free air handling to 25 psi, not for distribution of compressed air or gas Spears
®
Manufacturing Company
Due to Material Cost Variations, Prices Sub
j
ect to Chan
g
e. Check On-line Catalo
g@
www.spearsmf
g
.com
Threaded joints are used where piping system dismantling for occasional cleaning or modification is anticipated. Since thread-
ing reduces the effective wall thickness of pipe, pressure ratings of the pipe are reduced to one-half that of unthreaded pipe
using solvent cement welded joints. Valves, however, have individual pressure ratings substantially different from that o
f
pipe. As a result, no reduction in the valve’s specified pressure rating is necessary for threaded connections. Threaded systems
should be made with Schedule 80 pipe only, threaded with an ANSI general purpose tapered pipe thread (NPT). Schedule 40
pipe should not be threaded.
General Procedure Outline
Step 1: Apply Joint Sealant
Threaded connections require application of a quality
grade thread sealant to seal joint assembly.
WARNING: SOME PIPE JOINT COMPOUNDS
OR PTFE PASTES MAY CONTAIN SUBSTANCES
THAT COULD CAUSE STRESS CRACKING IN
THERMOPLASTIC MATERIALS. Spears
®
Manufac-
turing Company recommends the use of Spears
®
BLUE 75
TM
thread sealant which has been tested
for compatibility with Spears
®
products. Please follow
the sealant manufacturers’ application / installation
instructions. Choice of an appropriate thread sealant
other than those listed above is at the discretion of
the installer.
Step 2: Assemble Joint by Hand
Threaded pipe and valves or fittings should be initially
assembled “finger tight” (just enough to fully engage
thread clearance).
Step 3: Strap Wrench Make-Up
Threaded plastic pipe and fitting components should
always be installed using commercially available strap
wrenches. Do not use conventional pipe wrenches
which can damage plastic piping materials.
WARNING: THE SINGLE MOST COMMON
CAUSE OF THREADED JOINT FAILURE IS OVER
TIGHTENING. Tapered pipe threads produce radial
stress in female fittings. Over tightening can exceed
the stress limits of thermoplastic materials, resulting
in split fittings.
Apply strap wrench make-up of no more than one
to two turns beyond finger tight thread engagement.
Care should be taken in final positioning so as to
avoid the need to “back-up” the wrenched assembly.