Insert Fitting - Pull Off Resistance Testing

A FAQ we get is how do the Boshart Nylon, Poly and PVC insert fittings with 4 barbs and recessed clamp area perform compared to the competitor’s design with 5, 6 or 7 barbs the full length of the insert end? And the question of how much pull off resistance or weight holding capacity does a clamped insert connection provide when using the BMA Series “BRONZE” or SSMA Series “304 Stainless Steel insert fittings.

To answer these questions, we tested for pull / blow-off resistance under two types of force:

#1 - A PULL TEST on our digital tensile strength testing machine

#2 - A WATER PRESSURE TEST which also tested the fittings for leaking at extremely high pressures

The fitting assemblies were made up ensuring that the exact same amount of space between the ends of the inserts was maintained when testing BII fittings against the competitor’s fittings. The fitting assemblies were made up ensuring that the exact same torque was used on each clamp when testing Boshart “SWP” (SEALWELL) fittings against the competitor’s fittings.

Pull-Off Test #1

Pull-Off Test #2

Pull-Off Test #3

Pull-Off Test #4

Pull-Off Test #5

Conclusion #1

Boshart Nylon, Poly & PVC fittings with the four barbs and a single gear clamp have superior holding power performance over insert fittings with barbs the entire length of the insert end – this includes the competition’s 7-barb PVC insert fittings and, surprisingly, the design out-performs the industry standard bronze 7-barb fittings. With a clamp tightened in the recessed space between the barbs and the hex, the clamp can reduce the diameter of the pipe further than when pressing against two insert barbs. If the pipe tries to blow off or is subject to a strong pulling force or load the pipe can only move slightly until the reduced pipe diameter locks up against the first barb after the recessed area, making it impossible for the pipe to slip off the fitting.

Conclusion #2

Recent changes made to some brands of plastic insert fittings to have barbs the full length of the insert end, or in some case shortened to only four barbs without a recessed area to cut costs have reduced the pull off resistance.

Boshart Insert Fittings have incredible holding power and are the best design in the industry. Our fittings superior performance is due to the insert design which has holding power that is more than the tensile strength of the poly pipe.

Conclusion #3

When installing a submersible pump on polyethylene pipe (PE) or any application where pipe pull-off or blow-off is of concern the use of a Bronze or 304SS EXTRA-LONG insert adapter is recommended. The extra long adapters with 13 barbs allow for triple clamping, three clamps will provide a connection that is virtually impossible to pull apart by pulling on PE pipe.