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August 2022

PLASSON Flex Restraint for Axial Restriction



During 2019 we offered the Flex Restraint for Axial Restriction when using Large Diameter HDPE pipes for wastewater systems in Peru. Since then we supplied several thousands of PLASSON Flex Restraints to this market for wastewater systems.

The Total Solution

Flange System offered by a local Peruvian company is a special water-stop system approved by SEDAPAL Water public company of Lima, that fulfills the function of preventing the infiltration and exfiltration of water in the connections between smooth-walled HDPE pipes and concrete structures, guaranteeing their water tightness.

The product can be used in existing concrete structures or in concrete structures built in situ. Materials comply with ISO 4633 Standard “Specification for Rubber Seals, Gasket Rings for Water Supply, Drainage and Sewer pipes” and ASTM C923, standard “Specification for Elastic Connectors between Reinforced Concrete Manholes, Tubes and branches”.

Puddle Flange

Composition EPDM Rubber
Hardness 60 Shore A ± 5
Min. 9 MPa Min. 350%
Change of Hardness Max/Min Aging 7 days at 70°C Max. +8/Min.-5
Change in Tensile Strength Aging 7 days at 70°C Max. -20%
Change In Elongation at Break Aging 7 days at 70°C Max. +10% / Min. -30%
Compression Set | 72 hours at 23°C Max. 12%
Compression Set | 24 hours at 72°C Max. 20%
Compression Set | 72 hours at -10°C Max. 50%
Tear Resistance Min. 34 KN/m
Water Absorption -1% to 8%
Low -temperature Brittle Point (-40°C) No Fracture
Ozone Resistance bsence of cracks to the naked eye. No magnifying device
Chemical Resistance in 1N Sulfuric Acid. 1N Hydrochloric Acid. 22°C 48h No Weight Loss

Stainless Steel Clamps

Band & Case AISI 200/300 Stainless Steel
Push Block AISI 410 Stainless Steel Bright Hardened 35-40 Rockwell
Screw Acero Inoxidable AISI 200/300
Maximum Torque 60 in.lbs
Recommended Torque 30 in.lbs
Normative Reference SAE J1508/SAE J1670-2008
Construction No Welds

The Installation

The Puddle Flange should be stretched and pushed over the pipe in order for it to settle into the desired position. If necessary, a soap-based lubricant can be used. When working with existing concrete structures, a good quality concrete bonding agent should be applied to the opening in the structure to ensure proper bonding of the fresh concrete or mortar to the hardened concrete. Puddle Flanges are not designed to serve as anchor points for pipes and do not provide significant axial restriction, so they should not be used alone when there are strong axial loads on the pipe.

In the case of HDPE pipes, where strong axial loads are present, the use of a Flex Restrain fitting for axial restriction is required. The PLASSON FLEX RESTRAINT electrofusion fitting is a flexible bar that is welded to the pipe by electrofusion to create a fixed support that prevents axial movement of the pipes. To determine the quantity of electrofusion fittings for each connection, a theoretical calculation must be carried out, considering the diameter of the pipe, the thickness of the pipe, the variation in temperature day vs. night and the speed of temperature variation. Theoretical calculations are based on the information provided by the manufacturer, so the result of the calculations only apply to the specific manufacturer’s products.


In Situ construction of a concrete manhole with HDPE PIPE DN 1400 mm (~54″), puddle flange and flex restraint fittings for axial restriction.


PLASSON provided a simple and strong solution for a long lasting wastewater system in large diameter HDPE pipes.

Assembly of 1400mm wastewater line before placing in trench.