Lock Integrity of Machine-Wound PVC Liners

Machine-Wound PVC Locking Overview

SEKISUI’s Spiral Wound Liners consist of continuous strips of PVC that are wrapped and locked together by machinery. The locking occurs on the edge of the PVC strip where a male and female system are interlocked by the winding machine. The sheer force of the machinery makes the lock fully sealed. 

The locking mechanism itself is a strong dual mechanical lock. Each profile type (whether SPR™EX, SPR™TF/RO, or SPR™), involves a sealing material within the lock itself. When compressed and locked by the machinery it creates a water-tight seal that is impermeable to any intrusion.

Locking Processes for Each Method

Starting with SPR™EX – SPR™EX has a unique double-locking configuration. The secondary lock is formed using a hot melt adhesive which holds the liner at a constant diameter as it is being installed. The winding machine also inserts a high-strength steel “cutting wire” between the primary and secondary locks as the edges of the profile are locked together. 

SPR™EX PVC Profile

After the liner is wound from one manhole to the next, the end of the liner is held in position and the secondary lock is cut by pulling the cutting wire. The edges of the profile are then free to slide relative to one another, along the primary lock, thus expanding the liner to be a tight-fit. The primary lock contains a slow-setting lubricating sealant that, until it sets, aids the expansion process by acting as a lubricant. Upon expansion, the lock is fully sealed and impermeable to water/root intrusion.


SPR™TF/RO – For SPR™TF/RO, the mechanical locks contain 3 seals and 3 sealing materials. Inside the female lock, there is an O-ring made from Santoprene, a thin layer of hot melt on the inside wall and on the landing adjacent to the male lock there is another hotmelt layer. The 3 materials and their locations have been selected in order to provide an excellent seal in all situations.

SPR™ Steel-Embedded Profile

SPR™ – SPR™ contains a strong dual mechanical lock between each profile strip. In addition, each profile strip incorporates a co-extruded gasket creating a water-tight seal. The profile is locked with the assistance of a winding machine. The sealing material is compressed by main and sub locks mechanically and forms a strong structural liner within the host pipe.

Lock Integrity and Testing

SPR™EX Lock Integrity Testing

There have been numerous internal and 3rd party testing to ensure the integrity and water-tight nature of these locks. One such example is the 3rd party testing at Ramtech labs in Los Angeles, CA where SPR™EX underwent pressure and vacuum testing. The testing consisted of putting a SPR™EX liner under internal pressure (10.7 psi) and also 5% deflection. This was to see if the locks would keep their integrity under stress. All of these tests were passed.

In addition to these tests, SPR™ has been tested extensively internally. The tests consist of providing external or internal pressure to a wound PVC liner to observe the points when leakage would occur under extreme pressures. In addition to this, earthquake-resistant testing has taken place on SEKISUI Spiral Wound Liners. The tests simulated a magnitude 7.0 earthquake for 3 minutes at the SEKISUI manufacturing facility in Ritto, Japan. The results indicated that flows and PVC lock integrity was maintained despite severe displacement from conditions similar to a magnitude 7 earthquake. 


Providing test data and answering lock integrity questions is something we do often. Spiral Wound has a 4-decade installation history that spans across the globe serving a multitude of challenging applications. Please contact us for questions on Spiral Wound Lining

Do you want to test an application for a Spiral Wound project? Start by using our Spiral Wound calculator!

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