The precast concrete industry is finally focused on supplying their customers with preformed concrete inverts in manholes and lift stations.
The next consideration is to begin installing factory built thermoplastic inverts Base Liners (inverts) that ensure consistency of design and standards for quality. Because a bottom section of the manhole with a Base Liner is complete when set in the field, it does not require any secondary operation to complete the channels and benches; thus, preformed Base Liners also benefit underground contractors.
Lined invert w/ channels full pipe diameter, non skid bench surface
The integrity of a sewer collection system depends on the quality of structures to ensure the continued elimination of inflow and infiltration (I & I). If you analyze the anatomy of a manhole (not the most exciting endeavor), you realize the invert is critical to the continuous flow of sewage through the entire collection system. Further, when it comes to preventing unwanted inflow, enduring watertight pipe connections are critical.
Severely corroded/eroded invert
If the flow channel erodes, or if pipes connections fail and leak, the design integrity of the entire system is compromised. Likewise, if the invert base and channelization is not built to design specifications (they rarely are!), the flow design is compromised.
Over the last 25 years, our industry has come to recognize the importance of protecting At-Risk Concrete from microbial induced corrosion (MIC) that eats away at concrete surfaces.
Sure Grip CPL lift station 10′ x 50′ In PA
by Terre Hill Concrete
Many utilities are specifying and installing concrete protective liners (CPL) that protect the walls of At-Risk structures, pipe and tunnels in their system. Over 7 million sf of AGRU Sure Grip CPL has been installed in manholes and lift stations in North America, and many millions more around the world.
Low pH – However, protecting the walls doesn’t protect the inverts from the extremely low pH wastewater that flows through the base channels and over the benches.
Severely corroded manhole, Leesburg Fl
This low pH is caused by the MIC process that develops in the pipelines and adds sulphuric acid into the wastewater. The low pH wastewater erodes the concrete benches the same way low pH water in concrete swimming pools corrodes the walls.
The Predl System
For over 25 years, Predl Systems North America has produced Base Liners that replace the traditional, built – in – place, brick and concrete invert. Predl has installed over 10,000 Base Liners in the U.S, and Canada; Predl Europe has produced over 1.5 million Base Liners of the same design that have been installed in throughout Europe.
- Base Liner top view showing full pipe size channels
Predl Systems products offer solutions to corrosion in manholes and lift stations by protecting the structure from the base all the way to the street level. Predl products are made from polypropylene (PP), polyethylene PE, or fiber reinforced plastic (FRP).
Predl Base Liners are custom designed to fit all invert configurations: regardless of changes in elevation, type of pipe, or pipe diameters. Predl Base Liners are used in new precast, cast-in-Place, or rehabilitation applications.
Predl Bells are integrally cast into the concrete, they have a water-stop, a locked-in gasket, and a pipe stop, that combine to ensure lifetime protection against I & I.
Predl Bell cast in concrete
Cut-away Predl Bell,
locked-in gasket, water stop, pipe stop
You do not need to have a lined wall to use Predl Bells; they are used in place of rubber boots and cast-in gaskets to seal pipe in concrete walls . When you use Predl Bells, you do not need to use a hole former, or core holes post production. Predl Bells provide outstanding protection against overbelling and I & I; and, they work well in either precast, or cast-in-plece structures.
Base liner with Corprotect CPL with pre welded tubes ready to be cast into concrete
Predl PP Corprotect AGRU Sure Grip CPL is a proven system for protecting At- Risk concrete walls. Corprotect CPL resists ground water pressure, is highly resistant to abrasion, and provides a long lasting, gas tight and water tight seal against corrosion and I & I.
HDPE Eccentric Cone
Predl Cones are designed to line cones (corbels) in concentric and eccentric manholes. Predl Cones can be effectively used to rehabilitate old manhole structures.
Predl Convertible Collar seals chimney against street level I & I
Predl Convertible Collars complete the Predl System by sealing the chimney against inflow around the ring and covers at street level. Convertible collars can be used to rehab existing structures.
Work Together or Independently
Predl System’s family of products all work together, or they can be used independently. For example: you can use the Base Liner without lining the walls, you can specify the Predl Bells without the Base Liner, you can install the Convertible Collar by itself; or, you can use the Predl Cone and Convertible Collar when rehabilitating a manhole.
Easy Installation – Consistent Quality and Design
Predl Base Liners are supplied to precast companies complete with flow channels, benches, and Predl Integral Bells attached; they are ready to be cast into a structure. Gone is the need for hole-formers, coring, or rubber flexible boots connectors; there is no need to form an invert after the base section is cast; the entire casting and construction process is simplified.
Large 24 x 15 x 8 Base Liner on top of core at precast plant
After the manhole with a Predl Base Liner is set in the field, the underground contractor has no need to revisit the manhole to install an invert; and the utility pays for, and gets, a professionally designed, consistent quality, corrosion resistant, watertight invert that requires no future maintenance.