By Kayla Hanson, P.E.
Robust, reliable connectors and gaskets are critical components for liquid, water and wastewater storage, treatment and conveyance structures. Not only do connectors and gaskets help create continuous watertight seals that support a system’s proper function, they also protect the surrounding environment, soil and groundwater.
Follow these tips and best practices to ensure you get the most from your connectors and gaskets.
Three main ASTM standards exist for resilient (or flexible) connectors:
- ASTM C923, “Standard Specification for Resilient Connectors Between Reinforced Concrete Manhole Structures, Pipes, and Laterals”
- ASTM C1478, “Standard Specification for Storm Drain Resilient Connectors Between Reinforced Concrete Storm Sewer Structures, Pipes, and Laterals
- ASTM C1644, “Standard Specification for Resilient Connectors Between Reinforced Concrete On-Site Wastewater Tanks and Pipes”
The primary differences among connector types governed by these three standards are the hydrostatic test pressure to which the corresponding seals are adequate, the tensile strengths and tear-resistances.
ASTM C923-compliant connectors typically are used in sanitary sewer applications and tend to be buried deeper than the other connector types. Additionally, these projects tend to have more stringent leakage requirements and require more protections of the surrounding groundwater from wastewater than other drainage sewers. Therefore, they are designed to withstand greater pressure and have higher tensile strengths and tear resistances than other connectors to ensure flexibility and watertightness in higher-risk applications.
ASTM C1478-compliant connectors are used in stormwater applications. While leak-resistance is critical, the bury depth, test pressure requirements and level of risk associated with ASTM C1478-compliant connectors often is less than that of ASTM C923-compliant connectors.
ASTM C1644-compliant connectors are intended for use in onsite wastewater tank-to-pipe connections and usually are installed at the shallowest bury depths of the three connector types.
When a variety of structures are manufactured at a single precast facility, some precasters may use only ASTM C923-compliant connectors rather than using all three types. This is encouraged in many jurisdictions since ASTM
C923-compliant connectors satisfy the requirements of the other connector types, and using only one type of connector can help prevent confusion and errors in production.
Precast production and plant considerations
Cast-in connectors must be held in place rigidly during production so fresh concrete does not move or dislodge them during pouring. Be aware of the structure opening’s location and the position and dimensional tolerances.
Mandrels are used to hold connectors in place. Care should be taken to clean and maintain these mandrels so they retain their shape.
Connectors installed in formed or cored holes
Connectors installed into holes created with hole formers or by coring require careful preparation. Both hole formers and core bits need to be monitored to ensure they remain within the 0.20-inch
(5 mm) hole size tolerance set by most connector manufacturers.
“When a hole form is used, make sure it has routine maintenance, and it’s cleaned and inspected and within specification,” said Dan Brundage, Midwest territory manager with Press-Seal Corporation.
Brundage also stressed the importance of applying form release to the hole former while avoiding overapplication, which could cause inconsistencies in the hole’s surface finish that can impact the connector’s sealing ability.
Compression connectors – which may be cast-in or installed in a formed or cored hole – rely on the incoming pipe to push the connector out radially into the structure’s formed or cored hole to create the seal. The pipe’s outer diameter is greater than the connector’s inner diameter to help ensure a proper fit. Pipes to be used with compression connectors must have a smooth outside wall surface. An adapter must be used with corrugated or profile wall pipes to create a smooth surface to fit against the connector. The radial forces induced on the structure by the pipe can be significant. Ensure the structural leg between openings – and the area between openings and the top and bottom edges of the structure – is adequate to withstand the forces.
Additionally, it is recommended for the installing contractor to form or cut a beveled pipe edge on the incoming pipe when using compression connectors. This can help reduce the likelihood that the pipe edge will damage the connector during assembly.
Resilient connectors should be stored indoors prior to installation, kept dry and should have limited exposure to sunlight. Each stored box or supply of connectors must be clearly labeled. This is of particular importance in plants that use a variety of connector types. Precast product drawings and the corresponding inspection sheets also should clearly identify the required connector for reference on the production floor and during QC inspections.
When possible, install connectors in formed or cored holes shortly before shipping the precast products.
Connector suppliers offer sizing charts to determine the best connector for each unique pipe type, outside diameter and hole opening. A particular connector may satisfy a variety of pipe sizes. Whether the connector is cast-in or installed in a formed or cored opening in the structure, ensuring the hole dimensions are within the allowable tolerance is imperative for a proper fit and secure seal.
“There’s really a very small tolerance. It’s just 0.20-inch (5 mm) for the hole size. Hole sizes go up a couple inches at a time so you can’t interchange the connectors,” Brundage said.
Hole surface preparation
Preparation of formed or cored holes prior to installing connectors is key to achieving a uniform seal.
“Patch any imperfections,” Brundage said. “The hole must be clean and dry, and if the hole is cored, check for any exposed reinforcement. If there is exposed wire, it can be cut out, or the connector may be put in a slightly different position.”
The right tools for the job
Connector suppliers outline the proper installation procedures and any tools required for each unique connector, including socket and torque wrenches, torque limiters and jacking assemblies. Follow each supplier’s recommendations for installation and torque wrench calibration.
Expansion connectors – which are installed in formed or cored holes – include a metal- or glass-filled nylon adjuster band that runs along the interior circumference of the connector. The band presses the connector into the opening firmly and uniformly as the band expands. When expansion connectors are equipped with multiple adjusters, partially tighten each adjuster in an alternating pattern. This helps ensure uniform pressure throughout the connector until each adjuster is sufficiently tight.
Also be aware of the limits of the expanding band in relation to the manhole diameter. Narrower expansion bands sometimes require an increase in manhole size so the curvature of the manhole can accommodate the band.
However, wider bands exert less force per area on the connector and may not provide as strong of a seal.
Most gaskets for precast concrete structures typically conform to ASTM C1619, “Standard Specification for Elastomeric Seals for Joining Concrete Structures.” Various gasket classes are defined within ASTM C1619 in accordance with different sealing applications. The gasket classes specify different oil-resistance characteristics, tensile strengths and hydrostatic pressure ratings. Ensure the selected gasket class is appropriate for the gasket’s intended use:
- Class A: Low head pressure piping applications not exceeding 125 feet of hydrostatic head.
- Class B: Appropriate for Class A and Class E applications that also require oil resistance.
- Class C: Applications not exceeding 30 feet of hydrostatic head.
- Class D: Appropriate for Class C applications that also require oil resistance.
- Class E: Gravity flow sewer applications not exceeding 30 feet of hydrostatic head pressure.
Most profile gaskets require a single offset spigot configuration against which to bear, whereas O-ring gaskets and some profile gaskets require pipe spigots to have a confining groove in which the gasket is installed. The production simplicity of a single offset joint, particularly in comparison to a cast-in groove, makes single offset joints and profile gaskets a favorable choice for precast producers.
“The most common precast pipe or manhole joint type is a single-offset joint,” Brundage said. However, some instances specifically require O-rings, particularly for some deep-bury depths and high-pressure applications.
Most gaskets are made of isoprene or ethylene propylene diene monomer (EPDM), however nitrile gaskets are available for applications that require oil and petroleum resistance or jobs in proximity to airports or gas stations.
Nitrile gaskets have a higher durometer than isoprene gaskets and can increase required pipe insertion forces, especially in colder weather, so use care and consult the gasket supplier for guidance. Other materials such as neoprene are also available for certain applications.
Precast product and plant considerations
A precast product’s joint design depends on the product and application. Most pipe and manhole structure joints conform with ASTM C443, “Standard Specification for Joints for Concrete Pipe and Manholes, Using Rubber Gaskets.” However, additional standards exist for other structures and seals.
ASTM C443 states, “The annular space between the gasket-bearing surfaces of the assembled and centered joint shall be not more than 75% of the uncompressed height of the applied gasket including all manufacturing tolerances of the joint and gasket applied.”
This means that theoretically, when the adjoining structures are assembled and the joint is centered, a profile gasket should be compressed at least 25% simply as a result of the joint design. A perfectly centered joint is more readily attainable in vertical structures such as adjoining manhole riser sections as opposed to horizontal systems such as pipelines or manhole-to-pipe connections, especially with large-diameter pipe. As a result, profile gaskets could experience inconsistent compression and deformation around the joint. Consequently, profile gaskets are typically designed to be compressed at least 15% in straight alignment but no more than 50% of the original gasket height when the joint is in an off-centered position and all tolerances are considered. Consult the gasket supplier for guidance on the joint design, gasket selection and installation.
Like connectors, gaskets should be stored indoors before installation, kept dry, have limited exposure to sunlight and be organized into clearly marked boxes or bins labeled with the gaskets’ identification information. Prelubricated gaskets should be stored horizontally.
Gasket geometry and sizing
Profile gaskets come in myriad cross-sections and dimensions. Conversely, O-rings are solid ring gaskets with circular cross-sections.
Generally, gaskets should not be stretched to more than 30% of their original size, although the recommendations are supplier-specific.
“The key is to have a joint calculation in advance of us supplying the gasket,” Brundage said. “Each gasket is made for a specific diameter of pipe. If you, as an example, try to put 12-inch gasket on a 15-inch pipe, you can stretch it, but it’s going to be stretched so thin, and you won’t be able to reach the appropriate deformation limits.”
The size of gaskets for confined groove joints in relation to the confined groove in the spigot is critical. Unlike single offset joints, the grooves in which O-ring gaskets are installed have no additional annular space to accommodate extra gasket material, so a slightly oversized O-ring could damage the bell during homing. Consequently, they are sized not only by their cross-sectional area but also the overall volume of rubber for the complete gasket.
Joint surface preparation
Precast product joint surfaces should be smooth and free of imperfections such as bug holes, which might prevent uniform gasket bearing against the concrete. As with other sealants and connectors, the precast product’s joint also must be clean, dry and free of debris before applying a gasket. Improperly prepared bell or spigot surfaces may prevent the two adjoining components from homing and sealing.
Equalize all gaskets after stretching them onto pipe or manhole sections, but before applying lubricant for single offset joints. Apply lubricant to confined groove gaskets before putting them on the joint. Equalizing a gasket involves placing a screwdriver or other small, rigid object with a round cross-section between the gasket and the concrete structure to which it is applied and carefully running the tool around the circumference of the structure at least three times. This process evens the tension throughout the gasket to help prevent high-stress regions caused by stretching and applying the gasket to the spigot. Equalization helps ensure the gasket will bear consistently and maintain a uniform applied gasket height around the structure’s circumference.
Proper gasket lubrication of profile and O-ring gaskets is critical to gasket, joint and seal integrity. Liberally lubricate the bell and especially the lead taper. For O-ring gaskets only, also apply lubrication to the gasket.
Prelubricated gaskets can simplify the installation process, reduce clean up and help reduce soil and debris from contaminating the lubricant and compromising the finished joint. Talk with your supplier about how prelubricated gaskets perform in your plant’s specific joint designs.
Take care to avoid storing pipe with pre-lubricated gaskets outside in warm temperatures and in direct sunlight. Lubricant inside the mantle of prelubricated gaskets can become more fluid as its temperature increases, causing the lubricant to run to the bottom of the gasket tube. Take care to redistribute the lubricant throughout the gasket before the pipe is installed.
Get the most from your connectors and gaskets
Resilient connectors and gaskets are critical components to a variety of underground infrastructure systems. These seemingly simple rubber components are specially engineered to create watertight, leak-resistant or soil-tight connections depending on the precast system needs and applications. Keep these topics in mind in your plant and on the job site, and consult with your suppliers to evaluate your connector and gasket use to ensure you’re getting the most from every seal. PI
Kayla Hanson, P.E. is NPCA’s director of technical services.