A dependable drainage system starts with square-cut and properly joined cast iron, which helps establish leakproof connections and the longevity of the plumbing system. When it comes to ensuring the success of Hubless cast iron piping installations, Charlotte Pipe and Foundry recommends using shielded couplings that conform to CISPI 310 or ASTM C1277 for all no-hub pipe.*  

Standard no-hub couplings for cast iron certified by NSF International are designed to join cast iron soil pipe that does not use the more traditional hub-and-spigot connection method. This article explains the CISPI 310 standard coupling and how it is used with no-hub cast iron. 

For a high-level overview of how to cut and join cast iron pipe with Hubless couplings, explore our article on the topic. 

What is CISPI 310? 

CISPI 310 is the specification for couplings used in connecting Hubless cast iron pipe and fittings for sanitary and storm drain, waste, and vent piping applications. The coupling sleeve or gasket is housed inside a 301 stainless steel corrugated shield. Depending on the size of the shield, two or four 301 stainless steel clamps surround the shield and provide the sealing force. 

The Cast Iron Soil Pipe Institute provides technical information and expertise to the plumbing industry. In accordance with NSF-certified quality control guidelines, CISPI works to ensure products meet industry standards. 

Charlotte^® Standard No-Hub Couplings sold for use with Charlotte Pipe’s Hubless cast iron pipe and fittings proudly bear the CISPI 310 and NSF marks for quality. 

The Anatomy of CISPI 310 Couplings

Hubless couplings that fall under this standard are composed of three main elements, all working together to provide a positive, reliable, corrosion-resistant seal. 

1. The Shield: The 0.007-inch-thick type 301 stainless steel shield requires less band load to transfer pressure to the gasket, leaving more clamping load in reserve to compress the gasket. The bidirectional grooves create clamp-sealing pressure in both parallel and transverse patterns on the gasket and pipe, preventing system failure. 

2. The Clamps: Standard 301 stainless steel clamps and 5/16-inch hex-head 305 screws provide the sealing force needed for a secure fit. Couplings 1 1/2 inches through 4 inches use two clamps; 5-inch through 10-inch couplings use four clamps. 

3. The Gasket: The gasket is made from a properly vulcanized virgin compound in compliance with ASTM C564 (neoprene). The Charlotte No-Hub gasket features multiple sealing beads under the clamp bands. Neoprene has a maximum operating temperature of 212°F and has a maximum joint deflection of 5 degrees. 

Charlotte^® Standard No-Hub Couplings are available in sizes ranging from 1-1/2 inches through 10 inches and are designed for an installation torque of 60 inch-pounds for a proper seal. The entire assembly is corrosion resistant and is allowed by every model code in the US for both above and below grade installation. It is important to note that standard Hubless couplings are manufactured to CISPI 310 and ASTM C1277, while the medium- and heavy-duty couplings are manufactured to ASTM C1540. 

Standard Couplings vs. Medium- and Heavy-Duty Couplings 

Similar to standard-sized no-hub couplings, medium- and heavy-duty couplings are designed for joining no-hub cast iron pipe and installed using a torque wrench (to be calibrated between 80 or 120 inch-pounds for heavy-duty systems). Torque requirements may vary per manufacturer. Medium- and heavy-duty couplings have more clamps and yield increased surface-bearing contact between the coupling and the pipe or fittings. This inhibits movement and results in a more uniformly rigid joint. Charlotte Pipe offers three couplings designed for applications where more rigid joints are required:

1. Heavy-Duty “MD” (Yellow Shield) No-Hub Couplings
2. Heavy-Duty “HD” (Green Shield) No-Hub Couplings
3. 12- and 15-Inch Heavy-Duty No-Hub Couplings 

Rather than CISPI 310 or ASTM C1277, medium- and heavy-duty couplings fall under ASTM C1540, the standard specification for wider-width gasket, clamp assembly, and coupling. 

For a complete guide on joining Hubless cast iron with Charlotte^® Standard No-Hub Couplings, download the cast iron technical manual. 

*In Hubless cast iron installations, Charlotte Pipe’s warranty will not apply if products are joined together using unshielded Hubless couplings.