What diameter pull head is used when replacing a 4-inch cast iron drain using pneumatic pipe bursting?

Replacing a 4-inch cast iron drain size-on-size using pneumatic pipe bursting requires an expander pull head with an outside diameter between 5.0 and 5.5 inches to provide adequate clearance for 4-inch high-density polyethylene pipe.

Aging residential cast iron lateral drains suffer from internal rust corrosion, structural cracking, and root intrusion, prompting plumbing contractors to choose trenchless rehabilitation over destructive open-trench excavation. Trenchless lateral replacement minimizes surface disruption on residential properties, but selecting the correct head diameter remains critical to fracture brittle host piping cleanly without causing surface heaving or excessive friction drag on the replacement line.

If you only do one thing: Size the rear expander head diameter 10% to 25% larger than the outside diameter of the new pipe to maintain soil displacement and prevent line lockups.

• Size-on-size specification: Standard 4-inch IPS (Iron Pipe Size) HDPE (High-Density Polyethylene) pipe has an outside diameter of 4.50 inches, which pairs with a 5.0-inch to 5.5-inch pneumatic expander to provide the necessary 0.5-inch to 1.0-inch annular overcut clearance.
• Upsizing dimensions: Upgrading an existing 4-inch cast iron line to a 6-inch HDPE line (6.625-inch outside diameter) increases the required pneumatic bursting head expander diameter to between 7.5 and 8.0 inches.
• Operating pneumatic pressures: Pneumatic bursting heads require an air compressor delivering 90 to 110 PSI (pounds per square inch) to generate 300 to 600 reciprocating impacts per minute while attached to a constant-tension guide winch pulling at 2 to 5 tons.
• Trenchless sewer capability: Trenchless sewer line repair using pneumatic pipe bursting fractures the host cast iron pipe outward while simultaneously pulling continuous butt-fused DR11 or DR17 pipe through the original utility alignment.
• Pre-burst line evaluation: Clearing scale with Scour Jet hydro jetting equipment and running a CCTV (Closed-Circuit Television) camera inspection confirms wall thickness, lateral tie-ins, and pipe trajectory before digging launch and receiving pits.

• Watch out for: Expander heads exceeding 25% oversize in shallow runs with less than 36 inches of soil cover, which can cause surface heaving and damage parallel utility lines.
• Watch out for: Solid ductile iron repair sleeves, unmapped concrete encasements, or schedule 40 steel segments along the cast iron path that will not fracture under pneumatic impact and will stall the tool head.
• Watch out for: Failing to allow a 12-to-24-hour thermal relaxation period for newly pulled HDPE pipe before making final mechanical hub connections, which can shear sewer joints as the pipe contracts.

Complete a sewer camera inspection to map host line depth, bends, and material transitions, then select a 5.0-inch to 5.25-inch expander head for standard 4-inch size-on-size installations.