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Transitioning Between Ductile Iron and PVC Pressure Pipes

In some field situations, it becomesnecessary to transition between ductile iron (DI) pipe and AWWA C900/C905 PVCpipe made to the Cast-Iron equivalent Outside Diameter (CIOD) system. Pipes madefrom both materials use the same outside diameter regimen – meaning that theoutside diameters specified in the respective product standards are identical.Thus, it

would be logical to assume that the spigotof one pipe should fit into the bell of the other. However, there are threefactors to consider:

1.Actual outside diameters

2.Spigot-end bevels

3.Bell-socket depths


WHY DI SPIGOTS SHOULD NOT BE INSERTED INTO PVC BELLS

Actualoutside diameters

DI pipe ODs are held to tight tolerances inthe inside of the bell and the outside of the spigot, while the outside of theremainder of the barrel of the pipe is held to looser tolerances. As a result,the OD of field-cut DI pipe may vary. When inserting a field-cut DI spigot intoa PVC bell, this variation could create either:

1.Difficulty in joint assembly due to too large a DI outside diameter

2.Joint leakage caused by too small a DI outside diameter

Spigot-endbevels

DI pipe has a smaller bevel than PVC pipe.When inserting a DI spigot into a PVC bell, the relatively square, sharp edgeof the DI spigot can damage or dislodge the gasket during assembly.

Forthese reasons, insertion of a DI spigot into a PVC bell is NOT recommended.

Transition couplings are available thatprovide watertight joints between PVC and DI pipes. Typical products includesolid-sleeve couplings or mechanical-compression couplings. Use of one of theseproducts is recommended rather than inserting a DI spigot into a PVC bell.

INSERTING PVC SPIGOTS INTO IRON BELLS – EASILY ACCOMPLISHED

Bell-socketdepths

DI pipe has shorter bell sockets than PVCpipe. Prior to inserting a PVC spigot into a DI bell, two modifications arerequired:

1. Bevel: the beveled end of the PVC spigotshould be removed and the resulting square outer edge should be

ground off

2. Insertion line: because PVC pipe bellsare longer than DI bells, the PVC spigot cannot be inserted all the way to thepipe’s insertion line as would occur with a typical PVC-to-PVC pipe joint.Instead, the insertion line should be ignored and the PVC pipe should bebottomed in the DI bell. When the pipe is fully bottomed, there will be a gapbetween the insertion line and the end of the DI bell.

References: AWWA C151-09 standard forductile iron pipe; AWWA C900-07 and C905-10 standards for PVC pipe; Technical Bulletin:“Pipe Transitions Between Ductile Iron Pipe and AWWA C900/C905 PVC Pipe,”PWPipe