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When, Where, and Why You Need No-Hub Couplings
Cast iron piping is
still used in most commercial buildings like hospitals, hotels, vehicle
dealerships, banks, office buildings, schools, lube shops and countless other
facilities. Even though ABS or PVC piping can be used for commercial buildings
according to the Uniform Plumbing Code (UPC), oftentimes other local or state
building codes may specify cast-iron pipe be used due to various reasons. Some
codes limit plastic piping to no more than two story buildings. Some buildings
may fall under local codes for health or safety and cast iron piping may be
specified because it is not susceptible to burning
like PVC or ABS piping, should a fire occur.
Cast iron piping is
often used in many residential multi-story housing projects because it provides
a much quieter flow of waste water than either ABS or PVC plastics. If you have
ever been in a room on the first floor of a two story building where ABS or PVC
was installed and someone flushes the upstairs toilet, you would know what we
mean.
Although no-hub couplings
were designed for cast iron they are also a very handy way to repair ABS or
PVC. They can be especially helpful when the piping is in a hard to reach spot
or the pipe is unable to be moved in either direction to allow the repair to be
made with a solvent (glue-on) coupling. The pipe can be cut to remove the
damaged area and a no-hub coupling can be installed along with the replacement
piping.
ABS and PVC schedule 40
piping have a slightly larger overall outside diameter than cast iron pipe. There
is not a significant difference when comparing the outside diameter of
1-1/2″ or 2″ cast iron to 1-1/2″ or 2″ ABS/PVC pipe. For
these two smaller sizes you could use a no-hub coupling to connect ABS or PVC
directly to cast iron piping without a problem. However, if you are using a
no-hub coupling to connect 3″ or 4″ cast iron to ABS or PVC then you
will notice a more defined difference between the outside diameters of the cast
iron and the ABS or PVC pipe.
To make it easier to
adapt ABS and PVC to cast iron, the ABS and PVC fitting manufacturers created
the ABS and PVC No-Hub Adapter fitting. One side glues over ABS or PVC and the
other side is the same size as no-hub cast iron pipe. Without the use of these
special adapters, the inner gasket of a no-hub coupling will stretch too much
and not provide the best seal possible. Note: ABS and PVC are not compatible to
glue together so if you are using PVC then you will need a PVC No-Hub Adapter
fitting, and if you are using ABS you will need an ABS No-Hub Adapter fitting.