CPVC – Overlooking Expansion and Contraction is a Big Mistake

I would say the number one most over looked issue with CPVC fire sprinkler systems most fire sprinklers designers fail to address is dealing with expansion and contraction of the CPVC pipe.  All CPVC pipe is made from plastic which has many advantages over steel pipe;  plastic pipe is non-corrosive, lighter weight, cheaper then steel, and has great hydraulic characteristics.  However, it does have its draw backs.  One of which is its ability to expand and contract with the swings in ambient temperature due to the highly elastic nature of plastics.  As the sprinkler system expands and contracts over time, it puts additional stress on the fittings and joints holding the system together.  To much stress and the pipe or fittings may crack creating a slow, dripping leak in the system or may shatter the pipe joint completely.

All manufactures of CPVC provide an installation/design manual with procedures on how to help compensate for this….it is usually addressed in a section called “Thermal Expansion”, “Expansion & Contraction”, or something along those lines.

The Expansion Loop or Expansion Offset is the best way to minimize system failure due to expansion and contraction.  The pipe manufacturers installation guide will provide you with mathematical formulas to determine the exact length each loop needs to be.  The formulas will use information like; the pipe size, length of pipe run, and the expected range of temperature the pipe will be exposed to.  Pipe hangers and guides will also need to be placed at specific points on your loop or offset to support your pipe as it expands and contracts.

One more tip for preventing system failure due to expansion and contraction, use a flexible coupling, not a rigid coupling, on a grooved adapter when transitioning from steel pipe to CPVC pipe.  The flexible coupling provides enough deflection in the coupling that relieves the stress on the CPVC grooved adapter and CPVC pipe where it connects to the rigid steel pipe.  Again, your manufacturers installation manual will mention this necessary requirement.

In summary, CPVC pipe brings many advantages to fire sprinkler system installation.  However, the fire sprinkler designer must be aware of its limitations, and drawbacks.  Failure to compensate for expansion and contraction could be a critical error that could lead to water damage of the building it’s try to protect, and possible system failure.


Below are links to some manufacturer’s installation manuals:

Viking Corp, Tyco Fire, Spears Manufacturing, Harvel

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