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How to replace the Piston and Exterior Cap on a Manual Flush Valve

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The flush volume for Moen Commercial M-Dura Manual Flush Valves can be changed by installing a different Piston and Exterior Cap. This article offers detailed instructions on replacing both components within the flush valve assembly. It also includes the required preparation steps and a list of recommended tools.

For more information on determining the Piston and Exterior Cap needed for your flush valve, see Manual Flush Valve Basics and FAQs, see #7.

Preparation:
  • The water supply shut off valves must be turned off - see article How to Turn off the Water Supply to the Faucet.  Once the water is shut off, activate the handle to drain the residual water.
  • Recommended Tools: 5/64" hex wrench, 3/8" hex wrench
How to replace the Piston and Interior Cap:

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  1. Using a 5/64" hex wrench, loosen and remove Set Screw (B)
  2. Lift and set aside Exterior Cap (A)

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  1. Using a 3/8" hex wrench, loosen the Interior Cap (C).
  2. Remove and set aside Interior Cap (C). 

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  1. Remove the Piston (D) from the Flush Valve Assembly (E). 

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  1. Insert the new Piston (D) into the Flush Valve Assembly (E)

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  1. Replace Interior Cap (C) into Flush Valve Assembly (E)
  2. Tighten Interior Cap (C) with 3/8" hex wrench. 
  3. Replace Exterior Cap (A)

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  1. Using a 5/64" hex wrench, replace the Set Screw (B)
  2. Installation complete, turn the water on. 
 

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