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Vacuum Breaker Diaphragm Replacement

vacuum breaker
Series VBM thermoplastic vacuum breaker will last indefinitely when properly maintained with regular seal/diaphragm replacement.

Andy Ryan, Plast-O-Matic Valves

Important things to remember:

  1. Plast-O-Matic recommends keeping a spare diaphragm available for repairs.
  2. Seal life will vary with applications due to cycles, temperature, pressures, chemicals and concentrations.
  3. Based on the application, a periodic inspection and maintenance plan should be established.

Preparing for diaphragm installation:

  1. Before disassembling a valve for examination, cleaning or repair, make sure the liquid line is depressurized and drained.  (It should be noted that even after a pump is shut down to eliminate fluid line pressure there may still be pressure trapped in the piping system. One example of this would be head pressure located in a vertical run of pipe. If this situation is possible, extreme caution should be exercised to avoid injuring a worker. CAUTION: Avoid breathing dangerous vapors and avoid skin contact with chemicals.)
  2. Whenever disassembling a valve, it is wise to carefully inspect all the parts to ensure proper operation when it is reassembled.

Installation of diaphragm:

  1. Carefully remove and inspect the dust cap. 
  2. Unthread the union nut and remove the inlet housing to allow access to the diaphragm.
  3. Inspect the inner workings of the valve for debris of signs of chemical attack or wear.
  4. Remove the existing diaphragm and check that the internal stop (spider) is in good shape and properly installed.
  5. Install the new diaphragm with the legs properly positioned in the grooves and aligned with the spider.
  6. Reinstall the inlet by tightening the union nut by hand and then with a quarter turn with a strap wrench.  Do not over tighten.
  7. Reinstall the dust cap.


  1. Once the valve is reassembled restart the system/pump slowly and check for leaks.
  2. Cycle the system as to allow for operation of the vacuum breaker to verify correct operation.

Link to the VBM Installation and Maintenance Instructions sheet.