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Date:               October 30, 2007

Subject:           Ball Valve Downstream of Mechanical Line Leak Detector

All new and retrofit installations of mechanical line leak detectors should include a ball valve within 18” downstream of the MLLD.  The downstream ball valve facilitates:

1. Start-up

    

   • The (closed) ball valve limits the empty line area allowing MLLD’s to step through to full-flow mode at start-up.

   • The ball valve is cracked open to pressurize the (empty) line system without resetting the leak detector.

   • The ball valve remains partially closed to keep (fluid) pressure on the discharge end of the leak detector while line vapor is vented.

2. MLLD Replacement

    

   • Diminished chance for the line to “burp” fuel back through line upon MLLD removal.

3. Line Pressure During Fueling Operation

    

   • It is possible to have site specific conditions where demand exceeds functional out-put (the pressure needed to keep the leak detector open during fueling operations).   Where pump discharge pressure falls below the minimum pressure needed to keep the leak detector open, the ball valve may be partially closed.  Pressure between the discharge of the leak detector and the valve is raised, creating enough line pressure to keep the MLLD in the full-flow position.  This is an efficient, inexpensive means of balancing maximum flow and equipment utilization.  Leak detection is not compromised.

4. Diagnostics

    

   • Isolates pump from the line, enabling technicians to confirm check valve and packer o-ring problems.

5. Annual Test Requirement

    

   • Isolates the pump from the line for annual line tightness testing.

Last modified: November 15, 2008

Vaporless Manufacturing, Inc.

8700 E. Long Mesa Drive

Prescott Valley, Arizona  86314

E-mail:  vmi@vaporless.com

1-800-367-0185     Fax (928) 775-5309