Excessive hissing noise comes from the QDa exhaust pinch valve assembly - WKB9969

SYMPTOMS

• Excessive hissing noise comes from the QDa internal exhaust pinch valve assembly (KAD model)
• Instrument operates normally, no error messages or loss of performance
• Hissing noise is continuous during system operation
• QDa passes the source pressure test if the leak is small, but if the leak is large, the test fails
• High nitrogen consumption noted

ENVIRONMENT

• QDa versions with internal pinch valve assembly

CAUSE

  O-ring is fitted incorrectly in the pinch valve assembly, creating a minor nitrogen leak.

  The four screws of the pinch valve assembly are unevenly tightened.                                                                                                              

New Design since March 2024

FIX or WORKAROUND

1. Remove the pinch valve assembly and re-seat the O-ring (as shown) such that the curved profile faces outward.
2. Ensure that the four screws that hold the pinch valve assembly in place are evenly tightened.
3. If damaged, replace Pinch Valve (Internal) Part Number 700011173

ADDITIONAL INFORMATION

The leaking nitrogen is not from the source exhaust but from the nitrogen flow used to close the pinch valve; it does not represent a hazard to users.  

See related article: Loud noise coming from QDa pinch valve assembly - WKB75987