Azbil VDC - Page 58

Trouble shooting Azbil Corporation
8-2 VDC, VAC, VST, VAA - Diaphragm Control Valve
Symptom Cause / Verication / remedial measures
Fluid leaks out of gland Check for loose packing ange
Is grease volume su󰀩cient ?
Are there any scars on valve stem ?
Fluid leaks out of gasket Has bonnet nut been properly tightened
Faulty gasket (Scar, deformation)
Regardless of valve
opening, excessive uid
leaks out to downstream of
valve
Air Leakage in actuator
Apply supply air or atmospheric pressure to actuator.
(Check air source and positioner)
Is valve opening at true zero ? (Check lift)
Corrosion or erosion on plug or seat ring
Jamming on guide
Replace parts as required.