TL;DR
Cavitation noise in a control valve is caused by vapor bubbles collapsing in the valve body. Check the pressure recovery factor for the trim against the operating conditions; anti-cavitation trim may be required.
What you might see
- loud crackling or gravel-like noise from the valve body
- visible vibration in downstream pipework
- rapid trim erosion found at inspections
- noise worsens at lower valve openings
Likely causes
High pressure drop across the valve combined with low absolute downstream pressure, creating vapor collapse in the body
Liquid service operating below the fluid vapor pressure at the vena contracta
Valve operating at partial stroke where pressure recovery and velocity combine to cause cavitation
Trim Fl (pressure recovery) factor insufficient for the service conditions
Required tools
- Plant process data: P1, P2, fluid vapor pressure
- Sound level meter (optional, for before and after comparison)
- Combination wrench set for bonnet studs
- Anti-cavitation trim per Fisher easy-e part numbers
- LOTO kit
Safety first
- Cavitation causes rapid trim erosion and can lead to body wall erosion over time. Do not operate a cavitating valve beyond the next scheduled outage.
- Follow valve-isolation and bleed-down procedures before opening the bonnet for trim inspection.
Procedure
- 1
Record the inlet pressure P1, outlet pressure P2, and fluid vapor pressure Pv at operating temperature from plant instruments.
- 2
Calculate the valve pressure drop ratio: delta P / (P1 - Pv). If this ratio exceeds the Fl squared value for the installed trim, cavitation is thermodynamically confirmed.[1]
- 3
Inspect the valve trim at the next available outage. Look for surface pitting or erosion on the plug face and seat ring. Erosion concentrated near the seat orifice confirms cavitation damage.[1]
- 4
For immediate mitigation: reduce the pressure drop across the valve by splitting the drop across two valves in series, or raising the downstream pressure if the process allows.
- 5
Contact Fisher or Emerson to specify an anti-cavitation trim for the easy-e body in this service. Anti-cavitation trims use a staged-pressure-recovery cage to prevent vapor collapse inside the body.[1]
- 6
Install the anti-cavitation trim following the Fisher trim replacement procedure for the easy-e body. Verify the cage orientation matches the flow direction arrow cast on the body.
- 7
After trim installation, measure noise level with a sound level meter at the downstream pipe within 300 mm of the valve. Compare to the pre-modification baseline.
Sources
Fisher easy-e ED, ET, EZ Sliding-Stem Control Valve Instruction Manual, Fisher Controls (Emerson)
Fisher easy-e ED, ET, EZ Sliding-Stem Control Valve Instruction Manual, cavitation and flashing service guidance (general)
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