TL;DR
Cavitation is almost always low NPSH. Check the suction line for restrictions or air ingress, lower the pump speed, or raise the liquid level in the suction vessel.
What you might see
- crackling or popping noise from pump casing
- erratic discharge pressure
- impeller erosion pitting
- flow lower than expected
Likely causes
Available Net Positive Suction Head (NPSHa) below the pump's NPSHr, most often from a restricted suction line or low suction-vessel level
Suction pipe undersized or partially blocked by a partially closed valve
Air or vapor ingress through a worn shaft seal or loose suction flange
Pump operating far right of the BEP (best efficiency point) causing internal recirculation
Required tools
- Pressure gauge (0-30 psig, liquid-filled)
- Suction strainer wrench or spanner
- LOTO kit
- Pump performance curve (from Goulds submittal data)
Safety first
- Lock out the pump driver before opening the casing or touching the suction strainer.
- Hot or hazardous process fluids require appropriate face and body PPE before opening any flanges.
Procedure
- 1
Lock out the pump driver and close the suction and discharge isolation valves.
- 2
Inspect the suction piping. Verify the suction valve is fully open and the suction strainer basket is not blocked. Clean the strainer if restricted.[1]
- 3
Measure the suction static pressure at the pump flange with an accurate gauge. Compare to the NPSHr listed on the Goulds 3196 performance curve for your operating flow.[1]
- 4
Check the liquid level in the suction vessel or sump. Low level reduces static head and cuts NPSHa directly.
- 5
Inspect the suction flange gasket and shaft seal for signs of air ingress, bubbles in the sight glass or hissing are giveaways.
- 6
If the operating point is far right of BEP on the curve, throttle the discharge valve slightly to move the flow back toward BEP.
- 7
If NPSHa is structurally too low, lower the pump, raise the suction vessel, or increase suction pipe diameter. A 2x pipe diameter increase cuts velocity head loss by roughly 75%.
Sources
Goulds 3196 i-FRAME Process Pump Installation, Operation & Maintenance Manual, Goulds Pumps (ITT)
Goulds 3196 i-FRAME IOM, NPSH and cavitation diagnostic procedures (general)
View source
More guides for Goulds Pumps 3196
How to diagnose excessive power draw on a Goulds 3196 pump
High power draw is usually excess flow (system resistance dropped), higher liquid density than design, or internal binding. Measure amps and head to locate the cause.
How to fix a leaking mechanical seal on a Goulds 3196 pump
Seal leaks are most often caused by dry running or shaft misalignment. Confirm the seal flush is active before start and measure shaft runout before fitting a new seal.
How to diagnose low flow rate and pressure fluctuation on a Goulds 3196 pump
Low flow with reduced head points to a worn or trimmed impeller or internal recirculation. Measure differential head and compare to the rated curve to confirm.
How to fix a Goulds 3196 pump overheating at low or shutoff flow
Running below minimum continuous stable flow converts pump work into heat. Install or open a minimum-flow recirculation bypass to protect the pump.
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