Vertical pump impellor damage, Water service
Vertical pump impellor damage, Water service
(OP)
After less than two years of service a five stage, submerged suction, bronze impeller pump stop pumping. The first three impeller are destroyed with the vanes completely gone. The last two impellors are heavily damaged. This pump is in water service, approximately 800 gpm @ 360ft. There were no reports of high noise levels.
I'm assuming cavitation but it seems unlikely that this much cavitation damage could be done in such a short time.
Has anyone experienced this before? Could galvanic corrosion be the culprit?
Thanks
I'm assuming cavitation but it seems unlikely that this much cavitation damage could be done in such a short time.
Has anyone experienced this before? Could galvanic corrosion be the culprit?
Thanks





RE: Vertical pump impellor damage, Water service
have you checked the actual operating points?
I am thinking you may not be pushing to 360 ft since the pump continued to pump with 3 of 5 impellors gone.
what are the velocities near the 1st stage eye?
I would doubt corrosion, since bronze is more noble than most metals in a pumping system, I assume the other metals in the area are iron based. Also if it was galvanic then I suspect all the impellors would be equally gone.
Hydrae
RE: Vertical pump impellor damage, Water service
In order to determine if cavitation is likely, you need to verify that you have adequate suction head margin and adequate submergence. Even if both of these are good, any pre-rotation of the incoming fluid could cause cavitation. Operation at very low flow could result in suction recirculation cavitation. But for the damage to progress through three stages, I suspect abrasive erosion or low NPSH cavitation.
Johnny Pellin
RE: Vertical pump impellor damage, Water service
When you say the impellers were destroyed, what exactly do you mean? Any pictures?
RE: Vertical pump impellor damage, Water service
rmw
RE: Vertical pump impellor damage, Water service
RE: Vertical pump impellor damage, Water service
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RE: Vertical pump impellor damage, Water service
A possible explanation is to look for ppm content of NH4 in the water. Particular combination of pump material (impeller, casing etc) could activate galvanic corrosion on pump impeller as it bronze which has the lowest electrolytic potential. When it happens It does the job very fast.
You should also look to the high temperature of the water. Normally it should be limited to 45/50°C, above this temperature a special design is usually quoted (duplex SS etc).
I would be very interested to know the results of the investigation of your case
Thanks in advance
Rgds
Wimple
RE: Vertical pump impellor damage, Water service
Johnny Pellin