rocketscientist
Chemical
- Aug 19, 2000
- 86
We have 2 identical pumps, with one operating spare pumping from the sump of a water scrubber. The pumps draw from separate suction lines. These suctions are drawn from bellmouth elblows. These are els where the suction line makes an elbow drawing from the bottom of the tank. The clearence "C" is only about 200 mm, about 8 inches, between the opening of the 90 elbow and the tank bottom. The flow is about 1900 gpm per pump, simultaneously, through two 14-inch suction lines. Unfortunately, the D, the opening of the of the bellmouth is identical to the suction line, about 14-inch, i.e., about 350 mm. Also, because the tank is fiberglass, there could be deflection in the bottom of the tank. Often the packing breaks up, and this could be collecting in the bottom of the scrubber. The diameter of the scrubber is only about 3400 mm, i.e., 134 inches, or about 11.2 ft. The pump suctions fill about 180 degrees of one side of the vessel.
With two pumps running, with a combined flow of about 3800 gpm, there is severe cavitation. The cavitation is worst with 2 pumps running but still present with a single pump running. This makes me suspect that the bellmouth may be the problem. There is noticable vibration throughout the system. The vibration is passed to the tank wall. Below the liquid level, there is a loud thumping.
I suspect that it may be possible to treat this as a high volatile liquid issue and cutting the bellmouth may increase the available area for the suction.
Earlier, we ran at nearly 5000 gpm with the pumps. I designed two orifice plates to reduce the vibration and flow and this worked well but we still have hot bearings and cavitation. We are operating on cold water. Once we get to 60 C temperatures it will be much worse.
Any ideas on how I can reduce cavitation? How does cutting the bellmouth sound?
With two pumps running, with a combined flow of about 3800 gpm, there is severe cavitation. The cavitation is worst with 2 pumps running but still present with a single pump running. This makes me suspect that the bellmouth may be the problem. There is noticable vibration throughout the system. The vibration is passed to the tank wall. Below the liquid level, there is a loud thumping.
I suspect that it may be possible to treat this as a high volatile liquid issue and cutting the bellmouth may increase the available area for the suction.
Earlier, we ran at nearly 5000 gpm with the pumps. I designed two orifice plates to reduce the vibration and flow and this worked well but we still have hot bearings and cavitation. We are operating on cold water. Once we get to 60 C temperatures it will be much worse.
Any ideas on how I can reduce cavitation? How does cutting the bellmouth sound?