Air Elimination from Suction Piping
Air Elimination from Suction Piping
(OP)
We have an existing 6x4 end suction centrifugal pump unloading rail cars of fertilizer. We are having problems with air getting into the suction pipe as rail cars getting emptied (unloading multiple rail cars at once with many 4" hoses feeding into an 8" dia. suction pipe). NPSHA is not our problem but the air is causing problems. We have installed a 3/4" air "bleed" valve on the discharge side of the pump (near the pump). Is 3/4" just too small for this air bleed valve? Also, would a float or other style air eliminator located at the highest point in the suction piping help? I want to be sure we use the correct style air eliminator so we don't bring more air in on the suction side.
Tom Hansen





RE: Air Elimination from Suction Piping
Please describe the configuration of the suction piping.
Are the cars top unloading or bottom unloading, etc.?
You say you have an 8" suction pipe but you do not give the size of the pump suction nozzle.
RE: Air Elimination from Suction Piping
You've got a suction high point and air in the suction line. Suction lines are usually larger, hence slower velocity and easier to trap bubbles, so I'm wondering why the air is not being removed in the suction line right now? After the pump, its likely to be moving fast and possibly well entrained. Discharge doesn't seem like the best place.
Treat this as preliminary, if you plan on giving more info, but in the meantime you might consider doing this...
If you know the usual air to liquid ratio, size the valve for that air flowrate and install it at the high point of the suction line.
http://virtualpipeline.spaces.msn.com
RE: Air Elimination from Suction Piping
http://www.eng-tips.com/viewthread.cfm?qid=181062
RE: Air Elimination from Suction Piping
Tom Hansen
RE: Air Elimination from Suction Piping
(An eductor driven by compressed air, water or steam driven or a mech vac pump if you have one. Maybe a small self priming centrifgul could be run in parallel as a jockey to your main pump but connected to the "air space" of the "suction drum". If its got enough suction lift, it'll pull the air out when there is air present and give you a few more gpm when there isn't. The power drawn by or the increased noise of the self priming jockey pump will warn the operator. If the self primer has a lower head than the main pumps, then you could connect the self primer to a second positive pressure "separator" with float type air vent and dump the clear flow back into the main suction line through a globe valve to give it a bit of back pressure).
A vacuum system could be driven by same level switch used to warn the operator.
Let us know how you got on.
PS. I have absolutely no operating experience of such a system so please excuse the whacky ideas.
RE: Air Elimination from Suction Piping
RE: Air Elimination from Suction Piping
It seems to me the amount of entrained air from emptied cars would be variable and limited by the sealing effect of the liquid downloaded from the various rail cars. Thus, IMHO, the preferred location of the vent valve (piped away to a safe point) would be at the top of the 8-in suction manifold closest to the pump.
RE: Air Elimination from Suction Piping
I don't believe increasing the vent size on the pump outlet (discharge) will do you much good. As long as the inlet side has large pockets of air, the pump is going to have problems.
I'd recommend installing a loop seal (U-bend) on your suction pipe with your 3/4" vent at the top. Then, if the 3/4" isn't big enough, try a different valve. But only after you've gone to the "right" side of the pump.
Patricia Lougheed
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RE: Air Elimination from Suction Piping
so does anyone know of some good vacuum system
suppliers?
Tom Hansen
RE: Air Elimination from Suction Piping
http://www.eng-tips.com/viewthread.cfm?qid=181062