Suction Pump Submergence

[dicksewerrat]

I am working on a problem with 'vortexes' forming in a MH . there are 2 18 inch HDPE suction lines to 2 different pumps. They are moving 5300 gpm down 2 18 inch bypass lines. The suction lift is 18 feet. Submergence is 5 feet. I have a graph to pull minimum submergence from and a calculator for the same. the graph is based on velocity and calculator is based on inside Dia. and Q. Would separating the suction lines help? Or do we need to increase submergence ? And do you guys have any other suggestions. Thanks

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[bimr]

dicksewerrat, perhaps you can add detail on this application as I don't think some of the readers understand what you are doing.

My assumption is that this is a temporary bypass pumping installation to repair a gravity sewer. There is no need for a permanent solution, just something that will work for several weeks. The flows should also be somewhat diurnal.

 

[LittleInch]

So that's what you mean by bypass, I was wondering....

I would still go for slots equal to about 2 x the cross sectional area of the inner pipe or the same idea with a lot of holes drilled in it.

If this is a regular thing then maybe make up something which fits inside a 4' MH with strakes or guides to restrict swirl in the manhole section.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dicksewerrat]

I think they are looking at investing in some 'anti-rotational' fittings and they are going to cut slots in the bottom of the suction pipe.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[georgeverghese]

How do you prime this suction line for startup - is there a foot valve on each submerged suction line?

 

[dicksewerrat]

It is called vacuum assisted priming

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[Artisi]

Trust you pass on the final outcome / cure to the problem, either resolved or ongoing after any changes etc.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[georgeverghese]

Okay, with no foot valve and a decrease in suction lift to 14ft, that would clear issues with NPSH adequacy. One way of setting up vortex breakers is these slots on the suction pipe as suggested. Another way would be to install some antivortex baffles in this sump - perforating these baffles, if required, may still be acceptable.

 

[Artisi]

Have we seem a performance curve yet to ascertain if suction lift can be achieved - NO - so it is guess work.

This is a typical no data enquiry - lots of back and forth all based on the unknown ..........

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[dicksewerrat]

I will pass along how things are going in next couple of days. Traveling to the South next few days

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[dicksewerrat]

Here is the update. Before cutting slots in the suction pipes, they surcharged the main line by 1.5 feet to get to a suction lift of 16.5 from the original 18 feet. Vortex disappeared and flow rate through the pump went from 35% capacity to over 60% capacity. We were right on the calculated submergence point. I still would like to hear about some online classes for pumping. thanks again for the advice.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com