Accumulator on Sewage Force Main

[stanier]

A transient analysis of a municipal raw sewage force main highlighted a need to employ mitigation devices. The solution involving air valves and intermediate reflux vals cannot be implemented beauce the main is buried in a road. Pits would be a hazard as would construction.

Further modelling indicates that a gas accumulator will solve the problem. Please advise manfacturers of such devices that have successful applications in this inducstry. Also how frequently do they need to be maintained.

Sharing knowledge is a way to immortality

 

[BobPE]

stainer:

what are the surge pressures on the force main? what are the materials used in its construction? I am just curious to get some additional info? Void chambers are not good on wastewater mains. There are better ways to address the situation, maybe we can help with more info...

BobPE

 

[stanier]

THe rising mains that I am investigating are in cement lined ductile iron. The problems that I have include the rising main cannot be tankered to empty it as it is a National park, rough terrain, no access so sectioning with reflux valves is out. Other mains have problems with the main being a in a road so valve pits etc are a problem.

Pressures from the model indicate figures of 1850 kPa. The rising mains were put in some years ago to a standard with thrust blocks designed for 1220 kPa. So although the DICL would be OK for the pressure the thrust blocks are not.

I am about to remodel the lines with one way surge tanks that have a potable water supply to keep them topped up. I used this method at a major pumping station about ten years ago and I found out it is still operating OK.

I have since found Charlatte and Young who manufacture gas accumulators with a proven history on sewage. I am still investigating this equipment but it does come with the problem of them being registered pressure vessels.

Also the design pressure for standard equipment is limited to 7 bar. This is fine when they work as the transient is below the design rating. Should they fail then they could be exposed to the waterhammer and hence I am thinkinng that the design pressure needs to be raised.

Thanks BOB Keep the good thoughts coming.

Sharing knowledge is a way to immortality