back pressure valve for sewer forced main.

[Andres Macias]

Hi.

we have a really flat 2 km long forced main. and the topography doesnt allow us to have a below grade gooseneck. is there a device that could add backpressure to the forced main to keep the pipe full at all times? the sewage water is going from the triturator pump stations towards a gravity section of the sewer.

 

[Pinwards]

Maybe a pressure sustaining valve? Requires a certain internal pressure before it opens, so should keep your pipe full until the pumps kick back on.

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[Andres Macias]

thanks for your post. so far the pressure sustaining valves i have found are for water without solid particles. does anybody know of pressure sustaining valves that can handle the solid particles?

 

[swazimatt]

what about an external weight non-return valve?

What is the height difference between your outlet pipe invert and the highpoint on your pipe?

 

[TigerGuy]

Once everything has passed through the grinder pump, do you really have solid particles? The last one I designed was treated as regular water for all the calculations.

 

[swazimatt]

@tigerguy the flow is like water, however there are lots of chopped up particles (if using a macerator or macerating pump)these small particles can clog the small pipes on PSV or get stuck in the valve mating surfaces. Also the valves need to be protected from H2S produced in wastewater and not in water, the reason why lots of ww fittings are stainless steel

 

[bimr]

A few observations:

The force main should have a minimum continously operating flow rate of 2 ft/sec to avoid solids deposition.

If you operate the force main intermittently, the flow rate when the pump starts should initially be 3.5 ft/sec to resuspend the solids that settle out when the flow stops.

The best solution is to install a back pressure-sustaining valve on the discharge. The valve will stop siphonage. The valve needs to have a full port for wastewater applications.

You can get one from Red Valve, GA Industries or Ross Valve:

Singer

Eng Tips

 

[Andres Macias]

Thank you so much for your responses they are really helpful.

Andres.