Force Main Clean outs

[armyengr]

Can anyone tell me if clean outs are required on force mains? I know they are standard practice on gravity lines but I can not find reference in the muncipalities design guide. If they are required can you also direct me to a standard detail?

Thanks

 

[LittleWheels]

it is fairly standard to have scour valves at the low end of sewerage pressure mains in this part of the world.

 

[RWF7437]

Good practice is to design your force main to have NO low points so that cleanouts, or scour valves, are not needed. Actually, I've never heard of a "scour valve" in 48 years in the sewer business.
If you can't do this ( eliminate low points) then a manhole with a tee and gate valve would probably work.

You still need air/vacuum valves at high points.

good luck

 

[LittleWheels]

The scour valve lets you drain the pressure main into the wet well, useful if you need to do some work in the pressure main.

 

[cvg]

I believe "scour valve" = "blow off" which is a common term in this region...

 

[bimr]

a clean-out or blowoff is essentially the same thing.

Manholes serve that (cleanout) purpose in gravity sewers.

A blow-off is typically placed at the low points where gritty material could accumulate and restrict flow through the force main. It is recommended that a clean-out or blowoff be provided at low points, but it is not mandatory

 

[CivEnvEng98]

In my part of the world, cleanouts are for gravity systems but PIGGING STATIONS are for pressure mains.

Having the ability to pig a force main (and even water mains) is pretty important and most utility engineers reviewing your plans don't ask for them and frankly miss out on their importance.

There is no set in stone criteria or governmental requirement for pigging stations that I'm aware of. But there are common sense situations where I would consider their use. For instance: 1) upstream of a directional bore or any major dip in the force main, 2) most upstream location on a major transmission line, 3) inside any major sized pump station whether in-line or traditional wet well, 4) where ever the force main transitions more the 2 pipe sizes due to limitations on any given pig size.

Each utility typically has their own pig station "style" and I can elaborate on multiple designs but here is the cheapest way to do it:

cut in a X" x X" TEE fitting with a valve on either side of the "flow thru" and a spool piece on the branch pionting upward terminating about 12 inches below finished grade. the spool piece has a blind flange that is tapped with a 2 to 3 inch nipple so you can connect potable water (through an approved RPZ thank you) to push the pig through. A 36" or 48" RCP section on end with the bell side up with a manhole cover acts a traffic rated setup to access the blind flange to insert the pig and there ya go.

At the end of the day you might not need a pigging station at all. You have to take a bigger picture look at the force main system to see where you need 'em.

Good luck.

 

[rconner]

ASCE MOP No. 36 (WPCF MOP #8) 1977, "Wastewater Treatment Plant Design" contained the guidance, "On all low spots where gritty material is likely to accumulate and restrict flow through the pipe, a blow-off should be installed if practical."
I am not aware of this being mentioned in some later versions of various publications of ASCE, and also different organizations that also mention force mains (while the good intent is obvious, I guess "practical" could conceivably have a different meaning in different locations, or in a some different regulatory etc. environments than in 1977).

 

[armyengr]

Thank you to everyone that provided guidance on this subject. It was very helpful

 

[redbridge]

I install a pigging station on all new lift stations I design.