12" Force Main-Ball Valve vs Gate Valve 3

[jgailla]

We have an office argument going about the use of ball valves versus gate valves on a sewer force main. This particular project is a 12" force main running about 2.5 miles and discharging into a manhole, but I would like your opinions on sewer force main valving in general. The project is located in SE Georgia.

I think that gate valves are appropriate up to 20". Over 20" I would probably use a butterfly valve, although I haven't given it much thought because I've never designed a force main over 20".

I've reviewed four utility design standards from Florida and Georgia. Three use gate valves, and one uses plug valves. There is no local design standard, and we are basing our design on a military technical manual, which provides no guidance on this issue.

I would appreciate any of your opinions. Thanks.

 

[cvg]

butterfly valves are not recommended for force mains, they tend to trap debris...

 

[Ron]

jgailla...good to hear from you.

Ball valves are not good for high abrasion liquids like sewage can be.

Early in my career I designed WWT plants. We used gate valves, plug valves, and butterfly valves. Gate and Plug valves performed better. Butterfly valves, as someone noted, trap debris. If you use them post-comminutor, post-screening, or after a grinder pump, they are fine.

While any of them will sieze, gate and plug valves are easier to repair without removal. Butterfly valves generally require removal for repair.

Good luck.

Ron

 

[jgailla]

cvg, Good point. I hadn't thought about the debris issue. So would you use a gate valve, plug valve, or other on a large, say 36" force main?

Ron, Good to hear from you too. I've noticed you've been around here a little bit lately after a long absence. Hope work's not slowing down too much. I had no idea you ever did plant work. Your answer matches the other information I've been able to gather.

Any other opinions out there?

 

[cvg]

I think gate valves (resilient or double disk) are more typical on smaller forcemains and eccentric plug valves on the larger ones.

 

[dik]

Gate valves are also slower to operate and less of a 'hammer' effect.

Dik

 

[bimr]

Plug valves are perferred on wastewater applications.

If you remove or comminute the solids, then you have more options on the type of valve used. Butterfly valves are used on larger stations (with the solids removed).

Gate valves can be used.

Ball valves are never used.

 

[bimr]

Here is a link to a valve selection guide for your reference:

http://www.engvalves.com/itemfiles/valveselectionessentials.pdf

 

[Ron]

jgailla....work is good. We're busy at this point. Our Orlando group is a little slow this month, but still chugging.

Yes...spent first 18 months of my career designing,fabricating, and installing package water and wastewater treatment plants, filters, and associated systems. Great experience.

Last year I wasn't that active in Eng-Tips...I'm trying to change that.

 

[gerhardl]

Hello jgailla,

The answers and advice you have been given are typical selections for US. In Europe (for EN standards) eccentric plug valves are not that readily commercial available in all sizes, market and competition somewhat limited. Soft sealing gate valves are common for smaller versions, dominating up to 10 inches, but available and used for dimensions up to 20 inches and larger.

Parallell to this (good constructions of) knife-gate valves are used in treatment plants and on mains, typically up to 24 inches.

Knife-gate valves would be considerably cheaper than plug valves, and dependable with long-lifetime. Good constructions of plug valves will probably have longer lifetime and be somewhat more dependable over a long (twenty year plus) lifetime.

There exists one exception to ball-valves not recommended for sewer. In Berlin, Germany, the Erhard double-excentric ball valve (Tyco Waterworks), was selected for a main sewer, I believe in 40 inch (1000mm) requiring low builing height. This valve has a full bore, seat sealing fastened on the ball turned away from main stream when open, and in addition fairly large open room between ball and inner wall of housing beeing flushed clean by faster flowing part of main stream. This has proven a very dependable, trouble-free solution. Price at least as high as plug-valves.