Type of Valve

[lizgr]

Hi,
I am not too familiar with Valves. I have to select one to add at the end of a 12" PVC pipe that drains a man made lake when we want to lower the water level during the rainy season. So for the most part, there will be very little pressure in the line. Someone recommended a plug valve, but after reading some posts i'm inclined to recommend a ball valve. I need it to be water tight also. so no leaking.

Thanks in adavance.

 

[Duwe6]

Soft-seat butterfly valve. Either PVC or bronze, depending on how robust you want the valve. Bronze valve will be flanged.

 

[StevenHPerry]

12" seems a bit large for a ball valve, and it's toward the upper end of a plug valve too I'm sure.

I don't understand the water tight requirement exactly. If absolutely no leakage of water is allowed into your spillway, then maybe you are stuck with a gate, globe, plug, or ball and perhaps two of them.

Otherwise, butterfly is where I would start looking. If this is something you'll use once a year at a relatively known time, throw an extra blind flange at the outlet to control any small leaks during the dry season.

- Steve Perry

http://www.linkedin.com/in/stevenhperry

This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.

 

[Latexman]

No valve is going to be water tight forever. I'd put a blind flange just downstream of whatever valve you select. A plug valve or butterfly valve is fine, if you have a blind flange downstream.

How is your security? Can a mischievous person drain the lake when no one is looking? Over a long weekend? You may want a lockable valve or put the valve and blind flange in a secure area.

Good luck,
Latexman

 

[BigInch]

Must be a really long weekend to drain a lake through a 12".

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[Latexman]

Or a small lake.

Good luck,
Latexman

 

[BigInch]

Even a small lake would apparently be a minimum of 5 acres according to

http://en.wikipedia.org/wiki/Lake#Etymology.2C_meaning.2C_and_usage_of_.22lake.22

5 acres would be difficult through a 12" for sure. I could go with pond.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[lizgr]

BigInch thanks.. it's large pond... and the pipe is used to release some water.. and dont need a full fledge design Mr. Perry just need to choose one valve.. and you're right Latexman. Thanks all for your input.

 

[BigInch]

Unless you want to throttle it, I'd pick a gate, or ball valve. Whatever you're happy with. If you can't get a 12", cut it down a size or two with some reducers on either side, just keep it fully open, or completely closed. Butterflies, globes and plugs are better left for throttling purposes.. IMO.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[vpl]

My recommendation would be a gate valve, only used for isolation as Big Inch stated. Only reason for not suggesting a ball valve is the size -- I've not seen them in 12".

If you have some need for throttling capability then the butterfly valve would be good, but I'd back it up with a gate valve.

But, take my advise with a grain of salt. I work with nuclear components and we really don't like water going where it's not supposed to!

Patricia Lougheed

******

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[DLite30]

I would go with a gate valve. That way you don't have to worry about the polymer seats wearing out/getting damaged/leaking.

 

[zdas04]

The biggest ball valve I've ever seen had a car driving through it (demonstration valve in the manufacturer's warehouse). 48" are almost off-the-shelf items in some places.

But, big-inch ball valves are quite expensive.

I would use a knife gate valve (really thin) for this kind of application where the design pressure is a few dozen feet of head and the transient velocities can be really high. These valves have a resilliant seat (like most ball valves) where typical gate valves have a hard seat that foul easily in "drain the swamp" kinds of applications.

Butterfly valves work for this, but I've had problems with the plates breaking off in high-velocity liquid flows. The vibrations from von Karmaan Streets are just too hard on a bluff body in the flow.

I wouldn't use a plug valve for this application on a bet--if you don't lubricate a plug valve then it doesn't move and service like you're talking about is typically short on preventive maintenance programs.

David

 

[cvg]

how deep is the lake? and is the lake created by a dam? does the outlet pipe go under/through the dam?

For a dam with an outlet going through the embankment, normally the valve is on the upstream side, in the lake. this allows the outlet pipe to remain unpressurized except during operation of the valve. sediment and trash is an issue, the valve needs to pass trash without clogging. typical would be a slide gate. If this is a deep lake than differential pressure can have some impact on your selection and it will increase the torque required to open the valve.

 

[cloa]

lizgr say he want to lower the water level not drain it completely so the question should be how low potentially (most extreme case) does he want to lower the water level?

 

[BigInch]

The real question is why have a valve at all! Most artificial lakes can be level controlled quite well with a spillway of some kind, perhaps just an open pipe with inlet set to the proper elevation, pipe diameter and slope set for the max flowrate that would be needed.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso