Pressure Valve 3

[nckingfish]

I need some assistance on the type of pressure valve I need for a subdivision I am working on. I am a land development engineer in NC, USA.

This situation is that my proposed subdivision will be served by an 8" city water main that will not meet fire protection (20psi). The county has a 16" main across the street.

We are going to tap onto the 16" main with a valve that will "open" only when the pressure on the city side goes below a certain set amount (20psi). This will work in a fire situation (or when every one flushes at the same time).

The flow will be metered by the county and charged to the city, who will then spread it out to the homeowners in the subdivision.

My question is this. I am searching the internet for available suppliers but am getting confused on all of the options. Am I looking for pressure relief valves, pressure sustaining valves or a combination of the two?

Thanks

 

[JStephen]

Sounds like a pressure-sustaining valve to me?

Your pressure drops, this valve opens up, which instantly boosts your pressure, which shuts the valve back off- feedback effect. check how they handle that problem with the valves.

 

[nckingfish]

Thanks JStephen.

That sounds logical.

My water layouts are typically limited to tapping sleeves, gate valves, hydrants, and blow off assemblies. This is surely a little more complicated.

I've checked the CLA-VAL website, and others, and they seem to imply that a sustaining valve, sustains the upstream side (in my case the 16" high pressure side) to a constant pressure and doesn't allow the downstream (8" low side)"rob" it, no matter what the demand is.

Maybe this is a function a specfic type of sustaining valve.

I am just hoping someone has seen this situation before and can help me with the semantics.

thanks

 

[semo]

You need to be looking at a modified altitude valve. This valve will sense the downstream pressure and open when it reaches a low setting, then close when it reaches an upper setting.

You probably need to be talking with the Ames/Watts company or other control valve manufacturer. Giving them the specifics can help them design the solenoids that you need on the valve to correctly meet your conditions.

 

[nckingfish]

Thanks for the help!

 

[rconner]

I am not an expert in such designs; however, it would appear to me that the valve setting would need to be somewhat above "20 psi" (to avoid the pressure from falling below 20 psi in any of the reaches served by the 8" syustem?)

 

[Latexman]

In the chemical industry, this type valve is called a "self-contained pressure regulator". I am familiar with:

http://www.emersonprocess.com/fisher/

Good luck,
Latexman

 

[Pump2005]

We use CLA-VAL for our clarifier and standpipe altitude valves. They have an endless amount of products and uses.

 

[hydrae]

Don't use an altitude valve.

Use a 'pressure reducing-pressure sustaining' valve
All the diaphragm operated globe valve makers have them

The altitude valve will open WIDE on a low pressure signal and you want controlled flow

Assume normal pressure is 60 on both sides
set the pressure reducing control to 40 sensing the city side, when the city side drops below 40 the valve will open and maintain 40, if demand increase beyond what the 40 will provide, the pressure on both sides will drop, to prevent the city from over tapping the county, set the pressure sustaining side sensing the county to 30, this will ensure that no matter how bad the demand on the city side gets, the county will still provide service to its customers.

Of course adjust the number to fit your situation

This type of valve will operate completely on the pressure in the system, no power, no solenoids, no batteries.

Use a brand of valve that is common in your area, where you can get parts (today, not in three weeks) and reliable service. These valve require maintenance at least every 5 years. They should be operated at least once a year. Install it in a place where the valve can be gotten to. Have operations learn how to adjust it so when the firefighter says he wants more water it can be tweaked in the field.

Hydrae

 

[Ashereng]

I have heard the term "altitude valve" used several times.

Can someone describe what an "altitude valve" is? Is it an industry specific term?

Thanks.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[bimr]

The valve that you need is called a pressure reducing valve. However, if your subdivision is small, you probably want to use 2 valves in parallel. One valve would be sized for your regular low flows and the other would be sized for the fire flow.

You also want to get the check valve accessory feature so that you can not have backflow through the valve.

Contact Cla-Val for a model 90-01:
Pat Donnelly, Cla-Val
Phone: 704-541-7611
Fax: 704-541-7593
pdonnelly@cla-val.com

http://www.cla-val.com/pdfs/E-90-01.pdf

Ashereng

An altitude valve is more or less just a self contained pressure regulating valve.

Altitude valves are kind of specific to and developed for the water industry. They are self contained, usually hydraulically operated. They are balanced to use the line water pressure as the operating motive.

http://www.gaindustries.com/Html/01a_SAVV.htm

 

[Ashereng]

bimr,

Thanks for the explanation.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[bimr]

Some further comments:

The distribution system should ordinarily be designed to maintain a minimum pressure of 20 psi at ground level at all points in the distribution system under all conditions of flow. Normal working pressure in the distribution system should be between 35 psi to 60 psi. This is common water utility design practice.

I also agree with hydrae in that this is not the proper application for an altitude valve, but neither is it an appication for a 'pressure reducing-pressure sustaining' valve.

Of course, all these valve types are quite similiar and it just take different installation techniques are required to get different functions from the valves.

You can also run this application by the utility. They probably have standard valves that they want to use so that the new equipment will match their installed equipment.

 

[BRIS]

It is very much a question of semantics - all the valves referred to are essentially the same piece of kit "hydraulically operated, diaphragm actuated control valves" but with the external control plumbing and springs set up differently. Forget the semantics tell the manufacture what you want it to do. Pressure sustaining valves maintain a constant upstream pressure. Pressure reducing valves maintain a constant downstream pressure. This is what you want. The valve will attempt to maintain a pressure of 20psi. If it is greater it will close if it is less it will open.