What would you call a valve...?

[Stlshrk]

Still planning, designing, and likely over-thinking...

When searching for parts and components, what would I call a valve that only opens when pressure is above a given system pressure (and thus closes under it)? I'd prefer a nonelectric valve so that it would operate even during an power outage.

Anticipating a Homer Simpson-esk "DOH!" when I hear the answer.

 

[Redox]

A pressure relief valve?

What are you trying to do with it? Are you talking pressure relative to the atmosphere or differential pressure across the valve?

 

[Eric Johnson]

You might be more interested in an Automag valve, which only opens when the power goes out. But Redox is right--what you've described is a pressure relief valve. In hydronic heating systems, they're usually set for 30 psi.

 

[steam man]

All right Homer-we want more details on what your up to...........

Loosely speaking, in over pressure protection, a relief valve is used for liquids while a safety valve is for vapors. A safety valve can also incorporate a certain amount of 'blowdown', meaning it relieves at one pressure and resets at a lower pressure. I would suggest thinking of any safety-relief device to be a "last resort" plan of action. Also sized correctly according to its relief capacity. As Eric suggested an automag valve i.e., a "fail open" solenoid valve would be a first choice on power outage. A remote bulb thermostatic valve is also used for high temperature solutions on some boilers to keep a certain flow for cooling through a tankless coil to a drain. You may also have to consider a T-P valve (temperature-pressure) to comply with codes on a pressure vessels. Personally, I like design where you never get to the "endpoint of explosion".

 

[mtfallsmikey]

Or..a pressure differential bypass valve?

 

[steam man]

Or..a pressure differential bypass valve?

I guess the original post wasn't clear to me now exactly what he is looking for.

A differential bypass valve may be used though I don't have any experience using them in small hydronic applications. Here's one at (broken link removed). I assume it would be piped in from the pump discharge back to the pump inlet to regulate the system pressure. It would appear to work anytime you can expect a pump to get dead-ended. We need a hydronic guy with experience with them to explain their correct use.

There's also reducing valves typically used for boiler fill aplications.

As soon as we find out knowledge he is searching for we can narrow it down.

 

[mtfallsmikey]

Steam man, you are correct...commonly used with BB/radiators where TRV's are used. I'm putting one in myself on my system. Circs will blow when dead-headed!..opens on pressure drop.

 

[Stlshrk]

Sorry, wasn't able to check for a few days.

The measurement would be for system pressure accross the valve.

I apologize for the lack of details.

It is possible that I should take a step back as I assumed that this should be done by a part sensing a pressure drop, but there may be other methods (read better) to accomplish the same thing.

What we want is something that would close to prevent a flood into the house if there was a leak. We assumed if pressure dropped below a given point, but I'm definately open to other ideas. The way things are looking the house zone (for the heat exchanger in the forced air system, & dhw sidearm) will be the lowest places in the entire system. The outdoor portions of the system include the zone for the shop, furnace itself, & zone for the storage tank(s). They will all be at higher elevations than the house because the hydronic components for the house zone will all be in the basement, not to mention the lay of our property. I don't want the entire system to flood into the basement in the event of a leak in the house! So the bypass valve opening on low pressure may be the answer.

I just don't want to pump total system volume to the basement if there is a leak inside. Or, if a leak occurred during a power outage (or power is out due to whatever caused the leak) to gravity drain hundreds of gallons of water down there.

 

[Eric Johnson]

Steam man, you are correct...commonly used with BB/radiators where TRV's are used. I'm putting one in myself on my system. Circs will blow when dead-headed!..opens on pressure drop.

When you say "blow" do you mean literally (as in blow a gasket)? Or are you saying the pump stops working. I've had circs that run and sound like they're spinning, but they don't move any water. I assume that's a melted or otherwise compromised impeller, but that's just a guess.

 

[steam man]

Sorry, wasn't able to check for a few days.

The measurement would be for system pressure accross the valve.

I apologize for the lack of details.

It is possible that I should take a step back as I assumed that this should be done by a part sensing a pressure drop, but there may be other methods (read better) to accomplish the same thing.

What we want is something that would close to prevent a flood into the house if there was a leak. We assumed if pressure dropped below a given point, but I'm definately open to other ideas. The way things are looking the house zone (for the heat exchanger in the forced air system, & dhw sidearm) will be the lowest places in the entire system. The outdoor portions of the system include the zone for the shop, furnace itself, & zone for the storage tank(s). They will all be at higher elevations than the house because the hydronic components for the house zone will all be in the basement, not to mention the lay of our property. I don't want the entire system to flood into the basement in the event of a leak in the house! So the bypass valve opening on low pressure may be the answer.

I just don't want to pump total system volume to the basement if there is a leak inside. Or, if a leak occurred during a power outage (or power is out due to whatever caused the leak) to gravity drain hundreds of gallons of water down there.

I know there are safety shutoff valves used to secure water to a system by detecting water on the floor for instance. I forget where I have seen them but typically they are used to secure the water coming into a house. They also make alarms with dialers for the same applications. There are safety devices that will secure a fluid line with a flow above a certain point in what is typically unmanned industrial apllications. I don't know right off of anything that works on a pressure principle. My sister's house had a broken upstairs bathroom water line to a sink that failed. It ran for hours. What a mess.