Gyroscopic Investing

I know there are a lot of different types of engineer-ish people here so I figured I'd ask: is there such a thing as a reverse pressure relief valve? Basically a valve that closes with low pressure, rather than opens with high pressure?

Before anyone asks, this is for a reverse thermosiphon solar hot water system I am designing.

I'm only a software engineer, not a real one, but I'd be amazed if that didn't exist.

Pointedstick wrote: I know there are a lot of different types of engineer-ish people here so I figured I'd ask: is there such a thing as a reverse pressure relief valve? Basically a valve that closes with low pressure, rather than opens with high pressure?

Before anyone asks, this is for a reverse thermosiphon solar hot water system I am designing.

In hydraulic systems, this is called a check valve.

[edit] Upon re-reading - this may not be what you are looking for.  But I don't think I'm grasping the distinction.  I'm assuming that you want a valve that only allows flow in one direction and that the actuation is based on a pressure differential.  How is that different than a check valve or a pressure relief valve?  Sounds like a great project.

What I want is a basically valve that says, "Oh, 60 PSI, that's fine, let's stay open and let the water through. Uh-oh, pressure dropped to 20 PSI, let's close up and stop the flow of water!"

Except, you know, not actually a talking valve.

The idea is that these valves would go on the supply and return sides of the solar collector loop. In case the collector freezes or is damaged, and pressurized water starts shooting out, the pressure would drop and valves capable of mechanically sensing this would close, cutting off the flow of water and eliminating the freeze danger.

Pointedstick wrote: What I want is a basically valve that says, "Oh, 60 PSI, that's fine, let's stay open and let the water through. Uh-oh, pressure dropped to 20 PSI, let's close up and stop the flow of water!"

Except, you know, not actually a talking valve.

The idea is that these valves would go on the supply and return sides of the solar collector loop. In case the collector freezes or is damaged, and pressurized water starts shooting out, the pressure would drop and valves capable of mechanically sensing this would close, cutting off the flow of water and eliminating the freeze danger.

i deleted my first one earlier, but i am going to ask this stupid question anyway...... how does it know the difference between the drop in pressure from a leak and the drop from taking a shower?? the way i am imagining it the two valves would have to share information with each other... i should probably keep my mouth shut or wait till i see a picture/schematic before commenting

disclaimer ""i am not an engineer at all"" 

Pointedstick wrote: I know there are a lot of different types of engineer-ish people here so I figured I'd ask: is there such a thing as a reverse pressure relief valve? Basically a valve that closes with low pressure, rather than opens with high pressure?

Before anyone asks, this is for a reverse thermosiphon solar hot water system I am designing.

Offhand, it seems like a pressure sensor in combination with a solenoid valve and a simple controller (like an Arduino) might do the trick.  That would allow you to program valve behavior any way you like.  It's fundamentally how automated irrigation systems work, although they use timers and rain sensors instead of pressure inputs. 

I don't think a check valve is what I'm looking for since in the case of a rupture, the flow of at least one leg of the loop will be going in the same direction it was going in before the rupture.

As for the sensor/solenoid combination, I'd like to avoid any electronics if possible. I want this system to be as simple and cheap as possible--all mechanical stuff.

I admit I'm not an expert here, but I imagine the pressure drop for a shower or even a bath is probably pretty low compared to a full rupture. But that would be interesting to know for sure.

If no such mechanical valve exists, I'll just not use one and make sure the built-in freeze protection is bulletproof.

For a purely mechanical solution, I think Mark is on the right track with the check valve.  Some just prevent backflow, but others are set to close below a certain cracking pressure (like a spring loaded ball check valve), I'd search for a "normally open" variety for your application.

Hmm, I don't think that will work either because part of the design is that the flow can reverse on a daily basis, so a valve that only permits flow in one direction won't do it. Maybe I should explain a bit more about the design:

The idea is that it's a standard water heater, but with additional inlet and outlet ports positioned in the sides of the tank. The side port close to the bottom of the tank is the supply line for an evacuated tube solar collector, and its return line goes to the water heater's upper side port. When the sun is shining, it warms the water in the collector, causing it to rise and enter the tank, and colder water on the bottom to get pulled in automatically. When it gets cold enough to freeze the glass collector, the flow reverses due to convection, and hot water in the tank flows through the collector to protect it from freezing, but without much actual heat loss due to the vacuum insulation in the tubes.

The valves I'm looking for would be positioned right on the sides of the water heater. In case the outdoor collector does indeed rupture due to a failure of the reverse thermosiphon freeze protection mechanism, they would both close and then the tank would function as a standard electric water heater until the collector could be repaired, with no loss of service.

typically i would use a sqd  pressure switch and a solenoid valve . depending what you want they make reverse acting switches and valves . i use them for low water cut outs and high water cut outs .

i do it all the time on my control panel designs .  we always need a high water cut out , low suction cutout and  run pressure switch as well as alarm signals .

Sounds like you just need a couple of float valves.  When the water outside the tank "goes away" the floats drop and close off the line.

Desert wrote: I think I agree with MJ on this.  With the bidirectional flow requirement, I'd go with an active (solenoid-operated) valve, in combination with any sensor logic you need.  Plus that option should allow you to put at least a tiny bit of code in there somewhere. 

Nah, I hate code. Software is for features, not reliability. Gimme good old fashioned stone and metal for something that needs to work 24/7 for 100 years or more.

The solenoid valve idea might work but those things have a habit of burning out after a while. Instead I think what I'm going to do is isolate the collector loop from the potable water in the tank and use a tank that has a heat exchanger inside of it, and the fluid circulating through the collector and heat exchanger will be purified water. If the collector ruptures, the water that comes out is not pressurized and hooked up to an unlimited municipal water supply, so it's no big deal. This also avoids the problem of mineral buildup in the collector in my climate. We have super hard water in New Mexico.

Pointedstick wrote:

Desert wrote: I think I agree with MJ on this.  With the bidirectional flow requirement, I'd go with an active (solenoid-operated) valve, in combination with any sensor logic you need.  Plus that option should allow you to put at least a tiny bit of code in there somewhere. 

Nah, I hate code. Software is for features, not reliability. Gimme good old fashioned stone and metal for something that needs to work 24/7 for 100 years or more.

The solenoid valve idea might work but those things have a habit of burning out after a while. Instead I think what I'm going to do is isolate the collector loop from the potable water in the tank and use a tank that has a heat exchanger inside of it, and the fluid circulating through the collector and heat exchanger will be purified water. If the collector ruptures, the water that comes out is not pressurized and hooked up to an unlimited municipal water supply, so it's no big deal. This also avoids the problem of mineral buildup in the collector in my climate. We have super hard water in New Mexico.

sensor logic is the most reliable .  i did the designs for most of our major hospitals and  i use flow sensors and a control head .

floats in tanks are the worst . the crews used to have to untangle them  regularly inside these tanks .

we have sensors from turck i put in decades ago that are still just fine  and these were first generation .

Pointedstick wrote: Hmm, I don't think that will work either because part of the design is that the flow can reverse on a daily basis, so a valve that only permits flow in one direction won't do it.

Theoretically, two check valves with the desired cracking pressure installed in parallel (but oriented in opposite directions) may accomplish what you need.  Basically, there may not be one single valve that meets all your needs, but a combination with a clever system design might work. 

Libertarian666 wrote: I'm only a software engineer, not a real one, but I'd be amazed if that didn't exist.

This is an awesome answer to a surprisingly interesting topic.

Oh and I'm an accountant with no handy skillz so I'll immediately duck out of this convo and let the smarter minds speak.

Libertarian666 wrote: I'm only a software engineer, not a real one, but I'd be amazed if that didn't exist.

Ok I lied. Total thread hijack follow-up question. And you've probably already answered it elsewhere.  As a software engineer, what are your opinions on intellectual property?  I don't intend to get into a deep debate, but I'm curious about an anarcho-capitalist/software-engineer take on intellectual property.

i just e-mailed my co-worker who handled the plumbing end with your question as to whether such a valve exists .

i did the electrical design on the pumping control panels and he handled the plumbing end so lets se what he says . i will report back .

working two days  a month as a consultant still gets me free info  ha ha ha 

Thanks mathjak!

and the answer is :

ACV! Automatic Control Valve pressure controlled solenoid operated


boy my guys are good , even on a sunday i get answers .


i will be in the office wed if you need me to research it  for you , that is my day of the month to go in .

i believe we have access to the watts line .  see below cuts on the valves

http://media.wattswater.com/C-CACV.pdf

nothing beats keeping it simple .  being a panel designer i will  over think things  with technology using  sensors , probes and control heads .  the plumbers are the simpletons , just get an acv valve    .

moda0306 wrote:

Libertarian666 wrote: I'm only a software engineer, not a real one, but I'd be amazed if that didn't exist.

Ok I lied. Total thread hijack follow-up question. And you've probably already answered it elsewhere.  As a software engineer, what are your opinions on intellectual property?  I don't intend to get into a deep debate, but I'm curious about an anarcho-capitalist/software-engineer take on intellectual property.

I'll answer that in a separate thread, along with a recommendation for a related book I think is awesome so far (about 1/2 way through reading it.)

Tyler wrote:

Pointedstick wrote: Hmm, I don't think that will work either because part of the design is that the flow can reverse on a daily basis, so a valve that only permits flow in one direction won't do it.

Theoretically, two check valves with the desired cracking pressure installed in parallel (but oriented in opposite directions) may accomplish what you need.  Basically, there may not be one single valve that meets all your needs, but a combination with a clever system design might work.

This sounds like the best purely mechanical answer.  It sounds like you want something like:

<-20 psi = open
-20 to 20 psi = closed
>20 psi = open

Pointedstick wrote: I know there are a lot of different types of engineer-ish people here so I figured I'd ask: is there such a thing as a reverse pressure relief valve? Basically a valve that closes with low pressure, rather than opens with high pressure?

Before anyone asks, this is for a reverse thermosiphon solar hot water system I am designing.

did you need anymore info on the ACV VALVES ? i will be in the office wed . i only go in 2 days a month so let me know if you need anything else .

mathjak107 wrote:

Pointedstick wrote: I know there are a lot of different types of engineer-ish people here so I figured I'd ask: is there such a thing as a reverse pressure relief valve? Basically a valve that closes with low pressure, rather than opens with high pressure?

Before anyone asks, this is for a reverse thermosiphon solar hot water system I am designing.

did you need anymore info on the ACV VALVES ? i will be in the office wed . i only go in 2 days a month so let me know if you need anything else .

Yeah, is that a trade name or something? I had a hard time getting information about these.