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Need some engineering support - non-rocket related, but beer, so still good.

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soopirV

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Hi all- I come asking for fluid dynamic advice- other forums I've posted to have been fruitless, and I know there are a ton of brilliant folks here. I'm not sure how best to explain it, so I'll lay it out as a physics problem.
I need to automate the control the flow of water, both cold pressurized (from the hose bib, estimated pressure is 80 PSI), and hot (<180F) gravity fed (column height is no more than 36"). Both the in-flow and out-flow needs to pass through a pulse-sensor water meter (a vane connected to a magnet read by a hall effect sensor). My problem is: valves are either pressure-actuated (requiring a differential pressure of >=3-5psi from inlet to outlet), or gravity-feed (can open with up to 7ft of column pressure, but if greater than that, it fails closed and will not open). Additionally, my flow meter cannot be pressurized, so it has to be protected from city water. My plumbing is all 1/2" rigid copper, and my vessel is a converted beer keg (legally acquired, and amazingly tough stainless steel). It was so much work to put the holes in it that I have already, and don't want to have to put any more in it (please, I know I can easily solve this by adding a second hole to the bottom of the vessel, but doing that is simply not possible). I've come up with the following solution, but I don't trust my engineering chops enough to know if it's valid. My thought process: both valves are normally closed, and when the pressurized valve is open (lower), it will supply a small degree of pressure to the gravity feed valve (right), but given that the gravity feed valve fails closed if pressure limits are exceeded, it will not 'leak'. Once the supply valve (pressure side) is closed, and water is heated up, the gravity valve can be opened since the column height is much less than minimum spec. This way I can use the existing orifice I drilled a decade ago in the keggle, and modernize it with my arduino-based update. Figure 1 is a photo of my brewery: the vessel in question is the farthest left, on top. It has a large opening in the back to admit a 220VAC heating element, and a bulkhead fitting in the bottom for the fluid input and output. Figure 2 is my recreation of my design idea- the one on which that I need confirmation/correction.

Any design flaws that will prevent this from being successful? I'm not at the point of discussing coding, just the physical requirements.

Figure 1:welcome_snowpoint.jpg
Figure 2: Capture.PNG
 

Reinhard

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Is this the complete schematic of the plumbing? Does the vessel contain a vent?

If it contains a vent, everything looks fine.

If it doesn't contain a vent, something like this will happen: You open the city water valve. Water flows into the vessel and pressure will ramp up while the ullage gas above it will be compressed. It takes a short time for the system to reach city water pressure, but before this happens you will exceed the pressure rating of the flow meter and the maximum pressure that your feed valve can handle, so you won't be able to drain your system. In addition, if the heater control fails in the on state, the system pressure will increase even further until something fails in a hazardous way (anything between releasing an intense stream of hot water/steam and a boiler explosion).

Reinhard
 

Lowpuller

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What he said &#11014;&#65039;&#11014;&#65039;&#11014;&#65039;&#11014;&#65039;&#11014;&#65039;&#11014;&#65039;, this has the potential to be really bad.....
 

soopirV

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Is this the complete schematic of the plumbing? Does the vessel contain a vent?

If it contains a vent, everything looks fine.

If it doesn't contain a vent, something like this will happen: You open the city water valve. Water flows into the vessel and pressure will ramp up while the ullage gas above it will be compressed. It takes a short time for the system to reach city water pressure, but before this happens you will exceed the pressure rating of the flow meter and the maximum pressure that your feed valve can handle, so you won't be able to drain your system. In addition, if the heater control fails in the on state, the system pressure will increase even further until something fails in a hazardous way (anything between releasing an intense stream of hot water/steam and a boiler explosion).

Reinhard
What he said &#11014;&#65039;&#11014;&#65039;&#11014;&#65039;&#11014;&#65039;&#11014;&#65039;&#11014;&#65039;, this has the potential to be really bad.....
Thanks guys! No, it's not a complete schematic, and the vessel is basically just a 15 gallon pot, completely open on top. Fill it with cold water, heat it up, drain out the hot water into the mash tun to mash the grains.
 

Tonimus

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Does the gravity valve need to be reset if it over pressurizes? Is the city water a one-way valve? I would probably integrate a simple butterfly or ball valve to protect the hot valve. If you restrict the tubing between the city water and the flow meter to a smaller diameter than the flow meter is, you won't pressurize it, since the top of your tank is open.
 
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