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Thread: Replacing glycol reservoir DIY

  1. #1
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    Replacing glycol reservoir DIY

    so we are replacing the tiny little reservoir that came with our chiller and getting something more appropriately sized. for 3hp we got a 70qt Marine cooler. figure that should be a decent size, filled to about 15gals or so. the plumbing is the issue im a little stumped on here. the chiller likely started life as a CNC/lathe/etc type chiller, not a brewery chiller. hence the tiny reservoir.

    in any case, I can't figure out why it seems to have a bypass on the feed from the HX to the reservoir that skips the tank and just heads straight into the pump. it seems a bit odd to me, as the the tank is tiny, and it has a direct gravity feed right into the pump off the bottom, so why the bypass?

    here's a pic. excuse the shitty markups. blue is the feed from HX. yellow points to bypass line. reservoir is upper left. to the right of the tank you see the tee, and the HX cold feed is at 3 o'clock, but at the bottom of the tee is the bypass at 6o clock. which comes down and 90s and then meets the suction line, which comes directly out of the tank bottom. very strange and short bypass. can't figure out what the hell its really for, which means I can't decide whether to copy it or not into the new reservoir plumbing. maybe its intended to push glycol into the pump suction? with a bit of pressure behind it so as to avoid negative suction? just a guess.

    anyone familiar with these? or know why they'd plumb it this way?

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  2. #2
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    Quote Originally Posted by brain medicine View Post
    so we are replacing the tiny little reservoir that came with our chiller and getting something more appropriately sized. for 3hp we got a 70qt Marine cooler. figure that should be a decent size, filled to about 15gals or so. the plumbing is the issue im a little stumped on here. the chiller likely started life as a CNC/lathe/etc type chiller, not a brewery chiller. hence the tiny reservoir.

    in any case, I can't figure out why it seems to have a bypass on the feed from the HX to the reservoir that skips the tank and just heads straight into the pump. it seems a bit odd to me, as the the tank is tiny, and it has a direct gravity feed right into the pump off the bottom, so why the bypass?

    here's a pic. excuse the shitty markups. blue is the feed from HX. yellow points to bypass line. reservoir is upper left. to the right of the tank you see the tee, and the HX cold feed is at 3 o'clock, but at the bottom of the tee is the bypass at 6o clock. which comes down and 90s and then meets the suction line, which comes directly out of the tank bottom. very strange and short bypass. can't figure out what the hell its really for, which means I can't decide whether to copy it or not into the new reservoir plumbing. maybe its intended to push glycol into the pump suction? with a bit of pressure behind it so as to avoid negative suction? just a guess.

    anyone familiar with these? or know why they'd plumb it this way?

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Views: 118
Size:  100.3 KB
    It's one of those engineer features that's is installed by over-thinkers with all the details - This comment is totally in jest.

    I believe you are looking at a basic anti-vortex, designed to prevent cavitation of the pump. I could be wrong, but I am 95% certain this is the purpose. Basically, stir the pot with the return feed, but not in a circle. Some directly into the pump, and some into the pot to keep a "steady turbulence", avoiding the cavitation.

    I think this is what you mean by "negative suction", however that term would typically be used in a pump situated above liquid level requiring a "suction" (negative head pressure) to draw liquid into the pump. The gravity fed, atmosphere vented system you have pictured should not really have a negative pressure (practically speaking). It is not common in a gravity supplied setup unless the pump is severely over-sized (or positive displacement) and attempting to draw significantly more than can be supplied through the supply line. With this tubing, you would see it pinch shut on the supply side in a negative pressure situation.

    There are specifics to designing the pump feed inlet to avoid the need for anti-vortex, but that is the engineering mumbo-jumbo best saved for the DIY threads. I think you would be best served to copy any design that achieves the same effect of avoiding cavitation.

  3. #3
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    I've thought about it all night, and struggled to find a reason why this would be done.

    Best I could come up with:
    If the heat exchanger is on the return, it helps to make the coldest water leaving the heat exchanger go into the pump and not get "diluted" by going into the tank.

    I dont think you should worry about it.

    It does appear that you have a "Regenerative turbine" type pump. They are in between a centrifugal and a positive displacement pump in terms of flow-pressure. So more pressure than flow relative to a centrifugal. So use caution on your tank jackets. They also have very tight tolerances (again in between a centrifugal and PD) so make sure your piping is clean when hooking all this back up. Pipe tape, shavings, etc.



    Jeff





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  4. #4
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    Quote Originally Posted by UnFermentable View Post
    It's one of those engineer features that's is installed by over-thinkers with all the details - This comment is totally in jest.

    I believe you are looking at a basic anti-vortex, designed to prevent cavitation of the pump. I could be wrong, but I am 95% certain this is the purpose. Basically, stir the pot with the return feed, but not in a circle. Some directly into the pump, and some into the pot to keep a "steady turbulence", avoiding the cavitation.

    I think this is what you mean by "negative suction", however that term would typically be used in a pump situated above liquid level requiring a "suction" (negative head pressure) to draw liquid into the pump. The gravity fed, atmosphere vented system you have pictured should not really have a negative pressure (practically speaking). It is not common in a gravity supplied setup unless the pump is severely over-sized (or positive displacement) and attempting to draw significantly more than can be supplied through the supply line. With this tubing, you would see it pinch shut on the supply side in a negative pressure situation.

    There are specifics to designing the pump feed inlet to avoid the need for anti-vortex, but that is the engineering mumbo-jumbo best saved for the DIY threads. I think you would be best served to copy any design that achieves the same effect of avoiding cavitation.

    Ok. So i had the right idea on why it was plumbed that way. Maybe i might not have to worry then so much.

    The only question that leads me to is whether i need to worry about vortex in the new reservoir.

    In response to Jeff- the factory pump speed was making about 55psi. We had to put a vfd on the pump to get it slowed down to 15-17psi. So thats one factor id say might negate the need for the bypass. Th other is that the new reservoir is 70qt cooler vs probably 12ish qt cube from factory.

    So given the slower pump speed, the larger reservoir tank size, and the larger body of liquid ready to gravity drain into pump, im feeling like i can skip the bypass. I dont think the slower speed and the much bigger reservoir should be able to really allow a vortex that would deny sufficient gravity drain to the pump.

    As long as the new outlet on the cooler is at same height as pump inlet so it stays gravity fed id think that should be safe, no?

  5. #5
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    So I thought about this a bit more and the design could be a bit more dynamic than I originally explained. I really only referenced a vortex, but cavitation can be a major concern as well, but not likely for you, since you have made the VFD modification. You should be able to install a simple baffle (if needed) and adjust the VFD to optimal performance. Gravity fed would help prevent cavitation.

    At the higher velocities/pressures of the system design, cavitation may have been a much larger concern. Basically, by directing some of the returning fluid energy to the in-feed of the pump you might prevent cavitation by increasing the Net Positive Suction Head (NPSH) on the supply side of the pump, both preventing vortex and cavitation.

    The volume capacity of the reservoir is actually irrelevant, strangely enough. The depth of the reservoir is the real consideration, as that is what factors potential energy into the system in the form of gravity. The height of the supply above or below center-line of the pump adds or subtracts more potential energy. Then there is the reservoir outlet, and pump in-feed piping diameter and length to consider (friction loss). Bernoulli and some others. The idea is you need to have a greater NPSH than the vapor pressure of the liquid you are moving.

  6. #6
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    Sounds like we are visualizing it the same way. I think ill skip the bypass and just try to elevate the reservoir as much as i can for now.

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