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Thread: Difference between bypass valve and isolation valves?

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    Difference between bypass valve and isolation valves?

    Hi,

    Sorry if this has been asked before, I'm new to this forum. I have a solar pool heater with what appears to be the standard bypass/diverter valve and isolation valves (in and out). The previous owner of the house did not provide me with the owner's manual for the heater. I was wondering what's the difference between the bypass/diverter valve and the isolation valves? Seems like if the bypass/diverter valve is in the position to bypass the solar heater, then it doesn't matter what position the isolation valves are in, the water would just flow directly to the pool. Seems like the two serve the same purpose. Can someone explain when you would use one vs the other?

    Thanks,
    Steve

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    JasonLion's Avatar
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    Re: Difference between bypass valve and isolation valves?

    You use the bypass valve during normal operation to select between having the solar on or off. You use the isolation valves when you need to solar shutdown and isolated from the rest of the system, for example if the solar panels develop a leak.
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    Re: Difference between bypass valve and isolation valves?

    Thanks for the reply. Sorry, but I'm still not fully understanding the difference between the two. If the bypass valve is off, water is flowing directly to the pool, so the solar heater is isolated from the system. Just seems like the isolation valves are redundant.

    Maybe a better question is what position should I have my valves in during the winter. I live in Northern California where it only goes down to about 50F and I don't really need to winterize my pool. I still want to shut off my solar heater to save the additional electricity required to pump the water through it. I would think the bypass valve should be off so that water flows directly to the pool. What about the isolation valves? Should those be off too, or does it not matter since the bypass valve is already off?

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    Mod Squad jblizzle's Avatar
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    Re: Difference between bypass valve and isolation valves?

    Of course if you have automation, you need to ensure that the solar valve does not get turned on while the isolation valves are closed ... as you would not get any water flow and could damage the pump.

    In reality, I think the isolation valves may not really be required as the the diverter valve "should" stop all flow with the solar off anyway. But, that would not be 100% the case if a hole was added to the diverter to allow drainage from the rool even when the valve was not on solar. And the check valve on the solar return should keep water from going up to the solar backward. So, the isolation valves really become more of a back up.

    EDIT: looks like you responded while I wrote this ... I think you get it.
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    Re: Difference between bypass valve and isolation valves?

    You can close the isolation valves in the winter to ensure nothing flows by.

    But, you want to make sure you do this after the pump has been off for awhile so that the panels and plumbing will have fully drained.
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    Re: Difference between bypass valve and isolation valves?

    In many installs, water can still flow into the solar panels, even when the diverter has them turned off, by flowing backwards up the return pipe. You wouldn't get any real flow, since there is nowhere for the water to go, but it will pressurize the panels and could potentially get enough water into the panels to cause freeze damage to the panels in the winter.

    It is also possible for the diverter valve it's self to leak water into the solar panels at some slow rate. In fact solar diverts are often specifically designed to "leak" so that the panels can fully drain down when the pump turns off.
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    Re: Difference between bypass valve and isolation valves?

    Ah, I see. Thanks guys for the reply! Looks like the safest bet for me is then have both in the off position.

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    Re: Difference between bypass valve and isolation valves?

    Hey guys,

    So I went out and played around with the valves, and it looks like the return valve was closed this whole time! I've been running it this way for about a year now and everything seems to be working -- water is coming out of the jets, the pool cleaner is running fine, etc. Is this even possible? The water coming out of the jets *seemed* warm (although I can't really say the pool ever got warm), so I assumed everything was properly flowing through the solar panels.

    Strangely, the vacuum breaker is also installed on this line. I thought the vacuum breaker is supposed to be installed on the feed line to the solar panel? Maybe this isn't the return line and it's actually the feed line to the solar panel? It's the line coming from the highest point of the solar panel, so I assumed it was the return line. Also, (I'm not sure if this was intentional) but the valve on the other line was purposefully broken so that it was always in the open position. It would make sense that the original owner intended the return line to always stay open so as to not avoid damaging the system. Thoughts?

    Thanks,
    Steve

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    Re: Difference between bypass valve and isolation valves?

    Vacuum breakers can be installed in many different places. There are pros and cons to each location, but for the most part it will work more or less anywhere.

    The diverter is hardly ever turned far enough to send 100% of the flow through the panels. So there is nearly always a path through the system that does not run through the panels. That would keep your pool working even if the panels are blocked/turned off.
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    Re: Difference between bypass valve and isolation valves?

    You could add some pictures of the plumbing you are talking about as that could help the discussion. If the isolation valves are just PVC ball-valves, those have been know to break (maybe not intentionally).
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    Re: Difference between bypass valve and isolation valves?

    Quote Originally Posted by jblizzle
    You could add some pictures of the plumbing you are talking about as that could help the discussion. If the isolation valves are just PVC ball-valves, those have been know to break (maybe not intentionally).
    My ball-valve handles broke after the 2nd year. I was experimenting with the valves one day and the handles broke off. I keep the isolation valves open year round here in So Cal.
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    Re: Difference between bypass valve and isolation valves?

    Here's an image showing the two lines and from the solar panel. The left line leads to the lower portion of the panel (feed line?), while the right leads to the higher portion of the panel (return line?). You'll notice the handles on the left valve are broken. I believe the valve is in the open position. As noted in my previous post, I realized today that I've been running the system for about a year now with the right valve in the closed position. The bypass valve has been in the open position (allowing water flow to the solar panel). Pump seemed to be working fine -- water was coming out of the jets, pool cleaner was moving, etc. In the picture the bypass valve is in the closed position.



    Here's an image higher up showing the vacuum breaker on the right valve.


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    Re: Difference between bypass valve and isolation valves?

    The location of that solar 3-way is a little odd. Does all your water always go to these pipes? And the check valve location is a bit bizarre as well. Usually there is a check valve on the solar return, but this one appears to not even be in the solar loop.

    How about some more pictures of the pad / plumbing?

    I think you are correct that the water comes up through the check valve and the then with the valves as they are now, the water just crosses and goes right back down ... skipping the solar. If you turn the 3-way to shut off the shortcut (which BTW is not usually possible to do with that Pentair valve, so they must have removed some internal stops I think), then the water would go up to the solar and then would return down through the other ball valve that would need to be opened.
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    Re: Difference between bypass valve and isolation valves?

    Thanks Jbizzle,

    Now to come to think of it, when the pentair bypass valve was in the on position this past year, that little "off" tab was on the left. Maybe it needs to be on the right in order for it really to be off. Not sure what the internals of the valve are, but if the off tab were on the left, maybe the water then flows in the path of lease resistance, which is to the right and to the pool instead of up to the solar panels. That would explain why everything was still working when the right isolation valve (return path) was closed this whole time?

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    Re: Difference between bypass valve and isolation valves?

    You are correct. With the tab on the left, both pipes would have been open and most of the water would take the short-cut (all of it if the ball valve was closed like the picture).

    Solar works best at the highest flow rates the panels can handle, so your best heating will be when you are running all the water through the solar (if you have enough parallel paths in the solar to handle the flow). You can kind of get a feel for this based on how much the pressure goes up between no solar and full solar. If the pressure goes up a lot, then there may be too much resistance in the solar and some water should bypass the solar. Unfortunately, with the way the 3-way is setup, that is not really possible {the flow should go into the middle pipe and then the valve can divert some water both directions without restricting flow}.
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    Re: Difference between bypass valve and isolation valves?

    Ah, makes sense now. No wonder when it was 110F this past summer it didn't seem like the pool heated up! Gonna try running water through the solar panels tomorrow when the sun is up and fully hitting them. Hopefully the panels aren't leaking and actually work! The person I bought the house from didn't know how to operate the panels, and at the time I didn't either since I never owned a pool before.

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    Re: Difference between bypass valve and isolation valves?

    Is there an arrow on the check valve showing the direction of flow? It actually could be opposite of what we think ... although that check valve would make even less sense.
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    Re: Difference between bypass valve and isolation valves?

    I'll check tomorrow morning and get back to you.

    Isn't my setup similar to the diagram on page 19 in this link:
    http://www.heliocol.com/pdf/Heliocol-In ... Manual.pdf

    Seems like the idea is that when the pump is off, the solar panels drain down through the feed (left) line. The check valve prevents the water from then flowing back through the filter.

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    Re: Difference between bypass valve and isolation valves?

    Yeah, I suppose so. I have one right after the filter ... so that is why I thought it was odd being over by the solar pipes.

    But I also have one on the solar return so that when solar is off, the water does not try to go up the return line to the solar ... you just have to also make sure you close the ball valve when you have the solar off.
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    Re: Difference between bypass valve and isolation valves?

    There is no need to adjust the ball valve every time you turn the solar on/off. It is only for completely shutting down the solar system. Some water will flow up the return pipe with the solar off but ball valve open, but that is a relatively minor issue (just slightly shorter panel lifetime). If you were to move the ball valve frequently it will just break sooner rather than later.

    With a typical pool pump you need a very large solar system to ever want to send all of the water flow up to the panels. I don't know how many panels you have, but a typical setup would turn the diverter valve to somewhere between 45 degrees and 60 degrees, off tab towards the right, handle towards the left, when you want the solar system full on. Figuring out the ideal position is tricky without a flow gauge. More flow is better for heating efficiency, but when the flow goes too high it starts to shorten the panel lifetime, and that effect can be very dramatic if the flow is way too high, ie the panels can fail right away if the pressure gets too high.
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