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Solar Expansion Tank Questions

TJonesTJones Posts: 8Member
I recently purchased a house with a closed loop solar hot water system and am finding myself a bit puzzled by it.  I was hoping to get some info about it here.

My main question is about the expansion tank, it's a Solar Extorol S15 (image is attached).  There's a temp and pressure gauge on it, but the pressure gauge says 0.  I was concerned so I put a gauge on the bottom and it actually does have pressure and guessing the gauge is broken.  The gauge on the tank has a red arrow that I assume indicates the psi but it's pointing at 10psi.  Would this be correct.  The info I found online says it comes precharged at 25psi.  How do I determine the correct psi?

Second question is about glycol, there's what seems to be a pressure valve above the tank and it's covered in green stuff, I also notice it's spurting a little when we were running the hot water in the shower, is this normal or a leak?  There's a cap on it that was loose, should it be capped or do I just need to tighten the cap to stop the spurting?  Also, I don't understand how to fill it with glycol or check the level of the glycol.


  • hot_rodhot_rod Posts: 11,229Member
    the brass

    device is a float type air vent. It allows any air in the system to expel. Sometimes they spit a little under the cap to vent any air in the system. Also some brands have a crimp assembly point that can leak glycol after time. Consider replacing it with a vent designed for solar conditions and temperatures, if it is leaking.

    TThe expansion tank has a blatter in it with a pre-charged air space. The tank should indicate the pre-charge pressure, check it with a tire gauge on the cap at the bottom.

    If the system pressure gauge is working it sound like your system is low on glycol. It should have 12 psi or more depending on the height of the uppermost point, usually the collector.

    This link will take you to some good reading about solar thermal systems and a sizing formula for the expansion tank.

    i suggest at least 5 psi at the high point. calculate the distance from the tank to the top of the collector.

    Depending on the type and number of collectors and the amount of piping and fluid in the system, that #15 tank may be undersized. If the tank is undersized the pressure in the system may increase to a point where the pressure relief valve trips and dumps some of the glycol out.

    The system will go into stagnation conditions during power outages or when the tank is up to temperature. the expansion tank needs to be sized to handle the expansion from those high temperature conditions.

    Oversizing the expansion tank allows you to run higher fill pressure. This will raise the boiling point of the fluid and help prevent the glycol from flashing to steam.

    You will need a fill pump to add glycol into the system and I would check the ph of the fluid that is in the system. The ph drops as the glycol is overheated. The fluid may need to be flushed and replaced.

    You may want to find a solar contractor with the tools and meters to check the fluid and refill the system and look for any possible leaks.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • TJonesTJones Posts: 8Member
    Thanks for the info!

    I really appreciate the info, it was very very helpful.  I hope to gain some knowledge on this system but I will find myself an expert to look the system over.

    One more quick question... I'm on town water and near my meter is a pressure relief valve, I hear this valve release several times a day.  It seems to be at or around the same time in the mornings, say 7am and then last night it went off a few times n short bursts at night.  There's a timer connected to the solar system and I thought it was related to that, but it happens at night even after the timer is on off.  Would the solar system create pressure that is being expelled by this relief valve? Is this normal?

    Thanks again!
  • LarryCLarryC Posts: 331Member
    edited June 2013
    Potable water relief valve

    I suspect the relief valve goes off after the use of a fair amount of hot water, correct?

    I suspect that there is a check valve between the water meter and your water heater.  When you use hot water and the heater cools down, the tank is full of cooler water.  When the heater fires up and heats the water, the water expands but there is no place for the water to go.  The pressure builds up until the pressure is relieved by the relief valve opening, flushing a toilet, running a sink or something.

    If there is a check valve, you need to install a correctly sized expansion tank to accomodate the extra water volume created by heating a cool tank.  The expansion tank needs to be rated for the higher pressure of the water system.

    Was the water heater recently replaced because it was bulging and making snapping or cracking sounds?  When you first turn the water, does it come out at a high speed and then slows down to normal flow after a second or two?  Those are also indications of the system being over pressurized.
  • TJonesTJones Posts: 8Member

    Actually the relief valve typically goes off in the morning at like 7am when no water has been used for 8 hours and then it does happen in the evenings, we have usually used a fair amount of water on dishes and showers prior to it going off. 

    So I think I misunderstood what the pressure gauge was for that is above the tank, I see now that it's not measuring the air that I adjust at the bottom of the tank, but actually the pressure in the top with the glycol? or is it the system pressure?  Should I just change out the tank to try to fix this, looks fairly cheap and it looks like it just unscrews.

    Appreciate it!
  • SWEISWEI Posts: 7,356Member
    Tank charge

    is measured when there is no pressure on the water side.  It's much easier with an isolation valve and a drain -- so consider adding something like a Webstone Expansion Tank Pro or Ball Drain if you pull the tank.
  • TJonesTJones Posts: 8Member
    Another Question

    So would low air pressure in the bottom of the tank create less pressure in the top of the tank?  The bottom of the tank air pressure is only at 10psi, what is typical pressure for one one of these small tanks.  It says it comes precharged at 25psi? Would that be a good baseline. I think I read that you should turn off the water main, then check the tank pressure? The pressure should be equal to the water pressure coming out of my faucets?
  • SWEISWEI Posts: 7,356Member
    Tank precharge pressure

    should be equal to the standard wet-side pressure.  If this is the solar loop, set it to that pressure.
  • spdspd Posts: 21Member
    system pressure

    Dear sir,

    If there are stains on the piping, the system has lost glycol. Either 0 or 10 Psi is not enough, and the gauges are often inaccurate. Expansion tanks help keep pressure constant but they don't manufacture pressure. The pressure is low because you have lost fluid. Do you know if the system is making heat? My guess is that you need maintenance. Just because the pump becomes energized does not mean the Heat transfer fluid is circulating.
  • spdspd Posts: 21Member
    Gasket material, commercial balancing valves

    Dear Hot Rod,

    He needs to fill and fix his system easy as pie. Why would it need an air eliminator?

    Thanks for a previous response about flow setters, subsequently installed on a crucial installation, picture attached.

    Does any one know the type of material used used make the flat washers for Caleffi products and many other solar brands? Does any one have any clues on where to get an assortment kit of these?
  • TJonesTJones Posts: 8Member
    Finally talked to a professional

    I actually had a professional come out and take a look, because I couldn't make heads or tails of my system.  I have a much better understanding of it now.  Unfortunately the system was not functioning properly and I found out my hot water heater was cranked way up, so the solar system was just cycling non-stop wasting energy. Sounds like I need a new expansion tank, the system needs to be recharged and the temperature control module was not working.  That said, we turned the system off (the pump) and I am waiting on a quote for all the parts.  Meanwhile my relief valve on my panels keep puffing steam when the sun is out.  Should I drain my system and cover my panels until I get things working? 
  • hot_rodhot_rod Posts: 11,229Member
    drain 'em

    if they have glycol you are over-heating the fluid and could damage the copper tubing.

    Also over-heating the fluid will create a sludge that will need to b e purged and cleaned out of the tubes in the collector to assure good heat transfer.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • TJonesTJones Posts: 8Member
    How to drain?

    To drain the glycol loop, can I simply attach a hose to the drain near the pump? This may sound dumb, but does the water in the loop come from when it was "charged"? In other words it doesn't feed in from my town cold water supply or need to be shut off anywhere?  Do I have to use a pump to blow out the system or will gravity suffice for the majority of the water?  Thank you!
  • hot_rodhot_rod Posts: 11,229Member

    the pump and control first. Drain it into a bucket that you can seal off safely. Drain it in the morning or evening when the fluid is not too hot to handle.

    Recycle the old fluid at Quick Lube, Auto Parts stores, or a Safety Kleen location.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • TJonesTJones Posts: 8Member
    Good info

    Thanks for the info, how many buckets of water should I expect out of the loop?
  • TJonesTJones Posts: 8Member
    Another quick question

    If I drain the system of water, is there an easy way for me to pressure test the system for leaks? What's the best way to test it for leaks?  Thanks!
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