Solar vacuum tubes: installation question

[leodp]

Hi all,

I have bought a few solar vacuum tubes, old model which gets filled with water+antifreeze (not the heat pipe model), but I do not have the installation instructions.

On the solar panel head there are 30 plastic screw threads, where the tubes will be fixed. I have 2 questions concerning the installation of the tubes, hope somebody can help.

How do I fix the tubes? I was thinking of using silicone on the thread in order to hold and seal the tube. Does anybody know if these kind of tubes can sustain a high pressure (a few Bar)? That would be desirable, so that I can use a water tank in the basement, via a closed-circuit connection and pump.

Thanks, Leodp

[NT]

What matters re pressure is where the solar tubes are relative to the header tank. If the tubes are on the roof you've got next to no pressure in them.

NT

[leodp]

Sure, but at low pressure vapor can form much more easily if temps are high. Do you think the silicone sealing is ok for keeping the tubes in place?

Leo

[David Hansen]

On Mon, 3 May 2010 05:09:24 -0700 (PDT) someone who may be leodp wrote this:-

I imagine not the sort of stuff one sees in large orange sheds. Vacuum tubes reach high temperatures, quickly. You will need to investigate high temperature sealants. It might be worth looking at suppliers of car sealants.

Is one available which will seal at high temperatures and pressures yet not seal solid? No idea, when you find out let the rest of us know. However, as you presumably don't have, and cannot find, spare tubes this may not be a problem.

The tubes should be able to. The joints may not unless made properly.

You will need to consider the installation sequence carefully. The controls and water circuit should be tested before inserting the tubes. It would be sensible to shade the area from direct sunlight, so that you can fiddle with getting the tubes in and sealed without the pressure of things getting hot. When you think you are ready remove the shading, but keep it handy in case heat shows up problems.

[Vortex5]

I have no idea how this type of tube works mechanically, but I would be surprised if they were not designed to take several bar pressure.

In my case I have "heat pipe" type solar tubes which are about 7 metres vertically above the pump and thermal store.

The (sealed) system has a capacity of about 9 litres, with a 7 litre expansion vessel which is precharged to 1.25 bar with a 3 bar safety valve. Fluid is 45% propylene glycol.

System is cold charged to 1.5 bar (measured at the bottom) which means ~0.7 bar at the manifold.

In test "stagnation" (ie pump "off" but sun "on") the manifold stabilises at about 130C and system pressure 2.25 bar....so about 1.5 bar at the manifold.

D