Solar vacuum tubes is the main component of solar water heater and collectors.The evacuated tube is similar to a conventional thermos bottle and consists of two borosilicate glass tubes,with high chemical and thermal shock resistance. The inner tube is coated with a sputtered solar selective surface film. the tube jacket is evacuated to virtually eliminate heat loss by conduction and convection.
Each evacuated tube consists of two glass tubes. The outer tube is made of extremely strong transparent borosilicate glass, that is able to resist impact from hail up to 25mm in diameter. The inner tube is also made of borosilicate glass, but coated with a special selective coating (Al-N/Al) which features excellent solar heat absorption and minimal heat reflection properties. The air is withdrawn (evacuated) from the space between the two glass tubes to form a vacuum, which eliminates conductive and convective heat loss
Precautions about Evacuated Tube Installation
When handling the tubes take care not to break the bottom "tail" as this can cause the tube to loose its vacuum.
Take care when handling the evacuated tubes as they will break if bent, knocked heavily or dropped.
Please don’t unpack the vacuum tubes from their package untill you need to install them.
Ensure the tank is rotated to the correct position such that the tubes are installed perpendicular to the tank holes. If you are having difficulty installing the tube it is often because the tank is not correctly aligned.
Before inserting each tube, the black rubber ring must be pushed around 10 cm. onto the tube.
Prepare a small amount of one part dish washing liquid to one part water in a cup. This is used to lubricate the top of the tube for insertion, and also to act as a "glue" to prevent the silicone seal from leaking. If you just use water the tube will be easy to insert, but will leak once the tank is filled. Apply the liquid to the rubber ring inside the tank port, and also the top 10 cm. of the tube.
With the tube and rubber seal lubricated, insert the tubes with a twisting action until the bottom of the tube clears the bottom track. Pull the tube back down guiding it into the plastic cup in the bottom track. Until the seal dries the tube will seem very loose in the tank, this is normal. If you have used dish washing liquid, the seal will not leak.
Once the tubes are installed the system can be filled with water. If the tubes have already been exposed to strong sunlight for more than 10 minutes, cold water should not be introduced into the collector as the cold water entering the hot, dry tubes can cause them to crack. It is best to wait until early morning or evening when the tubes are cool. Another option is to cover the tubes with a cloth as soon as they are installed to prevent them from heating up. Remember that tubes will already be hot if they were exposed to the sun for prolonged periods prior to installation.
After the system is filled with water and leak-free, the tubes may be cleaned with soapy water or glass cleaner and soft cloth/paper.