Читать книгу Solar Water Heating--Revised & Expanded Edition - Bob Ramlow - Страница 25

Some evacuated tubes use a getter to ensure that all of the gasses have been removed from inside the tubes. Commonly made of pure barium, the getter will absorb any residual gasses left over after the vacuum has been drawn. The barium will leave a shiny silver coating on the bottom of the tube. If the tube loses its vacuum, this barium coating will be exposed to oxygen and will become white or foggy, clearly indicating that the vacuum has failed and the tube needs to be replaced.

Since the tubes themselves are not structural components of the system, a rack is usually constructed to hold them in place. There is typically a bottom rail that all of the tubes can rest in and be secured. The top of the tubes enter into the manifold and are secured there. Most mounting kits come with bracing members to connect the bottom rail to the manifold. This assembly can either be flush mounted to the roof or raised using struts. Because the tubes are removable from the manifold, they can be installed after the rack has been constructed. Evacuated tubes that use a heat pipe must always be mounted at a pitch of at least 25 degrees to ensure that the evaporation/condensation cycle will flow.