Tubing Connectors

 

This view shows the tubing which will be connected to the pipes.  It can be seen that the two tubes which are hanging down are bound with wire.  This is necessary as the only 5/16" (8mm) tubing I could obtain has rather thin walls.  Even a moderate curve causes it to flatten somewhat.  I wound some wire, which is in fact stainless steel welding wire of about 0.75mm diameter and quite springy, around a mandrel then stretched it to a pitch of about its wound diameter.  Twisting the tubing into the turns of wire enables quite small radius bends to be achieved, but the wire needs to be a close fit on the plastic tubing to prevent flattening. I had to add two pieces of wood to the front edges of the side panels because there was insufficient space to accommodate the pipe board and connecting blocks, without fouling the front facia, when it was eventually fitted.

The large black tube is the air transfer pipe made from a piece of rain-water overflow pipe, one inch inside diameter.  As it has an external spiral grove running along its length, it was necessary to seal it by winding a length of sponge rubber 'string' about 4.0mm diameter into the grove where the tube enters the wooden blocks.  This seems quite effective in preventing air escaping.  Alternatively a sealing compound could be used. Alternatively, a piece of thin-walled metal tubing, one inch outside diameter could be used at each end of the pipe.  These would need to be a tight fit into the wooden blocks.