A seam tracking device is developed according to the requirement to weld hollow steel balls of net frame nodes.

Existing models of joints 'were based on the semi-rigid beam-column joints of steel frames and had many limitations, so they were not suited to welded hollow spherical joints.

The drain valve is opened or closed by taking advantage of the change of liquid level of condensate water with the high-precision grinding stainless steel hollow float ball in the valve cavity.