Why does friction wear occur on a split wedge or double disc valve?

Friction wear on a split wedge or double disc valve primarily occurs because the seat and disc contact only in the closed position. When the valve is closed, the two surfaces come into direct contact, and as the valve operates, the movement can create friction between these surfaces. If there is insufficient lubrication, or if the material properties of the disc and seat are not optimal, this friction can lead to wear over time.

When the valve is in the open position, the disc is generally lifted away from the seat, minimizing direct contact and wear. However, during the closing and sealing phases, that contact becomes crucial. The nature of the design means that wear can be intensified at the point of closure, especially if the valve is frequently cycled or if there are any misalignments during installation that cause uneven contact.

Though improper installation, corrosion, or inferior materials can contribute to overall valve failure or decreased performance, they do not directly explain the specific mechanism of friction wear experienced when the disc and seat interface is engaged. The key factor here is the operating dynamics of the valve in its closed position, which directly involves the friction generated between the two contacting surfaces.