New Mexico Pipe Fitter Journeyman (JPF) Practice Exam

What causes friction wear on a split wedge or double disc valve?

1. The seat and disc are in constant contact.

2. The seat and disc are only in contact when closed.

3. The valve is used under high pressure.

4. Improper installation of the valve.

The correct answer is: The seat and disc are only in contact when closed.

The correct understanding of friction wear on a split wedge or double disc valve is rooted in the nature of how these components interact. When the seat and disc are only in contact when the valve is closed, this limited interaction reduces the potential for friction wear in operational states where the valve is open. During normal operations, particularly when the valve is opened, the disc is lifted away from the seat, minimizing contact and thus reducing friction. In contrast, if the seat and disc were in constant contact, there would be continuous wear from friction whenever the valve is in use. High pressure can contribute to wear and stress on the valve components; however, it doesn’t specifically cause friction wear in the manner described. Similarly, while improper installation can lead to operational issues and premature wear, the specific nature of friction wear in a split wedge or double disc valve is more directly related to how and when the components contact each other. The design's intent is such that friction wear is minimized when the valve is operated correctly and only contacts at the point of closure.