A poppet valve (Figure 40–51)can be a ball or a flat disc. In either case, the poppet valve
blocks fluid flow. Often the poppet valve has a stem to guide the valve’s operation. The stem normally fits into a hole acting as a guide to the valve’s opening and closing. Poppet valves tend to pop open and closed, hence their name. Normally poppet valves are held closed by a spring.