Spring-Loaded PTFE Packing Arrangements – Spring-loaded PTFE packing arrangements are very common. A spring loaded PTFE arrangement is illustrated in Figure 26.
The packing box rings sits at the bottom of the packing bore and provides a replaceable seat for the spring. The spring transmits force to the packing rings through a washer. Male and female adapters form flat surfaces on the top and bottom ends of the packing ring stack so that the packing mates squarely with other components. The packing follower compresses (loads) the entire packing arrangement as the packing gland nuts are tightened.
Because the packing rings are “V” shaped, the spring load forces the edges of the rings against the stem and the packing box bore to form a seal. The concave surfaces of the packing rings always face high pressure; therefore, process pressure also pushes the edges of the rings against the valve stem and the packing box bore. The orientation of the packing rings results in a pressure-assisted seal.
Spring-loaded PTFE packing arrangements are popular because:
• They have low friction.
• They are chemically compatible with a broad range of fluids.
• They provide a tight seal.
• They have a long cycle life.
• They provide constant loading because of the spring; therefore, they require minimal maintenance.