From Control Valves

Packing Materials

The most common packing materials available today are:

  1. Graphite: This is a pure form of ordinary carbon. In yarn or foil form, this material can meet most industrial plant criteria.

  2. TFE: TFE is highly resistant to chemicals and has low friction. The useful temperature limit is about 500° F. TFE is not abrasive to shafts and has a low extrusion tendency.

  3. Glass Fiber: Generally mixed with other materials, glass fiber has high strength and chemical resistance. It resists wear and abrasion but can damage shafts. Dimensionally stable, it does not cold flow when under compression.

  4. Metals: To meet the requirements of sealing and accommodating the walls of the packing box, most metals in this use are in the form of foil or ribbon. It is twisted or rolled, often in combination with other materials, to make a shape that will conform with the square cross section of braided or die-formed packing. Babbit, aluminum and copper are examples.

Other packing material variations are:

  • Graphite yarn interbraided
  • Graphite foil die-molded
  • Asbestos braid was a common material, but is not generally supplied presently.
  • PTFE V-ring

Packing must be largely impermeable to the fluid that it is sealing. When fibers, yarn or other forms constitute the packing, there are many passages between the neighboring fibers or yarns. Compression on the packing will eliminate most of these, but enough will remain in connected form to cause leaking. This requires special fluids in the packing to decrease its permeability.

12_Chapter_10-22.jpgWhen the process fluid is noxious or in any way might present an environmental hazard, the packing leakage must be controlled or otherwise contained.
© 1998 Instrument Society of America

Products & Services
Hydraulic Valves
Hydraulic valves contain and transfer the flow and pressure of hydraulic fluid in hydraulic power systems. They range from simple shutoff valves to precision control valves.
Valve Actuators
Valve actuators mount on valves and, in response to a signal, move a valve to a desired position using an outside power source.
Manual Valve Actuators
Manual valve actuators do not require an outside power source. They use a handwheel or lever to drive a series of gears whose ratio results in a higher output torque compared to the input (manual) torque.
Pneumatic Valve Actuators
Pneumatic valve actuators adjust valve position by converting air pressure into linear or rotary motion.

Topics of Interest

Packing Arrangements SINGLE PACKING This is an economical seal for many applications. Single packing consists of a stack of packing at the top of the packing box supported by either a spring or gland...

3.5 Compression Packing for Rotary Shafts and Valves 3.5.1 Introduction Compression packing is often known as packing , gland packing and also soft packing . The concept dates back to the beginning...

Live Loading Live-loaded Packing Grafoil packing is less susceptible to differential thermal expansion. However, graphite/filament packing systems on sliding stem valves require higher axial packing...

The material used to manufacture seals covers the entire range of engineering materials. Metals, plastics, elastomers and ceramics are all widely used and will be discussed in turn. In some cases...

Bonnets A valve bonnet covers the opening through which the internal parts are inserted. The bonnet serves as the mounting base for the actuator. It includes the seal which prevents fluid leakage...