Graphite Vs. Teflon Valve Packing: What Are The Major Differences?
At some point, all valves need to have the packing refreshed for continued reliable operation without leaks. There are a variety of materials used for packing valves. Many of them are specialized packing materials for pump shafts and industrial uses. The standard valve packing materials are graphite and Teflon or PTFE.
Graphite packing material is an inorganic form of pure carbon. Typically, graphite valve packings are black or dark grey, reflecting the natural state of the carbon materials. Teflon or PTFE is a synthetic polymer material that has many uses. Pre-treating PTFE tends to increase the lubrication factor for the polymer for better application.
In some cases, manufacturers combine graphite and PTFE to make valve and shaft packing more efficient. Understanding the advantages and disadvantages of Teflon and graphite as valve packing materials is critical to choosing the right packing material for your application.
PTFE, commonly known as Teflon, has gained much attention as a non-stick cookware coating. What is less well known is PTFE’s widespread use as packing for valves and rotating shafts. The nature of PTFE lends it well to the valve and rotating shaft packing. PTFE is highly resistant to many corrosive chemicals used in industrial processes.
In addition, you can combine PTFE strands with other substances, most notably graphite, to enhance the quality of the packing further. PTFE is a natural insulator that can inhibit heat transfer. Adding graphite or other materials can mitigate some of these insulating qualities and allow better heat transfer.
PTFE packing material made with lubricating materials dispersed through the fibers works better than those with surface lubricants. These impregnated PTFE packing materials last longer and perform better than other types.
Applications and Uses
PTFE packing materials offer many advantages in certain situations. Among the notable applications where PTFE materials are better suited for use are:
- Situations where chemicals, acids, strong bases, and other fluids may be present. PTFE is highly stable when in the presence of these kinds of chemicals.
- High-temperature applications, especially those where steam is present.
- Where friction may be an issue, low friction coefficients are more important when packing rotating shafts than on valves but is an important advantage of PTFE packing materials.
PTFE packing material sees more use in industrial applications where chemicals, hydrocarbons, fuels, and caustic materials are present.
The Downsides of PTFE
PTFE packing materials do have drawbacks that can limit the use of these materials. In particular, the following situations may prevent or severely restrict the use of PTFE packing materials.
- A pure PTFE packing material may exhibit cold flow or creep under pressure. This cold flow or creep occurs when the packing material experiences high temperatures and pressures. The PTFE packing may require frequent adjustments and maintenance to maintain a proper seal.
- PTFE is a poor conductor of heat and tends to absorb heat. This tendency may cause the PTFE packing material to negatively affect the valve parts, rotating shafts, and other structural components.
- A high coefficient of expansion is another characteristic of PTFE as a packing material. As temperatures increase, the PTFE may expand and put additional pressure on valve and shaft components.
- While PTFE packing materials offer resistance to a wide range of materials, these PTFE packing materials are not effective with molten alkali products.
Apart from the chemical resistance and lubrication qualities of PTFE, there are other advantages to using PTFE as packing material in many instances. Some of these benefits include:
- PTFE packing can be easier to install and remove when maintenance is due.
- The longevity of PTFE packing is exceptional, which reduces downtime for maintenance, maintenance costs, and the amount of routine maintenance required.
- The chemical resistance of PTFE makes this material a preferred choice in applications where you expect a wide range of pH in the system.
- PTFE packings are available in a wide range of configurations for both valve and pump shaft packings.
PTFE is a resilient and useful packing material utilized in a wide range of industrial applications. PTFE/Teflon packing materials are wise for valve and rotating shaft applications, with only a few exceptions.
Graphite as a valve and packing material has seen wide use for many years. Graphite is a naturally occurring form of carbon. In this natural state, graphite is probably the most stable form of carbon
Manufacturers braid long yarns of graphite to create and form the packing required to create graphite packing materials. This technique creates packing materials with a low coefficient of friction and a relatively high coefficient of heat transfer. The combination of these benefits creates packing materials with a wide range of applicability.
Graphite is sometimes mixed with other materials such as PTFE to create packing material with a blend of features to fit a particular need. The main uses of these blended packing materials are specialized industrial applications
Applications and Uses
Graphite packing for valves and rotating shafts offers several advantages. Among these advantages are:
- Installations that routinely involve high pressures and high temperatures
- Packing around rotating shafts that operate at higher than usual speeds
- Graphite packing materials are suitable for use with certain chemicals, acids, and hydrocarbon fuel applications.
In general, graphite is the most used packing material in most installations. Graphite has a long history of reliable use as packings in valves and around rotating shafts.
The Downside of Graphite as a Packing Material
Graphite packing is often the best solution for packing valves and rotating shafts. However, there are instances and applications where experts don’t recommend graphite packing. Some of these instances include:
- Don’t use graphite packing where strong oxidizing agents are present, especially at high temperatures.
- Solutions or mixtures of abrasive materials may severely reduce the longevity and integrity of graphite packing materials.
- Any application where extremely high temperatures exist is a poor choice for graphite packing.
Despite some applications where graphite is less than ideal, there are many more where graphite offers the choice solution for pump and rotating shaft packing. Consider some of these benefits.
- Overall lower cost than PTFE or composite packing materials
- Self-lubricating graphite requires lower maintenance costs
- Highly effective at sealing VOCs in valves and rotating shaft equipment
- In most applications, graphite packing does not require flushing
Graphite offers an ideal solution for valve and rotating shaft-packing under any circumstances. Graphite is an economical and efficient packing material outside of some extremes in materials, temperatures, and pressures.
How To Choose your Packing Material
There are several issues to consider when choosing which packing material best fits your situation. The most common of these issues include:
pH Level of the Material being Handled
The goal is to choose a packing material that is as inert as possible with the material you need to control in your system. Ideally, the packing material you choose should be non-reactive in pH between 0 and 14. Both PTFE and graphite packing yarns are available with this characteristic. However, always inquire from the manufacturer about specifics of the resistance of the packing material to non-standard chemicals.
Temperature Reactivity and Resistance
Carbon-based graphite packing materials are more highly temperature resistant than other forms of packing. Other materials, including PTFE, tend to break down at temperatures above 500 degrees Fahrenheit. This temperature cap makes these alternative materials unsuitable for high-temperature applications
Older equipment can present problems getting some packing agents to achieve a positive seal. Problems with older equipment often occur more with stuffing boxes and seals on rotating equipment. However, older valves may experience these problems as well. Older equipment that shows signs of pitting or other damage may benefit from graphite packing because of its ability to conform and create a seal.
It is always tempting to go with the least costly solution to any problem. However, cheap upfront is not always more economical in the long run. Choosing the low-cost option can translate into costly repairs later if the selected packing material fails before expected, causing damage and additional costs.
Other Available Options
There are other available options for packing valves and rotating shafts. Many of these offer superior performance in specific applications where graphite or PTFE don’t perform well. Among these options are:
- Blended synthetic and fiberglass yarns impregnated with PTFE. These packing yarns are often more resilient, offer fewer problems with extrusion and adapt better to adjustments.
- Where abrasion resistance is needed, aramid fiber yarns make excellent packing materials, especially when combined or enhanced with graphite or PTFE coatings.
- Caustic exposures may require a novoloid product that is PTFE coated. These novoloid products offer good extrusion protection and withstand many caustic exposures that a PTFE or graphite yarn cannot tolerate.
The Last Word – Know your Application Before you Choose a Packing
In the end, unless you fully understand the application, you cannot expect to choose the proper packing material for your valves or rotating shafts. Taking the time to match the features of your packing material with the requirements of your sealing situation will result in longer packing life, less maintenance and repairs, and lower overall operating costs.
Dennis is a retired firefighter with an extensive background in construction, home improvement, and remodeling. He worked in the trades part-time while serving as an active firefighter. On his retirement, he started a remodeling and home repair business, which he ran for several years.
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