So many machine parts and components are tweaked from the manufacturer’s original specifications to tailor their use and fit particular applications. This is why it’s important to understand not only what options are available, but also what benefits and weaknesses each of these options provide the overall process.
Therefore, before discussing the types of poppet valves and poppet materials currently available, it’s worth rewinding a stage and considering exactly what function the poppet valve has within a pneumatic system.
Poppet Valve Characteristics
Generally used to control the flow of compressed air, poppet valves are a type of check valve that is used to regulate and manipulate both the measurements and timing of the flow of fluid through a system. Due to the fact that poppet valves create an almost perfect seal when they’re closed, they can be used for either liquid of gaseous fluids and remain reliable when the fluid is placed under high pressure.
Unlike a pistol spool valve, poppets have an incredibly quick activation time and as such, can be used to tightly control precise quantities of compressed fluid. With this fast response time, friction is an important factor in the design and there’s a huge requirement for the valve parts to be hard-wearing. Not only does this fast opening/closing action require it to be produced from a durable material, heat dispersion has to be considered to prevent the components over-heating.
While the poppet valve is normally considered to be a cheaper alternative of valve due to both the simplicity of the design and the minimized erosion experienced on the inner seals, they have to be carefully designed into a system, as they are susceptible to pressure failures caused by either vacuums or strong back-pressures further down the system.
Poppet Valves in Industry
While poppet valves are versatile and currently utilized far and wide through many industries, their unique benefits make them ideally suited for certain applications. Common industries that make good use of these valves include:
- Blow-molding industries
- Chemical refineries
- Automotive industries
There is also no need for lubricants in the workings of a poppet. This makes them ideal for hygienic applications, such as machinery and equipment in both the food and drink industries and sterile environments, such as hospitals and laboratories.
There are two main classifications of poppet valve that are derived by the way in which they’re commonly used. These are generally referred to as:
- Normally-opened valves
- Normally-closed valves
They classifications take their name from the position in which the poppet valves generally operate. Whether the valve is primarily used to cut-off a supply or release the fluid flow, the reliability and overall characteristics in their design are relatively similar. As such, there are various poppet materials which have become commonly used in the production of poppet valves as they provide qualities which match the required criteria.
Poppet Materials to Choose From
With each of the different materials currently being used to form these valves, there are several factors which need to be addressed to varying degrees depending upon the task to which they will be used. These include:
- Durability relative to the frequency of use
- Durability relative to the duration of operating times
- Toughness of material and amount of pressure to be exerted upon them
- Environmental conditions
- Heat dispersion requirements
- Hygienic needs of the fluid stream
- Financial cost
While most of the poppet materials used will generally provide good all-round capabilities in each of the above areas, choosing the best-suited material for your purpose should account for all of the above and be used to create a comparison chart between your available options. While the financial cost is often the bottom line that many plant owners use to define their choice, all of the factors above cost on this list are more critical to a components ultimate success of failure in operation and should be treated with a higher priority.
Below we take a look at three of the most popular forms of poppet materials used in the production of poppet valves today.
Metal Alloys
Titanium has become one of the most popular choices for some industries such as the automotive and steam engines due to its low density, high relative strength and the fact that it can be hollowed to further aid its heat dispersion capabilities. They’re also a cheaper option along with various steel alloys, while other metals can provide an additional robustness to temperature, pressure and corrosive conditions that they’re required to operate in, such as nickel, zinc, chromium, or copper.
When considering the fatigue levels of any metal alloy for your application, it’s vital that you also consider what these fatigue levels are at the temperature at which the valves will be expected to operate at, rather than the fatigue levels at room temperature which will undoubtedly be different.
It’s also possible to further heat-treat metal alloys to increase their operating capabilities. However, this heightens the need for you to source your products from a trusted manufacturer to guarantee the quality of the product you’re buying.
Polymers
Both Nylon and polyether ether ketone (PEEK) polymers are now commonly used to produce poppet valves and offer lightweight, non-corrosive options that are both hard-wearing and impervious to absorption of all forms of liquids and gases.
One major benefit that polymers have over metal alloys is in the amount of noise that is produced as a side-product to their operation, making a much more pleasant work environment. However, this should not be a main consideration when choosing your material unless there is a scientific reason behind your choice. Polymers are generally not as durable as their metallic counterparts, although by adding carbon into a PEEK design it is possible to improve the overall strength of the material.
Polymer poppet valves do have the edge of metals where corrosive materials are concerned, though, and because they can be produced by injection molding, they are also a fiscally attractive alternative.
Ceramics
Carbon-fibre poppet materials can also be used. However, they are a more expensive option than metal alloys but often deliver increased performance in many areas. While they can be more fragile than metal alloys due to an inerrant brittleness caused by their molecular structure, they still offer a relatively high level of strength and durability which coupled with their resistance to heat and corrosion makes them an appealing choice for certain extreme conditions.
Meanwhile, Aluminum alloy is also being tested with an infusion of universally positioned ceramic material to strengthen the overall alloy, and improve it’s temperature threshold whilst retaining the low-density of aluminum. Known as a metal matrix composite (MMC,) this material is still in the development stage but may point to the direction which future poppets will be designed.