What is the Best Thermoplastic Valve Plate Material?
As with any choice in engineering, there is often more than one correct solution. When choosing the best material for any given task, part of the answer lies within logic, while part of the choice is also a subjective decision.
The choice of valve plate material used to produce a thermoplastic plate is one such example of how different materials are best depending upon the circumstance of their purpose. To determine what the best valve plate material is for your own specific needs, you should carefully consider certain criteria.
The role of the thermoplastic plate
The valve plate is an integral mechanism in the functionality of a control valve. Providing an adjustable barrier, the plate is ultimately responsible for allowing, stopping and throttling the flow of gas that runs through the valve.
As such, the plate needs to be capable of resisting the force upon it by the transportation of natural gas, both in terms of physical strength against the pressure of the flow and durability in withstanding abrasive forces. The valve plate also critically needs to form a hermetic seal in the line when the valve is closed. This means that it needs to be impervious to distortion of its physical shape.
When operating to a high degree of accuracy, the effect that the plate has upon the flow of natural gas should also be taken into account, however, this is largely a mere passing consideration for many industrial applications.
Valve plate material comparison: Thermoplastic vs. Metal
The fundamental choice in valve plate material can be simplified as being between a metallic or a non-metallic valve plate component. While metallic plates have traditionally been used because of the strength and hard-wearing properties metal alloys provide, thermoplastic materials have recently been able to match and even surpass those set standards.
Thermoplastic valve plate material also has the benefit of being self-lubricating, unlike metallic plates, which have this extra complication involved in their operation. The use of a lubricant produces extra maintenance needs and another factor to monitor. It also poses a potential problem of contaminating the natural gas passing through the valve if anything catastrophic affects the valves integrity. Another advantage of thermoplastic compressor parts can be found in their lack of magnetic properties. This is often important with the handling of certain fluids. It is especially common in the field of medicine and pharmacology.
Other than the increased durability, arguably the main benefit of using thermoplastics above metal alloys is their susceptibility to corrosion. From sour gas to simple moisture, metals are more reactive to chemicals than the inert plastics. Hydrogen embrittlement is also a major concern in the use of metal alloys, where-as this risk is completely negated when using the newer compounds.
While the strength and dimensional stability of these compounds are deceptive, the main role of a valve plate is to act as a seal between disparate pressure zones across a control valve. The added flexibility offered by these materials allows the plate to form a much tighter seal with the seat.
The immediate difference between the newer thermoplastic compounds in comparison to metallic plates can be clearly noted in their lightweight construction. This reduction in weight equates to less momentum in the movement of internals. This, in turn, results in less damage caused when impacts inevitably occur within the trim. If any piece of the plate was to break-off during regular operating conditions, this too would cause less of a problem than an equivalent loose part from a metallic plate.
PEEKing into the future
There is a wide range of different thermoplastic materials readily available for all types of engineering needs. Within this spectrum, PEEK (polyether ether ketone) has become a popular choice in modern valve plate material, due to its favorable properties in comparison to the alternatives.
PEEK offers added strength and endurance. It’s also highly resistant to stress fractures and corrosive chemicals whilst exhibiting a high heat threshold. PEEK is also available in different blends to modify its characteristics and performance levels.
A common variant is Carbon PEEK. As the name suggests, contains varying amounts of Carbon in the composition to provide extra strength. While this also makes the valve plate material more rigid, Carbon PEEK suffers less deterioration. It faces less warping and loss of structural integrity than regular PEEK. This provides a more durable option for hard-wearing applications. The hardest wearing version of this is referred to as Bearing grade Carbon PEEK which is additionally reinforced with graphite and PTFE (Polytetrafluorethylene) to produce a tougher but more expensive product.
Within the different blends of PEEK that are available, they can all be formed accurately through a process of injection molding. However, it’s vital to ensure that you rigorously test the formula to precisely identify the properties of the finished product.
Grading of thermoplastic
In addition to PEEK, there are various other thermoplastic materials ideal for the production of valve plates, including:
- PVC (Polyvinyl Chloride)
- CPVC (Chlorinated Polyvinyl Chloride)
- PP (Polypropylene)
- PVDF (Polyvinylidene Fluoride)
- ABS (Acrylonitrile-Butadiene-Styrene)
- EPDM (Ethylene propylene diene monomer)
- FPM (Vinylidene fluorine rubber)
- PTFE (Polytetrafluorethylene)
When deciding upon the best valve plate material for your needs, the cost of the part must also play an influential role in the decision. While practical aspects such as temperature considerations within the operating environment need to be accounted for, there can often be several realistic choices available to fit your needs.
To ensure that you make a choice suitable for your requirements, it’s advisable to carefully list all of the extremities in conditions that your component could potentially face within the system. This will then provide a safety buffer covering the theoretical possibilities of operation with your component. It will also provide a workable parameter to prevent choosing a material that is excessive for the demands it will face.
With the testing of new blends and compounds becoming readily available, give this list of parameters to a specialist engineer or trusted supplier to advise which valve plate material is best for your purpose. If you’re ever in doubt of their opinion, it’s always worthwhile receiving three independent quotes. Compare them against each other to validate the information you receive.
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