Product category:
Materials and components
News Release from: Victrex USA | Subject: Victrex Peek
Edited by the Engineeringtalk Editorial
Team on 19 June 2002
Polymer ring keeps compressors running
longer
Looking for ways to reduce compressor downtime in the petrochemical and natural gas industries, Cook Manley developed a novel compressor valve using Victrex Peek polymer for the seal ring component.
Looking for ways to reduce compressor downtime in the petrochemical and natural gas industries, Cook Manley of Stafford, TX, developed the patented field-repairable Moppet compressor valve which uses Victrex Peek polymer for the seal ring component "We've used Peek polymer for years on our radiused-disc valves with great success", says Charles Parks, plant manager at Cook Manley
"So, when we began developing the Moppet valve which is actually a series of individual radiused-disc valves encapsulated in modular cartridges we knew that Peek polymer would give us the reliability we needed for the seal ring.
"Because Moppet cartridges are interchangeable from valve to valve and from compressor to compressor", says Parks, "they can significantly reduce the end-user's inventory.
Damaged or worn cartridges can be replaced by pressing out the old cartridge and pressing in a new one.
This reduces compressor downtime and eliminates the need to outsource parts for repair or wait for replacements".
Because compressors in the petrochemical and natural gas industries operate in very harsh environments, it is essential that the valves maintain their dimensional stability.
"When compared to other materials such as nylon, Peek polymer is more dimensionally stable and will hold tolerances while in the end use customer's inventory", says Parks.
"Nylon will absorb moisture from the atmosphere or from within the compressor itself if it is subjected to any kind of moisture.
Peek polymer, being a semicrystalline material has extremely low moisture absorption and is thus very stable".
Peek polymer can also handle a much wider temperature range than nylon.
"For example", says Parks, "compressors can be used in a vacuum refrigeration type service or in a very high temperature, high pressure process service in a refinery.
Peek polymer can handle temperatures of 380-390F and under any pressure whereas nylon can only handle up to 280-290F depending upon the type of pressure being experienced".
Another reason why Cook Manley chose Peek polymer is its fatigue and flexural properties.
"When a compressor is running, the process can be very contaminated with dirt and liquids", says Parks.
"Unless the ring is flexible, it can snap under these conditions.
While there are many materials that are flexible in nature, very few have the fatigue strength of Peek polymer.
This is an essential property as a seal ring has to bend and flex millions of times.
For example, most of the large compressors run at about 300-330rev/min - which is relatively slow when compared to a car engine - but they must do it 24 hours a day, 7 days a week, 365 days a year.
That adds up to millions of cycles per year.
Other compressors can operate up to 2000rev/min".
The fact that worn parts can be replaced incrementally on-site and within a few minutes is a major factor in the success of the Moppet valve says Parks.
He reports that a major offshore oil and gas producer has been able to significantly reduce inventory by replacing 48 Clark plate compressor valves with the Moppet valves.
"With the Moppet valve, the people on the platform can do all the repair work themselves.
Previously, if an emergency arose, the company had to dispatch a helicopter to the platform, pick up the valves and bring them back to shore to be fixed.
The repaired valves then had to be helicoptered to the platform.
It was a very costly operation".
Parks also cites the example of the Hanover Company, a large compressor rental company, who substantially decreased valve repair costs by replacing OEM plate valves with Moppet valves.
According to Bill Peterson, area supervisor for Hanover, "At one station, we were replacing OEM plate valves every week.
We installed a set of Moppet valves over a year ago - and they are still going strong".
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