Details on Elastomer (seats and seals) - When should you use Teflon? Nylon? PEEK?
Elastomers are the seats and seals of the valve industry. Having the right elastomer can make the difference of a valve failing or lasting years in service. Elastomers typically have a lower melting/critical temperature than steel and knowing about them can go a long way to choosing the right valve. Keep in mind that like steel, elastomers come in a variety of grades and variations with different mechanical/chemical properties.
Typically Viton, Buna-N, and Teflon are used as seal material while Teflon, Nylon, and Devlon are used as standard seat material.
Click on one of the items below to jump to the description:
PTFE (polytetrafluoroethylene) - is a common synthetic seat material well known as the brand Teflon by DuPont. PTFE is used in many seal/seat material due to its low friction. high chemical resistance, and fire resistant properties. PTFE comes in a variety of grades typically being able to withstand temperatures of up to 260*C and down to - 240*C; however pressure in the line impacts temperature thresholds. Typically PTFE is used on 150#, and 300# ANSI valves; for larger pressure classes PTFE is not used due to its inability to decompress after being pressurized in line.
For more information on PTFE visit http://www2.dupont.com/Teflon_Industrial/en_US/tech_info/prodinfo_ptfe.html
RTFE (reinforced tetrafluoroethylene) - RTFE is a variation on PTFE (teflon) that typically has 15% glass filled fibre adding to the pressure that PTFE can normally withstand. RTFE should not be used in hydrofluroic acid and hot spring caustics (due to a reaction with the glass).
EPDM - ethylene-propylene diene monomer. EPDM has good abrasion and tear resistance with excellent chemical resistance to a variety of acids and alkalines. It is susceptible to attack by oil, strong acids and strong alkalines and should not be used in compressed air lines. It has good weather and ozone resistance working in temperature ranges of -20*F to 225*F. EPDM performs adequately in ketones and alcohols.
For more information on EPDM visit http://en.wikipedia.org/wiki/EPDM_rubber
Neoprene - this all purpose polymer has high resisliency, low compression, flame resistance and animal/vegetable oil resistance. It is primarily used for pulp and paper applications given that it is not recommended for oxidizing acids, chlorinated solvents, esters, ketones, aromatic hydrocarbons and hydraulic fluids. Neoprene is good for temperatures of -20*F to 225*F.
For more information on neoprene visit http://www.dupontelastomers.com/Products/Neoprene/neoprene.asp
Viton (Fluorocarbon) - This Dupont fluorocarbon elastomer is compatible with a broad range of chemicals. Due to its extensive chemical compatibility this material is a common seat/seal material in valves. It performs well in mineral acids, salt solutions, chlorinated hydrocarbons and petroleum oils. Viton works from -20*F to 400*F but is not suitable for steam, amine, or hot water service.
For more information on Viton visit dupont at http://www.dupontelastomers.com/products/viton/viton.asp?redirect=vitondotcom
Buna-N - Buna-N (Hycar or Nitrile) is an all purpose polymer with good resistance to water, solvents, oil and hydraulic fluids. It also displays good compressions, tensile strength and abrasion resistance. As Buna-N is unaffected by paraffin base materials, oils, alcohols, and glycerins it performs well in process areas. It works up to 225*F but should not be used in high polar solvents (acetons, ketones) chlorinated hydrocarbons, ozone and nitro hydrocarbon service.
For more information on Buna-N visit http://en.wikipedia.org/wiki/Nitrile_rubber
PEEK - Poly Ether Ether Ketone - is a high performance engineered thermoplastic. PEEK is considered a premium seat material with its excellent water/chemical resistance and due to the fact it is unaffected by continuous exposure to hot water/steam. PEEK is good for temperatures of -70*F to 600*F. PEEK is non-porous, high strength for high pressure applications and is suitable for high corrosion environments. PEEK typically adds to the torque requirement of the valve given the rigidity of the material.
For more information on PEEK visit http://en.wikipedia.org/wiki/PEEK
Nylon - Nylon seats are offered as a standard in many higher pressure and low temperature applications. Nylon seats are a common seat material for 600# valves though may appear in a variety of ANSI classes/pressure ratings. Nylon can be used in air, oil and other gas media but are not suited for strong oxidizing agents. Nylon comes in many variations and is typically good for temperatures ranging from -70*F to 200*F.
For more information on Nylon visit http://en.wikipedia.org/wiki/Nylon
Metal Seats - Metal (typically stellite) seats are used in severe conditions where flashing, hydraulic shock, abrasive media or trapped metal may exist in the line. Metal seats are typically hand-lapped to the ball in matching sets to ensure smooth operation and tight shut-off. Metal seats come in different classes of Shut Off including Class IV, V and VI.
Devlon - Devlon is a high molecular weight polyamide made by Devol specifically tailored for high temperature/pressure applications. Devlon comes in a variety of grades with Devlon V-API being the most common in the industry. Devlon is light weight yet performs well in impact and corrosive environments; Devlon works in temperatures of -40*c to 93*C
For more information on Devlon visit http://www.devol.com/engineering/default.asp?p=15
Delrin - Delrin is a type of polyoxymethylene (acetal, polyacetal and ployformaldehyde). It is a thermoplastic used in seat material due to its high stiffness, low friction and excellent strength. A product of DuPont, Delrin is susceptible to acids though it has high heat resistance and low water absorption. Delrin is good for temperatures of -40*C to 150*C. It can also be known as Hostaform, Celecon, Kepital, Duracon, Lupital and Ultraform.
For more information on Delrin visit http://www2.dupont.com/Plastics/en_US/Products/Delrin/Delrin.html
Contact - The Valve Pipeline
If a valve comes back from service, always cycle (open and close) the valve a few times outside before putting it back in stock or trying to do any repairs- it is possible for pressure to get stuck in the cavity of the valve.