In today’s guide, I will discuss all essentials of selecting the correct valve seat materials.
Ball valves are essential in allowing to cut or pass the flow and pressure of a piping system. Moreover, they are used in industries such as the petrochemical and pharmaceutical where leakage could represent a terrible consequence for the environment or the product itself. Therefore, the ball valve seat is critical in such situations since it is responsible for sealing the fluid inside and distributing the seating stress uniformly.
In the below picture, we have painted the valve seats in red color so you can identify where is the valve seat:
So, selecting the appropriate ball valve seat materials is vital to guarantee the performance of the valve and the safety of the product and the environment. The most common ball valve seat materials include PTFE, PEEK, and POM.
POM, called Acetal, POM-C, or Delrin, is trademarked by 3M. To select the most appropriate one, there are three main factors to consider:
Fluid compatibility refers to the material being capable of operating in contact with the fluid without having an adverse reaction.
PTFE, also known as Teflon, has very high chemical compatibility, which is why it is commonly used across different applications. Moreover, it is also produced in FDA grade, thus making it compatible with pharmaceutical, food, and drinks products. The only compatibility problem of the PTFE appears when exposed to fluorine or alkalies. We also do not recommend PTFE seats for pressures up to 350 bar.
PEEK is a material with very similar properties to those of the PTFE. Therefore, its fluid compatibility is also similar, including FDA grades. However, it may fail when exposed to sulfuric acid.
Finally, while POM fluid compatibility is extensive and includes radioactive applications, it is essential to highlight that it does not perform well with oxygen flow.
If you want to verify compatibility with the fluid of your application, you can use our compatibility tool here. Our tool allows you to select a material and will tell you how compatible it is with the specific seat.
Another critical aspect of selecting the appropriate ball valve seat materials is the range of temperatures where they can operate. Many materials react differently to temperature changes, and some lose their properties when the temperatures go above or below their normal operational ranges. If a ball valve seat loses its properties or experiences thermal deformation, the sealing power is lost, and the undesired leakage may occur.
We recommend selecting a high-temperature seat or a three-piece ball valve for Socket Weld valves. In that case, the temperature will increase and may melt the valve seats.
When it comes to PTFE, the operational temperature can be in the range of -45°C to 230°C. Now, if your application exceeds these limits, you will be better off using PEEK seats since this material can perform well within the range of -56°C to 315°C, including steam service up to 260°C. Those figures are theoretical since it needs to be added a safety factor.
POM is a more limited material when it comes to temperature. This material can only work at low temperatures within -56 °C to 100°C. However, POM would be an appropriate ball valve seat material for applications where pressure is more critical than temperature, which takes us to the next point.
Temperature ranges with safety factors:
POM PTFE PEEK -30ºC-40ºC-50ºC+100ºC+190ºC+250ºCSimilar to temperature range, pressure range refers to operating pressure values where the ball valve seat material will not suffer deformation or alter its properties. While some materials may be strong enough to withstand high pressures, others may fail at certain levels.
For example, PTFE ball valve seats will have no problems operating at pressures reaching the 350 bar.
You can refer to this table for maximum pressure ranges according to the valve diameter:
Valve Bore SizePOMPTFEPEEKDN6 DN10 DN13 DN20 DN25500 BAR OR MORE350 BAR500 BAR OR MOREDN 32 – DN40 – DN50450 BAR OR MORE175 OR 150 BAR APROX.450 BAR OR MOREAs you can see, there are many different aspects to consider. PEEK may be better for some applications because they need valves operating with hot water or steam. For others, the low friction coefficient of POM may be more relevant.
So far, we have only analyzed the maximum working pressure at ambient temperature. Depending on the temperature, the valve pressure is less. But when we arrive at very high or very low temperatures, the pressure that can withstand the valve is different. In the below graph, we see a comparison of the three seats for a 1/2″ valve (DN13) working pressure and temperature chart:
Also, there are variations of these materials, like the reinforced version of the PTFE called RPTFE that, with its 15%-25% glass fiber reinforcement, provides an improved lifecycle. Another example would be the TFM, a second-generation PTFE with better stress resistance and recovery and higher pressure capability, elasticity, and resilience. We have recently added TFM as an option for some specific valves.
An Oring or gasket is an elastic ring that prevents the fluid from leaking. This elastomeric material usually is FKM or Viton, NBR or Buna, FFKM or Kalrez, EPDM, etc. The temperature of the o-ring needs to be checked as well since it can melt if the working temperature of the valve is too high.
If you have any other questions, do not doubt contact us. And if you prefer, you can call us; we love to have a little chat with you.
A gasket sheet - often referred to as ‘gasket paper’, despite usually being made from silicone rubber, cork, nitrile or any other robust flexible material - is a large piece of sheeting intended to be used in making quick, cost-effective gaskets (seals), for joining surfaces or components together.
Gasket paper is sold in a wide variety of material types and thicknesses, with the best choice for any given application being entirely dependent on the nature of the task the gasket will be performing. In this guide, we’ll look at some of the different types and uses of gasket sheeting, and give a run-down of some of the various options on the market.
In its simplest form, a gasket is really just a small part cut out of some sheet material, very often in an ‘o-ring’ shape, that helps form a compressible leak-proof seal between two surfaces or components. Gaskets are usually made from a robust, flexible, and/or chemical/heat/acid-resistant substance.
They’re most commonly used in pipework and ducting systems, where they’re called flange gaskets. Here they help join two sections of pipe together seamlessly to form a continuous, non-leak channel through which liquids or gases can flow.
Some gaskets are defined by their intended application, such as vehicle gaskets in the engines of cars, planes, boats and more. Others are defined by their physical composition and materials, or by the specific nature of the role they’re made to perform (such as acid resistance or high-pressure functionality).
Buying gasket sheets is a cost-effective way to enable the production of new replacement or bespoke gaskets quickly and easily, as older ones eventually begin to stiffen, degrade or fail.
Important considerations to factor in when choosing gasket sheet materials include operating temperature, pressure, chemical compatibility and long-term cost-effectiveness of more robust products over cheaper but less reliable alternatives.
There are many different types of gasket paper on the market, all of which have their own strengths and advantages when used in specific scenarios. In this section, we’ll go over some of the most common and widely available types of gasket sheeting.
Rubber gasket sheet is often thought of as a sort of ‘entry level’ or general-purpose gasket material. It offers good protection against the passage of most gases, and can cope with mild acids/alkalis fairly well. However, the properties of natural rubber gasket sheet material (along with that of most other elastomers) make it a broadly unsuitable choice for oils, fuels, or very high pressure/temperature applications
Cork gasket sheet is another commonly found choice for gasket paper materials, and it offers several key benefits - it’s relatively economical, easy to compress, and doesn’t react aggressively in contact with very many substances (it’s generally suitable for oils, fuels and solvents). While it does have excellent vibration-damping properties, cork gaskets are seen as somewhat lacking in mechanical strength, particularly under significant flex or torsion.
Asbestos has various properties that traditionally made it a leading choice for industrial gasket applications. Asbestos gasket sheet is a tough and fibrous material that offers superb resistance to volatile chemicals and extremes of temperature - but it’s a particularly hazardous material to work in close proximity to.
For that reason, nearly all asbestos components today are being replaced with materials cut from non-asbestos gasket sheets of other compressed fibre material, combined with elastomers for added flexible strength. They’re good for use in a wide range of tough applications including oils, acids and steam.
Exhaust gasket sheet materials designed specifically for application in machinery, venting and extraction systems - particularly those used in turbo engine exhausts - need to be able to withstand very high temperatures over extended periods without failing.
Nitrile cork and multiple variants of non-asbestos fibre are common materials found all over the exhaust gasket sheet market - along with a range of older graphite laminate formulas, although these can be somewhat more prone to blowouts.
Other high-performance options include steel and copper reinforced gaskets. Whatever the material, it’s also important that exhaust gaskets offer good resistance to gas leaks, and are fairly easy to access and maintain.
One of the main challenges for high-temperature gasket paper material is that the better resistance to thermal extremes, the less flexible and compressible a material tends to be. Natural and silicone rubbers will struggle as the temperature rises beyond about 300 Celsius, whereas something like ceramic fibre can operate perfectly well at three times that - but the latter is very brittle compared to rubber seals, and therefore tricky to use in high vibration applications, or where leakage must be completely eliminated.
Graphite laminates and compressed foils are also good choices for some high-temperature gasket sheets, which often tend to demand resistance to high pressure, saturated steam or hot oils too. Unsuitable material choices for any of these elements can quickly lead to gasket failure when intense heat is added to the equation.
Nitrile rubber gasket material is a fairly broad-spectrum type, useful in a wide range of applications. It’s particularly effective at protecting against leaks of water, oils, hydrocarbons and silicone greases, and offers better performance under high temperatures than neoprene alternatives.
Nitrile rubber sheet suppliers also note that it’s relatively chemical resistant, but remains unsuitable for handling certain media such as strong oxidising agents, chlorines and ketones. Along with various other types of gasket paper, nitrile is available in sponge form too - these can be in open-cell varieties when compressibility is key, or closed-cell if leak prevention is the main aim.
Silicone sheet gasket material is fairly temperature-resistant and extremely flexible, with excellent waterproofing and electrical insulation properties. This makes it a sensible choice for gasket papers that need to be used in outdoor applications or around any powered machinery/components that may come into contact with moisture, although it’s not well suited to withstand oils or steams.
Like nitrile, silicone rubber gasket sheeting is also available in open-or-closed-cell sponge variants. Silicone gaskets are commonly found in food production environments when produced to the necessarily approved grade.
Graphite gasket sheet is something of a traditional material for gasket production, but still very widely used in a range of environments and applications. The higher the carbon content of the graphite gasket paper, the more flexible it will be, but also more brittle. For this reason, high-carbon graphite sheet gasket material is often sold reinforced with various metal cores or fillers.
Graphite gaskets are frequently found in high temperature or pressure environments, or where hazardous chemicals must be sealed away. Example industries include petrochemicals and refineries, steam services and vibration damping.
When looking for where to buy gasket papers and gasket sheeting materials, it’s important to speak to a supplier that knows exactly which types of material to recommend for which specific applications.
RS Components stock a wide selection of high-quality rubber, nitrile, silicone and graphite gasket sheets, as well as various other materials in a range of thicknesses and surface areas, from industry-leading brands and manufacturers.