Valve packing
Valve packing with technical advice from a specialist
The technology behind valve packing explained
Valve packing is the sealing system around the stem, and it is the single most important component in controlling fugitive emission from a valve. We approach valve packing from the question of what the plant has to do, not from the question of what happens to be in stock. In practice valve packing is rarely a standard question once medium and temperature move away from average. ISO 15848-1 distinguishes classes A, B and C, where class A is the strictest and in practice is only achieved with a bellows seal or a very high grade packing. API 609 is the construction standard for butterfly valves and separates category A for concentric designs from category B for offset and high performance designs. The packing set is the decisive component in emission control, because that is where stem movement takes place and where the leak path is created. With valve packing it pays to include phase changes in the medium, because those sharply increase the load on the seal. What weighs heaviest on valve packing in practice is the combination of temperature and differential pressure, not either one alone. How valve packing behaves under varying load says more about the quality of the selection than behaviour under steady load. API 641 is the American counterpart for emission testing of quarter turn valves and applies a limit of one hundred ppmv across the full test cycle. ISO 15848 defines how that leakage is measured, with part 1 as a type test on a prototype and part 2 as a production test on a delivered valve. With valve packing the difference between a good and a mediocre solution often sits in details that do not show on a drawing.
What to watch technically on valve packing
Because the stem moves, the packing has to seal against a moving surface, which is fundamentally harder than sealing a static joint. Operating conditions govern the service life of valve packing far more strongly than the nominal figures on a datasheet. We regularly see that a small change in the execution of valve packing makes a large difference to maintenance frequency. Graphite is the usual choice at high temperature, while PTFE and modified PTFE perform better at low temperature and against chemicals. Fugitive emission is the uncontrolled leak along the stem and the flanged joints, and in a process plant valves are by far the largest source. API 607 describes the fire test for quarter turn valves with a non metallic seat, where the valve must stay within a defined leakage limit after fire exposure. The German TA-Luft is not a standard but an administrative directive, and the 2021 revision explicitly refers to the measurement method from ISO 15848 for valves. A live loaded arrangement with disc springs keeps preload constant through thermal cycling and extends the interval between adjustments. Graphite is the usual choice at high temperature, while PTFE and modified PTFE perform better at low temperature and against chemical attack. Remember that flange gaskets and connections also count in an emission measurement, not only the stem. On valve packing we always check the full operating envelope, including start up and shutdown. A correct execution of valve packing accounts for real operating conditions and not only for design values.
Typical applications for valve packing
Packing selection is decisive on emission qualified valves, on steam service and on any duty with heavy thermal cycling. In VOC bearing processes the emission performance of the valves determines a directly measurable share of total plant emissions. In hydrogen and ammonia service emission weighs even heavier because of small molecule size and safety risk. During turnarounds valve packing is regularly on the critical path, and then predictability matters more than the lowest price. We see demand for valve packing rising in hydrogen and ammonia projects, where tightness requirements are high. Demand for valve packing reaches us mainly from projects where the standard range falls short. In an existing plant valve packing is often part of a wider question about availability and maintenance. In chemicals and petrochemicals emission control is not optional, because the permit imposes limits that are checked at every measurement round. What defines us is that we would rather spend an extra half hour on the specification than ship the wrong valve that comes back two months later. Our market is project driven and international, and we deliver worldwide to installers, EPC contractors and end users. In plants where valve packing is applied, the emphasis is on reliability rather than lowest purchase price. We supply valve packing both for new build and for replacement within existing installations.
Specifying valve packing correctly
Where there is doubt about valve packing we quote two executions side by side, with the trade offs stated explicitly. We advise writing the emission requirement into the basic specification rather than testing against it afterwards, because a later change is always more expensive. With an emission specification we first check which class and which test medium the project demands, because helium and methane carry different limits. When overhauling existing valves, upgrading the packing is often the cheapest route to meeting a tightened emission requirement. If a simpler type will do the job, we say so on valve packing, even when that means a smaller order. Standardising across several positions makes valve packing simpler in maintenance and in spare parts management. On valve packing we also state what an execution cannot do, because that prevents more problems than a list of advantages. We never recommend a heavier execution of valve packing than needed, because over specification only raises price and lead time. A low emission class often comes with higher operating torque, because the packing is preloaded more tightly. A live loaded packing system with disc springs maintains preload through temperature cycling and extends the interval between adjustments. A P&ID, a datasheet or even a photograph of the existing installation often helps us faster than a long description. Where valve packing forms part of a safety function we record the fail position and required stroking time explicitly. The right choice around valve packing starts with a full set of process data rather than with a request for a price.
Requesting valve packing from Dutch Valve Vision
Dutch Valve Vision stays available after delivery of valve packing for technical questions and for parts. Dutch Valve Vision supplies special valves for special applications from its base in Monster, the Netherlands, with QUADAX and PRUSS as the core brands in the programme. Even when the specification for valve packing is not yet finalised, you can bring the question to us. On valve packing we come back with a proposal that explains why we recommend a particular execution. For repeat orders of valve packing we record the configuration, so a follow up delivery is identical to the first. For shutdowns and turnarounds we look at accelerated routes, and in those cases we are honest up front about what is and is not achievable. We keep spare parts and overhaul kits mapped per project, so that a breakdown does not start with a search from scratch. We keep the configuration data for valve packing on file, which saves a great deal of searching if a fault occurs later. Documentation on valve packing has to be the kind a buyer or inspector accepts without discussion. We record which execution of valve packing was delivered, so a follow up delivery or spare part matches exactly later on. We supply valve packing as a loose product or as a fully assembled unit with actuator and accessories. You can reach us on +31 (0)70-2210560 and at sales@dutchvalvevision.com, and our office hours are Monday to Friday from 09:00 to 17:00.
Frequently asked questions about valve packing
What exactly does valve packing mean?
API 609 is the construction standard for butterfly valves and separates category A for concentric designs from category B for offset and high performance designs. Valve packing is the sealing system around the stem, and it is the single most important component in controlling fugitive emission from a valve. ISO 15848 defines how that leakage is measured, with part 1 as a type test on a prototype and part 2 as a production test on a delivered valve. The packing set is the decisive component in emission control, because that is where stem movement takes place and where the leak path is created. Our experience with valve packing comes from projects in chemicals, power generation, technical gases and offshore. This is one of the points on valve packing where suppliers differ most clearly from one another. The subject of valve packing touches both the construction of the valve and the way the plant is operated. Alongside QUADAX and PRUSS we represent Pibiviesse, Schroeder, Striko, Malbranque, Daume, FluoroSeal and Guichon, so we can select the right brand for each project.
Which executions of valve packing are available?
Fugitive emission is the uncontrolled leak along the stem and the flanged joints, and in a process plant valves are by far the largest source. Graphite is the usual choice at high temperature, while PTFE and modified PTFE perform better at low temperature and against chemical attack. The German TA-Luft is not a standard but an administrative directive, and the 2021 revision explicitly refers to the measurement method from ISO 15848 for valves. API 607 describes the fire test for quarter turn valves with a non metallic seat, where the valve must stay within a defined leakage limit after fire exposure. If you are unsure about this on valve packing, we are glad to put the question alongside the actual process data. We always explain why we arrive at a particular recommendation on valve packing, so you can follow the reasoning yourself. With valve packing the seat is the component that determines performance, and the body is rarely the limiting factor. Our customers work in chemicals, petrochemicals, pharmaceuticals, power generation, offshore and in hydrogen and ammonia projects.
Which materials are used for valve packing?
A live loaded arrangement with disc springs keeps preload constant through thermal cycling and extends the interval between adjustments. Remember that flange gaskets and connections also count in an emission measurement, not only the stem. Graphite is the usual choice at high temperature, while PTFE and modified PTFE perform better at low temperature and against chemicals. Because the stem moves, the packing has to seal against a moving surface, which is fundamentally harder than sealing a static joint. On valve packing we include start up and shutdown, because that is where the heaviest loading occurs. For valve packing a good specification up front is cheaper than a correction afterwards. The balance between required tightness and available operating force is a recurring tension on valve packing. We think along from the basic specification through to the tag plate, and supply documentation that a buyer or inspector accepts without discussion.
What should I watch technically on valve packing?
What should I watch technically on valve packing?
Which applications call for valve packing?
In chemicals and petrochemicals emission control is not optional, because the permit imposes limits that are checked at every measurement round. In VOC bearing processes the emission performance of the valves determines a directly measurable share of total plant emissions. Packing selection is decisive on emission qualified valves, on steam service and on any duty with heavy thermal cycling. In hydrogen and ammonia service emission weighs even heavier because of small molecule size and safety risk. In most projects valve packing turns out to be less standard than it first appears. The answer on valve packing depends strongly on operating conditions, which is why we always ask for those first. The application range of valve packing runs from simple utility duty to heavy process plant, with a corresponding difference in execution. Dutch Valve Vision supplies special valves for special applications from its base in Monster, the Netherlands, with QUADAX and PRUSS as the core brands in the programme.
What determines the price and lead time of valve packing?
We quote a realistic lead time rather than an optimistic one, because a missed delivery date costs more than an extra week in the planning. For an accurate quotation we need the nominal diameter, the pressure class, the medium, the operating temperature and the required actuation. A P&ID, a datasheet or even a photograph of the existing installation often helps us faster than a long description. On repeat orders we record the configuration, so a follow up delivery is identical to the first and installation holds no surprises. We see this come back regularly in enquiries about valve packing, and the answer is rarely a single sentence. On valve packing we prefer a well founded answer to a fast one that turns out to be wrong later. For valve packing you can come to Dutch Valve Vision for the selection, the delivery and the support afterwards. Bring us your question at sales@dutchvalvevision.com or +31 (0)70-2210560, even when the specification is not finalised yet.
What about maintenance and spare parts on valve packing?
For shutdowns and turnarounds we look at accelerated routes, and in those cases we are honest up front about what is and is not achievable. We keep spare parts and overhaul kits mapped per project, so that a breakdown does not start with a search from scratch. Lead times depend on the execution, because a standard size from a running series behaves very differently from a valve in an exotic alloy with NACE certification. A live loaded packing system with disc springs maintains preload through temperature cycling and extends the interval between adjustments. On valve packing we include start up and shutdown, because that is where the heaviest loading occurs. We see this come back regularly in enquiries about valve packing, and the answer is rarely a single sentence. We work on valve packing under a KIWA ISO 9001 certified quality system, which safeguards traceability. Our market is project driven and international, and we deliver worldwide to installers, EPC contractors and end users.
How do I request a quotation for valve packing?
Please also state the connection standard, the required leakage class and any project requirements such as NACE, PED or ATEX. If you have an existing tag plate or serial number, send it along, because that lets us work directly from the original configuration. Documentation such as material certificates, test reports and declarations is supplied as standard, matched to what the project requires. We come back with a proposal that explains why we recommend a particular execution, including the alternatives we considered. On valve packing we prefer a well founded answer to a fast one that turns out to be wrong later. In most projects valve packing turns out to be less standard than it first appears. We handle an enquiry for valve packing on its technical merits rather than as a price request that only produces a number. Send us your DN, pressure class, medium and temperature at sales@dutchvalvevision.com, or call +31 (0)70-2210560 to speak to a specialist.