Directional valves
Directional valves correctly specified and supplied
The technology behind directional valves explained
Directional valves route flow to one of several outlets rather than simply shutting it off, which makes them switching elements rather than isolation elements. There are assumptions circulating about directional valves that do not hold up under closer examination. It pays to understand the working principle behind directional valves first, because the limits follow from that principle. A ball valve closes with a bored ball turning through a quarter turn, which allows fast switching with a full bore. A balancing valve makes it possible to limit and measure flow in a branch, so that a system can be brought into balance. A throttling or control valve is intended to vary flow area rather than to shut off completely, and that difference drives the trim construction. On directional valves we always check the full operating envelope, including start up and shutdown. For directional valves this means that construction and operating conditions cannot be judged separately. In practice we find that most failures around directional valves come not from the material but from a wrong assumption during selection. A butterfly valve closes with a rotating disc in the line, giving the most compact and lightest solution at larger diameters. A gate valve closes with a plate moving across the flow, giving an almost unrestricted bore but requiring a long stroke and considerable height. Anyone looking into directional valves quickly runs into a choice that goes beyond picking a catalogue number.
What to watch technically on directional valves
Two way, three way and four way configurations each serve a different switching function in the circuit. How directional valves behaves under varying load says more about the quality of the selection than behaviour under steady load. With directional valves it pays to include phase changes in the medium, because those sharply increase the load on the seal. Switching time and repeatability matter more here than absolute tightness against the outside. Directional valves are not about shutting off but about routing flow to one of several outlets. Every valve type has its own working principle, and that principle determines where the type is strong and where it falls short. A check valve allows flow in one direction only and works without actuation, purely on the basis of the flow itself. Internal leakage between ports is the specification to watch, because it directly affects the function downstream. We regularly replace gate valves with metal seated butterfly valves, gaining on weight, space and operating torque. In our advice we also state what a type cannot do, because that prevents more problems than a list of advantages. What weighs heaviest on directional valves in practice is the combination of temperature and differential pressure, not either one alone. Operating conditions govern the service life of directional valves far more strongly than the nominal figures on a datasheet.
Directional valves in demanding installations
They are used in hydraulic circuits, pneumatic systems, machine control and in process lines with multiple routes. In utilities and water treatment butterfly and gate valves dominate through their price at large diameters. In chemicals the choice is driven mainly by medium compatibility and by the required tightness. Demand for directional valves reaches us mainly from projects where the standard range falls short. We see demand for directional valves rising in hydrogen and ammonia projects, where tightness requirements are high. On project supply we record per position which execution of directional valves was delivered, including materials and tests. For directional valves the sector determines which documentation and tests belong with the delivery. In process industry all types sit alongside each other in the same plant, each where that type is strongest. We work as a technical supplier rather than a catalogue reseller, which means we carry out the selection ourselves on the basis of medium, pressure, temperature and code requirements. 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. The application range of directional valves runs from simple utility duty to heavy process plant, with a corresponding difference in execution. During turnarounds directional valves is regularly on the critical path, and then predictability matters more than the lowest price.
What we look at when selecting directional valves
Standardising across several positions makes directional valves simpler in maintenance and in spare parts management. The required leakage class drives the choice between a soft and a metal seat more strongly than price does. We choose the type on the basis of the duty, because an isolation valve and a control valve are two different products. Face to face length and weight weigh heavily at larger diameters, and there a butterfly valve often beats a gate or ball valve. The cleaning and flushing procedure counts too on directional valves, because it can be more aggressive than the process itself. The required leakage class often drives the choice around directional valves more strongly than the budget does. On directional valves we check that the actuator is sized on torque at maximum differential pressure and not on an average value. Where there is doubt about directional valves we quote two executions side by side, with the trade offs stated explicitly. When standardising across a plant we advise deliberately limiting the number of different types. Dutch Valve Vision deliberately does not supply every type, but focuses on the specials where the standard market drops out. If you have an existing tag plate or serial number, send it along, because that lets us work directly from the original configuration. For directional valves we ask as standard for DN, pressure class, medium, temperature and required actuation. We never recommend a heavier execution of directional valves than needed, because over specification only raises price and lead time.
Directional valves supplied with technical advice
Even when the specification for directional valves is not yet finalised, you can bring the question to us. Our market is project driven and international, and we deliver worldwide to installers, EPC contractors and end users. For repeat orders of directional valves we record the configuration, so a follow up delivery is identical to the first. For directional valves you can come to Dutch Valve Vision for the selection, the delivery and the support afterwards. Documentation such as material certificates, test reports and declarations is supplied as standard, matched to what the project requires. On repeat orders we record the configuration, so a follow up delivery is identical to the first and installation holds no surprises. Material certificates and test reports are supplied with directional valves, matched to what the project requires. Tests around directional valves are carried out by us or on our instruction according to the requirements in the specification. A tag plate with project data belongs with directional valves as standard where the project requires it. Our specialists are happy to discuss directional valves on the basis of your P&ID, your datasheet or simply a photograph of the situation. We think along on the spare parts strategy for directional valves, so critical positions stay covered. Bring us your question at sales@dutchvalvevision.com or +31 (0)70-2210560, even when the specification is not finalised yet.
Frequently asked questions about directional valves
What exactly does directional valves mean?
Directional valves are not about shutting off but about routing flow to one of several outlets. A butterfly valve closes with a rotating disc in the line, giving the most compact and lightest solution at larger diameters. Directional valves route flow to one of several outlets rather than simply shutting it off, which makes them switching elements rather than isolation elements. A throttling or control valve is intended to vary flow area rather than to shut off completely, and that difference drives the trim construction. The answer to this question on directional valves changes as soon as the medium or the temperature changes. On directional valves we include start up and shutdown, because that is where the heaviest loading occurs. Once directional valves is correctly specified it disappears from the fault list, and that is exactly the intention. Dutch Valve Vision operates under a KIWA ISO 9001 certified quality system, which in the RFQ stage of chemical and offshore projects is usually a hard requirement.
Which executions of directional valves are available?
In our advice we also state what a type cannot do, because that prevents more problems than a list of advantages. A gate valve closes with a plate moving across the flow, giving an almost unrestricted bore but requiring a long stroke and considerable height. We regularly replace gate valves with metal seated butterfly valves, gaining on weight, space and operating torque. Internal leakage between ports is the specification to watch, because it directly affects the function downstream. We see this come back regularly in enquiries about directional valves, and the answer is rarely a single sentence. This is one of the points on directional valves where suppliers differ most clearly from one another. With directional valves the seat is the component that determines performance, and the body is rarely the limiting factor. 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 materials are used for directional valves?
A balancing valve makes it possible to limit and measure flow in a branch, so that a system can be brought into balance. Dutch Valve Vision deliberately does not supply every type, but focuses on the specials where the standard market drops out. When standardising across a plant we advise deliberately limiting the number of different types. Switching time and repeatability matter more here than absolute tightness against the outside. We always explain why we arrive at a particular recommendation on directional valves, so you can follow the reasoning yourself. In most projects directional valves turns out to be less standard than it first appears. That principle explains why directional valves behaves differently from a standard execution under heavier duty. Our customers work in chemicals, petrochemicals, pharmaceuticals, power generation, offshore and in hydrogen and ammonia projects.
What should I watch technically on directional valves?
What should I watch technically on directional valves?
Which applications call for directional valves?
In utilities and water treatment butterfly and gate valves dominate through their price at large diameters. They are used in hydraulic circuits, pneumatic systems, machine control and in process lines with multiple routes. In process industry all types sit alongside each other in the same plant, each where that type is strongest. In chemicals the choice is driven mainly by medium compatibility and by the required tightness. For directional valves a good specification up front is cheaper than a correction afterwards. Our experience with directional valves comes from projects in chemicals, power generation, technical gases and offshore. Our customers use directional valves in positions where a failure has immediate consequences for production. 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.
What determines the price and lead time of directional valves?
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. Documentation such as material certificates, test reports and declarations is supplied as standard, matched to what the project requires. For an accurate quotation we need the nominal diameter, the pressure class, the medium, the operating temperature and the required actuation. We keep spare parts and overhaul kits mapped per project, so that a breakdown does not start with a search from scratch. That makes directional valves a subject where discussion up front pays for itself in operation. If you are unsure about this on directional valves, we are glad to put the question alongside the actual process data. We handle an enquiry for directional valves on its technical merits rather than as a price request that only produces a number. We are based at Vlotlaan 641, 2681 TZ Monster in the Netherlands and can be reached on +31 (0)70-2210560 and at sales@dutchvalvevision.com.
What about maintenance and spare parts on directional valves?
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. On repeat orders we record the configuration, so a follow up delivery is identical to the first and installation holds no surprises. 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 shutdowns and turnarounds we look at accelerated routes, and in those cases we are honest up front about what is and is not achievable. On directional valves we include start up and shutdown, because that is where the heaviest loading occurs. The answer on directional valves depends strongly on operating conditions, which is why we always ask for those first. Documentation on directional valves has to be the kind a buyer or inspector accepts without discussion. We work as a technical supplier rather than a catalogue reseller, which means we carry out the selection ourselves on the basis of medium, pressure, temperature and code requirements.
How do I request a quotation for directional valves?
We come back with a proposal that explains why we recommend a particular execution, including the alternatives we considered. 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. A P&ID, a datasheet or even a photograph of the existing installation often helps us faster than a long description. We see this come back regularly in enquiries about directional valves, and the answer is rarely a single sentence. On directional valves we include start up and shutdown, because that is where the heaviest loading occurs. We supply directional valves as a loose product or as a fully assembled unit with actuator and accessories. Call +31 (0)70-2210560 or send your specification to sales@dutchvalvevision.com and we will pick it up.