Control valve: the working principle in practice
A control valve modulates the flow area in a line so that a process variable such as pressure, flow, level or temperature stays at its setpoint. The term control valve is used broadly in the market, which is why it helps to define precisely what it means in your case. There are assumptions circulating about control valve that do not hold up under closer examination. Cavitation occurs when local pressure drops below vapour pressure and the vapour bubbles then implode, which eats through trim in a short time. The difference with an isolation valve is that a control valve has to work accurately and stably in every intermediate position, while an isolation valve only has to be open or closed. Rangeability states between which extremes the valve still controls reliably, and outside that band control becomes unstable. In practice we find that most failures around control valve come not from the material but from a wrong assumption during selection. On control valve we always check the full operating envelope, including start up and shutdown. With control valve it pays to include phase changes in the medium, because those sharply increase the load on the seal. The Kv value states how many cubic metres of water per hour pass through the valve at one bar differential pressure, and that figure is the basis of every calculation. A control valve modulates the opening in the line so that a process variable such as pressure, flow, level or temperature stays at its setpoint. The subject of control valve touches both the construction of the valve and the way the plant is operated.
Material, seat and construction on control valve
The Kv or Cv value states the capacity of the valve and forms the basis of every sizing calculation. We regularly see that a small change in the execution of control valve makes a large difference to maintenance frequency. Operating conditions govern the service life of control valve far more strongly than the nominal figures on a datasheet. The installed characteristic differs from the inherent characteristic, because the rest of the system contributes its own resistance. The valve characteristic, whether linear, equal percentage or quick opening, defines how flow area relates to travel and therefore how the loop behaves. On gas and vapour service high pressure ratios produce noise and vibration, and a multistage trim is then used to divide the pressure drop. An equal percentage characteristic is used most often, because it largely compensates for the non linearity of the rest of the system. Most control problems in practice trace back to sizing rather than to the valve hardware itself. On commissioning we record the settings and calibration, so a later fault can be traced. PRUSS builds control valves for the heavier end of this spectrum, with steam, high temperature and safety functions as its core territory. A correct execution of control valve accounts for real operating conditions and not only for design values. For control valve this means that construction and operating conditions cannot be judged separately.
Control valve in demanding installations
Control valves are used throughout process industry, in power generation, in boiler houses and in utility systems. In chemicals and petrochemicals they control flows and levels in processes where medium properties weigh heavily. In power generation they sit around turbines, boilers and bypass circuits, where speed and reliability are decisive. Our customers use control valve in positions where a failure has immediate consequences for production. For control valve the sector determines which documentation and tests belong with the delivery. The application range of control valve runs from simple utility duty to heavy process plant, with a corresponding difference in execution. On project supply we record per position which execution of control valve was delivered, including materials and tests. In steam plant and boiler houses control valves handle the pressure and temperature control that keeps the installation within its design limits. 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. Our customers work in chemicals, petrochemicals, pharmaceuticals, power generation, offshore and in hydrogen and ammonia projects. In plants where control valve is applied, the emphasis is on reliability rather than lowest purchase price. Demand for control valve reaches us mainly from projects where the standard range falls short.
How to select control valve without mistakes
The cleaning and flushing procedure counts too on control valve, because it can be more aggressive than the process itself. Oversizing is the most common mistake, because an oversized valve only controls in the first few degrees of travel and wears there rapidly. On every selection we check for cavitation, flashing and sound level, because those three determine trim life. Correct sizing starts from the full operating envelope, so minimum, normal and maximum flow with their corresponding pressures. For control valve we ask as standard for DN, pressure class, medium, temperature and required actuation. Standardising across several positions makes control valve simpler in maintenance and in spare parts management. On control valve we check that the actuator is sized on torque at maximum differential pressure and not on an average value. Where control valve forms part of a safety function we record the fail position and required stroking time explicitly. During overhaul we measure trim and seat and advise whether reworking is sufficient or replacement works out cheaper. A control valve that audibly whistles or vibrates is telling you something about the selection, and that signal should be solved rather than insulated away. For an accurate quotation we need the nominal diameter, the pressure class, the medium, the operating temperature and the required actuation. Where there is doubt about control valve we quote two executions side by side, with the trade offs stated explicitly. The right choice around control valve starts with a full set of process data rather than with a request for a price.
Your enquiry for control valve at Dutch Valve Vision
Dutch Valve Vision stays available after delivery of control valve for technical questions and for parts. We think along from the basic specification through to the tag plate, and supply documentation that a buyer or inspector accepts without discussion. Our specialists are happy to discuss control valve on the basis of your P&ID, your datasheet or simply a photograph of the situation. We supply control valve as a loose product or as a fully assembled unit with actuator and accessories. For control valve you can come to Dutch Valve Vision for the selection, the delivery and the support afterwards. 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. Documentation such as material certificates, test reports and declarations is supplied as standard, matched to what the project requires. We keep the configuration data for control valve on file, which saves a great deal of searching if a fault occurs later. Material certificates and test reports are supplied with control valve, matched to what the project requires. On control valve we make sure the chosen execution demonstrably meets the stated standards rather than merely looking plausible on paper. We think along on the spare parts strategy for control valve, so critical positions stay covered. Requests can be submitted by phone on +31 (0)70-2210560, by e-mail at sales@dutchvalvevision.com or through the contact form on our website.
Frequently asked questions about control valve
What exactly does control valve mean?
Cavitation occurs when local pressure drops below vapour pressure and the vapour bubbles then implode, which eats through trim in a short time. On gas and vapour service high pressure ratios produce noise and vibration, and a multistage trim is then used to divide the pressure drop. The valve characteristic, whether linear, equal percentage or quick opening, defines how flow area relates to travel and therefore how the loop behaves. Rangeability states between which extremes the valve still controls reliably, and outside that band control becomes unstable. For control valve a good specification up front is cheaper than a correction afterwards. On control valve we prefer a well founded answer to a fast one that turns out to be wrong later. It pays to understand the working principle behind control valve first, because the limits follow from that principle. Our market is project driven and international, and we deliver worldwide to installers, EPC contractors and end users.
Which executions of control valve are available?
On commissioning we record the settings and calibration, so a later fault can be traced. The installed characteristic differs from the inherent characteristic, because the rest of the system contributes its own resistance. Most control problems in practice trace back to sizing rather than to the valve hardware itself. During overhaul we measure trim and seat and advise whether reworking is sufficient or replacement works out cheaper. If you are unsure about this on control valve, we are glad to put the question alongside the actual process data. We always explain why we arrive at a particular recommendation on control valve, so you can follow the reasoning yourself. What weighs heaviest on control valve in practice is the combination of temperature and differential pressure, not either one alone. 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 materials are used for control valve?
The Kv value states how many cubic metres of water per hour pass through the valve at one bar differential pressure, and that figure is the basis of every calculation. The Kv or Cv value states the capacity of the valve and forms the basis of every sizing calculation. The difference with an isolation valve is that a control valve has to work accurately and stably in every intermediate position, while an isolation valve only has to be open or closed. An equal percentage characteristic is used most often, because it largely compensates for the non linearity of the rest of the system. We see this come back regularly in enquiries about control valve, and the answer is rarely a single sentence. The answer on control valve depends strongly on operating conditions, which is why we always ask for those first. With control valve 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.
What should I watch technically on control valve?
What should I watch technically on control valve?
Which applications call for control valve?
In power generation they sit around turbines, boilers and bypass circuits, where speed and reliability are decisive. Control valves are used throughout process industry, in power generation, in boiler houses and in utility systems. In steam plant and boiler houses control valves handle the pressure and temperature control that keeps the installation within its design limits. In chemicals and petrochemicals they control flows and levels in processes where medium properties weigh heavily. On control valve we include start up and shutdown, because that is where the heaviest loading occurs. That makes control valve a subject where discussion up front pays for itself in operation. In an existing plant control valve is often part of a wider question about availability and maintenance. We think along from the basic specification through to the tag plate, and supply documentation that a buyer or inspector accepts without discussion.
What determines the price and lead time of control valve?
For an accurate quotation we need the nominal diameter, the pressure class, the medium, the operating temperature and the required actuation. 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. 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. We come back with a proposal that explains why we recommend a particular execution, including the alternatives we considered. The answer to this question on control valve changes as soon as the medium or the temperature changes. In most projects control valve turns out to be less standard than it first appears. Even when the specification for control valve is not yet finalised, you can bring the question to us. Send us your DN, pressure class, medium and temperature at sales@dutchvalvevision.com, or call +31 (0)70-2210560 to speak to a specialist.
What about maintenance and spare parts on control valve?
We keep spare parts and overhaul kits mapped per project, so that a breakdown does not start with a search from scratch. Documentation such as material certificates, test reports and declarations is supplied as standard, matched to what the project requires. 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 repeat orders we record the configuration, so a follow up delivery is identical to the first and installation holds no surprises. On control valve we prefer a well founded answer to a fast one that turns out to be wrong later. We always explain why we arrive at a particular recommendation on control valve, so you can follow the reasoning yourself. A tag plate with project data belongs with control valve as standard where the project requires it. 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.
How do I request a quotation for control valve?
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 quote a realistic lead time rather than an optimistic one, because a missed delivery date costs more than an extra week in the planning. In most projects control valve turns out to be less standard than it first appears. We see this come back regularly in enquiries about control valve, and the answer is rarely a single sentence. On control valve we come back with a proposal that explains why we recommend a particular execution. Requests can be submitted by phone on +31 (0)70-2210560, by e-mail at sales@dutchvalvevision.com or through the contact form on our website.