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Tag Archive: control valves

1. How to Select the Right Control Valve

   March 4, 2021 3:58 pm 2 Comments

   Control valves play a vital role in ensuring the efficiency of a fluid system. It is important to choose the one you use carefully. Otherwise, it may not operate or perform as expected, resulting in decreased process efficiency and/or system damage.

   There are many factors to consider when selecting a control valve for a fluid system, such as versatility, flow control stability, connectivity, and maintenance requirements. Below, we highlight how these control elements work and what selection considerations to keep in mind.

   How Does a Control Valve Work?

   Control valves regulate the flow of fluid through a system by restricting or expanding the fluid passageway. This function alters the volume of fluid that passes through the system within a given time frame (i.e., the flow rate) and the pressure of the fluid.

   A rising stem valve is one type of control valve. In this valve design, the valve stem raises and lowers the valve trim package to increase or decrease the size of the passageway, resulting in steady flow, increased flow, or decreased flow. This adjustment is made whenever the targeted process parameter is not at the right value.

   Key Control Valve Selection Considerations

   There are many types of control valves available, each of which can come in numerous designs, configurations, and sizes. This broad selection can make it difficult to choose which one is right for a given fluid system, but knowing what parameters are important can help facilitate the selection process. Some of the key control valve selection considerations include:

   • Is the fluid a liquid, gas, or steam? Is it inert or reactive?
   • Pressure rating. What are the standard and maximum pressure levels to which the valve will be exposed?
   • Temperature rating. What are the standard and maximum temperature levels to which the valve will be exposed?
   • Flow rate. What flow rate range should the valve be able to handle?
   • What is the flow coefficient (Cv)—the flow rate (GPM) for a pressure drop of 1 PSI across the flow passage—for the system? This value affects the size of the control valve needed.
   • Installation requirements. How should the system be configured? What are the piping size, upstream vs. downstream, and valve mounting requirements and restrictions?
   • Design. What type of valve is required? A straight through venturi, or globe valve? A standard service, medium service, or a severe service valve?
   • Industry/country standards. What industry and country standards are applicable? Key standards include American Petroleum Institute (API), American Society of Mechanical Engineers (ASME), Canadian Registration Number (CRN), and Pressure Equipment Directive (PED).

   Quality Control Valves From DFT®

   For control valves you can trust in your most critical fluid system applications, turn to the experts at DFT®! We are a premier manufacturer of check and control valves. Our control valve selection includes:

   

   • HI-100®. HI-100® valves are severe service control valves with an in-line straight-thru venturi design. They are designed for use in harsh operating conditions, demonstrating smooth operation in high or low temperatures and/or with process fluids carrying suspended particles (e.g., slurries). They also have quick-change trim that allows for in-line replacement, interchangeable upstream and downstream seats, and wear bushings to extend service life and reduce operating costs.
   • Ultra-Trol®. Ultra-Trol® valves are abrasive service control valves that are designed for use in erosive flow systems requiring flanged end connections. Similar to the HI-100® line, they have an in-line through ported venturi flow shape and a contained spherical ball, which help ensure smooth and efficient operation in high or low temperatures and with slurries.
   • MSV-100®. MSV-100® valves are medium service control valves that are designed for use in flanged applications where bench repairs are common. They have a similar seat and internal design to HI-100® valves. They are suitable for on/off service or modulating control applications involving gas, liquid, or steam systems.
   • LSV-100®. LSV-100® valves are economical Globe Style control valves designed for flanged applications. They have trims that can be replaced in the field through the bonnet. Suitable applications include on/off service and modulating control of gas, liquid, or steam systems.

   For information about how to select the right control valve, contact us today. To learn more about our valve products, check out our catalog or request a quote.

2. The Benefits of the MSV-100® Control Valve

   January 29, 2021 5:30 pm Comments Off on The Benefits of the MSV-100® Control Valve

   What is the MSV-100® Control Valve?

   The DFT® model MSV-100® control valve is a flanged medium service control valve available in the 600, 900, and 1500 class range that can handle a wide variety of fluids, including gases, liquids and steam. In addition, this valve can withstand high pressures up to 3700 psig and temperatures up to 1,000°F

   DFT® has manufactured world-class valves for over 75 years. The following blog and video provides an overview of the MSV-100® control valve along with its features, benefits, and common applications.

   The MSV-100® features an inline straight-thru venturi flow design which is cavitation resistant. Here you see pressurized upstream fluid filling the pipe, seating the ball, and achieving FCI 70 Class V type shutoff:

   

   As the MSV-100® valve opens, the fluid jet impinges upon the downstream replaceable liner which is hardened to prevent excessive wear. As a result, thru-body wear does not occur.

   

   The DFT® MSV-100® is a position seated design and the control element is a ball that is guided by the cage that positions it relative to the downstream seat by means of linear stem travel. The flow characteristic of the DFT® control valve is essentially linear over the complete stroke as shown here:

   

   At the intermediate position where the valve is designed to throttle, the MSV-100® provides fine modulating control.

   

   As the valve fully opens, it operates as a true venturi that can handle high-pressure drops. In the fully open position, if the fluid cavitates, this will occur in the mid-fluid stream, away from the valve body and pipe walls. The MSV-100® features trim that is easily replaceable on the bench and requires no special tools. This minimizes maintenance, downtime, and lowers the overall cost of ownership. Various trim sizes are available depending on the required flow capacity.

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   You May Also Like: MSV-100® Control Valve Cut Sheet

   

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   What Industries Use the MSV-100® Control Valve?

   The MSV-100® can be used for fluid, gasses, liquids, and steam. It has many applications across a variety of industries. Below is a partial list of applications this valve can be commonly used for:

   

   • Attemperator
   • Boiler Feed & Discharge
   • Chemical Lines
   • Condensate Lines
   • Crude & Refined Product Lines
   • Feedwater
   • Hydraulic Lines
   • Level Control
   • Pressure Control
   • Process Lines
   • Spray
   • Steam Lines
   • Turbine Bypass
   • Turbine Inlet Control
   • Turbine Drains
   • Water Lines

   The MSV-100® Control Valve From DFT®

   For customers that need control valves, DFT® is here to assist you. At DFT®, we offer a broad selection of check and control valves. Whether a customer requires a valve for a critical or non-critical application, we can meet their requirements. For more information about our product offerings, check out our catalog or contact us today. To receive pricing details, request a quote.

3. My Control Valve is Causing Problems, What Do I Do?

   January 31, 2015 4:36 pm Comments Off on My Control Valve is Causing Problems, What Do I Do?

   It’s my weekend off and I get a call from the plant. The level alarm has gone off and our process had to be shut down. It turns out that the level control valve has once again failed in its task. We do our typical “work around” to start up the system and operate the level control in manual until it’s fixed.

   It’s the Google age, so I spend Saturday night looking for help on the Internet. Unfortunately, by Sunday morning I am more confused than when I started. I need information that actually helps instead of making things worse—where can I find a solution in order to reclaim my weekends?

   Let’s start with the basics – What choices do I have?

   

   Often, the replacement choice is made simply on the basis of the pipe size in the line that is made by removing the old valve. Control valves come in many different configurations, but which one do I need?

   • Rotary Types:
     • Butterfly Valves use a flat disk that is rotated in the flow of fluid. They are well suited in larger line sizes where a minimal pressure drop (less than 50psi) is desired.
     • Ball Valves use a sphere with a hole through the center. The ball is rotated in the flow to adjust the flow of the fluid. They are generally best used in on/off situations.
     • Plug Valves use a cylinder to obstruct the fluid flow, and similar to ball valves, they feature one or more holes through the cylinder. Flow is regulated by rotating the cylinder within the valve chamber. Like ball valves, they are good choices for rapid shut off, but they can introduce turbulence into a process system in some conditions.

   • Rising Stem Types:
     • Globe Valves are named for their generally round bodies, and they use a linear rising stem motion. This design is easy to maintain in harsh environments.
     • Venturi-ball Valves employ the same linear rising stem motion. Designed for high pressure drops and easy maintenance.

   Since the pressure drop through the control valve for this level control application is over 100 psi, I know that I need a rising stem valve.

   What Trim Characteristic Should I Use?

   • Linear Trim – Changes in position are directly proportionate to changes in flow (a 10% change in valve lift produces a 10% change in flow). Linear trim is used in systems where the pressure drop through the control valve is the major pressure drop in the system
   • Equal % Trim – Equal changes in position cause an equal percentage change in the previous flow (a 10% change in valve lift produces a 48% change in flow for each position). Equal % trim is used in systems where the pressure drop through the control valve is generally less than the other pressure drops in the system.

   In order to choose the proper trim characteristic, I need to know what I am trying to control.

   • Liquid Level

     • Use Linear trim unless the criteria for Equal % trim is met
     • Use Equal % if the pressure drop at max flow is 1/5 that of the drop at min flow

   • Pressure

     • Use Linear trim for slow process changes
     • Use Equal % trim for fast process changes

   • Flow

     • Use Linear trim for varying set point
     • Use Equal % trim for varying load

   • Temperature

     • Use Equal % trim

   Since I am controlling the liquid level in this example with relatively constant pressure drops, I choose Linear trim.

   The DFT HI-100™ control valve is a good choice for this application. It is a rising stem control valve with a Linear characteristic. The valve has the Quick Change Trim feature that permits the in-line replacement of the internal trim.

4. Once Upon a Time This Valve Worked Well

   January 20, 2015 4:34 pm Comments Off on Once Upon a Time This Valve Worked Well

   Our process had to be shut down again.  It seems that the original valve is no longer up to the task.  Should I continue to simply repair the valve or should I look for another solution?  Up until now, it was far easier to repair the valve and/or replace it in kind … but my process efficiencies are going down and I need to find a solution.  Where do I start?

   Changing Conditions

   I pull out the valve data sheet and take a look at the original conditions.  Wow! I can see immediately that things have changed –

   • The plant has aged nearly 20 years;
   • We replaced the pump on that line 5 years ago;
   • We have modified the piping in the area of the valve;
   • We changed the fluid chemistry;
   • Instead of operating continuously, the plant is now cycling

   Every time conditions change, we need to review the impact upon the control system.

   Aging Systems

   As a system ages, it does not get any cleaner.  Whether it is due to pipe scale or there is other sediment in the system, a valve that worked in a clean system may not work as well in the older system.  We have periodically been pulling the valve with cage style trim in order to drill open the passages.  We have also noticed that the valve trim is wearing out more quickly.  The valve simply requires more maintenance.

   New Pump

   Installing a new pump can change how the system operates.  A new pump generally means that we have a new pump curve to work with.  The new pump curve means that the flows and pressures have changed from the original specification.

   Modified Piping

   We added a new branch line.  A closer look reveals (I use my 20D² rule of thumb) that the new line may have lowered the flow rate through the control valve.  Is it possible that the control valve is no longer properly sized?  The trim in an oversized control valve erodes more quickly than the trim in a properly sized valve.  Alternately, if the valve is undersized, I may be seeing high velocity erosion which also negatively affects trim life.

   Changing Chemistry

   Although we have always maintained our chemistry within recommended boundaries, we can see that our targets have changed over the years.  Newer technology allows us to more closely hit the mark.  Is it possible that this has tipped the balance and we are now seeing erosion-corrosion in the valve since the originally specified materials are no longer noble enough?

   Cycling vs. Base Loading

   When we changed from a base loading operation to a cycling operation, we started to strain our control valves.  Now they operate more frequently and often work in the low end of the range.  By changing the operation, I now need to have a valve that is suitable for severe service when previously I could use a standard valve.

   The DFT HI-100™ control valve can be a good choice when conditions change.  It deals well with dirty fluid, can be sized properly for the new conditions, is not subject to erosion corrosion and is designed to perform well in the most severe services.

5. The Importance of Good Information About Valves

   January 6, 2015 4:34 pm 3 Comments

   Proper valve selection is critical for ideal operation of any system. Improper valve selection can cause system underperformance or failure. The greatest problem when selecting valves is incorrect information.

   Often, we may only have access to incomplete or dated information regarding valve applications. Do we know enough about the system the valve will be used in or the main purpose of its use? This “bad information” can create a situation where the theoretical situation does not match reality.

   Good Information is Key

   “Bad information” comes in many forms. Original design specs might be difficult to obtain, and having those specs does not guarantee success. Occasionally, specs aren’t properly updated. Information that was good at first can fail to incorporate changes in process conditions. If the actual pressure, temperature, flow-rates or the media is different than that which was used to select the valve, it may fail or fail to work properly.

   When choosing a gate, globe, ball or check valve, we always want the valve to be operating in the full open or closed position. Control valve selection, however, targets 40% to 60% open for normal flows. When most control valves operate below 20% open or over 80% open, they can lose their ability to control properly.

   What information is required to properly size a valve? Fluid type, operating pressures and temperatures upstream and downstream of the valve, and the flow rates associated with these conditions are required information to have.

   Knowing What is the Right Valve for the Application

   There are many different types of valves available. They do not all work the same way or for the same purposes. Each valve type has its advantages and disadvantages.

   For proper control valve selection, it is important to understand how the valve is used to control system flow. For example: is the system tuned for a constant set point, or is it set to modulate a variable flow over time? The layout of the piping system and locations of reducers and elbows also impact valve performance.

   Often, choosing what seems to be the most efficient valve might not be the best valve for application. Replacing a valve “in kind” with an upgraded version of an older valve might actually do more harm than good.

   Poor Performance – Get Good Information

   Unfortunately, the blame for poor performance often lands on the installed valve when it is actually bad information that caused its failure. Simply repeating the bad information to select a different valve is doomed to have the same results. When DFT Inc. is asked to troubleshoot an installation, we start by collecting all of the available information and check for “bad information” concerning flow conditions and application mismatches with respect to the installed valves.

   Take the time to get good information. Fortunately, the information is more readily available today than it has been in the past through trending information. If you can provide actual system operational information, your chance for success increases significantly.