diaphragm manual manufacturer valve
Taken from What Is A Control Valve?: Process plants consist of hundreds, or even thousands, of control loops all networked together to produce a product to be offered for sale. Each of these control loops is designed to keep some important process variable such as pressure, flow, level, temperature, etc. within a required operating range to ensure the quality of the end product. Each of these loops receives and internally creates disturbances that detrimentally affect the process variable, and interaction from other loops in the network provides disturbances that influence the process variable.
To reduce the effect of these load disturbances, sensors and transmitters collect information about the process variable and its relationship to some desired set point. A controller then processes this information and decides what must be done to get the process variable back to where it should be after a load disturbance occurs.
When all the measuring, comparing, and calculating are done, some type of final control element must implement the strategy selected by the controller.
Contents:
- Chapter 1. Introduction to Control Valves
- What Is A Control Valve?
- Process Control Terminology
- Sliding-Stem Control Valve Terminology
- Rotary-Shaft Control Valve Terminology
- Control Valve Functions and Characteristics Terminology
- Other Process Control Terminology
- Chapter 2. Control Valve Performance
- Process Variability [ Dead Band ~ Actuator-Positioner Design ~ Valve Response Time ~ Valve Type And Characterization ~ Valve Sizing ]
- Economic Results
- Summary
- Chapter 3. Valve and Actuator Types
- Control Valves [ Globe Valves ~ Rotary Valves ]
- Control Valve End Connections [ Screwed Pipe Threads ~ Bolted Gasketed Flanges ~ Welding End Connections ]
- Valve Body Bonnets [ Extension Bonnets ~ Bellows Seal Bonnets ]
- Control Valve Packing [ PTFE V-Ring ~ Laminated and Filament Graphite ~ USA Regulatory Requirements for Fugitive Emissions ]
- Characterization of Cage-Guided Valve Bodies [ Characterized Valve Plugs ]
- Valve Plug Guiding
- Restricted-Capacity Control Valve Trim
- Actuators [ Diaphragm Actuators ~ Piston Actuators ~ Electrohydraulic Actuators ~ Manual Actuators ~ Rack and Pinion Actuators ~ Electric Actuators ]
- Chapter 4. Control Valve Accessories
- Positioners
- Other Control Valve Accessories [ Limit Switches ~ Solenoid Valve Manifold ~ Supply Pressure Regulator ~ Pneumatic Lock-Up Systems ~ Fail-Safe Systems for Piston Actuators ~ Electro-Pneumatic Transducers ~ Electro-Pneumatic Valve Positioners ~ Diagnostics ]
- Chapter 5. Control Valve Selection
- Valve Body Materials
- Designations for the High Nickel Alloys
- Pressure-Temperature Ratings for Standard Class [ Cast Carbon Steel (ASTM A216 Grade WCC) ~ Cast Chromium-Molybdenum Steel (ASTM A217 Grade WC9) ~ Cast Chromium-Molybdenum Steel (ASTM A217 Grade C5) ~ Cast Type 304 Stainless Steel (ASTM A351 Grade CF3) ~ Cast Type 316 Stainless Steel (ASTM A351 Grades CF8M and CG8M) ]
- Pressure-Temperature Ratings for ASTM A216 Cast Iron Valves
- Pressure-Temperature Ratings for ASTM B61 and B62 Cast Bronze Valves
- Face-to-Face Dimensions for Flanged Globe-Style Control Valves
- Face-to-Face Dimensions for Buttweld-End Globe-Style Control Valves
- Face-to-Face Dimensions for Socket Weld-End Globe-Style Control Valves
- Face-to-Face Dimensions for Screwed-End Globe-Style Control Valves
- Face-to-Centerline Dimensions for Raised Face Globe-Style Angle Control Valves
- Face-to-Face Dimensions for Separable Flanged Globe-Style Control Valves
- Face-to-Face Dimensions for Flangeless, Partial-Ball Control Valves
- Face-to-Face Dimensions for Single Flange (Lug-Type) and Flangeless (Wafer-Type) Butterfly Control Valves
- Face-to-Face Dimensions for High Pressure Butterfly Valves with Offset Design
- Wear & Galling Resistance Chart Of Material Combinations
- Control Valve Seat Leakage Classifications
- Class VI Maximum Seat Leakage Allowable
- Typical Valve Trim Material Temperature Limits
- Service Temperature Limitations for Elastomers
- Ambient Temperature Corrosion Information
- Elastomer Information
- Fluid Compatibility
- Control Valve Flow Characteristics [ Flow Characteristics ~ Selection of Flow Characteristic ]
- Valve Sizing [ Sizing Valves for Liquids ~ Abbreviations and Terminology ~ Equation Constants ~ Determining Fp, the Piping Geometry Factor ~ Determining qmax (the Maximum Flow Rate) or Pmax (the Allowable Sizing Pressure Drop) ~ Determining qmax (the Maximum Flow Rate) ~ Determining Pmax (the Allowable Sizing Pressure Drop) ~ Liquid Sizing Sample Problem ~ Sizing Valves for Compressible Fluids ~ Determining xTP, the Pressure Drop Ratio Factor ~ Compressible Fluid Sizing Sample Problem No. 1 ~ Compressible Fluid Sizing Sample Problem No. 2 ~ Representative Sizing Coefficients for Single-Ported Globe-Style Valve Bodies ~ Representative Sizing Coefficients for Rotary-Shaft Valves ]
- Actuator Sizing [ Globe Valves ~ Actuator Force Calculations ]
- Rotary Actuator Sizing [ Torque Equations ~ Breakout Torque ~ Dynamic Torque ]
- Typical Rotary Shaft Valve Torque Factors
- V-Notch Ball Valve with Composition Seal
- High Performance Butterfly Valve with Composition Seal [ Maximum Rotation ]
- Non-Destructive Test Procedures [ Magnetic Particle (Surface) Examination ~ Liquid Penetrant (Surface) Examination ~ Radiographic (Volumetric) Examination ~ Ultrasonic (Volumetric) Examination ]
- Cavitation and Flashing [ Choked Flow Causes Flashing and Cavitation ~ Valve Selection for Flashing Service ~ Valve Selection for Cavitation Service ]
- Noise Prediction [ Aerodynamic ~ Hydrodynamic ]
- Noise Control
- Noise Summary
- Packing Selection
- Packing Selection Guidelines for Sliding?Stem Valves
- Packing Selection Guidelines for Rotary Valves
- Chapter 6. Special Control Valves
- High Capacity Control Valves
- Low Flow Control Valves
- High-Temperature Control Valves
- Cryogenic Service Valves
- Customized Characteristics and Noise Abatement Trims
- Control Valves for Nuclear Service in the USA
- Valves Subject to Sulfide Stress Cracking [ Pre-2003 Revisions of MR0175 ~ NACE MR0175/ISO 15156 ~ NACE MR0103 ]
- Chapter 7. Steam Conditioning Valves
- Understanding Desuperheating [ Technical Aspects of Desuperheating ]
- Typical Desuperheater Designs [ Fixed Geometry Nozzle Design ~ Variable Geometry Nozzle Design ~ Self-Contained Design ~ Steam Atomized Design ~ Geometry-Assisted Wafer Design ]
- Understanding Steam Conditioning Valves
- Steam Conditioning Valves [ Steam Cooler ~ Steam Sparger ]
- Understanding Turbine Bypass Systems
- Turbine Bypass System Components [ Turbine Bypass Valves ~ Turbine Bypass Water Control Valves ~ Electro-Hydraulic System ]
- Chapter 8. Installation and Maintenance
- Proper Storage and Protection
- Proper Installation Techniques [ Read the Instruction Manual ~ Be Sure the Pipeline Is Clean ~ Inspect the Control Valve ~ Use Good Piping Practices ]
- Control Valve Maintenance [ Reactive Maintenance ~ Preventive Maintenance ~ Predictive Maintenance ~ Using Control Valve Diagnostics ~ Actuator Diaphragm ~ Stem Packing ~ Seat Rings ~ Bench Set ]
- Chapter 9. Standards and Approvals
- Control Valve Standards [ American Petroleum Institute (API) ~ American Society of Mechanical Engineers (ASME) ~ European Committee for Standardization (CEN) ~ Fluid Controls Institute (FCI) ~ Instrument Society of America (ISA) ~ International Electrotechnical Commission (IEC) ~ International Standards Organization (ISO) ~ Manufacturers Standardization Society (MSS) ~ NACE International ]
- Product Approvals for Hazardous (Classified) Locations [ References ~ North American Approvals ~ Loop Schematic (Control Drawing) ~ Comparison of Protection Techniques ~ European and Asia/Pacific Approvals ]
- Chapter 10. Engineering Data
- Standard Specifications For Valve Materials
- Valve Materials Properties for Pressure?Containing Components
- Physical Constants of Hydrocarbons
- Specific Heat Ratio (K)
- Physical Constants of Various Fluids
- Refrigerant 717 (Ammonia)
- Properties of Water
- Properties of Saturated Steam
- Properties of Superheated Steam
- Velocity of Liquids in Pipe
- Flow of Water Through Schedule 40 Steel Pipe
- Flow of Air Through Schedule 40 Steel Pipe
- Calculations for Pipe Other than Schedule 40
- Chapter 11. Pipe Data
- Pipe Engagement
- Carbon and Alloy Steel ? Stainless Steel
- American Pipe Flange Dimensions ? Diameter of Bolt Circle Inches
- American Pipe Flange Dimensions ? Number of Stud Bolts and Diameter in Inches
- American Pipe Flange Dimensions ? Flange Diameter?Inches
- American Pipe Flange Dimensions ? Flange Thickness for Flange Fittings
- Cast Steel Flange Standard for PN 16
- Cast Steel Flange Standard for PN 25
- Cast Steel Flange Standard for PN 40
- Cast Steel Flange Standard for PN 63
- Cast Steel Flange Standard for PN 100
- Cast Steel Flange Standard for PN 160
- Cast Steel Flange Standard for PN 250
- Cast Steel Flange Standard for PN 320
- Cast Steel Flange Standard for PN 400
- Chapter 12. Conversions and Equivalents
- Length Equivalents
- Whole Inch?Millimeter Equivalents
- Fractional Inches To Millimeters
- Additional Fractional/Decimal Inch?Millimeter Equivalents
- Area Equivalents
- Volume Equivalents
- Volume Rate Equivalents
- Mass Conversion—Pounds to Kilograms
- Pressure Equivalents
- Pressure Conversion—Pounds per Square Inch to Bar
- Temperature Conversion Formulas
- Temperature Conversions
- A.P.I. and Baumé Gravity Tables and Weight Factors
- Equivalent Volume and Weight Flow Rates of Compressible Fluids
- Viscosity Conversion Nomograph
- Other Useful Conversions
- Metric Prefixes and Symbols
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Related posts
Pressure transmitters are widely applied for a variety of measurement purposes, and they cause a lot of trouble. Zeros shift, lines plug, and readings become erratic.
But fundamentally, there’s no reason to have pressure measurement problems. All over the world there are transmitter installations giving consistent, accurate pressure readings in the most difficult applications. The key is to specify and install pressure transmitters wisely.
The heart (and in many cases, the limitation) of a pressure transmitter is the transducer (an overview is in the sidebar, Transducer Technologies, and a more complete treatment can be found in Reference 1). The critical factors used to select a transducer are its accuracy, the system pressure and temperature, and fluid characteristics.
Examine Accuracy
Controls experts such as Bala Liptok have said inaccuracy is probably a better measure of instrument performance. Engineers must recognize that many accuracy statements may be formulated based on laboratory-like conditions that are much more benign than the dirty and electrically noisy environment seen by a pressure transmitter inside a plant.
The engineer should ask the transmitter manufacturer two questions:
1. Is every transmitter tested to meet the accuracy specification?
2. If only a representative sample of transmitters is tested, what statistical method was used to develop the statement? Statistical criteria include the size of the population, statistical limits of error, and confidence.
Ask about effects of factors such as humidity and vibration on hysteresis, linearity, drift, and repeatability (Table I). Each pressure transmitter has an accuracy envelope determined by base accuracy, ambient and process exposure, and drift.
It is common for manufacturers to combine linearity, hysteresis, and repeatability into the base or nominal accuracy. The primary contributors to error are temperature and, in the case of differential pressure measurements, static pressure.
Determine Pressure and Temperature Ranges
Examine the pressure application and determine the maximum pressure that the transmitter will see.
Consider the following values:
1. The normal operating pressure range, low and high.
2. The maximum abnormal operating pressure range, low and high.
3. The maximum safe overpressure range (burst or damage limits).
4. Peak and frequency of pressure pulses.
The low limit of pressure must be considered if the transmitter can be damaged by vacuum and could be exposed to vacuum. Users should also pay attention to the hydrotest pressure associated with the line, though this does not tend to be a problem. Also, if the sensor is directly exposed to high temperature, the pressure rating will be limited by that temperature. Exposure to abnormal events (such as water hammer) must also be taken into account.
Once the pressure limits are determined, it is good practice to allow a 20% safety factor. If there is an overpressure or safety device, the pressure rating of the transmitter can be at the trip setting of the overpressure device.
Over-rating a transmitter can negatively impact its range and sensitivity. These two parameters have a direct correlation to the accuracy of the measurement. The installation of a pressure snubber or dampener could alleviate the need for the safety factor, as we’ll discuss later.
Select a transmitter with the operating pressures at 50-75% of the calibrated range. This assumes that there are not many expected upsets that could cause large swings in pressure. If there are large swings (widening the range) due to process conditions, installing a second transmitter to handle the additional range should be considered.
Consider both the process temperature range and the ambient temperature range. The process temperature range represents the normal and abnormal temperatures the transducer will be exposed to via the process. The ambient temperature range gives the amount of temperature error to allow for without degrading performance outside the limits set by the application.
Install Properly
Accurate, reliable pressure measurements depend on correct installation. Start with location: A transmitter with a small display 50 ft. in the air next to a ladder becomes an operability issue. If maintenance personnel can’t reach the transmitter, there is a maintainability, and possibly a safety, issue.
The manufacturer’s installation literature describes how much vertical and horizontal distance is required around the transmitter to ensure it can be placed in and out of service easily.
Determine if and how the instrument will be taken out of service for maintenance and calibration without shutting down the process or injuring personnel with leaks or spills. A root valve and secondary block valve can isolate the instrument from the process. Some manufacturers will furnish this item as part of the transmitter assembly, or a manifold can be furnished as a separate item.
To keep maintenance costs down, look for a transmitter with modular components. For example, modularity would allow one piece of electronic circuitry inside the transmitter to be replaced in lieu of replacing the entire transmitter.
Impulse lines connecting the process to the transmitter should be kept as short as possible. One manufacturer estimates that impulse lines represent more than half the problems associated with instrument performance.
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Instruments used in a liquid or condensable vapor should be mounted below the process connection. Impulse lines should be sloped down toward the instrument to prevent trapped gases inside the instrument or impulse lines. Transmitters should be bought with ports to allow venting of gas or draining as appropriate. Vertical lines are also generally sloped slightly to minimize the chance of vapor lock.
Instruments used in gas pressure measurement should be mounted above the process connection. Impulse lines should be sloped away from the instrument to prevent trapping liquids inside the instrument.
Route signal wiring away from power conductors per the spacing requirements listed in IEEE 518, Guide for the Installation of Electrical Equipment to Minimize Electrical Noise Inputs to Controllers From External Sources. Ensure that the signal shield is grounded only at one end and that conduit systems have intentional low points equipped with breather/drain assemblies for removing moisture.
Consider using block and bleed valves. The block and bleed valve has two purposes: for removing the instrument from the line without leakage, and for zeroing and testing the instrument. A bypass valve must be added if the measurement is differential pressure.
Dampeners, Seals, and Purging
Be aware of what types of transients could occur in the line where the transmitter is mounted. This is particularly important if a pressure transmitter is installed near a pump discharge. Pulsation dampeners are generally used to damp out process fluid pulsations, more often for signal fluctuations but possibly for protection against mechanical vibrations that might damage the transmitter.
One dampening technique is installing a pigtail in the impulse piping between the instrument and the process root valve connection, and some transmitters are available with built-in dampening. Signal pulsations are generally filtered by a dampener rather than time-delayed, so the output is an average of the pulsations. This raises the question of whether the transmitter will provide a representative signal.
Chemical seals serve several purposes in a transmitter installation:
* Preventing contact of potential noxious or corrosive process fluid with the transmitter.
* In certain cases, serving as a winterizing function in lieu of the electrical or steam tracing devices.
* Allowing remote mounting of a transmitter for better maintenance access (using a diaphragm and capillary-type seal). This can also alleviate some of the burdens associated with area classification if the diaphragm and capillary seal allows the instrument to be mounted outside the hazardous area. It is considered good practice to allow no more than 25 ft. of capillary tubing from the diaphragm to the transmitter. A downside to a capillary can be additional loop deadtime.
* Preventing solids or slurries from plugging the measurement element.
* Providing a larger surface area or process connection, which can improve sensitivity and help minimize plugging.
It is critical that the liquid in the seal be capable of withstanding the temperature at the process connection and the ambient temperature without freezing or gelling. The fluid should also be compatible with the process fluid so there is no major contamination problem should the seal break. Work with the transmitter or seal manufacturer to select the correct fluid.
Pay attention to the construction of the seal, and in general, look for fully-welded seals. In sanitary services, consider an approved self-cleaning seal. If vacuum is present, use a seal designed and constructed for that kind of service.
Purging is used to keep the instrument clear of process fluid that can cause plugging of the impulse lines or the transmitter. Purging is commonly used in applications involving solids, process fluids that are subject to solidification or plugging, and acid or basic fluids. The purge fluid must be compatible with the process and delivered at a higher pressure than the process, with check valves for backflow prevention. Reference 7 includes information on determining purge flow rates.
Before selecting the sensor type, if the specifier understands the measured process fluid and its characteristics in various temperatures and pressures, knows the conditions the transmitter will experience, and provides adequate room to install and maintain the transmitter, there’s an excellent chance the proper pressure measurement technology will be applied
6. Process Measurement Instrumentation, American Petroleum Institute Recommended Practice 551, Washington, D.C.
7. Manual on Installation of Refinery Instruments and Control Systems, American Petroleum Institute Recommended Practice 550, Part I, Section 4: Pressure (out of print).
8. Manual on Installation of Refinery Instruments and Control Systems, American Petroleum Institute Recommended Practice 550, Part I, Section 8: Purges, Seals, and Winterizing (out of print).
9. “How Accurate Is Accurate?” Bill Mostia, CONTROL Magazine, June, July, and August, 1998.
