Ball valves are versatile flow control devices suitable for extensive industrial applications. They are available in different sizes and designs, making them adaptable to diverse sanitary, petrochemical, and cryogenic applications.
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These valves control the flow of fluids through a hollow, pivoting ball that is either a full or reduced port. The dimensions of full port valves are equal to the internal diameters of the adjacent pipelines. The dimension of a reduced port (standard port) valve diameter is one pipe size less than the internal size of the adjacent pipe. For example, a 1&#; reduced port valve will actually use a ball with a ¾&#; port diameter.
Ball valves have several advantages over other industrial valves, with the most notable being:
They provide leak-tight seals.
They can open and close quickly.
They are more durable than most other industrial valves.
There are several ways to categorize valves. Each category or design determines the performance characteristics of the valve. The categories include:
Valve design based on ball movement: Floating and trunnion mounted
Port design: full port, standard, or V-port valve.
Body style: single body, split, top-entry, 3-piece or welded body.
There are a few questions that industrial engineers must ask before choosing ball valves. Finding answers to these questions guides the experts through the challenging valve selection process and helps select reliable ball valves that satisfy the requirements of the piping system. What are these questions?
1. What type of media will flow through the ball valve?
The first question that the engineers must address is the type of fluid that passes through the pipeline. Is it a liquid, gas or semi-solid (slurry)? Understanding the physical and chemical characteristics of the fluid helps analyze its behavior as it flows past the valve. Understanding the nature of the service fluid is vital for making decisions about valve materials, port designs and valve sizes. For example, when choosing a gas ball valve we must take into account its performance and reliability issues when working with combustible gases, like hydrocarbons, liquified natural gas or chemical vapors.
2. Which actuation methods will you use?
Pipeline designers must specify the type of valve actuation that will complement flow control operations. There are piping systems that require frequent valve operation and high precision levels. Other flow operations require a one-off activation of the ball valve. When choosing ball valves, the designer needs to quantify the frequency of valve operations. They also need to evaluate the energy requirements and complexity of actuation technologies. The available actuation methods for ball valves include:
Pneumatic actuation
Electric actuation
Manual operation
Hydraulic actuation
Evaluate additional actuation options like spring return or double-acting actuators as well. Understand the impact of add-ons like limit switches or pilot valves on the reliability of valves.
In processes that demand fast cycle times, pneumatic actuation for ball valves seems to be the most suitable choice. Engineers can install manually-operated ball valves in strategic pipe locations to facilitate pipeline isolation for maintenance or inspection. These low-cycle valves require operation a few times a year.
3. What are the temperature and pressure ratings of the pipeline?
Specifying the pressure and temperature conditions of the service fluid and the working environment is critical when selecting ball valves. The temperature ranges of the service fluid can alter the mechanical strength of the valve. If the temperature fluctuations are too high, the valve experiences non-uniform expansion and contraction that may lead to surface fractures with time.
Ball valves should sustain the pressure of the service fluid. Exceeding the designed pressure limits affects sealing quality and can cause premature wear. Select a ball valve with temperature and pressure ratings equal or higher to the ratings of the pipeline.
4. What are the estimated annual cycles?
The frequency of valve cycling affects the durability of a ball valve. Engineers should estimate annual operating cycles to determine the durability of different ball valves in the piping system. Other factors like maintenance and media abrasion affect the reliability of valves throughout their lifecycle.
The designers should estimate life expectancy of ball valves before choosing the actuation mechanism. If properly specified, ball valves can survive several tens of thousands of operations without failure. After understanding the cycling requirements, the engineers may settle on pneumatically actuated valves that guarantee better durability and reliability than electrically actuated counterparts.
5. How do you intend to use the ball valve?
While there are different types and brands of ball valves in the market, each has a definite application area. For instance, a steel ball valve for a chemical processing facility may not meet the specifications for use in a sanitary application. Ball valves provide shut-off for pipelines and can also provide directional control of fluids. When making selections for application-specific valves, the designer should understand whether:
The valve exclusively shuts off the flow.
The valve switches flow between sources.
Splits flow from one source to two different destinations (applies to 3-way ball valves).
Industrial applications operate under different pressure and temperature conditions. There are strict emission and leakage control requirements attached to diverse classes of ball valves. When selecting the ball valve, ensure that it meets minimum system requirements and regulatory specifications.
7. Which materials are used to manufacture the valve?
The type of valve materials comes down to the properties of the service fluid. When evaluating valve materials, engineers should verify:
Compatibility with the service media
Resistance to corrosion
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Cost
The most common materials for ball valve bodies are brass, stainless steel, plastic, Monel, Inconel, Molybdenum, Chromium alloys, nickel alloys or copper. Severe service ball valves require materials with better strength and corrosion resistance values like Monel or Inconel.
When examining valve materials, the designers should pay attention to the composition of seal materials. Soft-seated ball valves may use rubber seals or PTFE seals. For extreme fluid service, the ball valves feature metal-to-metal seats.
Which testing and quality assurance procedures does your valve vendor use?
When working with vendors or manufacturers, the company should request information about testing protocols and quality assurance measures that they use. Testing procedures analyze the performances of different ball valves, leak and emission tests and pressure tests to ensure valves are safe for specific applications.
Do not purchase ball valves because they are the cheapest in the market. Take an extra step to evaluate the quality assurance criteria and standardization marks on the valve body or packaging. There is no point in purchasing ball valves in bulk, only for them to fail after a few working cycles.
8. What certifications should the valve have?
The application of ball valves spans different industries. In each sector, appointed organizations certify products to verify compliance with health and safety regulations. Depending on the type of application, ball valves and their actuators are subject to the following certifications:
ANSI certifications: Determines the pressure and temperature ratings for pipe flanges.
NEMA certifications: Sets the standards for the design of electrically actuated ball valves.
NSF certifications: Provide guidelines for selecting ball valves in food, beverage and drug production facilities.
Ball valves should have certifications relevant to the fluid applications you are running within the facility.
9. What are the maintenance requirements for ball valves?
Ball valves do not typically require a high volume of maintenance interventions. They have simple flow control mechanisms and are less likely to fail. However, that does not preempt the fact that industrial valves, at times, will require maintenance. When selecting valves, establish a plan for inspection and maintenance. Maintain a lean inventory of repair and replacement parts like seals for valves and consumables for actuators. Manual ball valves may require fewer maintenance interventions than actuated valves.
Conclusion
Selecting ball valves for different industrial applications is not a simple process. It requires a careful review of the technical specifications of the pipeline, a balanced selection of manufacturing materials, and research on the different valve industry codes and standards. By answering the above questions, engineers and pipeline designers can make informed decisions and select reliable ball valves that provide long-term service.
As published in BSIC Journal
By Lisa Johnson
Many people think that selecting a slide gate or diverter for handling dry material should be a relatively simple process. They typically assume the only information they need is:
· Size of the opening
· Shape of the opening
· Available stack-up height
· Matching connections or hole patterns
But in reality, valve suppliers need more information to accurately select the right valve for the application. Costly mistakes can be avoided the more information about the application parameters a supplier has; like purchasing an expensive valve for a simple application, or buying an inexpensive valve that cannot handle a difficult. Valve suppliers should have the experience and knowledge to know what valves and valve modifications to apply for certain applications parameters. Make sure your supplier is asking the right questions.
So let's begin with the premise that each application for a slide gate or diverter valve has its own unique requirements. What are the factors that determine what type of valve is selected and what modifications are necessary?
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Valve Selection
Installation criteria determines which valve line is appropriate. The most critical question is "what is the valve intended todo?" Is a slide gate, diverter valve, iris valve or a butterfly valve needed to best fulfill the application? After this question is answered, you can follow up with these questions.
· What is the opening or orifice size?
· Is the opening square or round?
· Will the valve be used in differential pressure or gravity application?
· Will the valve be installed indoors or outside?
· What is the temperature of the air and material conveyed?
· Does the system use dilute, phase, dense phase, vacuum, or gravity to convey material? If pressure or vacuum, how much?
· What is the size of the conveying line?
· Are the lines tube or pipe? If the lines are pipe, is it schedule 10 or 40?
· Does the valve material contact need to be carbon steel, stainless steel, or aluminum?
· Will the valve be subject to wash-downs? If so, will it be washed with hot water or a caustic liquid?
· Will there be flow aides such as aeration or vibration if the valve is mounted below a bin/silo?
· What is the sequence of operations for the system, e.g., When are the flow aids activated in relation to the cycle of the gate valve?
· If the slide gate is designed for gravity and is mounted below a bin/silo, then how is the material conveyed into the bin/silo?
Then you need to consider the material characteristics.
· What is the material to be conveyed?
· Is the material in powder, granular, or pellet form?
· What is the particle size of the material?
· What is the weight of the material per cubic foot?
· Is the material sticky, abrasive, or corrosive?
· Is there spoilage or sanitary issues with the material?
· Will different types of material be conveyed through the same line? If so, are there cross contamination concerns?
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Actuator Selection
There are many types of actuators to operate the valve to open and close. Depending on system requirements and power availability, actuators can be automated or manual. Automatic actuators are available such as air cylinder, air cylinder with magnetic piston, electric actuator, explosion-proof electric actuator, and hydraulic actuator. Manual actuators available are hand wheel, hand crank, and chain wheel actuators. To define which one you'll need, you'll need to answer the following questions:
· What is the cycle frequency?
· Will the valve close on material? If so, will the material be standing or moving column?
· Is compressed air available?
· Does actuation speed matter?
· What are the cost variables for replacement and repair?
· Can I use manual actuation when the valve is only for maintenance purposes?
· Will the valve be outside in cold temperatures?
· Does it need to meet electrical classifications like Voltage, NEMA or ATEX?
Standard Modifications
Determine if the company that is manufacturing your valve offers standard modifications to suit application/material specific requirements. Some application specific factors that would need to be considered for valve modifications are:
· Duty Cycle
· Abrasive Duty
· Corrosion
· Chemical Compatibility
· Particle Size
· Friability
· Temperature
· Serviceability
· Food Specific
· Indoor/Outdoor Service
Some valve modifications that can serve these challenges in the bulk powder industry are Stainless Steel Material Contact, Water Wash Down, High Temperature Service, Cold Temperature Service, US Dairy Standard, Flexible Hose, Schedule Pipe Size, Clear Bonnet Covers, Straight Leg, Fabric Sleeve, Sealed Body, Stainless Steel Rollers, Seal Access/Removable Seals, Abrasion Resistant Blade, Clean In Place, Round & Square Transitions, 30 Degree Offset and Internal Diverter Linings, just to name a few.
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Valve Location & Orientation
Designate where the valve is to be installed and the orientation of the valve. The position of a slide gate or diverter valve in a system helps determine which accessories may be required for your application. For example, if a slide gate is to be mounted below a surge hopper, positioning controls may be required to meter material into the weigh hopper.
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Accessory Selection
There are four distinct areas to address when specifying accessories for valve.
1. Motion controls - Intermediate positioning is available via a variety of methods depending on specific installation criteria.
· VPO/VPC - relay control with manual adjustability
· AVP - PLC control with manual adjustability
· IVP - Infinitely Variable Position Control via 4-20mAsignal
2. Feedback - For added valve control, manufacturers can provide customers with push-button control panels to suit your valve control needs. Manufacturers can also utilize state-of-the-art valve/sensor manifold technology with a variety of PLC interfaces on multi-port diverter assemblies.
3. Safety Devices - A vented ball valve should always be installed in front of the air control valve in order to bring the slide gate or diverter valve to zero mechanical state before servicing. This style of ball valve bleeds off any residual downstream pressure contained in the air lines supplying the air cylinder. The ball valve should always be installed within easy arm's reach of the air control.
4. Fabricated Accessories - Fabricated transitions provide flexibility for customers with existing equipment. Transitions can address custom flange-to-flange dimensions. They may also be fabricated to contain flanges that match special bolt patterns, tube stubs, sock beads, or blind flanges that allow in-the-field hole placement and installation.
Features Selection
There are a number of different features available when selecting a slide gate or diverter valve. Each manufacturer will have their own standard products.
Adjustable Rollers- Externally greased hardened steel adjustable rollers are used to keep the blade dust tight.
Abrasion Resistant Liners - Abrasion resistant liners positioned at the inlet of the gate address potential wear issues that may exist from either the volume or the abrasiveness of the material being handled. The liners are replaceable when needed.
Abrasion Resistant Blade -The gate's blade can also manufactured of abrasion resistant steel. The combination of the abrasion resistant blade and liners are important in providing a gate that offers longevity and an exceptional life-cycle cost.
Displacement End Pocket - A displacement pocket displaces the material at the leading edge of the blade as the blade closes. Rather than the blade jamming and packing this material into an end seal, the blade stops part way into the pocket. Material falls away from the blade and re-enters the material flow stream area. This feature can increase the valve's service-life and reduce downtime costs related to maintaining and replacing end seals.
Bonnet Purge - The optional bonnet purge is utilized to keep material out of the body of the valve and in the material stream.
Replaceable Seals - Seals reduce interior valve dusting and can be replaced while the valve is inline.
Wear Compensating Seals - Pressure loaded, polymer bonnet seals offer a dual purpose. They act as a wiper for material that may be on the blade as the blade retracts. They also seal material from entering the bonnet area of the gate. The "live load" on the back of the seal strip continues to apply pressure to the seal even as it wears. At a certain wear point, seals may be accessed and replaced from the outside of the gate, while the gate remains inline.
Wear Reducing Material Deflectors- Material deflectors are placed around the inlet of the valve and protect it from the material flow stream. By deflecting material away from the hardened steel rollers and blade seals, this feature significantly reduces wear and downtime keeping the valve in service longer.
Available Sizes- Valve standard sizes will be dependent on the valve and the manufacturer. Contact your manufacturer for available sizes.
Return Pan - A return pan can be added to seal fine material internally or to atmosphere. With this feature, material that enters the bonnet of the valve is returned to the material flow stream, thus reducing material leakage to atmosphere.
Wear Resistant Bucket Design - A wear resistant bucket constructed from durable abrasion resistant steel and an optional ceramic liner can be added to reduce potential wear to the bucket. For even more durability, the additional of an optional honeycomb liner allows material to abrade on itself instead of the bucket.
Optional Configurations - Available in straight leg and wye line configurations.
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A lot of questions come in to play to select the right valve for your application. But, if you are prepared with the information for your manufacturer, you can be confident that you have purchased the solution to your needs. If your manufacturer doesn't ask specific detailed questions, you might end up paying too much for a simple valve that doesn't meet your requirements, and you'll end up wasting factory time and money to modify the valve for your application.
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