Ball Valve Selection Guide

Figure 1: A sectional view of a ball valve

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A ball valve is a shut-off valve that uses a rotary ball with a bore to control a liquid or gas flow. The rotary ball is rotated a quarter-turn (90°) around its axis to allow or block the flow through the valve. These valves are mostly preferred for their longer service life and reliable sealing property. There are many options available in the market when it comes to the selection of ball valves. However, the wide range of operation, connection type, circuit function, housing material, and many other criteria make the valve selection process complex. This article will walk you through the ball valve selection process.

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Step 1: Operation Type

The ball valve can be operated manually, electrically, or pneumatically. Different actuation methods all have their advantages and disadvantages.

Manual: You should select a manual ball valve if you have a low budget, no electricity/compressed air at installation, or if no automation is needed. If the ball valve needs to be turned on/off frequently or the system needs to be automated, a manual ball valve should not be used.

Automatic: Deciding between an electric ball valve and a pneumatic ball valve can be difficult. It typically comes down to what is available at the installation site (electricity or compressed air) and the torque needed (pneumatic ball valves have a higher torque, pneumatics are therefore used for larger sized valves). Electric ball valves have a higher initial cost but lower operating cost compared to pneumatic ball valves. For a more in-depth breakdown, read our electric vs pneumatic ball valve article.

Step 2: Circuit Function

Ball valves may have 2-way, 3-way, 4-way, or 5-way circuit functions based on the number of ports.

• 2-way ball valves: are the most common ball valves. These valves provide a straight flow path from input to output.
• 3-way ball valves: 3-way ball valves have three ports and are available with either an L or T bore. The L and T designations refer to the design of the internal bore, which will determine the direction of flow. A 3-way ball valve with a T or L port allows mixing, distribution, or redirection of flow direction for different applications. This makes this valve suitable for heating or cooling applications for water, chemicals and oils.
• 4-way ball valves: 4-way ball valves are not as common as 2- and 3-way ball valves, but it is important to know the variations. A 4-way ball valve is usually available in four different variations: L-port, T-port, X-port (LL-port), and straight.
• 5-way ball valves: are available as valves with perpendicular double L-bore; these 5-way valves are rare.

Read our article on the circuit function of ball valves to learn more about this topic.

Step 3: Housing Material

The housing material of the valve should be compatible with the fluid media being used for the application. Common materials and their features are:

Brass

• Suitable for neutral and non-corrosive media.
• Brass is versatile, durable and resistant to high temperatures.
• Not suitable for salt water (sea water), distilled water, acids and chlorides.

PVC

• Suitable for corrosive media such as sea water, most acids and bases, salt solutions and organic solvents.
• Not resistant to aromatic and chlorinated hydrocarbons.
• The temperature and pressure range is lower than that of brass and stainless steel.

Stainless Steel

• Very good general chemical resistance to almost any medium.
• Very abrasion resistant and resistant to high temperatures and pressures.
• Not suitable for hydrochloric acid, chlorides, bromine and bleach. On the other hand, swimming pool water has a low chloride concentration so the use of stainless steel here is possible.

Step 4: Seal

Ball valves have two seals. Seat rings, which are around the ball on the inlet and outlet, and an o-ring to seal the stem. Typically, the seat rings are made of PTFE. For both seals, the seal material should be compatible with the fluid media being used for the application. Common materials and their features are:

EPDM

• EPDM is very suitable for water, steam, ketones, alcohols, brake fluids, acids/alkalis in low concentrations.
• Excellent resistance to weather influences and ozone.
• Typical operating temperature range between -10° and 130°C.

FKM (Viton)

• FKM has an excellent overall chemical resistance to oils and solvents such as aliphatic, aromatic halocarbons, acids, animal and vegetable oils.
• Typical operating temperature range between -10°C and 120°C.
• It has good mechanical properties, resistance to compression, and suitable for high temperatures (not for hot water/steam).

NBR

• NBR has good resistance to compression, tearing, and wear.
• Compatible with oil products, solvents, and alcohol.
• Typical operating temperature up to 80°C.

PTFE (Teflon)

• PTFE is resistant to almost all fluids.
• PTFE is relatively hard; this makes it suitable for higher operating pressures and temperatures.
• Typical operating temperature range between -30°C and 180°C.

Polyoxymethylene

• POM is suitable for high-pressure and low-temperature applications.

CSM (Hypalon)

• Hypalon is noted for its resistance to chemicals, temperature extremes, and ultraviolet light.

Step 5: Connection type and size

There are different sizes and types of ball valve connections to connect them to a system. The common ones are:

• Standard/Threaded ball valve: Threaded connections are the most common form of connection type and used in a wide range of temperature and pressure applications.
• Flanged ball valve: These ball valves have a flanged connection to join the port to the piping system. These valves are often used on larger sized pipes. Choosing a flanged ball valve requires consideration for pressure ratings and flange compression class, which indicates the highest pressure it can withstand.
• Welded ball valve: In the welded connection, the ball valve is welded directly to the pipe. This type of connection is suitable for applications where zero leakage is required.
• True union ball valve: These valves have a solvent socket connection at each port. The center part of the valve can be easily dismantled and taken off while the valve is installed. This is suitable for quick repair and maintenance in the flow system.

To learn more about ball valve connection types read our technical article about ball valve connection types.

Step 6: Flow Coefficient (Kv)

The flow coefficient, or Kv value, is expressed as the flow rate in m3/h of water at 20°C at a pressure drop of 1 bar. The flow coefficient can be calculated as follows:

• Where:
• Kv= flow coefficient
• Q= flow rate (m3/hr)
• dP= Pressure differential (bar)
• SG= Specific gravity (water=1)

Use our sizing calculator to find the Kv-value and the corresponding valve size for your application. All of our valves are designated with a Kv value and so you can easily select the right valve size.

Step 7: Pressure

Make sure the ball valve can withstand the minimum and maximum pressures in the system. The material of the housing helps determine the pressure range of a ball valve. For maximum pressure, stainless steel usually has the highest rating, followed by brass and then PVC housings. It is important to review your ball valves data sheet to confirm the appropriate pressure range.

Step 8: Temperature

Ensure that the valve material can withstand the maximum and minimum temperature requirement of your operation. The housing and seal material typically determine the temperature range of a ball valve. Common ranges are below, but review your ball valve&#;s datasheet to confirm.

• Brass ball valve: -20°C to 60°C (-4°F to 140°F)
• PVC ball valve: -10°C to 60°C (14°F to 140°F)
• Stainless steel ball valve: -40°C to 220°C (-40°F to 428°F)

Step 9: Approvals & Standards

Depending on the application, ball valves may need to be made to certain standards or receive approvals from regulatory bodies to be used with certain applications, like drinking water or gas applications

• Drinking water: WRAS, KIWA, or DVGW approvals
• Gas: DVGW or EN-331 approvals.
• ATEX: The ATEX regulations are two EU directives detailing minimum safety requirements for workplaces and equipment used in explosive atmospheres.

Application Example

One of the most common ball valve applications is for a residential water line. We walk through our selection process for this ball valve based on the steps outlined above.

1. Operation Type: We can select a manual ball valve as this application requires no automation and can be manually operated.
2. Circuit Function: We can choose a 2-way ball valve with a straight flow path in this case.
3. Housing Material: Brass housing is suitable due to the compatibility with water.
4. Sealing material: We should choose a PTFE seal due to its compatibility with drinking water.
5. Connection type size: We can choose a Standard/ Threaded ball valve for drinking water applications.
6. Flow Coefficient (Kv): We can calculate the Kv value by knowing the inlet pressure, outlet pressure, and the flow rate of the water in m3 inside the residence. However, for common applications like a residential water line it can often just be sized off the surrounding pipe size rather than the Kv value.
7. Pressure: A brass valve can withstand a maximum pressure of up to 80 bar, sufficient for our goals.
8. Temperature: The valve should be able to withstand a temperature range of -20°C to 60°C. Therefore, a brass valve is best.
9. Approvals: If used for drinking water, ensure the valve is approved for drinking water applications.

Ball valve online selection!

As a manufacturer of high performance and engineered ball valves, we are often asked about what industry standards affect ball valve products and what should be referenced when specifying and ordering. The answer to that question is not nearly as straightforward as with the gate, globe, and check valves that have historically been the primary go-to valves in refining. With the more common &#;rising stem&#; valve types, standards such as API 600, API 602, API 603, etc. have taken a lot of the guesswork out because much of the design and sealing methods are well defined. However, as ball valves become more prevalent due to better sealing and reduced emissions, reliance on standards alone is not sufficient. Assurance that the installed product meets process requirements relies on much more.
 

There are several standards that influence the design and performance of ball valves. At a basic level, ASME B16.34, ASME 16.10 and others govern the dimensions and wall thickness (among other things) of most all valves used in the refining and chemical industries. Standards like API 641 (emissions for quarter-turn valves), API 607 (fire testing for both &#;soft&#; and metal seated quarter-turn valves), and API 608 (requirements for metal ball valves generally up to NPS 24 and class 600 rating) guide the industry.

However, none of these standards address the suitability of sealing materials for individual processes. Since these valves are typically used in applications where sealing is critical to the process, there are several open questions that must be addressed when specifying ball valves.

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1.  What is the pipe specification or process requirement? 
   This is almost always clearly stated and will help determine the body material of the valve.
2.  What is the valve process?
   Valve &#;trim&#; material determined by valve process. Internal components must be compatible with the process to resist attack, and it must have the mechanical integrity to operate safely and reliably.
3. What are the process conditions?
   Because seat and seal material must be compatible with the process conditions, these must always be confirmed with the end user.
4. What is the pressure / temperature?
   Seat rating acceptability is determined by pressure & temperature.

Guideline Considerations for &#;Soft Seated&#; Ball Valves

By at least a 10:1 ratio, &#;soft seated&#; ball valves dominate the refining and chemical markets. Although this is evolving as the costs of metal seated valves come down, soft seated ball valves will likely continue to be the most cost-effective solution in relatively clean services under 450ºF.

There are a wide array of options for seating material in these valves. The vast majority used in the refining and chemical industry are based on a form of Teflon &#; / PTFE. Apart from the base material, there are molecularly enhanced versions and compounds filled with glass, carbon fiber and/or graphite. One problem that exists in many specifications for these types of valves is the vague term &#;RPTFE&#; which (not so simply) indicates reinforced PTFE. Without information on the type of reinforcement, this can be misleading. For example, if a request is made for RPTFE in a plant with HF Acid (which dissolves glass) and a valve with glass-filled PTFE is installed, the results will be very undesirable.

In addition, manufacturers offer seat and seal materials like PEEK, Nylon, PCTFE, etc. for specific process requirements. All have certain properties that, when combined with specific seat designs, create allowable maximum (and minimum) temperature ranges and differential pressure.

It is well past the scope of this article to provide an application guide to all these seat types, but if you&#;re involved with selection or specification of these seat and seal materials, here are some guidelines to consider:

1. Always verify that the seat and seal materials are rated for the maximum or minimum design temperature, and the maximum differential pressure in the system where the valve is to be installed. All reputable manufacturers publish this information.
2. If specifying reinforced PTFE seat material, note any material limitations or requirements around the &#;filler&#;.
3. If automating, confirm the torque requirements of the specific seat material provided. This can vary greatly.
4. Whenever possible, include the design temperatures and pressures in the specifications. This is especially important in cryogenic or other extreme conditions.

What is a Severe or Critical Service Application?

A very common question asked in the valve and automation industry is: what is considered a severe or critical service valve application? There are several groups, MSS in particular, that are working on a more objective standard to provide guidance on this question.

As it pertains to ball valves in the refining and chemical industry, the question becomes: when should a severe or critical service metal seated ball valve be considered? This is a rapidly expanding segment of the market that is widely misunderstood. The correct answer to this question is: when process requirements exist calling for ball valves that operate and seal in conditions outside the range of typical products, test protocols and industry standards. This can mean many things to many people, and one must take care to not simply throw money at a problem hoping it goes away.

Choose a Metal Seated Valve for These Applications

In the petrochemical, chemical, and refining industries, some examples of applications where metal seats would be the preferred choice are:

• Coking services
• High pressure hydrogen and gas isolation
• Catalyst handling
• Reactor isolation (manual and automated)
• &#;High cycle&#; ball valves
• Heater isolation or&#;
• Places where reliable tight shut-off is important and soft seated&#; valves will not function due to high temperature, pressure, wear, solids, etc. For example, ball valves that have a pressure rating Class 900 or above, or valves with a design temperature requirement exceeding 450ºF, could be considered a metal seat application.

It is important to understand that metal- to-metal sealing in ball valves is a misnomer. If uncoated metal balls and seats are in direct contact, they would be damaged due to galling when operated and would never seal well. In reality, it is the ball and seat coatings that provide the sealing and allow the valve to cycle without galling. These coatings are generally lapped for tight shut-off and must resist chemical and thermal attack from the process in which the valve is installed.

The key to reliability of &#;metal seated&#; valves in any process application is the selection of the right coating, and the lapping / grinding process to &#;mate&#; the sealing surfaces.

A Deep Dive into Modern Coating Technology

There is simply no &#;one size fits all&#; for &#;metal-to-metal&#; sealing. Coatings are extremely application dependent. There are literally hundreds of material options and combinations, although certain technologies are more common.

Some of the more standard coating options are:

• High Pressure-HVOF
• &#;Spray and Fuse&#;
• Cobalt Overlays
• Chrome Plating
• Surface treatments like Nitriding that are more of a surface hardening than a true coating.

All have their positives and negatives in terms of performance in given applications and cost. The Cobalt overlays (commonly referred to as Stellite&#;) and Chrome Plating are still widely used in ball valves, as well as other valve types.

The most common ball and seat coating in severe service is the HP-HVOF process in which the coating mechanically bonds to the substrate material. In this process, a robotically controlled &#;gun&#; creates high kinetic energy allowing the coatings to be applied in a compressive state. The mechanical bond created is > 12,000 PSI bond strength for carbides, 5,000 &#; 7,000 PSI for chrome oxide ceramic. Some downsides to this process are that even at the lowest porosity, there is still poor sealing on gas applications. In addition, any carbon content makes these coatings susceptible to oxidation.

In the spray & fused process, the ball and seat surfaces are coated with a relatively thick layer of hardening material, then the part is heated to &#;fuse&#; (similar to welding) the coating to the base material for the highest possible bond strength and lowest porosity. This process is best for small molecule gas and particles.

Finally, is the plasma coating process where the specialty coatings are brought to a very high temperature prior to being robotically applied to the metal. This again creates a good bond strength, and coupled with the ceramic-like materials applied, creates a very corrosion resistant surface.

In Conclusion

Ball valves have been around for many years and represent a very large portion of our industry, but they still require attention to detail and an understanding of the applications in which they will be installed. While there is no such thing as &#;zero leakage&#; in valves, by clearly defining the process objectives and properly specifying these products, the greatest reliability can be achieved.

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About the Author

Barry Hoeffner, Director of Quarter Turn Products at Ladish Valves has over 30 years experience in the Chemical and Refining Industries. As a Chemical Engineer, Barry brings a unique perspective to the Flow Control space. His focus for the years in the Valve Industry has been in application engineering and development of severe service and engineered ball valves

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