SPECIAL TOPIC – Actuation & Automation V-Port Ball Valves vs. Globe Valves for Control Applications

In most process applications there are two different types of valves used: on/off and control. On/off valves are simply for allowing full flow or stopping flow completely. Control valves, in contrast have the ability to control the AMOUNT of flow, also known as throttling.

By Brian Booth – Assured Automation

When selecting a control valve for a signal. The positioner then controls the particular application, there are two dis- actuator accordingly (table 1). tinctly different valve styles to consider: Rotary valves such as ball, plug, and V-Port ball valves, which use rotary mo- butterfly valves are the most common tion; and lobe valves which use linear G type of on/off valves and are typically motion (figure 1). NOT recommended for throttling appli- No matter what type of valve is used for cations for two reasons: control applications the valve assembly 1) The seals will wear unevenly based on Figure 1: V-Port Ball Valve (rotary) vs. Globe Valve (linear) requires three main components: the partial exposure to the flowing media

1) Valve 2) The flow curve they produce is not Control Signal Closed 50% Open 2) Actuator ideal due to an uneven increase of flow 0-10VDC 0 5 10 when compared to the degree of rota- 3) Positioner tion (Figure 3). 4-20mA 4 12 20 Control Valve Operation V-Port Ball Valves 3-15 psi 3 9 15 The actuator, of course, operates the V-Port ball valves are a specialized ball Resulting Valve Position valve. The positioner controls the actuator. valve that are suitable for coarse con- Linear (globe) Down Half way Up The control system monitors conditions trol applications. At the same time, they such as flow rate, temperature, level, and can also provide reliable shutoff. These Rotary (V-Port ball) 0˚ 45˚ 90˚ pressure via sensors. The sensors send valves are constructed similar to full or Table 1 feedback signals to the controller which standard port ball valves with one ex- performs any logic, then sends a signal ception — the bore through the ball is ization evens out the flow curve, mak- to the control valve positioner. The con- “characterized” as opposed to a “circu- Globe Valves ing them suitable for, and sometimes trol signal can be a 0-10VDC or 4-20mA lar bore”. As the name states, the bore preferred for control applications. Globe valves use linear actuation and electrical signal, or a 3-15 psi pneumatic is a “V”, or wedge shape. This character- have been the preferred type of con- There are many different V-Port balls trol valve for decades. While they of- available to accommodate different fer more precise control due to a more flow ranges with the same valve body. linear flow curve (Figure 3) and do not The most common are 60˚, 30˚, and 15˚ We Make Easy! suffer the uneven wear in the mid po- Valve Automation (Figure 2). sitions, they do not typically provide a bubble tight shutoff.

Downsize Your On/O Valves Typically Globe valves have higher pressure drops than V-Port valves, (Typical Ball Valve) VA Series since the pressure exerted is trans- Compact On/O Valves ferred to the valve stem. They also re- • Smaller • Higher Cycle-Life quire greater force or a larger actuator • Faster • Less Expensive to seat the valve. • Lighter • Safer Choosing Between V-Port or Globe

When selecting a control valve for any application there are many factors to consider:

Valves shown are to scale. What valve configuration is required? This is an accurate size comparison of: pneumatically actuated 1” NPT On/O valves with Globe valves are available in 2-way dual (open/closed) proximity sensor limit switches flow control, 3-way mixing, or 3-way di- verting. V-Port Ball Valves are available 1-800-899-0553 in 2-way flow control.

Is bubble-tight shutoff required?

Globe valves are not typically used for applications where a bubble-tight shut- off is required although they could be used in combination with a simple on/off ball, butterfly, or plug valve, or any other type of shutoff valve. This of course adds to the cost and space requirements.

V-Port Ball Valves use the “floating ball principle” which will provide a bubble tight shutoff in addition to the modu- lating flow control. When the valve is Figure 2: Various common V-Port closed, the upstream pressure pushes profiles. Custom characterizations are also available. the ball against the downstream seat, thus enhancing the seal.

10 Valve World Americas | May 2018 • www.valve-world-americas.net SPECIAL TOPIC – Actuation & Automation V-Port Ball Valves vs. Globe Valves for Control Applications

What degree of precision is required? to maintain strict parameters. There is What flow capacity is required? tions (above 350˚F). Of course, there are (fine or coarse control) no contact between the plug and seat other factors that vary greatly that also For any given line size, a larger degree other than when in the completely Globe Valves offer finer degree of con- profile V-Port, i.e. 60˚ will provide a high- need to be taken into account. These in- closed position. trol capability than V-Port Ball Valves. er max. Cv than a globe valve of that clude operating pressure, temperature, V-Port Ball Valves are geared more to- and seat/seal material. All of these must How often will the flow need to be same size (figure 4). wards applications where infrequent be checked against the valve’s ratings. adjusted? adjustments are required. Frequent cy- Is cavitation a cause for concern? Is ease of maintenance an important Globe Valves are far better suited for cling of these will wear the seals more Cavitation is the occurrence of tiny ex- issue? high-cycle applications where the rapidly due to the constant contact of plosions caused by the media changing valve needs to be constantly adjusted the ball with the seats. pressure quickly and drastically caus- In many industries, particularly con- ing the media to vaporize and form a tinuous processes, downtime can be bubble. This phenomenon is very noisy extremely costly. Batch processes by and can be extremely damaging to the nature have designated start and stop- valve, the line, and the entire system. In ping times. This makes the ease of all cases, cavitation should be avoided. maintenance and downtime less costly. If cavitation IS a concern, a globe Globe valves will most likely need less valve is better solution. When media frequent seat replacements due to the is passing through a valve, there is lack of constant contact with the plug. always a pressure drop or head loss. Soft seats like TFE or PEEK will wear It is important to note that the result- ing final pressure on the downstream sooner than metal seats, such as stain- side is NOT the lowest pressure within less steel. When leakage rates exceed the flow path. There is point within the what is acceptable, the valve must path that is the highest velocity and the be repaired. Fortunately, most globe

X - % Open lowest pressure. This is known as the valves have a bolt on bonnet, that can Vena Contracta. The flow path in V-Port be removed for easy access to the plug ball valves produce a much lower Vena and “drop-in” trim. Contracta, making the chances of cavi- V-Port ball valves, on the other hand tation much higher. will have their seats wear sooner due Will high temperature media be to the constant contact of the ball and controlled? the seat. When a V-Port valve requires Figure 3 Y - % Max. Cv Globe valves should usually be selected repair, it is the same procedure as that for use in higher temperature applica- of a regular ball valve.

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www.valve-world-americas.net • May 2018 | Valve World Americas 11 SPECIAL TOPIC – Actuation & Automation

Figure 4

How much does it cost? solution. Typically, a V-Port Ball Valve will be 35% to 50% less than a Globe Valve. If there are no specific reasons listed ABOUT THE AUTHOR previously to choose one vs. the other, While considerably more expensive, then you should consider cost. V-Port Globe valves do still offer the many ad- Brian Booth is Vice President of Sales and Product Ma- ball valves are by far a more economical vantages listed (table 2). nager for all thermal and remote shutoffs, including the FireChek® and FM Fire- Safe Emergency Isolation Valves at Globe V-Port Assured Automation. The company is a leading provider of 2-way flow control, 2-way flow control Automated Valves, Flow Components, and Fire Safety Pro- Function 3-way mixing, ducts for industrial process control applications. Assured 3-way diverting Automation provides state of the art automation ranging from small equipment manufacturers to the Fortune 500 Positive Shutoff Not leak free YES manufacturing, chemical and pharmaceutical companies. The Assured Automati- Control Capability Fine Coarse on product line consists of a complete offering of standardized automated valve High Duty Cycle YES (constant) NO assemblies with a variety of commonly used accessory items. The company’s Flow Capacity Lower Higher complete valve automation services supply special automated valve assemblies Cavitation Prevention Preferred — designed around any specified products or particular applications. Full design High Temperature Preferred — capabilities are offered including AutoCAD, Solidworks or other commonly used Ease of Maintenance Preferred — design and drawing programs. In addition to standard products, Assured Auto- Cost — More economical mation develops customized solutions for specific customer requirements.

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12 Valve World Americas | May 2018 • www.valve-world-americas.net