What is the Best Type of Flow Control Valve for Your ...

Jan. 12,

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What&#;s the Function of a Flow Control Valve?

Flow control valves can serve a number of different functions within a hydraulic flow system depending on the specific type that is used. One of the most common uses of a flow control valve is to regulate the speed of motors or cylinders within the system. This function is possible due to the capability of a flow control valve to affect the rate of energy transfer at any given point in a system by impacting the flow rate.

The ability to reduce or increase pressure in a system has a number of benefits. System operators can use a flow control valve to rapidly depressurize a serviceable hose and change fittings quickly. They are also used in many consumer applications such as showers, faucets, and lawn watering systems to easily reduce the amount of water consumed without impacting the overall system performance. Flow control valves are also known for their reliability and typically have a long operating lifetime as they are not prone to clogging due to their design.

Due to these flexible performance parameters, flow control valves have found wide use in applications across materials handling, food processing, and automated factory and warehouse equipment.

The most common valve types in flow control industries include:

Continue reading to learn more about each of these types of flow control valves and their functions.

1. Gate Valves

Gate valves are general service valves primarily used for on/off, non-throttling service. Specifically, gate valves are used in applications requiring a straight-line flow of fluid with minimum Gate valves are one type of control valve restriction that is desired. Gate valves operate when the user rotates the stem in a clockwise to close (CTC) motion or a clockwise to open (CTO) motion. The gate moves up or down on the threaded step when an operator moves the stem, which is why it is a multi-turn valve; the valve must turn several times for it to go from open to closed, and it is a slow operation that prevents water hammer effects. Engineers also utilize gate valves when minimum pressure loss and a free bore are required. Typical gate valves have no obstruction in the flow path, which results in a minimal loss of pressure.

Gate valves may be used for several fluids. Generally, gate valves are applicable for potable water, wastewater, and neutral liquids; in temperatures between -20 and 70 degrees Celsius; maximum 5 meter/second flow velocity; and up to 16 bar differential pressure. Gate valves also are applicable for gases with temperatures between -20 and 60 degrees Celsius; maximum 20 meter/second flow velocity; and up to 16 bar differential pressure.

There are two types of gate valves: parallel and wedge-shaped. Parallel gate valves feature a flat gate between two parallel seats. Wedge-shaped gate valves are comprised of two inclined seats and an inclined gate that is just a bit mismatched.

A linear motion valve, globe valves stop, start and regulate flow. Globe valves initiate closure via a plug featuring a flat or convex bottom that is lowered onto a horizontal seat situated in the center of the valve. When a user opens the valve, the plug raises to allow fluid to flow. Globe valves are used for on/off and throttling applications because the disk of the valve can be removed from the flow path completely or it can completely close the flow path. While this type of flow control valve does produce slightly higher pressure drops than straight-through valves like a gate, plug, and ball valves, they are applicable in situations where the pressure drop through the valve is not a controlling factor.

The practical size limit for globe valves is NPS 12 (DN 300) because the entire system pressure exerted on the disc transfers to the valve stem. It is possible, however, to have globe valves larger than NPS 12 (DN 300), and manufacturers and engineers have created and used globe valves up to NPS 48 (DN ).

A butterfly valve is operated by rotating a disk within the flow area and, due to this design, it does not have linear flow characteristics.  This makes these valves less precise than the more common flow control valve types above. For this reason, it can often be dismissed as a flow control valve choice even though it is useful in some applications that do not require a very high degree of accuracy. They are also a very affordable valve option, which makes it worthwhile to consider them in the right applications.

4. Plug Valves

Plug valves come in a variety of configurations and are operated by rotating a cylindrical or cone-shaped plug within the valve body to regulate the flow through a hollow area of the plug. For flow control applications the most common design is an eccentric plug valve, which uses a half plug to create a higher seating force with minimal friction as it is opened and closed. This has the advantage of greater shut-off capability which is ideal for flow control situations.  

Ball valves are commonly used in flow systems across numerous industries due to their low cost, durability, and excellent shutoff capability. Similar to butterfly valves, they are not as effective for flow control applications that require a high degree of accuracy and control. One of the reasons for this is that a ball valve requires a high degree of torque to open and close that preventing an operator from making fine adjustments. There is also a certain amount of &#;play&#; between the stem and the ball which can make finding specific flow rates difficult. For flow control applications where a ball valve is possible, such as filling a tank to a reasonable degree of accuracy, a trunnion or v-port ball valve design is usually the best choice.

Know the Best Valves Supplier

Founded in March , SUPCON is one of China's leading manufacturers and suppliers of automation and information technology, products, and solutions. Its automation products and solutions are applied in over 35 countries and regions worldwide. Zhejiang SUPCON Fluid Technology Co., Ltd. is an important member of SUPCON. Our core products, industrial process control valves (Globe Valve, Ball Valve, Eccentric Rotary Valve, and Butterfly Valve). If you are interested in our products, please feel free to contact us!

Whether you&#;re implementing a simple piping system to assist with transporting materials through your processes or designing a complex multi-step system full of automated controls, monitoring, and more, flow control is likely essential to your project.

Stainless steel valves are a common way of implementing flow control. However, with the various designs and types available, choosing the proper valve configuration is essential to ensure safe, long-lasting performance and avoid common pitfalls.

In this guide, we&#;ll look at two common valve designs used for flow control -- ball valves and needle valves -- and discuss characteristics of both that could make either of them the ideal pick for your process.

What is Flow Control?

Flow control is an essential part of most piping systems. Before discussing how valves play a role in flow control, it&#;s important to discuss the basics of how flow control works and any considerations you might make when implementing flow control solutions in your system.

Understanding this fundamental topic will better help you to choose the ideal valve design for your needs.

At its most basic, flow control is the process of limiting or regulating the flow of liquids, gases, or any other substance which is flowing through your piping system. 

Flow control may take place within main piping lines to help control pressure and ensure smooth operation. Flow control is also an essential element of many monitoring and instrumentation systems. It helps reduce the risk of damaging sensitive instruments and provides greater control over the monitoring process.

While pipe size, routing, and pressure can influence how substances flow through the system, this is often a static situation. You wouldn&#;t frequently change any of these factors as doing so would be cost and time-prohibitive in most cases.

Valves offer a flexible means of providing variable or dynamic flow control, meaning you can easily increase or decrease flow based on the state of the valve and the desired factors.

Types of Flow Control

Flow control occurs in one of two ways: on-off control or throttling control.

On-off control functions how it sounds. The valve is typically fully open or fully closed, creating an on or off state. While the valve might work in some middle state between on and off, there is typically no accurate way to set the exact flow rate. 

Operating an on-off valve in an intermediary state may also cause damage to the valve or reduce its service life.

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Throttling control valves allow for variable flow rates with precision adjustment. Overall accuracy and the degree of control provided will depend on the valve type chosen and system parameters. 

Comparing Ball Valves and Needle Valves

This relationship between on-off valves and throttling valves is at the heart of comparing ball valves with needle valves. 

If you only need on-off functionality, there&#;s a strong chance that ball valves will be an ideal fit.

On the other hand, ball valves cannot begin to compete with the regulating capabilities of a needle valve. Where fine control is essential, needle valves win out every time.

But let&#;s look deeper at both valve types to understand why this is the case and help you determine which is best suited to your needs.

Ball Valves Explored

Ball valves get their name from their design. At the center of the valve, you&#;ll find a ball with a channel through the center. By rotating the ball 90 degrees, you expose this channel to the flow path, creating a fully opened or fully closed state.

The short-throw actuation of a ball valve makes it an ideal option for flow control where full open or closed states are common or where fast state switching is required.

The design also allows for an exceptional air-tight seal. Since the valve seat wipes itself with each actuation and parts within the valve are few, cleaning and maintenance requirements are minimal.

For high-flow operations, choosing a full port design means there is little worry about pressure drops. 

These factors combine to make it a versatile, cost-effective option for flow control in a wide range of piping processes.

But the rapid actuation and minimal travel distance that make the valve ideal for some uses make it unsuitable for situations requiring precision flow control or extended throttling use.

Finally, when used with suspended solids or sticky textures, it is crucial to monitor valve surfaces for build-up and abrasion. Failure to keep surfaces clear can lead to leaking and eventual valve failure.

Common industries where you might find ball valves in use include:

• Agriculture

• Construction

• HVAC

• Manufacturing

• Mining

• Oil and Gas

Stainless steel ball valves can increase corrosion resistance for brewing, petroleum refining, and operations in marine or seawater environments.

Needle Valves Explored

Needle valves use a needle-shaped plunger to block the path of flow through the valve. A threaded, rotating stem adjustment mechanism allows for fine control of the plunger positioning.

An obvious benefit of this level of precision is the ability to make minute adjustments to flow rates. This also makes needle valves popular for use in valve manifolds, allowing for easy mixing of multiple processing lines.

Most needle valves are also highly resistant to both hot and cold temperatures while providing exceptional service life in high-pressure or high-vibration environments.

Finally, they create a high pressure drop when open, allowing for even easier metering and control of processes.

However, these perks come with tradeoffs -- many of which center on the screw-tap adjustment method.

Needle valves are not suitable for situations that require rapid changes in the valve&#;s state. Moving through the full range of motion of the needle-shaped plunger often requires numerous rotations of the screw handle.

The fact that the handle rotates so freely also can make it hard to gauge if the valve is open or closed based on appearance alone. 

The pressure drop and precision control also create a highly restricted flow. As such, needle valves are rarely ideal for high flow rate scenarios and processes.

Industries where you might find needle valves in use include:

• Chemical processing

• HVAC

• Manufacturing

• Petrochemicals

• Pharmaceuticals

• Wastewater treatment

Common use cases for needle valves include automatic combustion control systems, fluid power systems, gas bleeder lines, metering systems, sampling lines, and vacuum systems.

Summary

• Flow control is the process of limiting or regulating the flow of liquids, gases, or any other substance which is flowing through your piping system. 

• Ball valves are ideal for use in situations sensitive to flow rate changes or requiring quick valve actuation.

• Ball valves are designed for on-off operation. Avoid extended periods of throttled operation.

• Needle valves offer flexible flow control options with designs allowing on-off, throttling, and fine metering operation depending on your needs.

• The threaded shaft design allows for fine-grained control of the needle-shaped plunger. However, this comes at the cost of quick actuation and makes it difficult to gauge the valve&#;s open or closed state visually.

• Matching the valve&#;s flow control characteristics to your intended use case will ensure that the valve offers long-lasting, efficient operation.

Unified Alloys offers a range of instrumentation valves and fittings from leading brands including Parker A-Lok, Parker Hannifin, and Ham-Let to provide effective monitoring, flow control, and isolation of critical elements in your piping process. With more than four decades of experience in various industries across Canada and North America, our team of sales analysts can help highlight options relevant to your industry, process, or requirements. Contact us today to discuss options and find out more about our selection of high-quality stainless steel products.

References

• Mako Products: Ball Valves vs. Needle Valves in Flow Control

• University of Florida Engineering: Matching Valve Type to Function: A Tutorial in Valve Selection

• Metalphoto of Cincinnati: What is the Best Type of Flow Control Valve for Your Application? Learn about Gate Valves, Globe Valves and Other Flow Control Valves

• Wikipedia: Needle Valve

• Wikipedia: Ball Valve

• ScienceDirect: Flow Control Valve

• Hays Fluid Controls: Flow Control Valves: Everything You Need to Know

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