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.
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.
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.
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.
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 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 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.
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.
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