How to Choose a Regulator

How to Choose a Regulator to Meet Your Fluid System Needs

Wouter Pronk, Senior Field Engineer, Swagelok

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Pressure regulators play a crucial role in many industrial fluid and instrumentation systems, helping to maintain or control desired pressure and flow in response to system changes. It is important to select the right regulator to keep the system operating safely and as intended&#;the wrong choice can lead to inefficiency, poor performance, frequent troubleshooting, and potential safety hazards.

Knowing how to choose the right regulator requires an understanding of the different types of regulators, how they function, and how they can be applied to meet the needs of your system. Read on to learn more about pressure regulators, their functionality, and how to determine the best option for your system needs.

At its most basic, a pressure regulator is a mechanical device designed to control either upstream or downstream pressure in response to changes in the system. These changes might include fluctuations in flow, pressure, temperature, or other factors that may occur during regular system operation. The regulator&#;s job is to maintain your desired system pressure. Importantly, regulators are different than valves, which control system flow rates and do not self-adjust. Regulators control pressure, not flow, and are self-adjusting.

There are two primary types of regulators: pressure-reducing regulators and back-pressure regulators.

• Pressure-reducing regulators control pressure to the process by sensing the outlet pressure and controlling their own downstream pressure
• Back-pressure regulators control pressure from the process by sensing the inlet pressure and controlling pressure from upstream

Your ideal choice of regulator depends on your process requirements. For example, if you need to reduce pressure from a high-pressure source before system media reaches the main process, a pressure-reducing regulator will do the job. Back-pressure regulators, by contrast, can help control and maintain upstream pressure by releasing excess pressure if system conditions cause levels to become higher than desired. Used in the right context, each type can help you maintain the desired pressures throughout your system.

 

Pressure Reducing Regulator

Process

 

Back Pressure Regulator    

 

Pressure regulators contain three important components that help them regulate pressure:

• A control element, including a seat and poppet. The seat helps contain pressure and prevents fluid from leaking to the opposite side of the regulator when flow is closed. Together with the seat, the poppet completes the sealing process while a system is flowing.
• A sensing element, typically a diaphragm or piston. The sensing element allows the poppet to rise and fall in the seat, controlling inlet or outlet pressure.
• A loading element. Regulators may be spring-loaded or dome-loaded, depending on the application. The loading element applies a downward, balancing force on top of the diaphragm.

These elements work together to create the desired pressure control. The piston or diaphragm senses upstream (inlet) pressure and downstream (outlet) pressure. The sensing element then tries to find a balance with the set force from the loading element, which is adjusted by user via a handle or other turning mechanism. The sensing element will allow the poppet to either open or close from the seat. These elements work together to remain in balance and achieve set pressure. If one changes, some other force must also change to restore balance.

In pressure-reducing regulators, four different forces must be balanced, as shown in Figure 1. These include loading force (F1), inlet spring force (F2), outlet pressure force (F3), and inlet pressure force (F4). Total loading force must be equal to the combination of inlet spring force, outlet pressure force, and inlet pressure force.

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Back-pressure regulators function similarly. They must balance spring force (F1), inlet pressure force (F2), and outlet pressure force (F3), as shown in Figure 2. Here, the spring force must equal the combined force of the inlet pressure force and the outlet pressure force.

Making the Right Regulator Selection

With an understanding of how regulators function, you can better evaluate how to match different regulator characteristics to the needs of your system. Some of the most important characteristics to consider include the following:

System Flow

Installing a properly sized regulator is key to maintaining desired pressure. The correct size is generally determined by the rate of flow in your system&#;larger regulators can handle higher flows while effectively controlling pressure, while smaller regulators are effective for lower-flow velocities. Sizing of regulator components is important, too. For example, it is more effective to control lower-pressure applications with a larger diaphragm or piston. All components should be sized appropriately based on your system&#;s requirements.

System Pressure

Since the primary function of your regulator is to manage system pressures, it is critical to ensure that your selection is appropriately rated for maximum, minimum, and operating system pressures. Pressure control ranges are typically prominently featured in regulator product specifications given their importance to proper regulator selection.

System Temperature

Industrial processes can range in temperature, and you should be confident that your choice of regulator can stand up to the typical expected operating conditions. Environmental factors are a consideration, as well as fluid temperatures and factors such as the Joule-Thomson effect, which causes rapid cooling due to pressure drops.

Process Sensitivity

The sensitivity of your process plays a role in determining the best mode of control to choose in your regulators. As noted, most regulators are either spring-loaded or dome-loaded. Spring-loaded regulators are controlled by an operator turning an external knob, which controls the spring&#;s force on the sensing element. Dome-loaded regulators, by contrast, use fluid pressure from within the system to provide the set pressure on the sensing element. While spring-loaded regulators are more common and tend to be more familiar for operators, dome-loaded regulators can help improve precision in applications that require it and may benefit automated applications.

System Media

Material compatibility between all elements of your regulator and your system media is important for component longevity and avoiding downtime. While some natural deterioration of rubber and elastomer components is expected, certain system media may contribute to accelerated deterioration and premature regulator failure. You can learn more about chemical compatibility of elastomer seals and other regulator components in our materials science training courses.

Watch the video below to learn more about selecting a regulator.

With a deeper working knowledge of the types of pressure regulators available and how they function, you will be better equipped to make the right selection. Your regulator supplier should be able to provide you with sizing information, pressure and flow requirements, temperature ranges, and the correct mode of control for your system needs. You can start the selection process by comparing different regulators in different applications with our Regulator Flow Curve Generator, then following up with a local pressure control specialist for more information.

However, the specific needs of your system go well beyond the contents of this blog. Available training opportunities can help fluid system professionals gain a more thorough understanding of how the right regulator can help increase safety while improving efficiency.

In addition, your regulator supplier should be able to help guide you toward the correct choice by working to understand your system requirements. Our experienced specialists can provide that guidance, drawing upon well-rounded application knowledge and engineering support to arrive at the appropriate choice for your system. If you&#;re interested in optimizing regulator performance, contact our team of pressure control specialists to start a conversation.

Talk to Swagelok specialists about regulator selection

soob said:

The pressure also falls off suddenly when you start drawing air, right?

Click to expand...

Charles (in GA) said:

Not if your plumbing is sized correctly and you have a good regulator.

Charles

Click to expand...

It's not that simple. A regulator is trying to maintain a pressure directly downstream of the diaphragm / disc that opens to allow flow. So if you have the regulator set at 100 psi, the reg. opens to allow enough flow from the high pressure side of the unit to the low pressure side so that the regulator senses 100 psi. The pressure needs to drop below 100 psi before the regulator will crack open and allow flow, and it will only open enough to maintain your set pressure.

The pressure seen at the point of use will be less than 100 psi otherwise there is no driving force for movement of air (flow). As far as the regulator's flow capacity (the large CFM numbers you posted), that is the regulator's flow capacity when there is a maximum pressure difference between the high side and the low side. Essentially, it is the air flow rate measured when the upstream pressure is at the valve's max rated pressure, and there is no loss downstream of the valve (open to the atmosphere or some other controlled "test pressure"). This requires the regulator to be completely wide open and flowing it's maximum capacity. It is NOT the flow rate of the regulator when you have it running through a 50' hose, several fittings, and a tool, while maintaining a static pressure in the line.

The ideal regulator would be one that uses the pressure at the point of use (the tool) and maintains an upstream pressure so that the tool receives the intended air pressure required for the task. This would be considered a remote sensing or "pilot operated" regulator but they are impractical for use in a garage setting, so the next best thing would be a regulator that was as close to the point of use as possible, high flow / low restriction fittings, and a regulator set pressure that is set with appropriate margin above what is desired at the tool to accomodate for the losses in the system.

You can accomplish this with even a cheap regulator if you just measure the inlet pressure to the tool you are using while in use and adjust the set pressure on the regulator until you achieve the desired pressure at the tool. If you do it this way, the regulator's flow and setpoint become irrelevant as long as the reg is not choking the flow in the system. Staging several regulators may be desireable to not exceed any individual tool's max pressure.

It's not that simple. A regulator is trying to maintain a pressure directly downstream of the diaphragm / disc that opens to allow flow. So if you have the regulator set at 100 psi, the reg. opens to allow enough flow from the high pressure side of the unit to the low pressure side so that the regulator senses 100 psi. The pressure needs to drop below 100 psi before the regulator will crack open and allow flow, and it will only open enough to maintain your set pressure.The pressure seen at the point of use will be less than 100 psi otherwise there is no driving force for movement of air (flow). As far as the regulator's flow capacity (the large CFM numbers you posted), that is the regulator's flow capacity when there is a maximum pressure difference between the high side and the low side. Essentially, it is the air flow rate measured when the upstream pressure is at the valve's max rated pressure, and there is no loss downstream of the valve (open to the atmosphere or some other controlled "test pressure"). This requires the regulator to be completely wide open and flowing it's maximum capacity. It is NOT the flow rate of the regulator when you have it running through a 50' hose, several fittings, and a tool, while maintaining a static pressure in the line.The ideal regulator would be one that uses the pressure at the point of use (the tool) and maintains an upstream pressure so that the tool receives the intended air pressure required for the task. This would be considered a remote sensing or "pilot operated" regulator but they are impractical for use in a garage setting, so the next best thing would be a regulator that was as close to the point of use as possible, high flow / low restriction fittings, and a regulator set pressure that is set with appropriate margin above what is desired at the tool to accomodate for the losses in the system.You can accomplish this with even a cheap regulator if you just measure the inlet pressure to the tool you are using while in use and adjust the set pressure on the regulator until you achieve the desired pressure at the tool. If you do it this way, the regulator's flow and setpoint become irrelevant as long as the reg is not choking the flow in the system. Staging several regulators may be desireable to not exceed any individual tool's max pressure.

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