Choosing a Regulator
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. For these reasons, it is important to select and install pressure regulators that can meet the specific requirements of your application. But because there are many types of pressure regulators available, each with specific functionality, making the right choice is not always intuitive. In this white paper, we will outline a simplified, five-step process you can follow to help you evaluate your own pressure needs and make an optimized regulator selection.
The Importance of Proper Pressure Regulation
Industrial fluid system processes rely on precise fluid temperature, flow, and pressure settings to operate as intended. Many system components play a role in maintaining your required process conditions—and one of the most important is your pressure regulator.
With a wide variety of pressure regulators available, it is important to make the right choice to keep your process fluid or analytical system operating safely and as intended. The wrong choice can lead to inefficiency, poor performance, frequent troubleshooting, and safety hazards.
Your ability to choose the right regulator requires an understanding of different types of regulators, how they function, and how they can be applied to meet the needs of your system. With this knowledge, you will be better equipped to make an informed and effective selection.
To help you make a proper selection, we have developed a simplified five-step process that can be applied to most industrial fluid and analytical systems.
What Happens if the Wrong Regulator Has Been Installed?
Pressure regulators are designed to control system pressure while accounting for changes in system parameters. If the wrong regulator has been installed, you will likely see either an increase or decrease in pressure downstream.
Each of these instances can compromise the quality and safety of your process. An unwanted pressure drop can lead to system inefficiencies or process problems. An unwanted increase can potentially damage sensitive analytical equipment or, in the worst case, create a safety hazard for facility personnel.
Step 1: Understand Your Process Conditions
Selecting the right regulator starts with a good understanding of the pressures, temperatures, and flow of your system, along with the material compatibility of your chosen regulator with system media.
Composition of Process Fluid
Liquid and gas process fluids have different behaviors that may impact your regulator selection. For example, pressure regulators can handle more flow with a low-density gas than they can with a high-density gas. Details like this will dictate adjustments to regulator sizing (see Figure 1).
Pressure Ratings
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 regularly expected operating system pressures.
Pressure control ranges—shown by their corresponding flow curves—are typically featured in regulator product specifications, given their importance to proper regulator selection. Two important questions to ask before making your selection include:
1. How is your outlet pressure related to your anticipated flow?
2. Is the expectation that outlet pressure is the same at minimal, normal, and maximum flow?
Temperature
Your fluid system’s operating temperature can influence regulator selection and operation as well. Be sure you understand your expected operating temperatures, and how they are influenced by other environmental factors, when making your choice.
Certain types of system media will dramatically change in temperature when experiencing a pressure change, and the intended function of your regulator is to alter pressure. This phenomenon is called the Joule-Thomson effect. Compressed natural gas, for example, can drop from a temperature of 20ºC to –65ºC when experiencing pressure drop (see Figure 2). If you have not made the proper accommodations within your fluid system, such a dramatic change can cause your regulator to freeze, preventing the regulator from doing its job. In a situation like this, you may need to install supplemental heating elements to prevent freezing conditions. Tools are available to calculate Joule-Thomson effects within your system, and you can often work with your regulator supplier to predict the potential effects.
Material Compatibility
It is also critical to ensure that your system media will be compatible with all parts of your regulator. Incompatibility can be detrimental to component longevity and may contribute to excessive system downtime.
For example, some internal components of your regulator may be negatively affected by system media even though the exterior of your regulator may appear perfectly fine. While some natural deterioration of rubber and elastomer components is expected, certain system media may contribute to accelerated deterioration and premature regulator failure (see Figure 3).
Now, having evaluated all of your expected system conditions, you can move on to Step 2.
Step 2: Determine Your Control Needs
There are two primary types of regulators: pressure-reducing and back-pressure regulators. Your regulator choice will depend on what you need it to do.
Pressure-reducing regulators control pressure to the process by sensing the outlet pressure and controlling downstream pressure.
Back-pressure regulators control pressure from the process by sensing the inlet pressure and controlling pressure from upstream.
The best choice for your application depends on your process requirements. If you need to reduce pressure from a high-pressure source before system media reaches the main process, a pressure-reducing regulator will be the correct choice. 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 (see Figure 4).
Used in the right context, each type can help you maintain the desired pressures throughout your system.
How a Regulator Works
Once you determine what function you need your regulator to perform, it can be helpful to understand the elements that work together to provide functionality.
Regulators are made up of the following parts:
• A loading element, typically a spring or dome, depending on the needs of the application. The loading element applies a downward, balancing force on top of the diaphragm
• 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 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
These elements work together to create the desired pressure control. The piston or diaphragm senses downstream (outlet) pressure. The sensing element then finds 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 (see Figure 5). 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.
Back-pressure regulators function similarly. They must balance spring force (F1), inlet pressure force (F2), and outlet pressure force ( F3), as shown in Figure 6. Here, the spring force must equal the combined force of the inlet pressure force and the outlet pressure force.
Once you have determined which type of regulator is suited for your purposes, move on to Step 3.
Step 3: Understand Regulator Behavior
It is important to account for real-world factors once a regulator has been installed. Remember: A regulator is a mechanical device, with no electronic inputs for control or detection. This means we need to closely understand several natural regulator behaviors that commonly occur under field conditions.
Flow Curve
Flow curves represent real performance of a regulator for a given set of system parameters (see Figure 7). The vertical axis displays outlet pressure with the horizontal axis showing downstream flow rate. The flattest, or most horizontal, part of the curve indicates where a regulator will preserve consistent pressure—even with substantial changes in flow. The far right of the curve indicates where the regulator will be fully open and not able to preserve a consistent pressure. Within this area—between where the pressure begins to decline rapidly to where it approaches zero—the poppet is reaching the limit of its stroke, resulting in a loss of control. At this point, the regulator is acting less like a pressure control device and more like a restricting orifice.
Lock-up
Lock-up occurs at the very start of the flow curve and refers to a drop from the specific pressure just above the set point that is necessary to completely shut the regulator off and stop flow. When flow is turned on—when a valve is opened, for instance—the regulator’s flow curve will demonstrate a drop in pressure to the set point. Lock-up is a typical part of regulator behavior, but a good regulator design should help keep it to a minimum.
Droop
Droop is part of common regulator behavior and begins immediately following lock-up. Droop occurs when flow requirements cause the regulator’s poppet to open wider. The spring will extend until it gradually loses force, leading to pressure loss or droop. Droop is to be expected at certain flows with every regulator, but maintaining a flow curve that is as flat as possible before pressure drops off is ideal. This is why it is so important to select a regulator configuration that best matches the needs of your application.
Supply Pressure Effect (SPE)
SPE, also referred to as inlet dependency, is defined as the change in outlet pressure due to a change in inlet pressure (see Figure 8). Under this counterintuitive phenomenon, inlet and outlet pressure changes are inversely proportional to each other. If the inlet pressure decreases, there will be a corresponding outlet pressure increase. Conversely, if the inlet pressure increases, the outlet pressure decreases.
A regulator’s expected SPE is typically provided by the manufacturer. SPE is usually depicted as a ratio or percentage describing the change in outlet pressure per change in inlet pressure. For example, if a regulator is described as having a 1:100 or 1% SPE, for every 100 psi drop in inlet pressure, the outlet pressure will increase by 1 psi. The degree of outlet pressure variation for a regulator can be estimated with the formula:
A common method for reducing SPE, especially within higher-flow applications where poppets are generally larger, is to use a regulator with a balanced poppet design. SPE can also be mitigated with a dual-stage regulator system setup. The first regulator reduces high inlet pressure, causing the second regulator to experience minimal pressure drop. However, this measure is not necessary for every application. You should be able to consult with your regulator supplier to determine the best configuration for your specific needs.
Now that you understand these important regulator behaviors, it is time to move on to Step 4.
Step 4: Identify the Right Loading Element
As explained earlier, the loading element in your regulator applies a downward, balancing force on top of the sensing element in order to help control pressure. Two types of loading elements are the most common: spring-loaded and dome-loaded.
Spring-Loaded Regulator
Spring-loaded regulators are the most common and tend to be most familiar to operators. Here, a spring applies force on the sensing element—either a diaphragm or a piston—which moves the poppet either closer to or further away from the orifice, controlling the downstream pressure. They are a reliable option for many general-purpose applications.
• Is controlled by an operator turning an external knob, which controls the spring’s force on the sensing element
• Uses a spring to apply downward, balancing force on the regulator’s sensing element (typically a diaphragm or piston) to regulate pressure
• Is an effective choice for general-purpose applications
A pressure-reducing, spring-loaded regulator:
• Controls pressure to the process by sensing outlet pressure and controlling downstream pressure
• Helps reduce pressure from a high-pressure source
A back-pressure, spring-loaded regulator:
• Controls pressure from the process by sensing inlet pressure and controlling upstream pressure
• Can help control and maintain upstream pressure by releasing excess pressure
Dome-Loaded Regulator
Dome-loaded regulators enable more dynamic pressure control to provide more consistent pressure as flow demands vary. The loading force within this type of regulator is not controlled by a spring but by pressurized gas housed in a dome chamber. The gas flexes a diaphragm, which moves the poppet away from the orifice and controls the pressure. They offer several advantages, including increased accuracy, lower SPE, and lower droop.
• Has a dome element that applies a downward, balancing force on the regulator’s sensing element (typically a diaphragm or piston) to regulate pressure
• Uses fluid pressure from within the system to provide the set pressure on the sensing element
• Can provide improved precision in sensitive applications
A pressure-reducing, dome-loaded regulator:
• Controls pressure to the process by sensing outlet pressure and controlling downstream pressure
• Helps reduce pressure from a high-pressure source
A back-pressure, dome-loaded regulator:
• Controls pressure from the process by sensing inlet pressure and controlling upstream pressure
• Can help control and maintain upstream pressure by releasing excess pressure
Dome-loaded regulators can be incorporated into a number of different configurations to maintain a very flat flow curve. They can be coupled with pilot regulators and external feedback lines to achieve highly accurate adjustments when the application calls for it.
Remember: All regulators will exhibit some droop. Depending on your system, droop may be acceptable. But when it is critical to keep the pressure constant as flow changes, a more sophisticated regulator configuration can help.
By now, you should have a better sense of which type of regulator suits the needs of your system. You should also be better equipped to anticipate the effects of natural regulator behavior on system performance. And you should be able to identify the proper loading mechanism to achieve the results you need. Now, it is important to follow some established best practices once your regulator is in operation, which we will cover in Step 5.
Step 5: Follow Operational Best Practices
Finding success with your regulator involves not only proper selection, but also following maintenance best practices throughout the regulator’s life. Like any other piece of industrial equipment, your regulator will be subject to natural wear and tear over the course of its life. But good maintenance practices will help maximize its usefulness as well as the safety of your fluid system.
The most common issue resulting from poor maintenance practices is a phenomenon known as creep. Creep is not a natural behavior of pressure regulators and results when a contaminant creates a very fine gap between the regulator’s seat and poppet (see Figure 9). As a result, system media will unintentionally flow across the seat, resulting in unwanted pressure increases downstream. This situation can become problematic and dangerous if your downstream components are not rated for the pressures that are creeping across the seat.
Several measures should be taken to mitigate creep and its effects:
Filtration
A good filter upstream of your regulator can help ensure that your regulator will only see clean fluids flow through it. The filter should be regularly cleaned or, if needed, replaced to deliver proper filtration.
Relief Valves
A relief valve can be installed downstream of your regulator to help mitigate the effects if creep does occur.
Spare Parts
Maintaining spare part kits for your regulator can allow you to fix any issue quickly. If you do not have them on hand, significant downtime may result while you wait for replacements to arrive after problems occur.
Additional Resources
Following these steps can help guide you toward making the right choice of regulator. However, these considerations may not account for everything your unique system demands. Your regulator supplier should be able to help provide further guidance if questions arise.
Experienced Swagelok specialists can provide that guidance, drawing upon well-rounded application and engineering knowledge to recommend the appropriate choice for your system. We offer several resources you can use to optimize the performance of your fluid system, including:
• Regulator Essentials training, where we provide a deeper dive into how to improve safety and enhance system efficiency through regulator selection
• Swagelok® onsite services, where we bring our technical expertise, application experience, and industry knowledge to your facility to help make fluid system enhancements with the right components
• Swagelok Reference Point, which offers industrial professionals’ insights and analysis intended to help decrease downtime, increase efficiencies, troubleshoot issues, and maintain a safe workplace
• The Swagelok YouTube channel, where you will find practical videos on fluid system best practices
Interested in optimizing regulator performance? Contact our team of pressure control specialists to start a conversation.