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.

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

You can find Beswick&#;s available pressure regulators in our online catalog: Click Here for Pressure Regulators

Pressure Regulators are found in many common home and industrial applications. For example, pressure regulators are used in gas grills to regulate propane, in home heating furnaces to regulate natural gases, in medical and dental equipment to regulate oxygen and anesthesia gases, in pneumatic automation systems to regulate compressed air, in engines to regulate fuel and in fuel cells to regulate hydrogen. As this partial list demonstrates there are numerous applications for regulators yet, in each of them, the pressure regulator provides the same function. Pressure regulators reduce a supply (or inlet) pressure to a lower outlet pressure and work to maintain this outlet pressure despite fluctuations in the inlet pressure. The reduction of the inlet pressure to a lower outlet pressure is the key characteristic of pressure regulators.

When choosing a pressure regulator many factors must be considered. Important considerations include: operating pressure ranges for the inlet and outlet, flow requirements, the fluid (Is it a gas, a liquid, toxic, or flammable?), expected operating temperature range, material selection for the regulator components including seals, as well as size and weight constraints.

Materials used in pressure regulators

A wide range of materials are available to handle various fluids and operating environments. Common regulator component materials include brass, plastic, and aluminum. Various grades of stainless steel (such as 303, 304, and 316) are available too. Springs used inside the regulator are typically made of music wire (carbon steel) or stainless steel.

Brass is suited to most common applications and is usually economical. Aluminum is often specified when weight is a consideration. Plastic is considered when low cost is of primarily concern or a throw away item is required. Stainless Steels are often chosen for use with corrosive fluids, use in corrosive environments, when cleanliness of the fluid is a consideration or when the operating temperatures will be high.

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Equally important is the compatibility of the seal material with the fluid and with the operating temperature range. Buna-n is a typical seal material. Optional seals are offered by some manufacturers and these include: Fluorocarbon, EPDM, Silicone, and Perfluoroelastomer.  

Fluid Used (gas, liquid, toxic, or flammable)

The chemical properties of the fluid should be considered before determining the best materials for your application. Each fluid will have its own unique characteristics so care must be taken to select the appropriate body and seal materials that will come in contact with fluid. The parts of the regulator in contact with the fluid are known as the &#;wetted&#; components.

It is also important to determine if the fluid is flammable, toxic, explosive, or hazardous in nature. A non-relieving regulator is preferred for use with hazardous, explosive, or expensive gases because the design does not vent excessive downstream pressure into the atmosphere. In contrast to a non-relieving regulator, a relieving (also known as self-relieving) regulator is designed to vent excess downstream pressure to atmosphere. Typically there is a vent hole in the side of the regulator body for this purpose. In some special designs, the vent port can be threaded and any excess pressure can be vented from the regulator body through tubing and exhausted in a safe area. If this type of design is selected the excess fluid should be vented appropriately and in accordance to all safety regulations. 

Temperature

The materials selected for the pressure regulator not only need to be compatible with the fluid but also must be able to function properly at the expected operating temperature. The primary concern is whether or not the elastomer chosen will function properly throughout the expected temperature range. Additionally, the operating temperature may affect flow capacity and/or the spring rate in extreme applications.

Operating Pressures

The inlet and outlet pressures are important factors to consider before choosing the best regulator. Important questions to answer are: What is the range of fluctuation in the inlet pressure? What is the required outlet pressure? What is the allowable variation in outlet pressure?

Flow Requirements

What is the maximum flow rate that the application requires? How much does the flow rate vary? Porting requirements are also an important consideration.

Size & Weight

In many high technology applications space is limited and weight is a factor. Some manufactures specialize in miniature components and should be consulted if overall size and weight are critical.  Material selection, particularly the regulator body components, will impact weight. Also carefully consider the port (thread) sizes, adjustment styles, and mounting options as these will influence size and weight.

Pressure Regulators in Operation

A pressure regulator is comprised of three functional elements

1. ) A pressure reducing or restrictive element. Often this is a spring loaded poppet valve.
2. ) A sensing element.  Typically a diaphragm or piston.
3. ) A reference force element.  Most commonly a spring. 

In operation, the reference force generated by the spring opens the valve. The opening of the valve applies pressure to the sensing element which in turn closes the valve until it is open just enough to maintain the set pressure. The simplified schematic &#;Pressure Regulator Schematic&#; illustrates this force balance arrangement. (see below)

(1) Pressure Reducing Element (poppet valve)

Most commonly, regulators employ a spring loaded &#;poppet&#; valve as a restrictive element.   The poppet includes an elastomeric seal or, in some high pressure designs a thermoplastic seal, which is configured to make a seal on a valve seat.  When the spring force moves the seal away from the valve seat, fluid is allowed to flow from the inlet of the regulator to the outlet.  As the outlet pressure rises, the force generated by the sensing element resists the force of the spring and the valve is closed. These two forces reach a balance point at the set point of the pressure regulator. When the downstream pressure drops below the set-point, the spring pushes the poppet away from the valve seat and additional fluid is allowed to flow from the inlet to the outlet until the force balance is restored.

(2) Sensing Element (piston or diaphragm)

Piston style designs are often used when higher outlet pressures are required, when ruggedness is a concern or when the outlet pressure does not have to be held to a tight tolerance. Piston designs tend to be sluggish, as compared to diaphragm designs, because of the friction between the piston seal and the regulator body.

In low pressure applications, or when high accuracy is required, the diaphragm style is preferred.  Diaphragm regulators employ a thin disc shaped element which is used to sense pressure changes. They are usually made of an elastomer, however, thin convoluted metal is used in special applications.  Diaphragms essentially eliminate the friction inherent with piston style designs. Additionally, for a particular regulator size, it is often possible to provide a greater sensing area with a diaphragm design than would be feasible if a piston style design was employed.

(3) The Reference Force Element (spring)

The reference force element is usually a mechanical spring.  This spring exerts a force on the sensing element and acts to open the valve.  Most regulators are designed with an adjustment which allows the user to adjust the outlet pressure set-point by changing the force exerted by the reference spring.

Regulator Accuracy and Capacity

The accuracy of a pressure regulator is determined by charting outlet pressure versus flow rate.  The resulting graph shows the drop in outlet pressure as the flow rate increases. This phenomenon is known as droop. Pressure regulator accuracy is defined as how much droop the device exhibits over a range of flows; less droop equals greater accuracy. The pressure versus flow curves provided in the graph &#;Direct Acting Pressure Regulator Operating Map&#;, indicates the useful regulating capacity of the regulator.  When selecting a regulator, engineers should examine pressure versus flow curves to ensure the regulator can meet the performance requirements necessary for the proposed application.

Droop Definition

The term &#;droop&#; is used to describe the drop in the outlet pressure, below the original set-point, as flow increases. Droop can also be caused by significant changes in the inlet pressure (from the value when the regulator output was set). As the inlet pressure rises from the initial setting, the outlet pressure falls. Conversely, as the inlet pressure falls, the outlet pressure rises. As seen in the graph &#;Direct Acting Pressure Regulator Operating Map&#;, this effect is important to a user because it shows the useful regulating capacity of a regulator.

Orifice Size

Increasing the valve orifice can increase the flow capacity of the regulator. This may be beneficial if your design can accommodate a bigger regulator however be careful not to over specify. A regulator with an oversized valve, for the conditions of the intended application, will result in a greater sensitivity to fluctuating inlet pressures, and may cause excessive droop.

Lock Up Pressure

&#;Lockup pressure&#; is the pressure above the set-point that is required to completely shut the regulator valve off and insure that there is no flow.

Hysteresis

Hysteresis can occur in mechanical systems, such as pressure regulators, due to friction forces caused by springs and seals. Take a look at the graph and you will notice, for a given flow rate, that the outlet pressure will be higher with decreasing flow than it will be with increasing flow.

Single-Stage Regulator

Single-stage regulators are an excellent choice for relatively small reductions in pressure. For example, the air compressors used in most factories generate maximum pressures in the 100 to 150 psi range. This pressure is piped through the factory but is often reduced with a single-stage regulator to lower pressures (10 psi, 50 psi, 80 psi etc.) to operate automated machinery, test stands, machine tools, leak test equipment, linear actuators, and other devices. Single stage pressure regulators typically do not perform well with large swings in inlet pressure and/or flow rates.

Two-Stage (Dual Stage) Regulator

A two-stage pressure regulator is ideal for applications with large variations in the flow rate, significant fluctuations in the inlet pressure, or decreasing inlet pressure such as occurs with gas supplied from a small storage tank or gas cylinder.

With most single-stage regulator regulators, except those that use a pressure compensated design, a large drop in inlet pressure will cause a slight increase in outlet pressure.  This happens because the forces acting on the valve change, due to the large drop in pressure, from when the outlet pressure was initially set.  In a two-stage design the second stage will not be subjected to these large changes in inlet pressure, only the slight change from the outlet of the first stage.  This arrangement results in a stable outlet pressure from the second stage despite the significant changes in pressure supplied to the first stage.

Three-Stage Regulator

A three-stage regulator provides a stable outlet pressure similar to a two-stage regulator but with the added ability to handle a significantly higher maximum inlet pressure. For example, the Beswick PRD4HP series three-stage regulator is rated to handle an inlet pressure as high as 3,000 psi and it will provide a stable outlet pressure (in the 0 to 30 psi range) despite changes to the supply pressure.   A small and lightweight pressure regulator that can maintain a stable low output pressure despite an inlet pressure that will decrease over time from a high pressure is a critical component in many designs.  Examples include portable analytical instruments, hydrogen fuel cells, UAVs, and medical devices powered by high pressure gas supplied from a gas cartridge or storage cylinder.

Now that you have chosen the regulator that best suits your application it is important that the regulator is installed and adjusted properly to insure that it functions as intended.  

Most manufacturers recommend the installation of a filter upstream of the regulator (some regulators have a built-in filter) to prevent dirt and particulates from contaminating the valve seat.  Operation of a regulator without a filter could result in a leaking to the outlet port if the valve seat is contaminated with dirt or foreign material.   Regulated gases should be free from oils, greases, and other contaminants which could foul or damage the valve components or attack the regulator seals.  Many users are unaware that gases supplied in cylinders and small gas cartridges can contain traces of oils from the manufacturing process.   The presence of oil in the gas is often not apparent to the user and therefore this topic should be discussed with your gas supplier before you select the seal materials for your regulator.  Additionally, gasses should be free of excessive moisture. In high flow rate applications, icing of the regulator can occur if moisture is present.

If the pressure regulator will be used with oxygen, be aware that that oxygen requires specialized knowledge for safe system design. Oxygen compatible lubricants must be specified and extra cleaning, to remove traces of petroleum based cutting oils, is typically specified.  Make certain that you inform your regulator supplier that you plan to use the regulator in an oxygen application.

Do not connect regulators to a supply source with a maximum pressure greater than the rated inlet pressure of the regulator.  Pressure regulators are not intended to be used as shutoff devices.  When the regulator is not in use, the supply pressure should be turned off. 

Installation

STEP 1
Begin by connecting the pressure source to the inlet port and the regulated pressure line to the outlet port. If the ports are not marked, check with the manufacturer to avoid incorrect connections. In some designs, damage can occur to the internal components if the supply pressure is mistakenly supplied to the outlet port.

STEP 2
Before turning on the supply pressure to the regulator, back off the adjustment control knob to restrict flow through the regulator.  Gradually turn on the supply pressure so as not to &#;shock&#; the regulator with a sudden rush of pressurized fluid. NOTE: Avoid turning the adjustment screw all the way into the regulator because, in some regulator designs, the full supply pressure will be delivered to the outlet port.

STEP 3
Set the pressure regulator to the desired outlet pressure.  If the regulator is non-relieving, it will be easier to adjust the outlet pressure if fluid is flowing rather than &#;dead ended&#; (no flow).  If the measured outlet pressure exceeds the desired outlet pressure, vent the fluid from the downstream side of the regulator and lower the outlet pressure by turning the adjustment knob. Never vent fluid by loosening fittings, as injury may result.

With a relieving style regulator, excess pressure will be automatically vented to atmosphere from the downstream side of the regulator when the knob is rotated to lower the output setting. For this reason, do not use relieving style regulators with flammable or hazardous fluids.  Be sure the excess fluid is vented safely and in accordance with all local, state and federal regulations.

STEP 4
To obtain the desired outlet pressure, make the final adjustments by slowly increasing the pressure from below the desired set point. Setting the pressure from below the desired setting is preferred to setting it from above the desired setting.  If you overshoot the set point while setting the pressure regulator, back off the set pressure to a point below the set point.  Then, again, gradually increase the pressure to the desired set point.

STEP 5
Cycle the supply pressure on and off several times while monitoring the outlet pressure to confirm the regulator is consistently returning to the set point. Additionally, the outlet pressure should also be cycled on and off to ensure the pressure regulator returns to the desired set point.  Repeat the pressure setting sequence if the outlet pressure does not return to the desired setting. 

Beswick Engineering specializes in miniature liquid and pneumatic fittings, quick disconnects, valves and regulators. We have a team of degreed Application Engineers ready to assist you with your questions. Custom designs are available upon request. Submit your inquiry on our Contact Us page or click the Live Chat icon in the bottom right of your screen.

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