September 2025
By Chris Jewell, Senior Product Manager Mooney™ Regulators and Becker™ Control Valves
The natural gas industry continues to navigate a time of unprecedented uncertainty. As many of the most seasoned experts step into retirement, a new generation of senior leaders begins to fill those roles. They face a changing landscape as regulatory and public scrutiny brings greater accountability for safety failures. At the same time, many utilities and regulatory agencies are considering their carbon footprint and looking for ways to reduce their impact on the environment.
While safety has always been the top priority for natural gas pipeline operators and distributors, several high-profile events have called our attention to blind spots that may have existed in earlier safety philosophies. Incidents like those in San Bruno, California, in 2010 and the Merrimack Valley in Massachusetts in 2018 have prompted a reevaluation of some of the most basic safety principles and priorities in the natural gas industry, particularly in the United States.
Metering and regulation station design is the first line of defense to protect pipeline and distribution systems from dangerous overpressure conditions. New products and technologies offer pipeline operators and utilities a wider range of options than ever before to improve the safety of their operations, especially when combined with many tried-and-true strategies to protect their workers and the public. A review of traditional strategies, as well as the new technologies available, is a worthwhile endeavor both for those new to the natural gas industry and for industry veterans with an eye toward continuous safety improvement.
Pressure regulation stations may typically be grouped into several categories according to the overpressure protection strategy they use, including:
- Single regulators
- Regulators with relief valves
- Monitor sets (both standby monitors and working monitor sets)
- Slam-shut valves, which may be integrated into stations with any of the above design philosophies
Single Regulator
The simplest and lowest-cost regulator station design consists of a single regulator. While single-regulator systems effectively and accurately deliver gas, these systems offer little to no overpressure protection.
Pressure regulators may be classified by failure type as either Fail Open or Fail Close. Fail Open regulators, such as Mooney™ Flowgrid™ regulators, are designed to fail in the open position when the control element is removed. Where a Fail Open regulator is used, a regulator failure will typically allow full, unregulated upstream pressure into the downstream line. Fail Close regulators, such as Mooney™ FlowMax™ and FlowMax™ HP regulators, are designed to fail to the closed position when the control element is removed. Fail Close regulators may offer some overpressure protection, as the regulator's intended failure mode will cut off the supply of gas downstream. However, the complexity of regulator failure modes means even a "Fail Close" regulator may allow an overpressure condition downstream. Regardless of whether the regulators used are Fail Open or Fail Close types, single-regulator systems should be used only where other overpressure mitigation strategies are in place.
Fig. 1: A station with a single regulator and no additional overpressure protection.
Regulator and Relief Valve
In Regulator and Relief Valve systems, a relief valve (which may be a back-pressure regulator or a more conventional, dedicated relief valve) is installed on a branch line downstream of the regulator. The regulator in this station type is typically a Fail Open regulator. In the event of a regulator failure, the relief valve prevents overpressure by opening to allow excess gas to escape into the branch line. The relief line then typically exhausts the relief gas to the atmosphere. This is an effective overpressure mitigation strategy but growing concern worldwide about atmospheric natural gas emissions limits how and where this arrangement may be used.
Emissions from relief valves may be limited by venting to a bleed-to-pressure system or into a holding tank, but special attention must be given to the exhaust capacity for this type of system.
In some cases, a small or “token” relief valve may be used to mitigate overpressure risk due to thermal loading, when the regulator must be opened during startup, or similar events where the overpressure risk can be avoided while relieving less than the full pipeline load. This strategy is effective for mitigating these types of overpressure risks, but does not account for the risk of overpressure due to a regulator failure or similar high-capacity event.
Fig. 2: A station with a regulator and relief valve.
Standby Monitor Systems
Two pilot-operated regulators may be installed in series in a monitor system. The most basic and most common of these is a standby monitor system (also called a monitor-active system), where one regulator serves as the active or working regulator, and the other regulator operates in standby mode under normal conditions, monitoring the downstream pressure and taking over control when a failure in the active regulator allows higher pressure to bleed downstream.
In a standby monitor configuration, the monitor may be installed either upstream or downstream of the working regulator. Placing the monitor downstream of the regulator of the working regulator may provide an advantage if the failure is caused by abrasive material in the fluid media - the upstream active regulator may act as a strainer to filter out damaging material before it can impact the downstream regulator, even after the upstream regulator has failed. Alternatively, installing the monitor upstream of the working regulator may limit any turbulence effects on the system, as turbulence from an upstream monitor will be minimal. Installing the working regulator downstream may also improve noise mitigation, especially if the pipeline size increases directly downstream of the regulator.
Fig. 3: A standby monitor station
Differing Failure Modes
Traditionally, station design philosophy has prioritized maintaining the gas supply to the consumer without interruption. This has especially been true in the United States. More recently, however, this philosophy has evolved to recognize the value in automatically shutting off the gas stream to prevent dangerous overpressure conditions. While the traditional approach calls for regulators that fail open, whether used as a worker or monitor, many operators now specify that the regulators must have opposite failure modes, typically pairing a Fail Open worker with a Fail Close monitor. While this can provide some overpressure protection, the complexity of regulator failure modes mentioned previously means that differing failure modes alone should not be relied on as a failsafe method to prevent overpressure conditions downstream.
Working Monitor Sets
By adding a second pilot to the upstream regulator in a monitor set, the station can be configured as a working monitor, also called a two-stage pressure cut with a monitor override. In a working monitor, the upstream regulator reduces the inlet pressure to some intermediate value between the required inlet and outlet pressure, with the second pilot monitoring the downstream pressure, and the downstream regulator makes the final cut to the required delivery pressure. This configuration has several advantages over a traditional standby monitor set, including:
- Distributing the pressure cut across both regulators reduces the load on both regulators. This can extend the life of the diaphragms and other seals in each regulator.
- In the event of a regulator failure, either regulator can take control and maintain the proper downstream pressure for the entire station. If the upstream regulator fails, the downstream regulator will continue to regulate downstream pressure normally. If the downstream regulator fails, the monitor pilot on the upstream regulator will engage, causing the upstream regulator to control the pressure required and the downstream sensing location. While not a complete additional layer of redundancy, this mutual monitoring provides additional insurance that a regulating station will continue to function as expected in the event of a regulator issue.
- With pressure transmitters or gauges on the interstage pressure, a working monitor system can provide some failure diagnostic information while the station remains online.
To take full advantage of the working monitor function, both regulators should be of the fail-open type, as a fail-close regulator in either position may prevent the other from assuming full control of the operation. Advantages of working monitor redundancy may be comparable to the protection offered by differing failure modes in standby monitor sets, especially considering the complexity of true regulator failure modes.
Fig. 4: A working monitor station
Slam-shut Valves
Emergency shut-down valves, called SSVs or slam-shuts, have grown in popularity recently. Originally introduced in the early 2000s, slam-shut valves enjoyed some initial adoption in Europe, Latin America, and other regions, but struggled at first to gain a foothold in North America due to the strong preference of operators and utilities not to interrupt the gas supply to the customer. This mindset began to change over the course of the 2010s, and slam-shuts are now specified as part of nearly every regulator station by many of the largest providers in North America. Their adoption is nearly universal worldwide.
Slam-shuts are typically paired with other overpressure protection methods to maintain a safe supply of gas to customers as long as possible before the slam-shut will finally engage at the last opportunity to prevent an overpressure situation downstream. Slam-shuts may be supplied as stand-alone devices or integrated into a regulator.
When integrated into a pressure regulator, the Slam-shut valve must have an independent seat or seal, separate from the primary regulator seal, to operate effectively. In many regions, slam-shut valves must also be tested to a higher standard of safety and quality than a typical regulator in order to be classified as a safety device.
A common configuration will consist of a working regulator and a monitor regulator with a slam-shut on the monitor, but the slam-shut may be installed on either the worker or monitor, or on either regulator in a working monitor set, and be equally effective. Many regulator stations now feature two parallel streams with a worker, monitor (or working monitor) and slam-shut on each stream. This allows robust protection from overpressure conditions, while still maintaining gas supply to the customer network in all but the most extreme circumstances. In these configurations, four total regulator failures must occur before the supply is completely shut off:
- When the worker on the primary line fails, the monitor on the primary line takes over.
- If the monitor on the primary line fails, the slam-shut on the primary line cuts off flow through the primary line, and the worker regulator on the auxiliary line engages to maintain the pressure downstream.
- If the worker on the auxiliary line fails, the monitor on the auxiliary line engages to maintain flow.
- Only when the primary worker, primary monitor, auxiliary worker, and auxiliary monitor fail does the auxiliary slam-shut engage to prevent a dangerous condition downstream by sealing off the gas supply.
Slam-shut valves may also prevent emissions into the atmosphere in the event of a line break or similar loss of containment downstream. If large enough, uncontrolled release of gas will result in a loss of pressure in the line downstream of the slam-shut. When equipped with under-pressure sensing capabilities, a slam-shut valve can detect this loss of pressure and seal the line to prevent any further escape of gas into the atmosphere.
Mooney™ Flowgrid™ regulators may be equipped with slam-shut valves from the factory, and most existing Flowgrid regulators may be retrofitted to include a slam-shut valve using a factory-supplied kit. Mooney™ Slam-shut valves may also be offered as a stand-alone device. For ease in access, installation, and maintenance, the Mooney™ Slam-shut controller on 2"-6" valves may be mounted on either side of the valve, and are available with a variety of trip options, including overpressure or under-pressure protection, dual-function controllers with both overpressure and under-pressure protection features, dual-function, dual sense controllers capable of reacting to either overpressure or under-pressure conditions in separate locations, remote manual trigger capabilities, and other options.
Fig. 5: A dual-run station with a worker and monitor with integrated Slam-shut valve on each run.
Noise Abatement
While we've focused primarily on protecting pipelines from overpressure situations, occupational safety and ergonomics are important factors to consider when designing regulating stations, as well. Noise generated by pressure regulators can pose a safety risk to personnel at the site, and a nuisance to neighboring properties. Common safety regulations restrict the allowable noise from a pressure regulator to 85 dBA when measured one meter from the pipeline center, and one meter downstream from the outlet of the working regulator. Some areas may impose more strict limits on locations such as a property line, especially in environmentally sensitive locations, or in urban areas where a regulating station may have neighbors close by.
Noise may be reduced at the station by optimizing the inlet and outlet pressures at the station, and the flow through the station. Additional noise mitigation efforts may include using working monitor setups or other multi-stage pressure reductions, or by installing noise-reducing trim in the regulators themselves. Noise-reducing trim in regulators typically works by routing the gas through a convoluted or tortuous path through the regulator, attenuating the noise by introducing smaller pressure cuts within the regulator itself. This often comes at the expense of capacity through the valve, with more aggressive noise mitigation having a greater impact on the regulator's capacity, so care should be taken to optimize noise considerations with the capacity requirements of the regulator.
Mooney™ Flowgrid™ and FlowMax™ HP regulators may be equipped with either single- or multiple-stage noise abatement trim options. Some regulators may be offered with single-stage noise attenuation options that have negligible impact on the flow capacity, while some multi-stage options may reduce noise up to 25 dBA and reduce the regulator's capacity by less than 25%.
Fig. 6: A cut-away view of a FlowMax HP regulator showing two-stage noise abatement trim.
Safety Up Front
In today's fast-moving energy market, operators must balance constantly shifting needs, including capacity, cost, reliability, and many other factors. Among all of these, safety must remain at the forefront. Proper design of metering and regulation stations with a safety mindset can help operators prevent safety concerns even before they arise. With the variety of options available, Mooney™ Regulators from Baker Hughes can help operators keep safety in front while optimizing performance across the board.
About Baker Hughes
Baker Hughes (NASDAQ: BKR) is an energy technology company that provides solutions for energy and industrial customers worldwide. Built on a century of experience and with operations in over 120 countries, our innovative technologies and services are taking energy forward – making it safer, cleaner and more efficient for people and the planet. Visit us at bakerhughes.com.