Pressure relief valves (PRVs) are mechanical devices by design, protecting equipment and personnel fully independently of the process control system. As such, they provide no inherent feedback, but fortunately there are many accessories that empower plant personnel to monitor PRV operation.

My article on pages 69-72 of the November 2026 issue of Hydrocarbon Engineering, titled “Improving performance amid pressure,” discusses these devices, and it highlights cases where PRV monitoring has significantly improved plant operations and reduced emissions.

Lack of PRV visibility

PRVs use mechanical methods to sense process conditions and open as necessary to prevent internal pressure from exceeding equipment limits. Without monitoring systems in place, their operation may go completely unnoticed by plant personnel.

Venting can result in product loss, excess emissions, and/or process control issues. Hazardous releases usually must be reported, but accurately determining the release quantity may be difficult or impossible without the ability to monitor the PRV. Moreover, leaks or cracks may go unnoticed for weeks or months and can compromise the ability of the PRV to perform its protective role.

Monitoring accessories provide operational visibility, empowering personnel to respond promptly to leakage and relief events.

PRV monitoring devices

TopWorx GO proximity switches detect the open/close status of Anderson Greenwood 96A series vacuum breakers on LNG storage tanks

The simplest way to detect PRV lifting is by adding a limit switch on the bonnet of the PRV. The switch provides an immediate and accurate indication of when the PRV lifts and reseats. However, limit switches cannot detect a leaking PRV disc or a failed bellows, and this method leads to emissions overreporting because it must be assumed that the PRV is fully lifted for the duration of the relief event.

In contrast, position transmitters measure proportional lift using a linkageless sensor to detect the spindle position. This allows sites to accurately determine the released vapor quantity, and it can also help identify simmering and chattering.

An acoustic level/temperature transmitter installed on the PRV discharge can detect even low-level seat leakage, and in bellows PRV applications, a pressure transmitter can help identify bellows damage.

PRV monitoring successes

In pilot-operated PRV applications, a Rosemount 3051 differential pressure transmitter provides a very accurate indication of valve lift, allowing plant personnel to accurately calculate the release quantity.

At one steam plant, when a PRV lifted it would dramatically impact boiler level control, requiring prompt intervention to avoid a boiler trip. There was no PRV monitoring system, so operators would be unaware of any issue until the boiler level alarm triggered. After adding a limit switch to the steam PRV spindle, operators were informed immediately when the PRV lifted, allowing them to intervene before the boiler reached an alarm state.

At an LNG storage facility, large vacuum relief devices protect tanks from implosion.

A vacuum relief device lift event in this application indicates there could be an interspace pressure imbalance, potentially creating a purging gas control issue or other hazard. As a result, it is imperative that the operators know when a vacuum relief device lifts and how long it remains open.

After experiencing false alarms and failures with cheap limit switches, the facility upgraded to fully sealed proximity switches. The new switches proved far more reliable, significantly improving operations and reducing maintenance hours.

To address frequent PRV bellows failures in a high-temperature, corrosive process, a chemical plant installed a high temperature-rated Monel bellows PRV with a mounted pressure transmitter. The solution provided an extended service life and immediately indicated when bellows damage occurred.

Improved visibility, improved operations

PRV monitoring technologies have varying price points and capabilities, so different applications require different solutions. Process manufacturers can use the information these devices provide to respond more quickly to lift events and to better understand and address their causes, resulting in improved plant performance and reduced emissions.