Detect and prioritise railway brake air leaks with the FLIR Si1-LD

A key milestone in this legacy was achieved in April 1869, when inventor George Westinghouse patented the fail-safe air brake system; a breakthrough that transformed rail safety and is still in widespread use today.

The fundamental principle behind Westinghouse’s air brake system is both simple and highly effective: it uses air pressure not only to apply the brakes but also to ensure they activate automatically in case of failure. Each carriage in a train has its own reservoir that is charged with compressed air. When the system is at full pressure, the brakes are released. Any drop in pressure, such as what would occur during a compressor failure or if cars become uncoupled, triggers the brakes to engage automatically. This mechanism ensures that trains come to a safe stop even under emergency conditions.

In modern rail systems, the locomotive’s compressor typically charges the main reservoir to between 125 and 140 psi (8.6 and 9.7 bar). The brake pipe, running the length of the train, is then pressurised, commonly at 90 psi for freight and 110 psi for passenger trains. When the train operator moves the brake handle to reduce this pressure, it signals each car to apply its brakes using the air stored in its reservoir.

Importantly, this design relies on maintaining a steady air pressure. A sudden drop, such as from a ruptured hose, will result in an emergency brake application. However, gradual leaks, while not triggering emergency protocols, can significantly reduce system efficiency. These small leaks place increased demand on the air compressor, potentially reducing the lifespan of mechanical components and driving up energy costs. Over time, they may indicate more serious faults within the braking system.

Identifying these subtle leaks amidst the ambient noise of a busy rail yard is a complex challenge. The acoustic signature of a small air leak is often drowned out by surrounding machinery, making conventional detection methods time-consuming and often unreliable.

Modern Leak Detection: Introducing the FLIR Si1-LD

To address this challenge, FLIR has developed the Si1-LD handheld acoustic camera, a highly sophisticated tool designed to detect compressed air leaks with precision, even in noisy environments typical of rail infrastructure. Using 96 ultra-sensitive microphones arranged in a compact array, the Si1-LD detects ultrasonic sound waves emitted by escaping air, translating them into visual representations that are displayed on a bright 5-inch HD screen.

The Si1-LD operates across a frequency range of 2 to 100 kHz, enabling it to locate even the smallest leaks. From a distance of just 2.5 meters, it can detect leaks as small as 0.01 litres per minute. For larger leaks, the detection range can extend to an impressive 130 meters allowing maintenance personnel to conduct inspections from a safe distance, even on moving or electrified stock.

One of the standout features of the Si1-LD is its ‘Band Pass Filtering’ technology. This advanced function allows users to isolate specific frequencies, effectively filtering out background noise and homing in on the frequencies emitted by air leaks. In environments such as rail maintenance depots or outdoor tracks with ambient industrial noise, this capability is essential for accurate diagnostics.

Prioritising Repairs for Maximum Efficiency

Upon completing a leak inspection, engineers often find multiple leaks of varying size and severity. In these cases, determining which to repair first can be critical for both safety and energy efficiency. The FLIR Si1-LD helps streamline this process with its onboard leak size quantification feature. This function estimates the size of each leak, allowing maintenance teams to prioritise repairs based on potential air loss and energy savings. Addressing the largest leaks first can significantly reduce operational inefficiencies.

Secure and Versatile Data Management

Data security and transferability are essential in modern industrial environments. Many rail organisations have restrictions on the use of USB devices for cybersecurity reasons. While wireless transmission may seem like a viable alternative, many rail facilities lack robust Wi-Fi coverage, or limit access for third-party devices.

To address this, the FLIR Si1-LD is compatible with an accessory data cable that enables direct transfer of inspection images and results to a PC or laptop, without the need for USB drives or Wi-Fi access. This ensures secure, flexible data handling, even in remote or high-security locations.

Usability and Practicality

A frequent concern among railway maintenance personnel is the complexity and learning curve associated with new diagnostic equipment. FLIR has listened to this feedback and developed the Si1-LD with simplicity and ease-of-use in mind. Its intuitive design enables users to conduct advanced acoustic inspections with minimal training. It’s a true point-and-shoot device: once aimed at the suspected leak area, the camera automatically identifies and displays leak locations, complete with size quantification.

To ensure durability in the field, the Si1-LD is housed in a robust casing and comes with a rugged hard-shell carry case. This provides excellent protection during transport and use, whether in the workshop or on remote rail routes.

The Bigger Picture

In the UK, the railway braking systems market was valued at approximately £373 million in 2024 and is forecast to grow at a compound annual growth rate (CAGR) of 3.3% through 2031. This growth is being driven by stringent safety regulations, a growing emphasis on predictive maintenance, and the increasing demand for energy-efficient transportation solutions.

Minimising air leaks in braking systems not only enhances safety and reliability but also supports environmental goals by reducing unnecessary energy consumption. With pressure mounting on the rail industry to cut emissions and improve efficiency, tools like the FLIR Si1-LD are becoming indispensable in the modern rail maintenance toolkit.

For a look at how acoustic imaging supports broader maintenance operations beyond braking systems, explore how the FLIR Si2-Pro is transforming maintenance shed efficiency.