Dry Pipe Sprinkler Systems | SonaVu™
To mitigate the risk of fire damage in commercial and industrial buildings, fire sprinkler systems are installed following NFPA 13 guidelines. An industrial fire sprinkler system instantly delivers water to the flame source the instant an alarm is tripped, dousing the flames and extinguishing any chance of damage to physical assets and building personnel. Fire sprinkler systems must be maintained and not classed as "run to failure". They are the most important fire and safety element in any strategic asset management plan.
In cold climates, where the threat of pipe freezing is real, dry pipe sprinkler systems connected to a valve isolated water source are used. In dry pipe sprinkler systems, piping and components are kept under pressurized gas – either compressed air or nitrogen – at a nominal pressure of 40PSI. The alarm system is tied to an automatically actuated valve mechanism which opens the flow of water while releasing the compressed gas. Although slower to react than wet systems, dry pipe sprinkler systems still provide adequate protection where conditions dictate their use.
These dry pipe sprinkler systems are found in unheated warehouses, storage facilities, outdoor parking lots and loading docks. Ceiling sprinklers are used in sports and public arenas, as well as commercial freezers.
Proper maintenance of dry pipe sprinkler systems is critical to ensure their reliability. Leaks are a major concern as pressure drops can trigger false alarms that cause unnecessary water damage. In nitrogen charged systems, the loss of gas is expensive. In compressed air charged systems the constant cycling of the compressor to satisfy the false demand of leaks is wasteful and contributes to undesirable greenhouse gas emissions, as well as wear and tear on the compressor.
Fire safety companies turn to ultrasound as a popular inspection method for detecting pressure leaks in dry pipe sprinkler systems. These instruments detect high frequency sound produced by the turbulence found at the leak source. As ultrasound is highly directional, identifying the location of a leak is easy. Detectors are not affected by other sounds. This allows for effective inspections even during noisy, peak production times.
The National Fire Protection Association (NFPA) asserts common sense rationale for the selection of dry pipe systems over wet systems in NFPA13: STANDARD FOR THE INSTALLATION OF SPRINKLER SYSTEMS:
8.16.4.1.1 Where any portion of a system is subject to freezing and the temperatures cannot be reliably maintained at or above 40°F (4°C), the system shall be installed as a dry pipe or pre-action system.
Dry pipe sprinkler systems come with added complexity that wet systems do not. They require a compressed gas (air or nitrogen) source and automated controls that tie the alarm system to an automatically actuated valve. Dry pipe fire sprinklers require more maintenance and this calls into question their reliability if maintenance and service lapses. One thing is certain, it is imperative that idle dry pipe sprinkler systems are free of compressed air leaks.
The Danger of System Leaks in Dry Pipe Sprinkler Systems
Leaking dry pipe sprinkler systems can cause damage to property and assets even if there is no fire. System pressure drops may trip the supply valve. All measures possible to maintain a leak-free dry pipe sprinkler system are paramount as a poorly maintained dry pipe sprinkler system could be the cause of catastrophic fire damage, physical injury, and death.
A differential pressure of five times the water supply maintains the system in a closed, dry state. The typical pressure inside the pipes is 40 PSI however it can be much higher. At 40 PSI, a pressure drop to 6 PSI must happen to open the water feed valve. That pressure drop must never be contributed to leaks or other poor maintenance techniques.
Many dry pipe sprinkler systems are equipped with a low-pressure switch that monitors any drop of 10 PSI below normal. A 10 PSI drop will not open the valve, but it will alert maintenance to investigate. Pressure drops are a reality most often caused by leaks, and sometimes caused by compressor failure.
NFPA 72: National Fire Alarm and Signalling Code (17.16.2.2.1) requires air pressure to be monitored so changes of 10 PSI below the nominal value are quickly detected.
Finding Dry Pipe Leaks
When dry pipe sprinkler system leaks reach a critical state, it is time to conduct a leak survey. Ultrasound is a well-known and established technology for finding compressed air leaks. The technology works fast, can detect leaks at a distance, and require little or no training on the part of the inspector.
Ultrasound works by hearing the turbulent flow prevalent at the leak site. As compressed air or nitrogen escapes through tiny orifices the air molecules are excited. You may be familiar with the hissing sound of air escaping through a compressed air line. This turbulence has peaks at 40kHz (ultrasonic) making ultrasound detectors the ideal instrument for finding leaks fast, in any environment.
The 40 PSI system pressure of most dry sprinkler apparatus’ is more than adequate to create turbulence for detection.
New Advances in Ultrasound Technology
SDT Ultrasound Solutions is a pioneer of ultrasound detection technology for close to five decades. The leadership from SDT has already contributed to massive energy savings, dramatic reduction in CO2 and other greenhouse gas emissions, and higher levels of safety for industry workers around the globe. Its latest product, SonaVu™, continues a three-generation legacy that has helped companies remain viable through a variety of economic climates.
SonaVu™ is a multi-frequency acoustic imaging camera that blends visual and auditory senses to faults that threaten the reliability and safety of dry pipe sprinkler systems. Its 112 highly sensitive sonic sensors work in concert with a precision optical camera. SonaVu™ brings the power of superhuman hearing to focus on its vibrant color screen.
The SonaVu™ sensor array is configured to work over long distances and large fields of detection. This is ideal for dry pipe sprinkler systems where leaks in overhead piping as far as 20 metres (65 feet) or more are common. Turbulence from the leaks are heard in the heterodyned audio output and displayed on the SonaVu™ acoustic imaging camera. A color-coded circular display indicates the intensity (loudness) of each leak. SonaVu™ inspectors can choose to document the leak location in images or with the industry leading 25 frames per second video capture feature.
After each dry pipe sprinkler system installation inspection, the captured images and video files are downloaded to PC for report generation. SonaVu™ is the perfect companion for dry pipe sprinkler system inspections and fire safety service providers should consider offering this leak detection to their clients.
Leaks in dry pipe sprinkler systems are hazardous and detract from its ability to extinguish fires. But they are also wasteful. Leaks cause the air compressor to cycle on continuously to maintain minimal pressure requirements. If nitrogen is used, then this exotic gas is wasted and so is your money.
Contact SDT to discover strategies that educate every stakeholder and empower them to take action. Fire sprinkler maintenance should not be taken for granted. There’s simply too much at stake.
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