History and Operation of Automatic Testing of Flow Switches for Wet Systems
Written by Matthew S. Mueller, CET
Matthew Mueller entered the fire service in 1995 and spent twelve years as a firefighter/paramedic actively saving lives and property.
Mr. Mueller moved into the private life safety industry in 2007 and has dedicated the remainder of his career to ensuring that existing life safety systems that protect life and property are maintained and serviced. He is currently the Inspector Development Leader with USA Fire Protection, a subsidiary of APi Group, training the next generation of life safety inspectors.
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Recently, one of our inspection crews came upon a site that had installed a corrosion inhibiting system, and in their attempt to conserve the inhibiting agent, had also installed automated flow switch testing devices. Since this was our team’s first encounter with this type of device, I wanted to put together some of the history behind these devices, as well as their operation to share with others. It is important to note that these types of automated testing devices still require testing with the ITV at a minimum frequency of once every 3 years.
2011 – 2017
Beginning as far back as the 2011 Edition of NFPA 25, the Standard has made reference and allowance for the automated testing of some devices:
4.5.7 * Automated Testing.
(Reserved)
The annex continues:
A.4.5.7
Some devices, such as waterflow alarms, can be tested automatically. Some things to consider include the following:
- Automatic tests should be arranged to test the same functions as the required tests.
- Components and arrangements of automated tests should be listed for the purpose and designed so that failure of the testing equipment should not impair the operation of the system unless indicated by a trouble or supervisory signal in accordance with NFPA 72.
- Failure of a component or system to pass an automatic test should result in an audible trouble signal in accordance with NFPA 72.
- Not all tests required by NFPA 25 can be suitable for automatic testing.
- Periodic visual inspection including the use of video should be performed.
This was all that was mentioned regarding automated testing at that time. This allowance was unchanged until the 2017 Edition, which added some additional requirements for automated testing, including the requirement that water actually flowed passed the paddle of a flow switch. This was intended ensure there was water in the piping, and not just a paddle free floating in an empty space. The same edition included a requirement that “The testing shall discharge water where required in this standard” (NFPA 25, 4.6.6.4 2017 Ed.) and added the requirement for a minimum 3 year frequency on such discharge. At the time, there was only one type of approved automatic testing device, which consisted of a bypass line with a circulating pump, that took water from after the switch, and circulated it back past the paddle like depicted in the image:
This type of device, however, was expensive. It involved cutting out a section of pipe and replacing it with the entire contraption. Most models required AC power to be installed near the flow switch to operate the circulation pump as well. The manufacturer eventually came out with a version that utilized mechanical tees for installation on existing pipe, however it still was a costly option for any facility that was looking to reduce water flow for whatever reason they deemed important.
2020 – Now
Due to advancements in technology, as well as increased awareness of the corrosion that occurs anytime fresh water is introduced into the piping, the 2020 Edition removed the requirement to flow water at all during each semi-annual test, however it did require any device that performed automated testing be capable of verifying in one way or another that water was present at the flow switch. This allowed Potter Electric Signal Co. to develop the type of testing mechanism that our crew encountered in the field. This device uses an electronic retard, as well as a servo mechanism to electronically move the paddle to confirm alarm functioning, presence of water, and/or damage to the paddle itself. The automated test is initiated by a key switch located either near the flow switch itself, or it can be remotely located in a central location. More information from Potter’s website is below.
(Courtesy of Potter Electric Signal Company, LLC)
Here are links to both the Potter Electric Signal sales flyer, and datasheet if you are interested in more details on this device. One interesting item to note from the manufacturer’s instructions is that while they require an ITV be present in a system in which the device is installed, they do not mention the need to flow water. This opens the possibility that NFPA may consider removing the requirement to flow water at some point in a future edition.
Now that we’ve “broken the seal” so to speak with these types of automated devices, I anticipate more and more that they will show up in the wild.
