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When to install and Monitor Isolation Valves?

Updated: Jan 14, 2022

Isolation Valves in Domestic and Residential Fire Sprinkler Systems meeting the requirements of BS9251 are an interesting topic. With the introduction of monitoring of Isolation Valves coming in the revised BS9251:2020 due out later this year, FloWatch look at where isolation valves should be installed and what should be monitored?

What does the current British Standard Say?

Section 3.28 of BS9251:2014 defines a "Stop Valve" as "manually operated valve for controlling the flow of water into the sprinkler system pipework which is normally kept in the open position."

Section 5.11 Sub-section C and H of BS9251:2014 provides the following for Valves within a Sprinkler System:

"Valves should be suitable for sprinkler systems and be installed in accordance with the manufacturer’s instructions. The system should have the following (see Annex A):

b) a lockable full bore stop valve. The valve should normally be locked in the open position to prevent accidental or deliberate interruption of the water supply to the sprinkler system;

h) measures to prevent tampering with components of a sprinkler system that would isolate the water supply from the rest of the sprinkler system."

So from the British Standard we can establish that each system requires a lockable full bore stop valve which is locked in the open position to prevent accidental or deliberate interruption of the water supply. However, in reality where are Stop Valves being installed?

Stop Valves are required on each zone of the Sprinkler system. A Category 1 system, such as a single dwelling, is likely to have a single Stop Valve located on the point of entry of the Sprinkler Water Supply at the same point as the flow switch and test point. This is normally incorporated into a Residential Sprinkler Valve Set as per the image below:

However in Category 2 and 3 systems a valve set is installed per zone. In most instances this is one per floor, or alternatively in a block of apartments one per apartment. However, in Cat 2 and 3 type systems where the system is arranged as a zone per floor with one flow switch covering multiple apartments, we often see Lockable isolation valves outside each apartment.

Why are isolation valves installed outside each apartment??

When the system has been arranged as a floor per zone we see many Fire Sprinkler Contractors installing a separate lockable isolation valve outside the apartment. This allows an individual apartment to be isolated from the sprinkler system. This can sometimes be to aid the installation process. For example, to test the sprinkler system. If the contractor is installing sprinklers to say 10 apartments on each floor, the ideal testing solution would be to pipe all 10 and all corridor pipework and test the installation per zone from the riser. However, in the real world, sometimes time constraints on program do not allow the installation of all 10 apartments prior to testing due to follow on trades requiring systems tested so closing up of ceiling can commence. Therefore having an isolation valve outside the apartment allows the contractor to setup a test rig for each individual apartment and then shut off the stop valve once tested leaving the system under pressure while other trades work around the sprinkler system.

Another reason for installing isolation valves outside each apartment is that in the event of a sprinkler activation and repair work needing to be undertaken, just the individual apartment where the activation has occurred can be isolated leaving the rest of the system in full working order, whereas if there was a single isolation valve for that floor / zone, all apartments within that zone would be isolated.

Are there any disadvantages to installing multiple isolation valves after the Main Stop Valve?

The simple answer is yes. Isolation Valves are another point on the system that can be isolated and prevent the system from operating when required. Yes Stop valves are lockable and should be locked in the open position. However as explained in our recent Blog, the Effectiveness and Efficiency of Sprinkler Systems," Fire sprinkler systems have failed to operate when required in approximately 6 - 8% of all recorded and investigated fires within sprinkler protected buildings with the majorities of these failures down to the system being isolated. Therefore the less Stop Valves installed on a sprinkler system the less chance of part of the system being isolated. However a counter argument is that having multiple isolation valves helps to prevent accidental isolations as only the part of the system required to be isolated can be isolated meaning that rather than isolating 10 apartments in a single zone, only 1 apartment can be isolated if required.

Will this change in BS9251:2020?

BS9251:2020 has just been released for public comment therefore anything contained within the British Standard is subject to change once all the comments have been reviewed. However, in the recent issue for public comment it contained the following in regards to Stop Valves in section 5.15:

"Except for category 1 systems, all valves which control the flow of water to the system should be electrically monitored for the open position.

Stop valves should not be installed downstream of the control valve or pump set except for zone control valves which should be monitored for the open position. "

So two main changes that are introduced by BS9251:2020. All stop valves will require electrical monitoring and valves are discouraged except those on each zone. Therefore either each apartment should be treated as a zone and have a flow switch or there should be no isolation valves outside of each apartment where the floor is configured as a zone.

How will we electrically monitor Stop Valves?

Easy! By using a monitored isolation valve or monitored Valve set. These types of valves as indicated in the image below incorporate a pre-wired switch which will allow a signal to be sent to a monitoring device if the valve is not in the fully open position. Then all you will need to do is connect the valve set up to a Fire Sprinkler Monitoring system, such as the FloWatch 9251 Sprinkler Monitoring system, which will raise an alarm in the event that the valve is not in the fully open position.

The FloWatch 9251 can monitor both stand alone monitored isolation valves, or Monitored Valve sets consisting of the flow switch, monitored isolation valve, pressure gauge and test point.

FloWatch provide a complete design of the monitoring system and will bespoke this design to each project taking into consideration the configuration for that project. FloWatch can also provide monitoring of water levels within storage tanks and pump fault.

FloWatch will also provide advice on alarm configuration and where required can monitor flow switches on the FloWatch 9251 Monitoring System providing visual and audible alarms in the event of a system activation.

For more information please contact to arrange a demo.


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