Introducing water mist technology – Part 2

Water mist technology is still a relatively new concept in terms of fire suppression, yet it is proving to be an exciting development in the industry. As the industry evolves, so do the regulations, laws and requirements in order to improve safety and enable development. These can vary largely from country to country, and even region to region.

The way in which a water mist system operates is a similar mechanism to the traditional sprinkler system in that the nozzles are usually activated via a bulb which blows at a particular temperature allowing for the activation of the mist via a low-pressure water piping system.

Here we have a look at how some water mist nozzles are produced and installed – from arriving as a large ‘bar’ of metal, to becoming the efficient water mist nozzles we see installed in many new projects/developments across much of the globe today.

The metal arrives for cutting

Here at Dual Mist Ltd, Stainless Steel 304 is used for many parts as it is extremely durable and corrosion resistant in comparison to other similar metals. The body is machined out of Brass CZ121, which arrives as large bars of metal that are delivered to the warehouse in 3m lengths. This is then cut into two smaller parts ready to insert into the machine. Not all water mist companies have the ability to machine the parts they require in-house although it can prove very beneficial for cost and production purposes as we are about to see.

Machining

The steel is fed to a Nakamura WT150 CNC lathe. This high-performance Japanese machine tool is equipped with carbide tooling and high-pressure through coolant systems, with the twin-spindle and twin-turret making haste of the otherwise complicated parts. A Citizen M532 Sliding Head Lathe is used for the smaller parts.

A Citizen L12 also makes the filters with a capability of drilling 365 holes in 51 seconds, completely automated – this means it can turnover an incredible 4,000 filters in a weekend completely unmanned.

The brass heads are also de-burred on the machine, removing all sharp edges before being polished and sent for Electroless Nickel Plating. This provides a corrosion-proof coating to the brass, enabling it to become much more durable. All components are then inspected for dimensional accuracy before the assembly stage.

Assembly

There are many small parts of various shapes and sizes that make up the nozzle – In the DM4R nozzle, (as seen on the leak-testing pic) there are a total of 13 parts or ‘components’. These parts are then meticulously put together and assembled by the production team requiring a fair amount of labour before the final product is achieved. Various stages include tightening with specially adapted tools, pressing using a hand-press and using a particular ‘Locktite’ formula at some stages which is a threadlock that prevents fixings from coming loose during the operational lifetime of the product. The final stage of assembly is carefully loading the bulb and applying the correct load to it using a torque wrench.

The assembled nozzles are then placed on another machine in order to be labelled and uniquely identified using a serial number. At Dual Mist Ltd this is done on a Technifor Laser Engraver fitted with a 4th axis unit before they are ready to be placed through the various stages of testing.

Testing 

Cull Testing

Also known as bubble testing in layman’s terms, this test is to ensure no damage has occurred to the bulb during assembly and is a critical test for LPCB approval. The test involves using a high-powered microscope to measure the size of the bubble in each bulb before placing in warm water in order to shrink the size of the bubble to nothing. Once this is checked, the nozzles are then left to rest and return to room temperature before the bubble is measured once again in order to ensure it has returned to the original size within a small tolerance.

Leak Testing

Every nozzle is also stringently tested for leaks by applying 24-bar pressure for 1 hour and ensuring no water has escaped. It is rare for any leaks on the production line, but this is an extremely vital stage of the testing as leaks could occur if dirt is trapped within the seal face.

Activation Testing

On a monthly basis, random nozzles are also tested for activation by placing the nozzle on a pressure jig at various pressures and applying heat to the bulbs. The nozzles should all activate cleanly across the entire pressure range specified to that nozzle.

Approvals

At Dual Mist Ltd, these tests are not just to assure the quality of the production line but are also an important part of the LPCB Approval. These approvals enable customers to recognise that the products they are buying are made to the highest possible quality standard in the region. 

The disadvantage to this is that the Approval Testing system can be both costly and time-consuming – sometimes needing to be booked several months in advance and requiring years of hard work to achieve. 

The nozzles produced by Dual Mist have been put through their paces at BRE Global in terms of both fire testing and component/type approval.

Tamper proofing

In order to ensure that nobody is tempted to interfere with the grub screw holding the bulb, a small plastic bung is pressed into the grub screw. The pressure load setting on the bulb is then subsequently fixed.

The nozzles are then ready to be packaged and sent off for installation.

Installation

Rather than having to use the heavy and labour-intensive metal pipes often used in high-pressure systems, low-pressure water systems can use CPVC piping. This is a special type of fire-resistant plastic enabling quick installation. Instead of threading each pipe, a heated glue can be used to quickly build large pipe networks. These networks are approved to handle up to 12 bar pressure. The nozzles are screwed into a special pipe adaptor using a half-inch gas fitting.

An electric control panel is fitted for the system control along with pumps and a water tank, usually with a mains feed.

The system is tested, signed off and handed over to the client.

Conclusion

As we can see there are many stages to go from metal to nozzle head with each nozzle taking a significant effort by various professionals to finish to the approved standard. 

Not only do water mist nozzles require multiple stages of machining and assembling, they must also undergo a string of tests in order to be approved for installation. Once installed, there are even further tests undergone, sometimes by third-party organisations in order for the entire fire suppression system to finally be handed over to the client. 

Water mist technology assures safety, quality and assurance through the stringent testing that is required.

With the recent publication of water mist standards, particularly in Britain over recent years, building developers can now be assured that the quality required for water mist systems is now at an equivalent standard to other suppression systems.

For more information, go to www.dualmist.com