Just like the Fire dept must hook up a fire engine to a hydrant at a working fire for adequate water flow .
|Controller for Fire Pump made by Firetrol|
|Typical diesel fire pump|
|Flow switch showing internal components Manufactured by System Sensor|
|Flow switch with cover in place|
But that is where the problem starts recently on a job we ran into to a problem with a new generation variable speed pump.
In older systems the pumps where one speed period and you had a steady continual flow which was not always a good thing some times you could hit a situation where you had too much or too little flow depending on how many heads activated and how much water was available . To solve this problem they recently developed variable speed pumps which match the flow rate to the volume of water needed. But when we went to test recently a brand new multiple wet and dry pipe system in an extremely large distribution warehouse the first Wet Stand Pipe activated as designed . when the inspectors test port was opened at the end of the piping system which is designed to simulate one head activating the pump came on with in 5 seconds and started providing flow then with in 30 seconds the fire alarm activated ,perfect test. Then on to Wet pipe 2# the pump comes on and a minute and half goes by no fire alarm activation? OK whats going on we know this flow switch was working because when the pipes where first filled it went into alarm. So after checking several things we found out that on pipe 2# the small flapper handle in the flow switch was not staying in position
as the first test and was modulating up and down with the pump as it went up and down in speed. the problem this wet pipe 2# was much smaller piping set up than other system and was allowing more variation in the pump speed. To get around the problem we set the retard mechanism to 10 seconds and the alarm sounded the Fire Marshal was worried and rightly so .What if off only one head went off on a weekend when facility is closed and switch did not sense it ? The Sprinkler Tech ,Fire Marshal and myself running and witnessing the test have never in 30+ years we each have in experience in the field run across this before but now that its a possible problem it needs to be addressed and possibly a new switch and standards put in place to prevent just such a scenario from happening.
While variable speed pumps make sense there could be very major water damage problems should a sprinkler head fail and activate start flooding the building and fire alarm not sense it and while any time the pump runs it starts a supervisory signal to central station it could be misinterpreted as just a pump test and just logged instead of some one getting a call to find out whats going on. UL and NFPA need to be looking into this matter but we will see as usual how long it takes for them to respond to a very dangerous potential happening . By the way I now they read this blog.
Once again we have a situation where we bring new technology on board with out thinking thru all its ramifications
|Wet Pipes 1# 2# at far left Pre -Action Dry Pipes 1#2# at Right|