Master Stream Operations: Bringing In the Big Guns
2000 GPM master stream operations
Now let’s talk about low flow operations. Picture a large fire that has totally consumed the structure ending up with a large pile of burning rubble left to be overhauled? This is where the digging power of a high velocity stream can really have a positive effect. The following smooth bore tip sizes and corresponding nozzle pressures and flows have been successfully used in this type of operation. One point to remember is that the goal in this type of operation is to produce velocity, not high flows.
|1-1/8" tip up to 180 PSI NP||=||
1-1/4" tip up to 180 PSI NP
1-3/8" tip up to 180 PSI NP
This deck gun is using high pressure smooth bore tip operation
Working a brush fire from a fixed master stream appliance is a heck of a lot easier than pulling hose. When possible, a fixed master stream can make very large sweeps in burn areas with the above mentioned high pressure stream operations. In fact, the 1-1/8" tip application will more likely be the tip of choice for this operation.
Now let’s talk about blitz attack operations from the booster tank. NFPA requirements for tank to pump flow delivery capabilities state that a minimum of 500 GPM shall be delivered. Unless a department has specified their apparatus to deliver more, this is the flow rate capability they will have.
A very high percentage of fire apparatus have the 500 GPM maximum capability. A popular tip application for a 500 GPM Blitz attack is the 1-1/4" tip @ 115 PSI NP which delivers a flow of 495 GPM. This moderately high nozzle pressure produces a hard-hitting stream capable of penetrating deep into the fire which could very well be needed in an offensive Blitz attack operation. The 100 PSI automatic nozzle will also work well.
Calculating the Pump Discharge Pressures
The pump discharge pressure for specific flows should be developed from flow tests using a flow meter and a handheld pitot gauge. Now the dilemma. With the big flow range capability that a master stream has, what pump discharge pressures should be listed on the pump chart?
To list all would make for a cluttered pump chart. Before giving the magic numbers, it is important to have a thorough understanding of the maximum flow limitations for the appliance itself, for it is these limiting factors that will be used to establish the pump discharge pressures. There are three specific categories that have maximum allowed limitations. They are:
1) Manufacturers have a maximum allowed inlet pressure for their appliance. The inlet pressure is at the point where the appliance is connected to the discharge plumbing of the apparatus. Any pressure higher than that number is unacceptable.
2) Manufacturers have a maximum allowed flow for their appliances. Any flow higher than this is unacceptable.
3) Manufacturers have a maximum allowed nozzle reaction for their appliance. Any nozzle reaction higher than this is unacceptable. A flow of 1250 GPM with a nozzle pressure of 100 PSI seems to be the common denominator for all makes of the 1250 GPM appliance. A flow of 2000 GPM with a 100 PSI nozzle pressure is the common number for the 2000 GPM appliance.