Master Stream Operations: Bringing In the Big Guns
So what pump discharge pressure should be listed on the pump chart? The answer is simple. The pump operator should plan on throttling up to the maximum allowed figure of one of the above listed three categories (whichever comes first) unless something stops him. Does this mean that every time a deck gun operation is placed into service the pump discharge pressure needs to be maxed out? No. The pump discharge pressure is the number that the pump operator will try to reach unless something stops him. Some of the things that may stop the operation from going to maximum pressure are:
1-run out of water
2-run out of throttle
3-run out of RPMs
4-the stream accomplishes its goal
5-other rules set by the department
6-orders from the company officer
1250 GPM Master Stream Appliance
The three most common manufacturers of the 1250 GPM master stream appliances for the municipal fire service are;; Task Force Tips, Akron Brass and Elkhart Brass. Listed below are the specs for each of the three brands of these appliances in the fixed mode.
|Task Force Tips||200 PSI inlet pressure||1250 GPM max flow||631 NR|
|Akron Brass||200 PSI inlet pressure||1250 GPM max flow||631 NR|
|Elkhart Brass||200 PSI inlet pressure||1250 GPM max flow||631 NR|
When using the nozzle of choice the maximum allowed pump discharge pressure will be determined from one of the three the categories mentioned above.
Smooth Bore Nozzles
For smooth bore tips ranging from 1-1/8" to 1-1/2" the inlet pressure of the master stream appliance now becomes the required pump discharge pressure, the pressure the pump operator will be trying for. It is the first of the categories reached. The flow and nozzle reaction at the maximum allowed inlet pressures are below there respective limits.
Again those numbers are; TFT-200 PSI, Akron-200 PSI, Elkhart-200 PSI. The 1-3/4" tip can fall under the maximum allowed inlet pressure category or the nozzle reaction category. Design of the appliance and discharge plumbing will dictate which category comes first. The 2" tip will most likely be stopped by the limitation of the nozzle reaction reaching rated flow of 1188 GPM at a 100 PSI nozzle pressure with a 628 lbs nozzle reaction.
Flow tests should be done to determine all pump discharge pressures for smooth bore nozzles listed on the pump chart.
This concept for developing the pump discharge pressures can also apply to fixed gallonage, selectable gallonage, and automatic combination nozzles. Again flow tests will determine which of the three limitations will ultimately set the maximum pump discharge pressure for the operation. It may very well be the same pressure as the smooth bore tip operation. If not, a separate pressure on the pump chart for the combination nozzle will need to be listed.