Chapter 6 - Extinguishing Systems Flashcards
Most standpipe systems are what?
Wet.
What is the major player in standpipe systems?
Head pressure.
For a pump to push water upper riser it has to do what?
Overcome the weight of the water, The head pressure.
Until a riser is completely full of water the pressure in the riser is solely due to what?
The head pressure.
Unless the riser is full of water what pressurizes the system?
Head pressure alone.
The pump can only generate riser pressure in excess of the head pressure when what?
The riser is full of water.
In years leading up to 1993, NFPA standards required standpipe outlet pressures to be between what psi?
65 to 100 psi.
What is the most common PRD?
Orifice restrictors which are simple metal discs, or washers with holes drilled in them.
What are the two ways of restricting the amount of water flowing through the outlet?
Partially obstruct the standpipe outlets waterway.
Restrict the distance the valve can be opened.
PRD’s only restrict pressure when?
When water is flowing.
PRVs limit the discharge pressure when?
Under both flowing and static conditions.
Pressure regulating valves limit the discharge pressure how?
To a specific level regardless of how much pressure is pumped into them.
Pressure reducing valves reduce pressure how?
To a certain percentage of inlet pressure.
Which valves are more efficient and more expensive?
Pressure regulating valves.
Which valve is most often used in high pressure gas applications?
Pressure regulating valve.
PRVs used for standpipe outlets are almost always what type?
Pressure reducing valves.
PRVs used as inline valves are what type?
Pressure regulating valves.
What are two type of PRV stand pipe outlets?
Factory adjusted and field adjusted
What significant problem do PRVs present to firefighter safety?
Firefighters cannot significantly increase their outlet pressure by pumping into the system.
What are PRVs usually characterized by?
A wide bonnet beneath the valve wheel.
Some other anomaly.
Some field adjustment PRVs have visible calibration numbers that are often mistaken for what?
Outlet pressure settings.
What does not exist in buildings built since 1993?
PRDs.
After 1993 outlet pressures may be what PSI?
Anywhere from 65 to 175 psi.
What needs to be known about the outlet before connecting to it?
It’s flow pressure.
Standpipes are constantly pressurized by small electric pumps called what?
Jockey pumps.
How long will the pump continue to run for if the demand is discontinued?
10 minutes.
What is the pressure at which the system’s PRVs, PRDs and sprinkler piping are calibrated?
Churn pressure.
What is the biggest factor for the difference between the rated capacity pressure and the churn pressure between pumps?
Pump size.