Hydraulic Calculations Flashcards
What is pressure?
How is it measured?
Pressure is a form of energy
Expressed in psi(pounds per square inch), or kPa(kilopascals)
What is elevation pressure?
How do you calculate it?
Height of water above a specific reference point
Calculated by 0.433 x feet in a change of height.
What is static pressure - non-flowing?
The pressure of a fluid on a body when the fluid is at rest
What is residual pressure-flowing?
Force exerted on the inside walls of a pipe when water (or any fluid) is flowing through it
Think of pressure as ___
energy
What is C value?
What are the C value of black steel and plastic piping?
Hazen Williams C Value Table
Lower C values mean more friction higher C values mean less friction.
Black steel (wet system) C value 120
Plastic pipe C value 150
What is laminar, or streamline flowing?
The water particles move in straight-line paths
What is turbulent flow?
the pattern is highly irregular, with a constant churning of the water
What is friction?
resistance to flow, between the fluid and the walls and the fluid particles themselves.
How do we overcome friction within a piping system?
Energy must be spent; this is called pressure.
What is total equivalent length?
Fitting pressure losses are represented as how much pressure would be lost if the water were to flow through a straight piece of pipe.
What are the three basics of hydraulic calculations?
- Sufficient water flow from every sprinkler if they were all to open.
- Water supply must be capable of developing enough flow, at the correct pressure.
- minimize cost.
The procedure for a hydraulically calculated system:
- Hazard classification
- Spacing of sprinklers
- Piping arrangement.
- Amount of water needed at each sprinkler
- Determine number and location of the most demanding sprinklers.
- Start at most remote location and work backwards towards the water supply, calculating the flow and pressures necessary to make sure that each sprinkler head has sufficient water flow.
- Compare demand calculated with water supply
What are the three methods used to determine how much water is needed at every sprinkler head?
- Density/Area method
- Specially listed sprinklers. Contains minimum flow requirements.
- Following NFPA 13 tables or sections. This method is applied to the large drop sprinklers, the EFSR sprinkler and was originally applied to residential sprinklers.
Most residential sprinklers fall under the specially listed category.
Q = K√P
Q=the flow necessary from the sprinkler in GPM
k= the k factor for the sprinkler
P = the pressure necessary at the sprinkler in PSI
N= Ac/As
N = the total number of sprinklers to calculate Ac = the area from the density/area curves As = the area of coverage for the typical sprinklers in the system
NBL= 1.2(square root of area) / s
NBL= number of sprinklers to calculate on a branch line area= the value selected from the density/area curves S = distance between sprinklers on the branch line
Where is the most remote/ most demanding sprinkler head usually located?
It’s usually the first head on the furthest away branch line from the water supply.
The physics of water flowing through the piping actually make the sprinklers closer to the water supply more demanding because they are exposed to a higher pressure and will therefore discharge more water if they open
It is important to make sure that the actual ___ area covered by the sprinklers is at least equal to the ___ area.
the sum of the sprinkler head coverage has to exceed the area of the actual floor area.
Area adjustments may be necessary depending on the following systems/situations.:
- dry-pipe sprinkler system
- double interlock pre-action systems
- high temperate sprinklers(extra hazard occupancies only)
- sloped ceilings
- un-sprinklered combustible concealed spaces.
For dry-pipe sprinkler systems, the design area selected from the density/area curves is required to be increased by 30% due to ___
time delay- to account for the delay of getting the water to the sprinklers. The fire could grow 30% during that time.
Double interlock pre-action sprinkler systems require the same area adjustments as a ___ _____ system
dry pipe system. For the same reasons.
High temperate sprinklers in extra hazard occupancies the design area can actually be decreased by ___% but never below the minimum threshold of ____ sqft
25% but never below the threshold 2000 sqft.
1) fewer sprinklers tend to open in extra hazard fires when high temperature sprinklers heads are used.
2) the heat affects just the heads at the fire location
3) higher densities of water
Quick response sprinklers in light and ordinary hazard occupancies the design area can be reduced by a figure between __% and __% depending on the ceiling height.
What conditions need to be met?
___ pipe system only
___ ft maximum ceiling height
No ____ ceiling pockets
Although the design area can be less than ___ sqft it can be less than _ sprinklers.
Can be reduced by 25-40% only if the following conditions are met:
1) It is wet pipe system only
2) 20 feet maximum ceiling height
3) no unprotected ceiling pockets
4) design area cannot be less 1500 sqft and no less than 5 sprinklers.