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14 Cards in this Set
- Front
- Back
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5 principles of friction loss - DRISL |
Diameter - friction loss increases directly with decrease in hose diameter Roughness - increased friction loss with increased toughness of hose interior Independent of pressure- if flow rate of running line is constant, friction loss will the same if pressure is 1000kPa or 10000kPa SQUARE - Square of the flow rate (halve flow rate, quarter friction loss). Faster water is flowing, more resistance and friction loss occurs Length - friction loss increases in longer hoses |
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6 Principles of pressure in fluid in a container - “PRODDS” |
Perpendicular Rest Outside Depth Density Shape |
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Formula for pressure |
P= force x area |
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What is the function of the branch? |
The branch converts the energy of water pressure into kinetic energy Branch has a shut of valve so can close down the branch if needed The larger the nozzle diameter the less velocity of water from the nozzle.(at constant flow rate) The smaller the nozzle diameter the higher the volume (at constant flow rate) Velocity of water from nozzle varies inversely with the nozzle size |
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Formula for rate of discharge through branch nozzle |
L/min = 2/3 x nozzle diameter squared x square root of (Px100) nozzle diameter pressure at nozzle |
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Optimal nozzle pressure |
For fog branch- 700kPa - this is the maximum pressure that can be delivered to nozzle from the pump For foam branch - 550kPa Advantages of optimal nozzle pressure: Produces best jet Longer reach Better striking power Larger volume of water Avoid excessive turbulence and jet reaction |
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What is a jet reaction? |
Force Water projected from the branch causes equal and opposite reaction causing hose and branch to recoil in direction opposite to the flow. Can throw branch operator backwards if they are not prepared Also contributes to fatigue of branch operator after period of time counteracting jet reaction force. |
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Dangers of jet reaction (2) |
Injury from loss of balance / falling over / fatigue Risk of an uncontrolled branch and potential for serious injury |
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Atmospheric pressure |
100kPa @ sea level Pressure in the air from the atmosphere Used to “lift” water from static source up to appliance pump Pump (primer) removes air from suction hose - reduces internal hose pressure, atmospheric pressure lifts water up into the hose. Atmospheric pressure 100kPa in theory can create a head of 10m . In practice 7.5m head (Max 8m). This is due to energy lost when water enters the pump and in moving water through hose and strainers. |
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Lift efficiency |
The greater the vertical lift to be overcome, the less water delivered to the incident - Pump output L/minute reduces as the vertical lift distance (m) increase |
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Lift efficiency |
The greater the vertical lift to be overcome, the less water delivered to the incident - Pump output L/minute reduces as the vertical lift distance (m) increase |
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Negative pressure and suction lift |
Static water supply is at an air pressure below that of the pump Negative air pressure is not strictly negative, just lower than normal atmospheric pressure |
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Gravity |
Force exerted by earths gravity: mass x acceleration due to gravity |
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What influences jet reaction? |
Jet reactions proportional to flow rate and pressure (jet reaction= flow rate x square root of pressure) More water (flow) = more jet reaction More pressure = more jet reaction |
