ESCONDIDO FIRE DEPT TRAINING MANUAL Section DRIVER OPERATOR Page 1 of 14 Hydraulics Revised

Transcription

1 DRIVER OPERATOR Page 1 of 14 HYDRAULICS Hydraulics applied in the dynamic fire ground environment is an art that comes with study and experience. The following describes the factors that must be mastered to accomplish this. Good Engineers are those that can apply the science of hydraulics to the needs of an incident. DEFINITIONS AL Appliance Loss in PSI Appliance loss is the amount of energy used up in the turbulence of the water flowing through an appliance. C D EF Capacity in Gallons Diameter Equivalent Flow The amount of water flowing through a hose that is not a 2-1/2" hose which creates the same friction loss rate as that created in 2-1/2" hose. F FLR Factor Friction Loss Rate The amount of energy or pounds pressure lost due to the turbulence of water in contact with the lining of a hose. It is measured in 100' lengths of 2-1/2" hose. GG Gravity Gain The amount of pressure gained due to the energy gained when water drops. GL Gravity Loss The amount of pressure lost when pushing water up.

2 DRIVER OPERATOR Page 2 of 14 GPM H Hg Gallons Per Minute Head in Feet Mercury Measured in inches. 30 inches of mercury is equal to 14.7 psi. HP Head Pressure PSI - H times.434. IP Intake Pressure The pressure exerted by a water source on the intake side of a pump. LL Length of Hose Equal to 100' L Length of Hose Equal to 50' NP Nozzle Pressure Pressure at which water leaves the nozzle. NR Nozzle Reaction Water leaving a nozzle produces a reaction equal to 1.5(d)2 x NP. PP Pump Pressure Pressure at which water is discharged from the pump. PSI SL SSL T Pounds Per Square Inch Standpipe Friction Loss - 25 psi Aerial Platform System Loss normally the same as sprinkler and standpipe loss 25 psi. Ton Pounds

3 DRIVER OPERATOR Page 3 of 14 TFL Head Total Friction Loss Head is the vertical distance, measured in feet, between the surface of water and the point being considered, and is important because the amount of head determines the amount of pressure. Head becomes pressure because: 1. For each foot of head, water exerts a pressure of.434 pounds per square inch at the base. 2. Each feet of head develops one pound per square inch pressure at the base. Simplify to 2.3 feet. The head may be determined, if the pressure is known, by utilizing the following formula: H = 2.3 P Water pressure caused by head is directly proportional to its depth. As a column of water 1" square and 1' high weighs.434 pounds, a pressure of.434 psi is exerted for each foot of head. Pressure may be determined by utilizing the following formula: Fire Ground P =.434 H For fire ground hydraulics 5 psi added for each floor above the ground floor will overcome the effect of the weight of the water that acts against pump pressure. For example, add 10 psi for a nozzle operating on the 3 rd floor. Likewise, while much less common, 5 psi subtracted for each floor below the ground floor from pump pressure counters the weight water adds to below grade pressure. Wild land pump pressures in terms of pressure losses due to elevation are a guess. The topography undulates. Most of the time the hose lay progresses upslope, but not always. Generally, the Engineer will start at the pressure the nozzle being used requires plus the FL for the amount of hose. A 3/8 smooth bore requires 50 psi and a combination nozzle requires 100 psi. Pressures will necessarily increase as the length of hose increases to overcome friction loss. The nozzle person must communicate with the Engineer to adjust pump pressures. Discharge

4 DRIVER OPERATOR Page 4 of 14 Discharge is the quantity of water issuing from an opening and is usually calculated in gallons per minute (GPM). In computing total discharge, three items must be considered: Area of the opening. Velocity of flow. Time of flow. The basic discharge formula is: discharge equals area X velocity; this may be expressed as Discharge = AV. This formula is simplified and a constant, 29.7 is obtained; the constant is rounded off to 30 as this figure is more convenient and the solutions are sufficiently correct for practical purposes. The formula in use is: Dis = 30 D 2 X Sq. root of NP This is the main formula used to determine smooth bore nozzle flow at different tip sizes Discharge from Open Butts Due to the shape of the discharge opening, less water is obtained from open hose butts or from hydrant openings than would flow from a smooth bore nozzle tip of the same diameter. The discharge is considered as approximately 90% that of a smooth bore nozzle of equal size having the same pressure. It is necessary to insert the constant.9 in the formula to represent the difference: Dis = 30 D 2 x Sq. root of NP x.9 As both 30 and.9 are constants, this formula can be simplified by multiplying 30 by.9 to obtain: Dis = 27 D 2 x Sq. root of NP As opposed to the discharge formula for smooth bore nozzles, the flow from an open butt is less (x.9) since nozzles are engineered to add shape to the water that passes through it reducing hydraulic turbulence. Discharge from Sprinklers Sprinkler heads are normally considered to have 1/2" openings; the discharge may be calculated by use of the formula: Dis = (1/2 P + 15) x number of heads flowing Initial pump pressure to sprinkler systems is: 100 psi with no smoke showing 150 psi with smoke showing

5 DRIVER OPERATOR Page 5 of 14 Many buildings are built enclosed and a well-developed fire can exist without any smoke showing. The Engineer must take many indicators to consideration when determining whether to flow 100 or 150 psi to a sprinkler FDC. If in doubt flow 150 psi. Buildings that utilize a fire pump system may not require pumping to the system as long as the fire pump is working. The Engineer assigned to the system must hook up to the FDC and be ready to take over if necessary. Combination Systems Combination systems supply both the sprinkler and standpipe system through one FDC and riser. In this case the Engineer must pump to the hose line off the standpipe to ensure adequate nozzle pressure and volume rather than the 100 or 150 GPM for sprinkler only systems. Standard Measurements Atmospheric pressure at sea level is 14.7 psi = 30 inches of mercury = 33.9 feet of water (maximum theoretical lift). Therefore, 1 inch of mercury = 1.13 feet of water. A column of water feet in height will exert a pressure of one psi at its base. A column of water one inch square and foot high weighs.434 pounds. One gallon of water contains 231 cubic inches and weighs 8.35 pounds. 1 Cubic foot = 1728 cubic inches. 1 Cubic foot of fresh water weighs 62.5 pounds and contains 7.5 gallons (7.481). Pump Pressure Pump pressure is the amount of pressure in pounds per square inch (psi) indicated on the pressure gauge or any given discharge gauge. Visualize operating the pump on a fire engine. You are standing at the pump panel. You are turning the throttle out which increases the rpm of the engine (and thereby the pump) and you notice the pressure gauge at the pump panel increase from 50 psi to 100 psi. This is energy created by the pump which makes the water move through the plumbing on the fire engine. The pump pressure is telling you the amount of pressure being developed at the discharge side of the pump and up to the discharge outlets on the fire engine. Note: True and accurate pump pressure can only be completed with water flowing. Adjusting pump pressure with while static or with no water flowing gives a false reading. The pump pressure will drop when the nozzle is opened and water flowing. This can leave the nozzle team with inadequate pressure for operations. Fire Ground In Escondido, the City s core, hydrant pressure is around 100 psi. Some southern parts of the City, hydrant pressures can be 200 psi and above. On hilltops and some of the more rural areas of the City, hydrant pressure can be much lower, some near 40 psi.

6 DRIVER OPERATOR Page 6 of 14 What the hydrant gives the Engineer will affect how the pump needs to be adjusted to deliver adequate nozzle pressure. An engine at idle will cause the pump to generate between 40 and 60 PSI. Without a hydrant line the Engineer usually will need to throttle up to supply hose lines. With a hydrant line and the pump engaged at idle, the Engineer often doesn t have to throttle up to deliver adequate pressure. In some cases, especially with smooth bore nozzles the discharge valve may actually need to be gated down to deliver the proper nozzle pressure. It is only when and if additional lines are added or GPM is increased that pump pressure at idle with a hydrant line becomes inadequate and the Engineer will need to throttle up. If hose lines are placed into service and a hydrant line is connected later, a changeover will need to be completed as the hydrant line is opened. The changeover process allows the Engineer to open the hydrant line while compensating for the added pressure by throttling and gating down in order to maintain proper nozzle pressure. Once again an accurate changeover is dependent on water flowing. Foam Pump Settings Most of our apparatus are equipped with a foam pump. The suggested foam settings are listed below. The crews and pump operator may adjust the settings as needed for the incident. For example, in the wildland environment.1% may be adequate for light duff and ground cover. The operator and crews must understand that foam is effective long before it can be seen. Only the required percentage to achieve the desired effect should be used. Default.2% (some may say.3; acceptable as well) Structure pre-treat -.5% Bees 4 6% or as high as it will go. Friction Loss The pressure registering on the pump pressure (PP) gauge will not be the same at the nozzle because energy (pressure) is being used to overcome friction loss in the hose. Friction loss is determined by recognizing that water, as a non-compressible fluid, exerts pressure equally against its confining material. Therefore, fluid pressure must be determined as a rate of water flow versus the friction index of the substance it is flowing through. Fortunately, in the case of fire hose, the friction loss rate (FLR) is a simple function of the square of the amount of water flowing. Specifically, the total gallons per minute (GPM) divided by 100 and then squared and then doubled, has been found to be an adequate fire ground formula for computing the friction loss rate. FLR - 2Q 2 Where Q = 100 GPM 100

7 DRIVER OPERATOR Page 7 of 14 The GPM for this formula is for water flowing through 2 ½ hose. If using a hose diameter other than 2 ½, the GPM must be multiplied by a factor to determine the equivalent flow. See equivalent flows EF below for further explanation. Friction is the resistance to motion due to contact with surfaces. The flow of water through pipes and hose lines is retarded by friction caused by the rubbing of the water on itself and against uneven interior surfaces of the carrier. This, together with obstructed flow caused by bends, constrictions, fittings, and valves which make the water stream change its shape, reduces the velocity and discharge. Energy in the form of pressure or velocity is expended in overcoming the friction of the flowing water. The four fundamental rules governing friction in pipes and hose lines are: All other conditions being equal, the loss by friction varies directly as the length of the line. In the same size hose, friction loss varies approximately as the square of the velocity of flow. For the same discharge, friction loss varies inversely as the fifth power of the diameter of the hose. For a given velocity of flow, the friction loss is independent of the pressure Energy (pressure) is also used up by pumping water higher than the pump. Water weighs 8.35 pounds per gallon and the effort of lifting this weight uses up some of the engine pressure. It takes.434 pounds per square inch (psi) to lift water one (1) foot. Just as it takes energy to lift water, energy is gained by dropping water. In fact, an equal amount.434 psi is gained in energy for every one (1) foot water is dropped. For fire ground hydraulics,.434 is rounded off to.5 psi. Facts which you must have as a pump operator in order to determine pump pressure (PP) are: Amount of hose in the lay Size of the hose Size of tips or GPM flowing Nozzle pressure Elevation differential between the pump and the nozzle Appliance loss These six facts are needed, in all cases, to solve pump pressures; make sure you gather these facts and put them on your scratch pad or in your memory bank. Fire Ground For systems and appliance loss: 5 psi per floor

8 DRIVER OPERATOR Page 8 of psi for standpipe/aerial 25 PSI for system loss for aerial is a generic FL. In Escondido the system loss is factored into the 150 PSI starting pressure and the pressure is adjusted using the flow meter based on incident needs. If you are pumping a handline through the water way then the 25 PSI should be factored in. 5 psi for 1 ½ to 1 ½ gated wye with both sides in service this is for wildland use only. Amount of Hose in Lay In order to solve the amount of friction loss in a hose lay you must know the entire length of the hose lay. Friction loss rate factors are computed on 100' lengths of hose. When hose is doubled, as in the case of siamesed lines, it is necessary to average the lengths. This procedure will be described later under wyed lines. Remember: LL's = 100 feet of hose. Size of the Hose The size of the hose and the GPM flowing determine the amount of friction loss for each 100-foot section of hose. With a given flow, the smaller the diameter of hose the more friction loss involved. This is because a greater proportion of the water pushed through actually comes into contact with the interior surface of the hose than in the case of a larger hose. A larger diameter hose allows a relatively larger percentage of the water to flow through without contacting the interior surface. The formula for determining FLR is based on GPM through 2-1/2" hose. All flow rates through various size hoses must be converted to an equivalent flow as if it were flowing through 2-1/2" hose. The first step is to determine the actual number of gallons per minute flowing through the size of hose used in the lay. This is a function of the nozzle used and the pressure supplied at the nozzle. Nozzle Pressure The next step in the simplification of fire ground hydraulics is to establish nozzle pressures for all nozzle streams. This department has established the following as the desired nozzle pressures (NP): 50 psi NP on hand lines with smooth bore nozzles 100 psi NP on 1-1/2", 1-3/4" and 2-1/2" hand lines fog nozzles 80 psi NP on master stream smooth bore nozzles 100 psi NP on master stream fog nozzles psi

9 DRIVER OPERATOR Page 9 of 14 ¼ / ½ ¾ / / / / / * 1200 * Do not exceed 1000 GPM when the Apollo Monitor is in the portable mode- do not exceed 75 lbs. Nozzle pressure for 2 smooth bore tip in the portable mode. Equivalent Flows (EF) CONVERSION OF GPM FLOW IN OTHER THAN 2-1/2" HOSE TO EQUIVALENT FLOW OF 2-1/2" HOSE. Up to now we have described a simplified method of establishing friction loss rate in 2-1/2" hose by using the formula FLR =2Q 2. To calculate friction loss in various size hose other than 2-1/2", we have developed factors to convert the larger and smaller hose flows to GPM flow that creates the same amount of friction loss as in 2-1/2" hose. These factors are based on comparison of friction in hose of other than 2-1/2" to that of 2-1/2" hose. These factors are derived from comparison tables in NFPA Booklet "Nozzle Pressures on the Fire Ground" and actual flow tests. Fire Ground These calculation have been done and exist as our Pump Chart carried on the apparatus. To Determine Average Lengths of Wyed Lines

10 DRIVER OPERATOR Page 10 of 14 When the average comes out to a 1/4 or 3/4 length, round off to the nearest 1/2 or full length respectively. This is used if you have two lines of unequal lengths wyed off of one supply hose. The supply line comes off of one discharge. For instance if you have a wyed line with one side at 100 ft. and the other side 200 ft., the pump pressure would pump to 150 ft. Be mindful that the GPM must be added for the supply line calculation. Relay Pumping Operations Relaying of water can be accomplished when the activities of personnel and equipment involved are coordinated by the officer in charge, and upon receipt of specific information such as: 1. Amount of water needed to extinguish the fire. 2. Size and length of available hose. 3. Apparatus available for pumping purposes. 4. Time required setting up the relay. 5. Maximum distance one pumper can deliver the GPM. 6. Topography of the district over which the relay is to be made. The quantity of water (GPM) needed to effectively handle the situation must be estimated, because every succeeding phase of the relay will be governed by this estimate. Since friction loss in hose used for relays will be one of the factors determining the distance between engines, the largest hose available should be used to minimize the number of engines required in the relay. The distance from the water supply to the fire is secondary in estimating the amount of hose required for the relay. Primarily, it is the length of hose between individual engines that must be determined. The hose line or lines leading to the fire from the last pump do not materially affect relay operations, and there is no need for them to enter relay computations. The operator of this pump may assume it is connected to a water supply for extinguishing the fire. The condition of the hose will also have an effect on the length of hose lines between pumps. The pump pressure of the pumps in the relay should not exceed the pressure of the annual hose test. When calculating pump pressure to be pumped by a relay pumper, an intake pressure of 20 psi should be maintained at the intake of the next pumper in line. On this basis the pressure, which the hose can withstand, minus intake pressure, could be used to overcome friction loss and gravity loss, if it exists. ( = 230 psi)

11 DRIVER OPERATOR Page 11 of 14 With the friction loss rate determined, because of the GPM flow, the maximum amount of hose between pumps, without exceeding the maximum pump pressure, can be determined. When distance is not a determining factor, (short relays) a pump pressure less than maximum could provide sufficient intake pressure at the next pump in line. It is logical to expect engines of varying capacities to be used in each relay operation. It must be considered that the capacity of a pump diminishes as the pump pressure exceeds a certain pressure. Class A pumps will deliver about one half of capacity at 250 psi PP. Lower discharge capacity engines, compared to those of higher discharge capacity, should be taken into consideration. The largest capacity pumper should be placed at the source of supply. More time will be needed to complete a relay than would be necessary to make a regular hose lay. This unavoidable delay should be considered in determining how large the fire will be by the time relayed water is available. The differences in elevation between the water supply and the nozzle will have a decided effect on the placement of engines in the relay, and upon the total number required. It is now evident that several things must be considered to keep within the maximum allowable pump pressure: Total friction loss developed in the quantity of water flowing, which has to be overcome by the pump. The gravity loss (GL) or gravity gain (GG), if it exists. The intake pressure (IP) at the next pump in line. After the size and number of hose lines are decided upon, the number of pumps necessary to transport the desired flow to the pump engaged in the firefighting can best be determined by the following formula: Fire Ground Number of Pumps = TFL + GL - GG Maximum PP - IP This version of relay pumping is geared toward situations when more than two apparatus are needed to pump and flow rates that tax the amount of available hose to complete the lay. More commonly, we use a scaled down version of relay operations in the wild land environment and occasionally to boost pressure to an engine operating in an area with low system pressure. Almost always only between two engines. In these cases the Engineers must determine approximate fire flow. The second Engineer then accounts

12 DRIVER OPERATOR Page 12 of 14 for friction loss for the hose between the engines based on flow and adds a minimum of 20 PSI to that pressure. This should give the units pumping the attack lines enough pressure and volume to safely continue their operations. As always when two engines are involved in pumping evolution, coordination is the key. Estimating the Available Flow from a Hydrant The ability to calculate the available flow (GPM) remaining in a hydrant can be of great advantage to both the pump operator and the commanding officer, particularly at the fire ground, as well as in pre-planning surveys. REMEMBER that to be an efficient fire fighter you should know as much about the water supply in your district as possible prior to an emergency. To estimate the available flow from a hydrant the rule is: determine the percentage of drop between static (at rest) and residual (remaining pressure with water flowing) pressures. This percentage of drop will indicate the estimated available flow; i.e., <10 percent drop, 3 more like volumes; <15 percent drop, 2 more like volumes; <25 percent drop, 1 more like volume. If more than 25 percent drop--no more like volumes. Therefore, to estimate the available flow from a hydrant, the following must be applied: 1. Note the static pressure on the compound gauge after the hydrant has been opened to let water into the pump, but before opening any discharge gate. 2. Note the residual pressure on the compound gauge after getting the line into operation at the standard nozzle pressure; and 3. Determine the percentage of drop. Estimating Static Pressure To estimate static pressure if it was not noted when the hydrant was opened at the fire ground, will usually be impractical because of allowable time. However, if it is deemed necessary, the following procedure may be used: 1. Note the flowing pressure on the compound gauge with the first line in operation. 2. Place another nozzle delivering the same GPM into operation and note the drop in flow pressure. 3. Divide the drop pressure by 2 and add to the flow pressure that was noted when the first line was in operation. This is the estimated static pressure.

13 DRIVER OPERATOR Page 13 of 14 Escondido Fire Department Pump Chart The Pump Chart is carried on all pumping apparatus and is our quick reference for pumping operations. It incorporates all the calculations necessary to give the pump operator the figures at a glance to determine proper pump pressures rather than the more time consuming use of the formulas.

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