Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department Hydraulics

Chapter 8 Required Pump

Discharge Pressure

Second Edition

Eugene Mahoney

Brent Hannig

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

• Explain the variables that must be considered in order to operate a pump at maximum efficiency on the fire ground.

• Discuss the use of the required pump discharge pressure (RPDP) formula and its application to various pumping configurations.

• Explain the development of the RPDP formula.

Fire Department HydraulicsFire Department HydraulicsObjectives

Upon completing this chapter, the reader should be able to:

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics

• Determine the RPDP for single lines at ground level.

• Solve problems to determine the RPDP for a single line

wyed into two lines at ground level.

• Determine the RPDP for layouts of siamesed lines into a

single line at ground level.

• Solve problems to determine the RPDP for lines laid

uphill.

Objectives, cont.

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics

• Solve problems to determine the RPDP for lines laid

downhill.

• Determine the RPDP for lines laid into standpipe

systems.

• Determine the RPDP for lines laid into portable

monitors.

• Determine the RPDP for lines laid into deck guns.

Objectives, cont.

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics

• Solve problems to determine the RPDP for lines laid into

ladder pipes.

• Solve problems to determine the RPDP for lines laid into

aerial platforms or other elevated master-stream

devices.

Objectives, cont.

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics

• The friction loss problems in Chapter 7 considered

only friction loss in the hose; therefore, the problems

could be solved entirely by using the friction loss

formula.

• This chapter considers hose layout configurations

involving the need to solve for discharge and those

involving elevation and appliances.

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

• The formula introduced in this chapter is a pencil-and-paper formula.

• It is referred to as the required pump discharge pressure formula.

Fire Department HydraulicsFire Department Hydraulics

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics

• The pump discharge pressure must be sufficient to provide for pressure losses due to:

– The nozzle pressure.

– The friction loss in the hose.

– Back pressure.

– Forward pressure

– Appliance friction loss.

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department HydraulicsDevelopment of the Required Pump

Discharge Formula • The commonly accepted formula for determining the

pump discharge pressure is:

– PDP = NP + TPL

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics

• PDP = NP + TPL

– PDP = pump discharge pressure (psi)

– NP = nozzle pressure (psi)

– TPL = total pressure loss, including friction loss in the hose, pressure loss in appliances, and pressure loss due to elevation

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department HydraulicsDetermining the Required Pump Discharge

Pressure• RPDP = NP + FL + BP + AFL – FP

– NP = nozzle pressure– FL = friction loss in the hose– BP = back pressure– AFL = appliance friction loss– FP = forward pressure

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics• Back pressure refers to those situations where the

nozzle is being discharged at a point above the pump.

• When these situations are encountered, .5 psi is used for each foot of head. Head is the vertical distance above the pump where the nozzle is being used.

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

• Appliance friction loss refers to the loss of pressure

as the water flows through fittings such as reducers,

increasers, manifolds, siameses, wyes, standpipe

systems, portable monitors, and aerial apparatus.

• For the purpose of solving problems, no loss will be

considered whenever the flow through an appliance

is less than 350 gpm.

Fire Department HydraulicsFire Department Hydraulics

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Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics

• When the flow is 350 gpm or greater, a loss of 10 psi is used.

• An exception is the friction loss for master-stream appliances. In these appliances, a loss of 25 psi is

considered as standard, regardless of the flow.

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics• Forward pressure is a term used to identify a

situation where the discharge from a nozzle takes place at a location below the pump.

• As with back pressure, .5 psi is used for each foot of head.

• Head is the vertical distance below the pump that the nozzle is being used.

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics• If a single line taken off a pumper is used to supply a

single nozzle tip, the pressure produced by the pump will need to be sufficient to provide for the nozzle pressure and the friction loss in the hose.

• If several lines are taken off a pumper and provided with individual tips, the required pump discharge pressure for each of these lines must be calculated individually, which may result in the required pump discharge pressure on one or more of the lines being less than the required pump discharge pressure for another of the lines.

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department HydraulicsRequired Pump Discharge Pressure

Problems • If a constant-flow, constant-pressure nozzle is used in

a problem, it is only necessary to solve for the friction loss in the hose layout and add the result to the nozzle pressure to solve the problem.

• However, if smooth-bore tips are used in the same type of problem, it is necessary to determine the amount of water flowing before the friction loss in the

hose can be determined.

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics• The standard established for handheld smooth-bore

tips is 50 psi.• 80 psi has been established for master-stream

smooth-bore tips.• For fog nozzles, both hand-held and master-stream

nozzles, nozzle pressures of 100, 75, and 50 psi are available.

• A nozzle pressure of 100 psi is used on most fog nozzles.

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department HydraulicsRPDP Example

• Problem: Engine 6 is pumping through 400 feet of a single 1-1/2-inch hose that is equipped with a 5/8-inch tip.

• What is the required pump discharge pressure if the nozzle pressure is 50 psi (Figure 8.2)?

• First, determine the discharge from the tip:

– Discharge = 29.7D²√P

– D = 5/8-inch or .625

– P = 50

– gpm = 82.02

Mahoney, Hannig, Fire Department Hydraulics, 2nd Ed. ©2009 by Pearson Education, Inc., Upper Saddle River, NJ

Fire Department HydraulicsFire Department Hydraulics• The next step would be to figure the friction loss in

the hose:

– FL = CQ²L

– FL = 24(.82)²4

– FL = 64.55

– RPDP = FL + NP

– Solution: RPDP = 114.55