PRESSURE LOSS
The discharge pressure indicated on the Master or Pump Discharge pressure gauge will be less than the actual pressure found at the nozzle. The are several causes for this pressure loss.
1. Friction Loss.
2. Elevation Loss
3. Appliance Pressure Loss
FRICTION LOSS

Friction loss is the amount of pump pressure lost while forcing water through hose, appliances, nozzles and adaptors. The amount of pump pressure lost at the nozzle will depend on three primary factors.
1. the hose diameter.
2. the total length of the hose assembly.
3. the flow rate (GPM) through the hose.

The only accurate way to measure this pressure loss is to use in-line gauges. However, there is a mathematical formula that can be used to reasonably estimate the friction loss in hose of a specific diameter flowing a specific GPM.
Using that formula:
1 3/4 inch hose flowing 150 gpm will experience 17 psi Friction Loss per each 50 foot length.
2 1/2 inch hose flowing 250 gpm will experience 6 psi friction loss per each 50 foot length.
5 inch hose flowing 500 gpm will experience 2 psi friction loss per each 100 foot length.

An interesting trait of friction loss is the if the flow rate through a hose is doubled, the friction loss increases four times. In the 5 inch hose example above,  if we double the flow rate to 1,000 gallons per minute, our friction loss will increase by a factor of 4. The 2 psi friction loss we experienced flowing 500 gpm has now increased to 8 psi friction loss per 100 foot section (2 x 4 = 8).

If a pump operator can remember these friction loss numbers, and easily multiply the friction loss per length of his in his/her head, they could calculate the friction loss in any hose assembly used on the fireground. However, many of us have difficulty doing this, so STFD has done two things.
First, establish a minimum flow rate for 1 3/4 and 2 1/2 inch hose when operating at structure fires.
Secondly, round off the friction loss per length to a number that can more easily be calculated in your
head.

Those rule of thumb friction loss numbers are:

15 - 5 - 2

15 psi friction loss for each 50 foot section of 1 3/4" hose when flowing 150 gpm.
5 psi friction loss for each 50 foot section of 2 1/2" hose when flowing 250 gpm.
2 psi friction loss for each 100 foot section of 5 inch hose when flowing 500 gpm.
If flow through the 5 inch hose is doubled to 1,000 gpm, the friction loss will increase to 8 psi per 100 foot section. (Remember, when the flow rate is doubled, the friction loss is 4 times greater). So, when using 5 inch hose to supply a 1,000 gpm ground monitor, the pump operator should estimate a friction loss of 8 psi per length. Since it is easier to work in multiples of "10", this number is often used instead of the actual pressure loss of 8 psi.



ELEVATION PRESSURE LOSS
A one square inch column of water, twelve inches high weighs 0.434 pounds. This weight, or downward pressure, is simply a measurement of the effect of gravity. To overcome the force of gravity and push water above the fire pump, we need to use some of our pump discharge pressure. The amount of pump discharge pressure lost in this process if called "Elevation Pressure Loss". To put it simply, we need 0.434 pounds per square inch of pressure to raise a one inch square column of water twelve inches. Once again,  it's easier to work in round numbers, so we will round off 0.434 to one-half (0.5) psi. If we needed to raise water a  distance of ten feet, we would lose 5 psi of pressure at the nozzle (0.5 times 10 feet). This pressure loss would not be displayed on any of our pump panel gauges, but would be felt at the nozzle. To compensate for this pressure lose due to elevation, the pump operator must increase his discharge pressure 5 pounds for every 10 feet of elevation.



APPLIANCE PRESSURE LOSS
Pressure is lost whenever we force water through hose appliances, including master stream devices. If the flow rate through the appliance is less than 350 gpm, the pressure lost is insignificant and need not be considered by the fireground pump operator. However, when flow through the appliance is 350 gpm or higher, that pressure loss will increase to the point where it may adversely impact pressure at the nozzle. Each appliance is different, so the actual amount of this pressure loss may vary depending upon its' design. For that reason we have identified another rule of thumb for estimated appliance pressure loss.

If the flow rate through the appliance is less than 350 gpm, there is no significant pressure loss and the pump operator need not take it into consideration..

If the flow rate through the appliance is 350 gpm or higher, the operator should estimate a pressure loss of 10 psi per appliance.

When using any master stream device (ground monitor, deck gun or elevated master stream), the pump operator should estimate a pressure loss of 25 psi at the appliance.

In respose to several questions regarding the written test for the annual pump certification, I have placed this pump operation review on the website.
NOZZLES & NOZZLE PRESSURE
Commonly used fire service nozzles have a recommended operating pressure of between 50 and 100 psi. The  specific nozzle pressure (NP) required is determined by the type of nozzle.
Automatic Nozzles use an internal, spring loaded baffle that slides forward or backward in an attempt to maintain its' designed operating pressure. When operated below the recommended nozzle pressure, the baffle is at its' rear most position which creates a smaller orifice (opening). This smaller opening creates additional back pressure in an attempt to attain the designed operating pressure and maintain good stream construction. Under this condition however, the nozzle may not deliver the advertised flow rate (gpm).

When operated at its' designed nozzle pressure, the baffles position allows the nozzle to produce its' advertised flow rate, controllable nozzle reaction force and a good fire stream.

When nozzle pressure rises above the designed pressure, the baffle slides forward to increase the orifice size in an attempt to maintain its' designed operating pressure. This larger opening allows for a higher gpm flow rate, but can dramatically increase the nozzle reaction force and increase the risk of the nozzle person loosing control of the hoseline.

The "standard" automatic nozzle is designed to operate at 100 psi pressure. However, manufacturers also sell automatic nozzles designed to operate at 75 psi or 50 psi. Task Force Tips has an "Dual Pressure" automatic nozzle that can be switched from 75 psi mode to 100 psi mode by the nozzle person. To identify a dual pressure nozzle, look at the tip end for an hour glass shaped knob and a blue or red label. If the blue label is visible, the nozzle is set for 100 psi operation. If the red label is visible, the nozzle is set for 75 psi operation. CAUTION: if set in the low pressure (75 psi) mode and pumped at 100 psi NP, nozzle reactions forces will be higher than normal and may result in injury.

SMOOTHBORE NOZZLES are simply a shut off valve with a fixed tip of a specific opening size. The recommended nozzle pressure is established to provide a known flow rate while keeping the nozzle reaction force within safe parameters. The recommended nozzle pressure for smoothbore handline nozzles is 50 psi. Smoothbore master stream nozzles have a recommended nozzle pressure of 80 psi.

NON-AUTOMATIC NOZZLES including special purpose (attic, piercing and distributing nozzles) are typically designed to operate at 100 psi nozzle pressure.

PRESSURE GOVERNOR SYSTEMS
The pressure governor system is designed to do one of two things.
- maintain the pump pressure set by the operator, or
- maintain the engine speed set by the operator.

When operated in the pressure mode, the system will attempt to maintain the pump discharge pressure as set by the operator. To do this, system sensors monitor pump pressure and will either increase or decrease engine speed (impeller speed) to maintain that pressure. In the pressure mode, the governor system can also automatically take pre-programed steps in response to pump cavitation (the anti-cavitation protection). If pump discharge pressure drops due to a reduction or loss of intake pressure, the PGS will increase engine speed in an attempt to maintain pressure. Engine speed may increase up to the maximum governed speed during this event. If, after several seconds, the previously set discharge pressure is not achieved, the governor system will return the truck to idle. Some older PGS systems will also disengage from pressure mode and return to "standby mode".

When operated in the throttle / RPM mode, the system will maintain the engine speed as set by the operator. In the throttle mode, pump discharge pressure can vary dramatically as nozzles are opened and closed. Throttle mode offers nozzle crews no protection from over-pressurization, or a reduction of flow as other discharges are opened or closed. Also, in throttle / rpm mode, the anti-cavitation feature is not functional and the operator must carefully monitor intake pressure and be prepared to respond to cavitation should it occur.

The operator should use pressure mode in the following situations:
- fire attack when connected to a hydrant with sufficient water supply.
- when operating as the attack pumper in a water relay.
- when operating from the apparatus water tank.

Throttle mode should be used:
- when operating as a supply or relay pumper in a water relay.
- whenever the water supply is unreliable or insufficient.
DETERMININING PUMP DISCHARGE PRESSURE
The correct pump discharge pressure (PDP) must overcome the total pressure loss experienced within a hose line and still provide the recommended operating pressure at the nozzle. To calculate the correct pump discharge pressure, the operator must add the following:

nozzle pressure + friction loss + elevation pressure loss + appliance pressure loss = PDP.

Elevation pressure loss and appliance pressure loss may not be a factor in every situation. If not, they may be removed from the equation.
COMMOM PUMPING PROBLEMS
The pump operator must be able to recognize and properly respond to a number of common pumping problems that may occur on the fireground.

Pump Cavitation occurs when trying to discharge more water that you have coming into the apparatus.
Signs of pump caviation include:
- intake pressure is 20 psi or less
- intake hose is soft when squeezed.
- pulsating intake hose
- an increase of engine speed does not result in an increase of pump discharge pressure.

Pump Overheat occurs when the pump is engaged and no water is being discharged or circulated through the pump. Friction between the impeller and the water creates heat that could damage the pump packing, pump seals, or in severe cases, warp pump components.
Signs of pump overheat include:
- outlets that are warm or hot to the touch.
- water being discharged is warm or hot.

Engine Overheat occurs when engine temperature rises above its' normal operating range. Overheat can be caused by a mechanical problem, low coolant levels, low engine oil, "over working" the engine or insufficient air flow required for adequate cooling. Newer fire apparatus have a feature that will automatically reduce engine speed if the engine begins to overheat. This reduction of engine speed is an attempt to reduce temperatures by reducing the work load.
Signs of Engine Overheat include:
- engine temperature gauge reading above the normal operating temperature
- a 'hot' odor from the engine.
- steam from the engine.
- a reduction of engine speed that was not initiated by the pump operator.

Water Hammer is the sudden stoppage of water flow that results in a change in direction of energy. The severity of any water hammer will depend upon the discharge pressure and how quickly the valve is opened or closed. The pressure spike that occurs can be up to four times the discharge pressure.
Signs of Water Hammer include:
- a momentary increase or decrease of pressure.
  (A momentary pressure increase indicates that a valve was closed too quickly, or that water flowing under
  high pressure has reached a closed valve. A momentary decrease of pressure indicates that a valve may
  have been opened too quickly and a water hammer may occur when that flowing water reaches a closed
  nozzle or valve.)
- a loud 'bang' from the pump.


PUMP PANEL GAUGES AND CONTROLS

The Master Intake Gauge displays the pressure or vacuum present at the intake of the pump.

The Master Pump Discharge Gauge registers the pressure as it leaves the pump, but before it reaches the gauges for each individual discharge line.

The Individual Discharge Gauge displays the actual pressure being supplied to individual discharges and hoselines.

The Pumping Engine Coolant Gauge displays the temperature of the coolant in the engine that powers the fire pump.

The Pumping Engine Oil Pressure Gauge shows that an adequate supply of oil is being delivered to critical areas of the engine that is powering the fire pump.

The Pumping Engine Throttle is used to increase or decrease the speed of the engine that is powering the fire pump.

The Tachometer indicates the engine speed in RPM.

The Voltmeter provides a relative indication of battery condition and alternator output.

The Water Tank Level Gauge displays how much water is remaining in the apparatus water tank.