Definitions & Types of Pumps

Types of pressure in fire service:
Static pressure, Residual pressure, Flow pressure
Normal operating pressure, Negative pressure

The pressure exerted in all directions at a point in a fluid at rest.

The pressure remaining in a system while water is flowing.

The forward velocity pressure at a discharge opening when water is flowing

The pressure found in the water distribution system during normal consumption demands.

Also called vacuum . Pressure that is less than atmospheric pressure 14.7

Atmospheric pressure – the atmosphere that surrounds the earth has depth & density & exerts pressure upon everything on earth.
Capacity – The maximum amount of water a pump will deliver at the indicated pressure.
Displacement – Movement of a given amount of a fluid w/ each stoke of a pump.
Flow {GPM} – Gallons per minute, the measurement of the amount of water moved through a fire pump.
Friction loss – Loss of pressure created by the turbulence of water moving against the interior walls of the hose or pipe.

Head Pressure (gain of loss) – Water pressure due to elevation. For every 1’ increase in elevation, 0.434 psi is gained.1 M in height 10 kPa is gained. Head in the fire service refers to the height of water above the discharge orifice to convert head in feet to head in pressure divide the number of feet by 2.304 which is the number of feet that 1 psi will raise a column of water.

Hydrant pressure – The force of water when it enters the pump from the distribution system.

Hydrant pressure will decrease as the discharge increases, this is due to friction loss in the after system. If the flow is increased too much, the pressure in the system may be reduced below 0 psi. Operation at pressures below 20 PSI Residual is dangerous because it increases the possibility of cavitation.

Net engine pressure – The actual amount of pressure being produced by the pump.
NPDP When taking water from a hydrant it is the difference between the intake pressure & the discharge pressure.
when drafting it is the sum of the intake pressure & discharge pressure
NOTE intake pressure is credited for lift & intake hose friction loss & is added to the discharge pressure.

Nozzle reaction – The counterforce directed against the people or device holding a nozzle by the velocity of water being discharged.
Pump discharge pressure – The actual velocity pressure(measured in PSI) if the water as it leaves the pump & enters the hose line.

Vacuum – A pressure that is less than normal atmospheric pressure.
Velocity – The rate of motion of a particle in a given direction, speed.
Water hammer – When the flow of water is suddenly stopped, the resulting surge is referred to as a water hammer.

Positive displacement pumps –
a. Piston Pump
b. Rotary Gear Pump
c. Rotary Vane Pump
Positive displacement pumps seldom used to produce fire streams in the modern FD. They are still necessary because they can pump air & centrifugal pumps cannot PDP are used as priming pumps to get water into the centrifugal pumps during drafting operations.

Centrifugal pumps - kinetic energy type, it imparts energy to a liquid by means of centrifugal force produced by a rotating impeller. Centrifugal pumps are widely used because of its design simplicity, highly efficiency, wide range of capacity & head, smooth flow rate, & ease of operation & maintenance.

Impeller (revolving disk)
Made of Bronze
Eye of the impeller (center of disk) is the area of lowest pressure and is the location where the water enters the pump.
The impeller is made of two sides called shrouds and blades separate the shrouds.
Diffusion vanes are the internal pockets that are formed by the shrouds and blades.
Casing (made of cast iron)
Volute is the term for the spiral shaped or ever increasing passageway

Pump Transmission
Power is supplied to the pump transmission by a split gear case. The power is diverted from the rear axle The gear ratio is set to match the engine torque curve to the impeller shaft. The impeller will turn at a ration of 1:2.28 times faster.

Centrifugal pumps are limited by the amount of work they can do and this workload is based in pound-gallons

Rated Capacity for a 1250 GPM Pump
100% capacity @ 150 psi = 1250 GPM
70% capacity @ 200 psi = 875 GPM
50% capacity @ 250 psi = 625 GPM

These pumps take advantage of both incoming volume and pressure from a water source. These pumps have 100% slippage, which prevents damage to the pump and engine. This allows the pump to run even when all operational hoselines are shut down. If all operational hoselines remain closed for an extended period of time the water that is in the pump will begin to heat up.They create a smoother flow, which creates a better fire stream.

These pumps are not able to pump air. These pumps will need a positive displacement pump in order to prime the centrifugal pump.These pumps can be damaged by contaminated water.
Pumping insufficient quantities of water can cause damage to the pump from cavitation.

Any liquid, at any temperature, forms a vapor over its surface, which produces a certain amount of pressure. This vapor pressure increases as the liquid temperature rises. When the vapor pressure is equal to or greater than the pressure surrounding the liquid, the liquid boils. Vapor pressure is important because of the way it affects pump operation.

The single & multi stage pumps operate basically the same, both use housing encased disks called impellers to throw water to the outside of the casing to create velocity or pressure.
The single stage pump has only one impeller to discharge water
The multi stage pump has two impellers that can be used in series or parallel operation to increase the pressure or to increase the volume of water discharged.

Successfully drafting water depends upon the ability to create a partial vacuum within the pump and intake hose. A positive displacement pump can pump air as it operates making it self priming.Centrifugal pumps are not self-priming & therefore require an external pump to operate from draft and in instances when the pump is filled with air.

High rpm required
1,000-1,200 rpm
Most require oil
Seals gaps
Preserve and prevent corrosion
New KME’s are fluid less, the tips of the vanes become sacrificial

Uses an oil supply to
help the pump maintain
efficiency of the pump. The oil fills any irregularities in the
housing. There is a vent in the oil line from the oil reservoir to the priming pump, since the pump is usually lower than the water tank, a siphon action would drain the tank after the primer has been used. This vent breaks the siphon but small enough to allow the priming pump to draft the oil out of the tank when the primer is in use.