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Fire Pump Theory. Pump Types. Section 180. Class #2. Background of fire pumps.
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Fire Pump Theory Pump Types Section 180 Class #2
Background of fire pumps Over the past 200 years, legends have grown up about antique fire apparatus. Old fire engines or “masheens” as they were know, had to be carried by hand. This machine had the essential fire pump, & a piston pump with a goose-neck metallic pipe called a break. Firefighters would move the break in an up & down motion called stoke, pumping water out of the apparatus to combat fire. Modern technology has drastically changed pump design. The centrifugal pump replaces the positive displacement pump as the main type of pump on a modern fire apparatus. What has not changed is the necessity to understand & master modern day fire pumps & apparatus.
Types of Pumps used in the Fire Service • Positive displacement pumps – 1. Piston Pump 2. Rotary Gear Pump 3. Rotary Vane Pump • Centrifugal pumps -
There are various classifications of fire pumps. • One main classification is according to the • method of energy that is imparted to the liquid: • Displacement pump - imparts energy by • mechanical displacement; piston, diaphragm, plunger, screw, vane & gear pumps • Centrifugal pump - kinetic energy type, • it imparts energy to a liquid by means of • centrifugal force produced by a rotating • impeller
Positive Displacement Pumps Rotary Vane Pump Rotary Gear Pump
Piston Pumps 1. 3. 4. 2.
Single / Multi stage centrifugal pumps Operating principles of single stage pumps • 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.
Diagram of how the multi stage pump operates Pressure {Series} Volume {Parallel}
Another view of multi stage pump operation Pressure {Series} Volume {Parallel}
Major Components of the Centrifugal Pump • Discharge • Volute • Impeller • Vanes • Shroud • Casing • Stripping edge • Hub • Eye 1. 2. 7. 3. 8. 4. 9. 5. 6.
Centrifugal Fire Pumps How they work…
Pressure Relief Systems A pressure relief valve is sensitive to pressure change & its ability to relieve excessive pressure within the pump discharge. An adjustable spring-loaded pilot valve actuates the relief valve to bypass water from the discharge to the intake chamber of the pump.
Pressure Control Governors When activated, the governor Uses trapped air & water in area A as a reference pressure for the piston that controls the engine throttle. A change in pump pressure affecting area B moves the piston adjusting the engine pressure.
BREAK BREAK BREAK Break BREAK BREAK
Fire Pump Primers 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. • Primers fall into three categories: • Positive displacement pumps • Exhaust primers • Vacuum primers
Positive Displacement PrimersRotary Vane Primer Require a relatively high RPM as compared to a rotary gear primer& can be driven either mechanically from the pump gear case, or by an electrical motor.
Positive Displacement Primers Rotary Gear Primer Uses an oil supply to help the pump maintain effeciency of the pump The oil fills any irregularities in the housing
Exhaust Primers • Operates on the same principle as a foam eductor. Exhaust gases are prevented from escaping to the atmosphere by the exhaust deflector. Gases are diverted to a chamber where the velocity of the gases passing through a venturi creates a vacuum
Vacuum Primers • Simplest of all primers, it makes use of the vacuum already present in the intake manifold of any gasoline engine.
Conditions that can cause damage to the pump • Cavitation – a condition in which vacuum pockets form in a pump & cause vibrations, loss of efficiency, & possible damage • Water Hammer --the force created by the sudden acceleration/deceleration of water
Corrective measures to prevent damage to the pump To prevent cavitation the engineer must not discharge more water than the supply can furnish. To prevent water hammer, all discharges must be opened/shut slowly.
Auxiliary Cooling Systems The primary function of auxiliary coolers is to control the temperature in the apparatus engine during pumping operations. Two types of auxiliary coolers: 2. Immersion type • Marine type
Descriptions Marine type – inserted in one of the hoses used in the engine cooling system is such a way that the engine coolant must travel through it as it circulates through the system the cooler itself contains a number of small tubes similar to the flues in a steam boiler. Immersion type- the engine coolant passes through the body of the cooler, water being supplied by the fire pump passes through a coil or tubing mounted inside the cooler so that it is immersed in the coolant
Intake/Suction Hose Characteristic Soft suction hose is used to transfer water from a pressurized source {hydrant} to the pump intake Range in size from 2 ½” to 6”, can be constructed of the same material as smaller fire hose Hard suction hose is used to draft water from an open water source. Also used to siphon water from one portable tank to another, usually in tanker shuttle operations. Range is size from 2 ½” to 6”, constructed of a rubberized reinforced material designed to withstand the partial vacuum conditions created when drafting
