In the Fire and rescue services, the pumps whether as a portable, a trailer, or built-in in the appliance, has a vital role to play, depending on the scale of operation . Knowledge of its performance, is important equally to the leading fireman, sub officer, and the station officer, who takes the impact of the operation as the first turn out on the fire ground, This notes are for these first turn out i/c .
A pump is a machine driven by an external power for transmitting to a fluid, - water in our case, to project it as a jet or spray .The power may be provided manually by the operator or coupling the pump to a suitable engine or motor .
Pumps fall in three categories:
1) Positive displacement pumps : Force pumps, lift pumps, bucket & plunger pump ,Are not used as an active operational pumps in the fire service . Rotary and semi rotary pumps are used to circulate oil in the internal combustion engine, and stirrup pumps in the CIVIL Defence, for extinguishing scattered fires after an air raid during wars.
2) Centrifugal pumps – negative displacement pumps is the operational pump for fire fighting purposes. These pumps can pump only liquids , not gases.
3) Ejector pumps:(Jet pumps):-Assists operation in certain situations or play an auxillary part in a centrifugal pump or appliance .Lifts water from heights beyond the normal suction lift(24 Feet).
Centrifugal pump is the standard fire fighting pump, which is compact, reliable, easy to maintain, can be coupled to a variety of drivers-electric motors, steam turbine, and internal combustion engines. Other advantage of a horizontal or vertical centrifugal pump is the relation of discharge to pressure at a constant speed. ie: The discharge is reduced when pressure head is increased. There are pumps ranging from 500GPM to 5000GPM.Pumps are rated for gallons per minute. Portable pump capacity is 60 to 120GPM.Centrifugal pumps consists of two main parts: A rotating disk(Impeller) fixed rigidly on a shaft .Receives liquid at its centre and discharges with high velocity to its periphery. The casing or the body converts this velocity energy to pressure energy. When high pressure water flow is required two or more impellers are assembled on one shaft as a single unit to form a multistage pump. The discharge from the first impeller enters the suction of the second impeller, then to the third impeller and so on. Multistage pumps can be operated on low RPM to give high discharge and has this advantage for industrial uses.
EJECTOR PUMPS: Consists of a jet, the cross sectional area of which, is proportioned to give a high velocity to the liquid or gas to be propelled. The jet is directed into an intake tube which gradually expands in diameter. At one point the –the throat inside the tube, the pressure falls below that of atmospheric pressure. The gas or liquid to be pumped out is then forced into the tube by the atmospheric pressure, and pumped out through delivery.
Ejector pump system is employed at the following areas:
1. System of exhaust ejector priming for lifting water from open source.
2. Foam inductors-(Ventriui principle) Ejector pumps are used to lift water from areas where standard fire pumps cannot approach .ie: Ships holds and basement of buildings. Confined spaces where normal pumps likely to stall if run for long duration. This can also lift water from a depth of 60 to 80 Feet whereas normal fire pumps can lift only water from 24 Feet.
ADVANTAGES OF NEGATIVE DISPLACEMENT PUMP(CENTRIFUGAL):
1. Wear and tear is less.
2. Continuous flow of water
3. Can be operated at high speed (RPM) to achieve maximum discharge of water.
4. Pump will function when delivery valves are shut and will not affect the engine.
5. Simple in construction and occupies less space.
Requires priming when lifting water from open source .
Priming is removing the air present inside the pump casing and suction hose, so that the atmospheric pressure forces the water upto the pump casing .This is necessary only in negative displacement pump-centrifugal
Three types of priming Systems is in operation currently for the centrifugal pumps:
2. Exhaust ejector
3. Water ring
Reciprocating Primer :- A small piston( force pump )is connected to the suction side of the main fire pump by means of a pipe , having
A valve , normally kept closed , by means of a pipe , with a valve, which is kept closed normally , by means of a spring. The piston
pump is driven by the main pump shaft , either by a friction cone clutch, or a wheel type friction drive . Before priming the air valve is
opened and the piston pump drive engaged, by shifting a lever . The piston pump commences operation,. On its down stroke , pressure inside the cylinder decreases and on its up stroke the air is forced out through the waste pipe ,. After several strokes the air inside is removed completely, . water from the open source creeps in to the pump casing , and priming is completed , indicated by water flowing out of the waste pipe, . the priming lever is returned to its normal position. And the main pump is operated as the situation requires. The priming speed is 1000 R.P.M, and not to exceed 1500 R.P.M.
Exhaust ejector primer :- Priming in this system is done by diverting the exhaust gases from its normal path to the silencer, to a nozzle, and discharged at very high speed through a throat pipe, ;Here the jet pump principle is used . the high speed air thru the jet draws air and discharges through a waste pipe. When priming is completed water flows out , Now the jet valve is closed and exhaust gases is returned to its normal path to the silencer. To make the operation simpler. The two valves are linked by a rod so that when one opens the other closes. The efficiency of the exhaust gas primer depends on the speed of the gases leaving the discharge nozzle. Therefore the priming is done at high speed to give the gases high velocity.
Water Ring Primer: This primer may be automatic or manually operated. The drive for the primer is taken through a driving wheel on the main shaft to a friction wheel by engaging a lever. The principle here is to rotate an impeller with a hollow centre, in a elliptical housing. Inside the hollow centre is a stationery boss which projects from the housing cover. The boss has two suction and delivery ports in the periphery which communicates with the primer suction and delivery connections. The housing is filled with water before priming. When an impeller spins the water inside the housing is compelled to move outwards by the centrifugal force and forms a ring of water within the contour of the housing and creates a hollow electrical vortex. The water ring expands and reduces in diameter with each revolution. This creates a pumping action and the air from the casing is pushed out followed by the water, entering the suction. When water flows out the priming unit held down by a spring is released automatically and priming is completed.
The weekly output test monthly test and sixth month deep lift test not less than 24 feet if conducted regularly as per the drill schedule will keep the pumps duty worthy and reliable.
T.V K Raman
Retd. Fire Office SAIL
Phone : 24470848
Email : email@example.com