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FT 01 FIRE PHASE

PUMPS AND PRIMERS OBJECTIVE 1. State the categories of pumps.

REFERENCE

2. Manual of Fireman, Part 2 Chapter 1. CONTENTS

3. Introduction. To introduce what is a pump and a primer.

4. Definition of Pump. A pump is a machine driven by external power for transmitting

energy to fluids. The power may be provided by the operators own effort or some other suitable mechanical device. 5. Pumps fall broadly into three categories:

a. Positive displacement pumps. b. Centrifugal pumps. c. Ejector pumps.

6. Positive Displacement Pumps. A positive displacement pump is one in which

energy is imported to fluids by displacement between a plunger or rotor and the casing of the pump, the moving parts making an air-and-watertight joint with the casing i.e. with each stroke/rotation of the plunger/rotor, a fixed amount of fluid is displaced. Within this category there are four main types:

a. Force Pumps. Pumps having a solid plunger which creates a vacuum on the up-stroke and pressure in the down-stroke.

Fig. 1: Diagram Showing the Operation of a Force Pump Left: Single Acting. Right: Double Acting

Downstroke

Upstroke

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b. Lift Pumps. Similar to force pumps but having a hollow piston with a valve through which water can pass freely in one direction only. Normally used for wells.

Fig. 2: Diagram Showing the Operation of a Lift Pump c. Bucket and Plunger Pumps. A combination of both Force and Lift Pumps,

having a hollow piston and a trunk which forces water out on down stroke.

Fig. 3: Diagram Showing the Operation of a Bucket and Plunger Pump

d. Rotary and Semi-Rotary Pumps. Pumps operated by means of projection

or projections from a concentric or an eccentric axis which move round a partially cylindrical chamber in such a way as to pick up fluid at one stage of their travel and discharge it at another. Peristaltic pumps are rotary pumps without valves in which a flexible tube is continuously squeezed, and are also auditable for pumping a fluid with solids in suspension, as pumped by a peristaltic pump.

Down Stroke

Valve

Trunk

Plunger

Upstroke

Plunger Valve

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Peristaltic Pump Rotary Pump

Fig. 4: Rotary and Semi-Rotary Pumps 7. Centrifugal Pump. If comprises a wheel with vanes or blade called an impeller in a

housing or case called volute. Water is produced as the water is rotated by the impeller at high speed. The pump works on centrifugal force principle. Centrifugal force can easily be understood by imagining a bucket of water swung at arm’s length; if it is swung fact enough centrifugal force will keep the water in the bucket. 8. Centrifugal force. The tendency of a revolving body to fly out from the centers of

rotations.

a. Construction:

(1) The Impeller. A circular metal casting mounted on and rigidly keyed

to a shaft by which to be rotated. Rotation of the impeller causes water to be discharged from the periphery at high velocity by centrifugal rise. This induces partial, vacuum to be created at its.

Driven Wheel

Out

In

Inlet

Gear Pump

In Out

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Fig. 5: Sketch Showing the Construction of a Typical Impeller

(2) The Casing. The function of the casing is to convert kinetic energy of

the water when it leaves the impeller to pressure energy. This done by reducing the velocity of the water. In order to reduce turbulence and velocity (and in steady a floe to the water as possible, the methods used are:

(a) A volute. It is shaped like the shell of snail and water thrown

from the impeller enters passage which steadily increases in cross-sectional area until it reach the delivery outlet.

(b) Guide Vanes. They are fixed vanes in the casing adapted to

guide the water along its correct path. A ring of guide vanes is sometimes referred to as a guide ring or diffuser. It is quite common to have guide vanes to reduce turbulence at the periphery of an impeller in a volute casing so that the conversion of kinetic energy to pressure energy is started by the guide vanes complete by the volute (Fig. 6).

Fig. 6: The Casing

9. The pressure and quantity of water produced by a pump is governed by:

a. The Speed of Impeller. The faster the impeller rotates, the greater will be

the quantity and also pressure of water. But the speed at which the impeller can be run is limited, or cavitations will occur.

Impeller

Guide Vanes

Water Inlet

Volute

Water discharged at periphery

Water inlet

Vanes

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b. The Size of the Impeller. The larger the size of the impeller, the greater will

be the quantity and also pressure of water. c. The Number of Impellers. Two impellers in a pump will only double the pressure output but the quantity of water produced remains the same as what was produced by the first impeller.

10. Two-Stage Centrifugal Pump:

a. A two-stage pump is, in effect two effects two single-stage pumps coupled together. If two identical single-stage pumps running at the same speed, were go to work with the first one discharging through a short length of hose into the suction inlet of the second, then, neglecting friction loses the water would be discharged from the second pump at twice the pressure at which it entered the inlet of that pump. This is exactly what happens in a two-stage pump except that the two impellers are coupled on the one rotating shaft and the guide vanes or diffuser are extended to guide the water at a steadily decreasing velocity the periphery of the first impeller to the inlet of the second. b. Characteristics of Centrifugal Pumps:

(1) At any given speed, when there is no flow, the pressure is a t a maximum.

(2) When the pressure decreases progressively with an increase in the discharge as the delivery valves are opened.

(3) Both pressure and flow increase as the pump speed is increased and vice verse.

(4) The power (BUP) absorbed by the pump increases as the flow increases.

11. Peripheral Pumps. Sometimes known as the re-generative pump output pressure

which are three or four times as great as those developed by conventional centrifugal impeller of equal diameter and running at the same speed? Most suitable for hose reel applications.

a. Operating Principle. The casing forms a torrodial channel at the

periphery or the impeller, except between the adjacent inlet and discharge ports. The water enters the channel at the inlet port and is moved forward along it by smearing force file the water is dragged along by the rotation of the impeller, and

Fig. 7: Two-Stages Centrifugal Pump

Diffuser Passages

Water Inlet

Impellers

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radically outwards between the impeller vanes by centrifugal force. After striking the outer rim of the channel the water separates and moves down the sides of the channel to re-enter the impeller at the base of the vanes. This action, in which kinetic energy imparted to the water by the impeller, is immediately converted back into pressure energy as the water returns in the channel travels from the inlet to the discharge port and the cumulative effect produces a large increase in pressure. The path followed by the water is helical as shown by the arrows in Fig. 8.

Fig.8: Diagram Showing the Operating Principle of Peripheral Pump

12. Ejector Pumps. Work on venturi principle.

a. Venturi Principles.

(1) Either a liquid or a gas can be employed as operating medium or propellant. Consists of a jet and a throat. The jet to impart a high velocity to the propellant and directed into the throat.

(2) The throat is a constricted tube which gradually expands in cross-sectional area until it reaches the same area as it had before the constriction.

Fig. 9: Diagrammatic Arrangement Showing the Operating Principles of a Jet Pump.

(3) Due to the gap between the orifice and the narrowest portion of the throat, the high velocity propellant entering the throat will entrain the liquid or gas which surrounds the jet and draws it into the tube with the stream.

b. Construction. Ejector pumps used for fire-fighting consist of a metal body

having a water inlet to supply the jet, a suction inlet and a delivery outlet. Water is used as the propellant, which is usually supplied under pressure from the conventional fire pump (called a primary pump when used in this way.

Throat

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c. Operation. The water produced by the primary pump is delivered to the nozzle of the ejector pump. With the venture effect created when the propellant leaves the nozzle to enter the throat, the water that is intended to be removed will be entrained into the suction inlet of the pump until it is caught up in the jet stream and passed to the discharge side of the pump, from which it is delivers trough hose to the discharge point.

d. Types of Ejector Pump:

(1) Noble ejector pump:

Fig. 10: Diagram Showing the Construction of the Hughes ‘Noble’ Ejector Pump.

(2) Aquator Ejector pumps:

Fig. 11: Diagram showing the construction of the merry weather Aquator Ejector Pump

e. Advantages of Ejector Pumps

(1) Light and easy to handle.

(2) Can be used in situations where it would not be possible to place a normal pump, i.e. basement and ships holds.

(3) Their operation is unaffected by oxygen deficient atmosphere.

(4) Once set up they require no attention.

(5) No moving parts.

Discharge Jet Supply

Suction

Suction Threat

Outlet Connection

Water Inlet Connection

Suction Inlet

Base

Strainer

Two Stages Ejector Nozzle

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(6) The primary pump supplying the water (propellant) can be suitably sited away from the fire for refueling, running adjustments etc.

13. Pump Glands and Seals. At the point where the pump drive shaft enters the casing

is the pump gland, the purpose of which is to prevent leakage. A traditional type of gland consists of renewable to ensure an adequate seal without exerting too much pressure on the shaft and consequent friction between shaft and packing. 14. Glands of this type are kept cool by water from the pump, and are often also lubricated with grease by means of a grease point to provide a seal and prevent overeating when the pump is run without water, as when priming. Pumps should not be run for long periods without water as the lubricant in the gland is quickly dissipated and damage is likely to occur to the shaft. Such damage, in addition to a leakage of water when pumping, would also make priming difficult. 15. Lubrication of glands of glands of this type should be carried out frequently, and at the intervals specified by the markers. Adjustments should be mane from time to time as required, and should be made when the shaft is rotating and the pump is delivering water. Two glands are shown in Fig.12, one of which has provision for greasing.

Fig. 12: Two Typical Pump Glands, the One on the Right Having Provision for Greasing. 16. Priming is only necessary with centrifugal pumps. Centrifugal pumps cannot ‘pump’ air and are not, therefore, self-priming. A separate primer has to be provided. Some types can, however, be arranged to engage and cut out automatically without any action on the part of the operator, and these are known as automatic primers. 17. The priming devices suitable for use with centrifugal pump are:

a. Reciprocating. b. Exhaust ejector. c. Rotary:

(1) Water ring. (2) Sliding vane.

d. Water seal. 18. Of these the rotary sliding vane and the water seal primers are now not widely used, but all types are described in the following paragraphs:

Lantern Ring Packing Adjusting Sleeve

Packing Greasing Point Adjusting Nuts

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a. The reciprocating prime (Fig.13) consists of a small piston (force pump) which is driven from the main pump drive shaft either by a friction drive, either of when are brought in and out of the main pump inlet is connected to the suction side of the main pump by means of a pipe in which is situated a priming valve (a).

Fig.13: Diagram Showing the Operation of a Reciprocating Primer.

b. When the pump is to be primed the priming valve (a) is opened, and the primer is thus connected with the pump casing and suction. The drive is then engaged and the piston (b) on its down-stroke causes a reduction in pressure in the cylinder until the piston uncovers the inlets port (c): then air from the pump and suction flown in. On its upstroke the piston causes the air to be forced through the outlet valve (d) and discharged through the waste pipe (e). As the air from the pump casing and suction exhausted, water will follow, and when all the air has been priming pump is then disengaged and the valve (a) closed. Normally the priming speed is about 1,000 rpm with a maximum of 1,500 rpm which must not be exceeded.

19. Exhaust Gas Ejector Primer. This type of primer, which is operated by the exhaust

gases from the engine, is shown in diagrammatic form in fig.14. When the pump is to be primed, the priming valve (a) is opened, and the exhaust valve (b) closed. The effect of the closed valve (b) is to divert the exhaust gases from their normal passage down the exhaust pipe to the silencer and conduct them to a nozzle (c). The gas discharges from this nozzle into a throat (pipe (d)) and, on the principle of the jet pump, draws the air from the suction and pump casing through the valve (a).

Priming Valve

Spring Outlet Valve

Inlet

Piston

Suction Inlet

Pump

Waste Pipe

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Fig. 14: Diagram Showing the Operation of an Exhaust Gas Ejector Primer

20. When all the air has been exhausted water will follow, and steam will be seen discharging from pipe (d). The water and exhaust gases will follow their normal courses into the pump and silencer respectively. With the exhaust gas ejector type primer, the efficiency depends on the speed at which the gases leave the discharge nozzle. Priming is for this reason carried out at high revolutions a fully open throttle, and hence exhausts gas velocity. 21. Rotary Primers:

a. Water-ring Primer. Depend on a water ring to from a seal, widely used in

the fire service, which can be arranged for either automatic or hand operation.

b. Construction. A impeller (a) with a hollow centre, rotates in an elliptical

housing (b). Inside the hollow centre is a stationary boss (c) which is a projection from the housing end cover. This boss has two suction and two delivery ports in its periphery which communicate with the primer suction and delivery connections. When the impeller rotates the liquid in the housing, thus creating a hollow elliptical vortex. This liquid ring rotates in the housing with the impeller and as it rotates from the minor diameter, it moves radically outward between the impeller vanes. After it passes the major diameter and rotates toward the minor diameter, it moves radically inwards. As the liquid moves inwards this air is forced into the discharge ports in the central boss. Since the impeller is located centrally in the elliptical housing there are two pumping actions in each revolution?

Pipe

Ejector Nozzle

Exhaust Gases

Exhaust Valve

Priming Valve

From Suction Inlet

To Silencer

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Fig. 15: Diagram Showing the Operation of Water Ring Primer

c. Sliding Vane Primer:

(1) The sliding vane primer extracts the air from the suction and pump casing by positive displacement. A typical primer of this type is illustrated in Fig.16. The rotor (a) which is set eccentrically in the casing is fitted a number of blades which being carried in slots, are free to move radically under the influence of centrifugal force. When the rotor is set in motion these blades fly outwards, and remain in contact which the pump casing, extending and withdrawing as the rotor revolvers.

Fig. 16: Diagram the Operation of the Sliding Vane Rotary Primer.

Housing

Discharge Port

Discharge Port

Water Ring

Impeller Stationary Boss

Suction Ports

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(2) A close chamber is thus formed between any two blades into which air is forced by atmospheric pressure as the blades pass the inlet (b). As the rotor (a) revolves, the blades are forced into their slots.

(3) The volume of the closed chamber therefore gradually decreases and the air in is corresponding compressed. Consequently when the out let (c) is reached the air is expelled, the pressure in the chamber to that of the atmosphere.

(4) After passing the outlet (c) volume of the closed chamber expands, reducing the pressures below atmospheric so that when the inlet (b) is again reached, further air from the suction enters. The process chamber in turn. Primers of this type are not now widely used by fire brigades.

d. Water Seal Primers:

(1) With this type of primer (Fig. 17) a trap is fitted to the pump to ensure that a little water is always kept in the base of the casing is. When the pump is started any air present in the casing is entrained with this water by the action of the impeller and driven out through the primary throat (a). Because at this stage the primary throat has sufficient capacity for all the water in the pump, none remains to fill the secondary throat (b) and the drop in pressure between the two allows the water in the separator chamber (c) (which is nor freed of air by the reduced velocity) to re-enter the pump down secondary throat.

Fig.17: Diagram Showing the Operation of the Water Seal Primer

Outlet (d)

Separator Chamber (c)

Primary Throat (a)

Secondary Chamber (b)

Pump

Air

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(2) This process continues, the same small quantity of water being used over and over again, and drawing out additional air each time until all the air has been exhausted from the suction and pump casing, and water enters the pump. There is then too much water to be passed by the primary throat alone and the flow in the secondary throat therefore reverses and water flows from both (a) and (b) through the separator chamber (c) to the delivery outlet (d). (3) Water seal primers are used extensively in contractors’ types of pump. They are not ideal for fire brigade use as priming is comparatively slow, the maximum lift is limited.

22. Power Take-Off. The power take-off is a device by which the full power developed at the gearbox of an appliance can be diverted, when required, from its normal path down the transmission to the rear axle, and instead to drive a fire pump. In fire brigades a power take-off is used to drive the main fire pump and/or a hose reel pump. 23. Three types of power take-off used for driving fire pumps:

a. From the gearbox; (top take-off) b. From the drive shaft to the gearbox; (sandwich take-off)

c. From a transfer box d. Are shown diagrammatically in Fig.18.

Fig.18: Diagram showing types of power take-off: (a) from the gearbox; (b) from the drive shaft to the gearbox; (c) from a transfer box

(a) TOP

P.T.O

To Back Axle

(b) SANDWICH

To Back Axle

(c) TRANSFER BOX

P.T.O

To Back Axle

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24. Cooling System. Internal combustion engines used to propel appliances are normally water cooled. This is achieved by water circulating through the engine block and radiator assisted by a water circulatory pump. Cooling is effected by the induced draught set by a fan behind the radiator, and by the movement of the appliances during which the ram effect of the air assist further in keeping the radiator, engine block and oil sump cool. This letter condition is non-existent when an appliance is stationary and in the portable and trailer pumps, and it is usual to provide supplementary means of cooling for fire brigade pumping appliances. 25. Supplementary cooling systems may be:

a. Direct. b. Indirect open circuit. c. Indirect closed circuit.

26. Direct Cooling System. In the direct system (Fig.19), which was in general use before the Second World War, water is passed direct from the pump to the water jacket in the cylinder block, and after circulating through the water passages in the engine is discharged to waste via the overflow from the header tank.

27. Indirect Cooling system (Open Circuit). In the indirect open circuit cooling

system (Fig. 20) the water from the fire pump does not go directly into the engine cooling system but passes through a coil installed in the header tank and than discharges to waste. The system is, in fast, a heat exchanger in which the cooling water passing through the coils extracts heat from the engine cooling water.

Dual Filter Header Tank

Pump

Engine

To Waste

Fig. 19: Diagram Showing the Layout of an Indirect Open-Circuit Cooling System. Inset: the Operation of the Filter Valve

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28. Indirect Cooling system (Close Circuit). Supplementary cooling systems on

modern appliances are heat exchangers of the closed-circuit type. In a closed-circuit system water is suppliant through piping from the delivers side if the pump, and instead of being discharged to waste, is returned to the inlet side of the pump after extracting heat from the engine cooling water. When pumping, the return pipe to the pump is, therefore, perceptibly warm to the touch. These system are entirely automatic in action, having no valves, filters or controls and come into operation as soon as water in the pump is under pressure. 29. The problem of stationary running is not only one of keeping the engine cooling water overheating, but also of limiting the temperature of the engine lubricating oil, particularly if the sump is not of large capacity, and in some cases where a supplementary cooling circuit is fitted, a by-pass is provided in the piping to cool the oil the engine sump.

Fig. 21: Diagram of a Closed-Circuit Cooling System with the Heat Exchanger Built into the Radiator.

Close Circuit

(water as pump)

Heat Exchanger

Thermostat Close Circuit

Fresh Water (Anti Freezer)

High Pressure

Low Pressure

Flushing and drainage valve

Cooling Coils Header Tank

Filter in use

To Waste

Cylinder Block

Dual Filter

Fig. 20: Diagram Showing the Layout of an Indirect Open-Circuit Cooling System. Insert: the Operation of the Filter Valve.

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Fig. 22: Diagram of a Closed-Circuit Cooling System, Showing The Heat Exchanger as a

Separate Unit Through which the Cooling Water Circulates.

Close Circuit

Fresh Water (anti-freezer)

Close Circuit

(Water as pumped)

Fig. 23: Diagram of a Closed Circuit Cooling System on a Portable Pump.

Pump

Cylinder Head Water Tank