FIRE SERIVCE EQUIPMENT

CENTRIFUGAL PUMPS

Introduction• Brief history of fire pumps• First piston fire pump used in Alexandria, Egypt

about 2,200 years ago.

1. Piston pumps improved many times but remained in use into this century It was replaced with the rotary gear pump in 1906 with the gasoline-powered engine

1. The rotary gear pump was replaced with the centrifugal pump about 1911

Type of pump

• There are 3 types of pumps1. Positive pump

A. Force pumpB. lift pumpC. bucket & plunger pump.

2. Centrifugal pump which fire department most use it.

3. Ejector pump.

Centrifugal pumps

• Centrifugal pumps are more efficient than others for fire fighting for several reasons:

1. Can use positive pressure from fir hydrants

2. Freedom from pulsation

3. Less weight

4. Cost less

General Pump Principles

• Positive displacement pump. • It is easier to understand• the theory of fire pump operation if we study

these pumps in the order they evolved. First were the

• POSITIVE DISPLACEMENT PUMPS. There are two types of positive displacement pumps:

1. - PISTON PUMPS

2. - ROTARY TYPE PUMPS

Fire Pump

• The theory of positive displacement.

The theory of positive displacement pumps is based on the principle water cannot be compressed. The volume and weight of water remain the same regardless of the pressure applied to it

Mechanics of positive

• The mechanics of positive displacement. Positive displacement pumps are mechanical devices with a means of increasing the volume of a chamber.

1. - Increasing chamber volume pulls water in.

2. - Decreasing chamber size forces water out.

• Positive displacement water delivery. Positive displacement pumps deliver more water during one part of their stroke than during others.

Piston pumps

• Piston pumps create a difference in pressure by enlarging the cylinder capacity as the piston is forced upward.

1. - Enlarging volume decreases pressure, drawing water into the pump.

2. - Forcing the piston downward decreases volume , increasing pressure which forces the water out.

3. - Check valves direct the water toward the desired direction of travel

Rotary-type pumps• Rotary pumps consist of a casing divided into separate suction

and discharge chambers by a rotor.1. - The rotor is located so that travel from the suction chamber to

the discharge chamber displaces a quantity with each revolution.2. - Water forced into the chamber is prevented from returning by a

barrier formed by rotor. The chamber remains filled.3. - As the filled chamber rotates, its volume is compressed forcing

the water out of the discharge outlet.4. - As the rotor turns, an amount of water equal to that drawn in is

discharged.5. - Increasing the speed directly increases the volume of water

pumped.

• There are two types of rotary pumps used in the fire service – • ROTARY GEAR PUMPS and ROTARY VANE PUMPS.

Pumps. (a) Reciprocating. (b) Rotary. (c) Centrifugal.

Rotary gear pump

• The rotary gear pump. The rotary gear pump has two rotors that look like gears or lobes. When the pump is operating:

1. - The lobes fit together like gears.2. - The lobes disengage at the intake side of the pump.3. - The separated lobes trap a volume of water between

them and the pump housing.4. - The rotors continue to turn forcing the water along the

pump discharge.5. - At the discharge, the lobes re-engage forcing the water

out the discharge outlet.

Rotary vane pump

• The rotary vane pump. The rotary vane pump has one vane instead of meshing gears. The rotor is mounted off-centre (eccentric 0 to the housing. The rotor has vanes that slide in and out of grooves cut into the rotor. As the rotor turns, the vanes are forced against the pump housing.

1. - Water is drawn into the space of increasing volume created by the rotor, vanes, and rotor housing.

2. - As the rotor continues to turn, the water is forced along as the chamber decreases in volume.

3. - The point of discharge is the point of smallest chamber size along the rotor-vane path.

Rotary-type pump priming

• Rotary type pumps operate on the positive displacement principle. They are self-priming. For this reason, they are the preferred priming devices installed on most fire appliances.

Centrifugal Pump Principle

• Centrifugal pump defined. The word “centrifugal” means to proceed away from the centre or to develop outward.

• Centrifugal force is that energy that tends to throw or impel and object outward from the centre of rotation.

Centrifugal pump theory

• In theory, centrifugal pump operation depends on the centrifugal principle.

1. - A rapidly revolving disc tends to throw water outward. The disc is called an “impeller”.

2. - The water is introduced at the centre of impeller. 3. -The point of water entry into the impeller is called “the

inlet eye”.4. - The impeller is a hollow disc with internal blades that

guide water being thrown to the outer edge.

A diagram showing the parts of centrifugal Pump

Centrifugal pump impeller operation

• Centrifugal pump impeller operation.

A revolving disc, known as an impeller, rotates very rapidly. Water introduced through a suction tube enters the impeller at the “inlet eye” is forced along the impeller blades and then through openings into the space in the casing. This space in the casing is called the “volute”. As the water is forced along the impeller blades, it is given momentum or velocity.

Volute principle

• The volute principle. Most centrifugal pumps are designed on the volute principle. The volute in a centrifugal pump is a spiral shaped space in the pump casing.

1. - This space exists between the outer edge of the impeller and the casing wall.

2. - The space constantly becomes greater as it approaches the discharge outlet.

3. - The space is required because the volume of water thrown from the impeller becomes greater toward the discharge outlet.

Purpose of the volute

• The purpose of the volute. The volute enables the pump to handle an increasing volume of water. At the same time, the volute permits the water velocity to remain constant.

Volute function

• The volute function. Rotating the impeller creates velocity in the water. The velocity converts to pressure as it reaches the confined space of the discharge pipe.

• The close fit between the impeller and the casing prevents water flow back into the pump.

Centrifugal pump operation.

1. - Pressure forces water into the inlet eye. (Pressure may be atmospheric or another source such as hydrant pressure).

2. - The impeller forces the water outward. 3. - The volute conducts the water out through the discharge

outlet.4. - The discharge pressure and capacity (volume) are

regulated by adjusting the:• -- Pump speed (impeller RPM)• -- Transfer valve setting (volume or pressure)• -- Discharge valve opening• -- Nozzle size (diameter )

Main assemblies

• Main assemblies. • To operate a centrifugal pump requires no:• - Check valves• - Pistons or plungers• It does not work on positive displacement. It

operates on the principle of centrifugal force. To operate, the pump requires three assemblies:

1. - the impeller shaft2. - the pump drive3. - the pump casing

A diagram showing the construction of centrifugal Pump

Impeller shaft assembly

• Impeller shaft assembly. The impeller shaft rotates the impeller (s). A centrifugal pump may have one to four impellers.

• The impellers are connected to the same shaft so to rotate at the same speed . Shafts are stainless steel.

A diagram showing the construction of the impeller

Pump drive

• Pump drive. The pump drive is engine power transmitted through the transmission and intermediate gear to the pump shaft. The pump drive also establishes proper engine-to-pump ratio.

• Pump casing. The pump casing contains water passageways and volutes.

Centrifugal Pump Types

• Two types of centrifugal pumps. There are two basic types of centrifugal pumps - SINGLE STAGE and MULTI-STAGE.

• Single stage centrifugal pumps. A single stage pump consists of only one encasing into which one single impeller is encased.

• - Pressure is increased by increasing impeller RPM.• - Volume is the result of impeller design so is

constant.

• more than one impeller mounted on the same drive shaft.

• - Each impeller is enclosed in its own casing.• - Each impeller casing is part of a common pump

casing or body.• - The combination of each impeller and casing is

called a “stage”.• - Two stage pumps are common on fire appliances.• - Three and four stage pumps are also used.

Pressure and volume operation.

• The operation of multi-stage pumps requires an understanding of SERIES and PARALLEL modes.

• In the SERIES mode, the pump routes water from one impeller to the next to generate PRESSURE. In the PARALLEL mode, the water is routed through the passageways separately to the impellers and outlets to generate VOLUME or capacity.

Volume or capacity operations

• The volume or capacity (both terms have the same meaning) of a fire pump is obtained when the various stages of the pump are connected in parallel.

Function in the volume mode

• When a centrifugal pump is placed in the “volume” position, all passageways from the various stages (impellers) are arranged to work with each other side-by-side. When all stages are working together in parallel arrangement, the volume or capacity is equal to the sum of all the stages. Parallel pump operation provides full volume or capacity.

Output capacity in the volume mode

• An example of a two stage centrifugal pump operating in volume is as follows. Two 1000 litres per minute impellers are operating with their control valves (called Transfer Valves) set so the impeller will pump its capacity into a common discharge. When these impellers are rotating at the correct speed, they will each be delivering 1000 litres per minute. So, the output of the two impellers are 2000 litres per minute. This volume (2000 litres per minute) will be the rated capacity of the centrifugal pump.

Water flow in the volume mode

• The water enters both housing at the same time from a common source. The water leaves the pump through a common discharge.

Pressure or series operation.

• The pressure position of a multi-stage centrifugal pump is used to increase pressure when desired pressure is not available when the pump is in the volume mode. The increase in pressure is achieved by

Function in the pressure mode

• Series operation requires each separate stages of the pump to be connected so that water travels in a single continuous path. From one stage into the second stage, thereby increasing the pressure at each stage, while the volume remain the same. The pressure pumped by both stages are combined.

Water flow in the pressure mode

• At a given speed (RPM), a two stage centrifugal pump in series (pressure) position will develop twice the pressure that it will in parallel position as long as the impeller capacity is not exceeded. A three stage pump would increase pressure three times, while a four stage would increase the pressure four times.

Output capacity in the pressure mode

• An example of pressure or series is as follows. Two 1000 litre per minute impellers are operating with the transfer valve set on pressure. The first impeller will pump its capacity of 1000 litres per minute into the eye of the second impeller at a certain pressure. The second impeller picks up 1000 litres per minute and doubles the pressure. Thus, 1000 litres per minute, half the pump capacity of a 2000 litre per minute, is delivered at twice the pressure.

Priming Systems

• Priming theory. Lifting water from an open source and discharging it requires removing the air from the pump and suction hose.

1. - Air removal means creating a partial vacuum called a “pressure differential”.

2. - The pressure differential causes atmospheric pressure (1 bar of force) to force water into the pump, replacing the air.

• There is one limitation - the force of atmospheric pressure itself.

1. - The height water can lifted to create a draft is limited to a distance between 7.3 to 8.5 m.

2. - The exact distance depends on the efficiency of the pump.

Priming defined

• Replacing the air with water in a pump is called PRIMING.• PRIMING DEVICES• Priming devices suitable for use with centrifugal pumps are:• a. Reciprocating • b. Exhaust Ejector • c. Rotary • d. Water Seal

• Centrifugal pump priming device. Centrifugal pumps are various types of priming devices.

Positive displacement priming devices

• Small rotary gear and rotary vane positive displacement pumps.

1. - Expel the air from the centrifugal pump

2. - Use oil to lubricate priming pump and create a tighter seal around gears or vanes. Reduces priming time.

Positive displacement primer lubrication

• Rotary gear and eccentric vane primers will expel air from the pump without lubrication causes excessive wear and noise. Introducing oil into these primers also makes them more efficient, reducing pump priming time.

Positive displacement Pump

Engine vacuum primers

• The apparatus engine intake vacuum is taken from the manifold to operate another priming device.

1. - Opening the priming device control valve creates a partial vacuum in the pump - pressure differential.

2. - Atmospheric pressure forces water into the pump.

Engine exhaust primers

• The apparatus engine exhaust operates another type of primer.

1. - An exhaust ejector is mounted on the exhaust pipe.

2. - The exhaust ejector is equipped with a venture tube to create a pressure diffential in the pump. The operation of this device is similar to the vacuum primer.

Pump Gauges

• Pump gauge types. There are two primary gauges on centrifugal pumps - COMPOUND GAUGE and the PRESSURE GAUGE.

1. The compound gauge. The compound gauge is an instrument giving a pressure or vacuum indication on the same dial. This gauge is mounted on the intake side of the pump.

• The compound gauge gives the water intake pressure or vacuum.• - The “pressure” side of the dial reads in bars or psi (positive pressure).• - The “vacuum” side of the dial reads in inches of mercury (negative

pressure). Thirty inches of mercury equals atmospheric pressure at sea level.

Pressure gauge

• The pressure gauge is mounted on the discharge side of the pump. It indicates the pump discharge pressure (positive pressure only). The pressure gauge gives reading in bars or psi.

• Gauge design and operation. Gauges are delicate instruments and must be properly cared for.

Portable Fire Pumps

• 1 Portable pumps uses and types. There are several uses for portable fire pumps in the fire service. These pumps are the centrifugal type. Portable pumps are grouped into categories by their pressure and capacities.

• 2 Grass and brush fire fighting pumps. Small streams at high pressure are required for grass and brush fire fighting.

• .3 Water supply pumps. Pumps delivering large volume at low pressure are required for filling water tanks used to supply fire apparatus pumps.

• .4 De-watering pumps. Portable pumps are used for salvage work. Often water must be removed from basements and other below ground levels.

• Extinguishing agent pumps. Special portable pumps are used to reservice apparatus agent tanks at accident scenes.

• Airport fire departments use AFFF pumps as part of on-scene agent resupply equipment.

• Causes for prime loss. A pump may fail to prime or priming may be lost during the pumping operation. There are two basic causes for pump prime failure:

1. - Air leaks2. - Blockage of the suction hose

• Air leaks. The gauges will read zero (“0”). Causes of air leaks are:

1. - Air trapped in the pump (called “Air Lock”)2. - Strainer too close to the water surface 3. - An intake cape loose4. - Air leak (hole) in the suction hose5. - Suction hose connection or suction hose/pump connection

loose6. - A leak in gauge, gauge drain, or gauge connection.

Blockage of the suction hose• The pump fails to prime. The pump fails to prime but

compound gauge gives a good reading. Check for the following:

1. - Blockage of the strainer2. - Blockage or obstruction in the suction hose3. - Damaged or kinked suction hose4. - Water level too low to obtain or maintain a draft

• Prime loss during operation. The following may cause a pump to lose prime while operating:

1. - Increasing water pressure too quickly2. - Delivery hose kinked3. - Closing branch too quickly

Pressure loss

• Pressure loss at branches may be caused by:

1. - Fire hose burst

2. - Hose connection disconnect

• Cavitations. Air and water being discharged from the branch is normally caused by the strainer not being sufficiently submerged.

Pump Tests

• Pump test frequency. Fire appliances are tested:

1. - At least annually

2. - The appliance has extensive repair

Types of pump tests.

1. - Dry vacuum test. A check for air leaks in the pump or pump piping.

2. - Priming test. A test of the pump’s ability to obtain and maintain a prime.

3. - Capacity test. A test of the pump’s capability to deliver its rated capacities at:

• -- 10 bar (150 psi)• -- 13.5 bar (200 psi)• -- 17.5 bar (250 psi)4. - Overload test. A test of the appliance’s reserve

power.

Accuracy of tests

• Correctly conducting tests requires precision test equipment and compliance with manufacturer’s guidance and a recognized agency’s standards