Pumping Apparatus Driver/Operator — Lesson 10

Pumping Apparatus Driver/Operator — Lesson 10 Pumping Apparatus Driver/Operator Handbook, 2nd Edition Chapter 10 — Fire Pump Theory

Learning Objectives 1. Select facts about positive displacement pumps. 2. Complete statements about the operation of positive displacement fire pumps. 3. Answer questions about centrifugal pumps. 4. Complete statements about the operation of centrifugal pumps. (Continued) Pumping Apparatus Driver/Operator

Learning Objectives 5. Match centrifugal pumps to their characteristics. 6. Answer questions about changeover. 7. Select facts about pump wear rings and packing rings. 8. Identify characteristics of pump mounting and drive arrangements. (Continued) Pumping Apparatus Driver/Operator

Learning Objectives 9. Answer questions about intake and discharge piping. 10. Select facts about valves. 11. Distinguish between types of valve actuators. 12. List purposes of drain valves and bleeder lines. (Continued) Pumping Apparatus Driver/Operator

Learning Objectives 13. Identify characteristics of various automatic pressure control devices. 14. Match pump primers to their descriptions and operating techniques. 15. Match pump panel controls and instruments to their descriptions. (Continued) Pumping Apparatus Driver/Operator

Learning Objectives 16. State the primary function of an auxiliary cooler. 17. Explain the operation of marine- and immersion-type auxiliary coolers. Pumping Apparatus Driver/Operator

Positive Displacement Pumps • Have been largely replaced by the centrifugal pump for use as the main fire pump on modern fire apparatus • Are still a necessary part of the overall pumping system on modern fire apparatus because they pump air (Continued) Pumping Apparatus Driver/Operator

Positive Displacement Pumps • Are used as priming devices to get water into centrifugal pumps during drafting operations • By removing the air trapped in the centrifugal pump, water is forced into the pump casing by atmospheric pressure • Types • Piston • Rotary Pumping Apparatus Driver/Operator

Operation of Piston Pumps • Piston pumps contain a piston that moves back and forth inside a cylinder. The pressure developed by this action causes intake and discharge valves to operate automatically and provides for the movement of the water through the pump. (Continued) Pumping Apparatus Driver/Operator

Operation of Piston Pumps • As the piston is driven forward, the air within the cylinder is compressed, creating a higher pressure inside the pump than the atmospheric pressure in the discharge manifold. This pressure causes the discharge valve to open and the air to escape through the discharge lines. (Continued) Pumping Apparatus Driver/Operator

Operation of Piston Pumps (Continued) Pumping Apparatus Driver/Operator

Operation of Piston Pumps • This action continues until the piston completes its travel on the forward stroke and stops. At that point, pressures equalize and the discharge valve closes. (Continued) Pumping Apparatus Driver/Operator

Operation of Piston Pumps • As the piston begins the return stroke, the area within the cylinder behind the piston increases and the pressure decreases, creating a partial vacuum. At this time, the intake valve opens, allowing some of the air from the suction hose to enter the pump. (Continued) Pumping Apparatus Driver/Operator

Operation of Piston Pumps (Continued) Pumping Apparatus Driver/Operator

Operation of Piston Pumps • As the air from the suction hose is evacuated and enters the cylinder, the pressure within the hose and the intake are of the pump is reduced. Atmospheric pressure forces the water to rise within the hose until the piston completes its travel and the intake valve closes. (Continued) Pumping Apparatus Driver/Operator

Operation of Piston Pumps • As the forward stroke repeats, air is again forced out of the discharge. On the return stroke, more air in the intake section is removed and the column of water in the suction hose is raised. This is repeated until all air has been removed and the intake stroke results in water being introduced into the cylinder. The pump is now primed, and further strokes cause water to be forced into the discharge instead of air. (Continued) Pumping Apparatus Driver/Operator

Operation of Piston Pumps Pumping Apparatus Driver/Operator

Single-Acting Piston Pump • Works when the forward stroke causes water to be discharged, and the return stroke causes the pump to fill with water again • Does not produce a usable fire stream because the discharge would be a series of surges of water followed by an equal length of time with no water Pumping Apparatus Driver/Operator

Double-Acting Piston Pump • Has two additional valves to produce a more constant stream • Receives and discharges water on each stroke of the piston Pumping Apparatus Driver/Operator

Piston Pump Characteristics • The output capacity is determined by the size of the cylinder and the speed of the piston travel. • There is a practical limit to the speed that pump can be operated, so the capacity is usually determined by the size of the cylinder. (Continued) Pumping Apparatus Driver/Operator

Piston Pump Characteristics • Have not been used as the major fire pump in pumpers for many years. • Are still in service for high-pressure stream fire fighting Pumping Apparatus Driver/Operator

Multicylinder Pumps • Are more practical to build than one large single-cylinder pump • Are more flexible and efficient because some cylinders can be disengaged when the pump’s full capacity is not needed • Provide a more uniform discharge Pumping Apparatus Driver/Operator

Rotary Pumps • Are the simplest of all pumps in design • Were used extensively as the major pump on older fire apparatus • Are now used as small capacity booster-type pumps, low-volume high pressure pumps, and priming pumps Pumping Apparatus Driver/Operator

Operation of Rotary Gear Pumps • Two gears rotate in a tightly meshed pattern inside a watertight case. The gears contact each other and are in close proximity to the case. (Continued) Pumping Apparatus Driver/Operator

Operation of Rotary Gear Pumps • With this arrangement, the gears within the case form watertight and airtight pockets as they turn from the intake to the outlet. • As each gear tooth reaches the discharge chamber, the air or water in that pocket is forced out of the pump. (Continued) Pumping Apparatus Driver/Operator

Operation of Rotary Gear Pumps • As the tooth returns to the intake side of the pump, the gears are meshed tightly enough to prevent the water or air that has been discharged from returning to the intake. Pumping Apparatus Driver/Operator

Rotary Gear Pump Characteristics • Produce amount water dependent upon the size of the pockets in the gears and the speed of rotation • Are very susceptible to damage from normal wear, sand, and other debris; can be prevented with bronze or soft metal gears Pumping Apparatus Driver/Operator

Rotary Vane Pump Characteristics • Are constructed with movable elements that compensate for wear and maintain a tighter fit with close clearances as the pump is used (Continued) Pumping Apparatus Driver/Operator

Rotary Vane Pump Characteristics • Are one of the most common types of pumps used to prime centrifugal pumps • Are more efficient at pumping air than a rotary gear pump because the pump is self-adjusting Pumping Apparatus Driver/Operator

Operation of Rotary Vane Pumps • The rotor is mounted off-center inside the housing. The distance between the rotor and the housing is much greater at the intake than it is at the discharge. The vanes are free to move within the slot where they are mounted. • As the rotor turns, the vanes are forced against the housing by centrifugal force. (Continued) Pumping Apparatus Driver/Operator

Operation of Rotary Vane Pumps • When the surface of the vane that is in contact with the casing becomes worn, centrifugal force causes it to extend further, thus automatically maintaining a tight fit. • As the rotor turns, air is trapped between the rotor and the casing in the pockets forced by adjacent vanes. (Continued) Pumping Apparatus Driver/Operator

Operation of Rotary Vane Pumps • As the vanes turn, this pocket becomes smaller, which compresses the air and causes pressure to build up. This pocket becomes even smaller as the vanes progress toward the discharge opening. (Continued) Pumping Apparatus Driver/Operator

Operation of Rotary Vane Pumps • At this point, the pressure reaches its maximum level, forcing the trapped air out of the pump. The air or water is prevented from returning to the intake by the close spacing of the rotor at that point. (Continued) Pumping Apparatus Driver/Operator

Operation of Rotary Vane Pumps • The air being evacuated from the intake side causes a reduced pressure (similar to a vacuum), and water is forced into the pump by atmospheric pressure until the pump fills with water. • At this point, the pump is primed and forces water out of the discharge in the same manner as air was forced out. Pumping Apparatus Driver/Operator

Centrifugal Pumps • Are utilized by nearly all modern fire apparatus • Are classified as nonpositive displacement pumps because they do not pump a definite amount of water with each revolution. Rather, they impart velocity to the water and convert it to pressure within the pump itself. (Continued) Pumping Apparatus Driver/Operator

Centrifugal Pumps • Have virtually eliminated the positive displacement pump as a major fire pump in the fire apparatus (Continued) Pumping Apparatus Driver/Operator

Centrifugal Pumps • Consists of: • Impeller — Transmits energy in the form of velocity to the water • Casing — Collects the water and confines it in order to convert the velocity to pressure • Volute — Is a water passage that gradually increases in cross-sectional area as it nears the pump discharge outlet (Continued) Pumping Apparatus Driver/Operator

Centrifugal Pumps (Continued) Pumping Apparatus Driver/Operator

Centrifugal Pumps • The impeller in a centrifugal pump rotates very rapidly within the casing, generally from 2,000 to 4,000 rpm. • The volume capacity of the pump is dependent on the size of the eye of the impeller. The greater the eye, the greater the flow capacity. (Continued) Pumping Apparatus Driver/Operator

Centrifugal Pumps • Main factors that influence discharge pressure: • Amount of water being discharged • Speed at which the impeller is turning • Pressure of water when it enters the pump from a pressurized source (hydrant, relay, etc.) Pumping Apparatus Driver/Operator

Operation and Construction of Centrifugal Pumps • The operation of a centrifugal pump is based on the principle that a rapidly revolving disk tends to throw water introduced at its center toward the outer edge of the disk. The faster the disk is turned, the farther the water is thrown, or the more velocity the water has. (Continued) Pumping Apparatus Driver/Operator

Operation and Construction of Centrifugal Pumps (Continued) Pumping Apparatus Driver/Operator

Operation and Construction of Centrifugal Pumps • If the water is contained at the edge of the disk, the water at the center of the container begins to move outward. The velocity created by the spinning disk is converted to pressure by confining the water within the container. • The water is limited by the walls of the container and moves upward in the path of least resistance. (Continued) Pumping Apparatus Driver/Operator

Operation and Construction of Centrifugal Pumps • This shows that pressure has been created on the water. The height to which it raises, or to extend to which it overcomes the force of gravity, depends upon the speed of rotation. (Continued) Pumping Apparatus Driver/Operator

Operation and Construction of Centrifugal Pumps • The centrifugal pump consists of two parts: an impeller and a casing. The impeller transmits energy in the form of velocity to the water. The casing collects the water and confines it in order to convert the velocity to pressure. Then the casing directs the water to the discharge of the pump. Pumping Apparatus Driver/Operator

Single-Stage Centrifugal Fire Pumps • Are constructed with a single impeller • Are used on front-mount pumps, PTOs, separate engine-driven and midship transfer pumps • May provide capacities up to 2,000 gpm (8 000 L/min) • May have a double suction impeller to minimize the lateral thrust of large quantities of water entering the eye of the impeller (Continued) Pumping Apparatus Driver/Operator

Single-Stage Centrifugal Fire Pumps Pumping Apparatus Driver/Operator

Multi-Stage Centrifugal Fire Pumps • Have an impeller for each stage mounted within a single housing • Have impellers that are usually mounted on a single shaft driven by a single drivetrain • Have identical impellers of the same capacity • Have the capability of connecting the stages in series for maximum pressure or in parallel for maximum volume by use of a transfer valve (Continued) Pumping Apparatus Driver/Operator

Multi-Stage Centrifugal Fire Pumps Courtesy: Hale Fire Pump Company Pumping Apparatus Driver/Operator

Multi-Stage Pumps in theParallel (Volume) Position • Have impellers that take water from a source and deliver it to the discharge • Causes impellers to be capable of delivering its rated pressure while flowing 50 percent of the rated capacity; therefore, the total amount of water the pump can deliver is equal to the sum of each stage (Continued) Pumping Apparatus Driver/Operator

Pumping Apparatus Driver/Operator — Lesson 10