Pumps

Describe the basic operation of the three common types of air compressors.

1.Reciprocating-The reciprocating compressor normally consists of the following elements to act with the compressing element to compress air. •A system of connecting rods, piston rods, crossheads, and a crankshaft and flywheel for transmitting the power developed by the driving unit to the air cylinder piston. •A self-contained lubricating system for bearings, gears, and cylinder walls, including a reservoir or sump for the lubricating oil, and a pump, or other means of delivering oil to the various parts. On some compressors a separate force-fed lubricator is installed to supply oil to the compressor cylinders. •A regulation or control system designed to maintain the pressure in the discharge line and air receiver (storage tank) within a predetermined range of pressure. •An unloading system, which operates in conjunction with the regulator, to reduce or eliminate the load when starting the unit or to ensure pressure is at a satisfactory level when operating 2.Centrifugal-The air particles enter the eye of the impeller, designated D in Figure 38. As the impeller rotates, air is thrown against the casing of the compressor. The air becomes compressed as more and more air is thrown out to the casing by the impeller blades. The air is pushed along the path designated A, B, and C. The pressure of the air is increased as it is pushed along this path. The impeller blades curve forward, which is opposite to the backward curve used in typical centrifugal liquid pumps. Centrifugal compressors can use a variety of blade orientation including both forward and backward curves as well as other designs 3.Rotary-The rotary compressor is adaptable to direct drive by induction motors or multi-cylinder gasoline or diesel engines. The units are compact, relatively inexpensive, and require a minimum of operating attention and maintenance. They occupy a fraction of the space and weight of a reciprocating machine of equivalent capacity. Rotary compressor units are classified into three general groups; slide vane-type, lobe-type, and liquid seal ring-type

State the purpose of the following centrifugal pump components: A. Casing B. Gaskets C. Impeller D. Volute E. Shaft F. Bearings G. Seal rings H. Shaft seals

A. Casing-The pump casing provides the housing for the majority of the major pump components. The inlet (suction) and outlet (discharge) connections are integral to the pump casing B. Gaskets-Gaskets are semi-soft flexible materials used to seal mating surfaces or flanges. C. Impeller-The impeller is the rotating component of the pump that converts the mechanical energy of the prime mover (the pump motor) into kinetic energy (speed) in the fluid. D. Volute-The volute is a gradually expanding spiral, integral to the casing. It reduces fluid velocity and increases fluid pressure. The interaction of the impeller and the volute is what makes a centrifugal pump work. E. Shaft-The impeller is mounted on the pump shaft. The impeller is held on the shaft with a key and a keyway. It is pressed on/off the shaft. The shaft connects the prime mover to the impeller. F. Bearings-The shaft is supported by bearings. Bearings provide two types of support, radial support for side to side motion and axial support for movement along the axis. The radial support is provided by anti-friction journal bearings. The bearings that provide the axial support are called thrust bearings. G. Seal rings-A seal is needed between the impeller and the casing. The seal ring is actually comprised of two parts, the casing ring and the wear ring. The casing rings and wear rings together provide the seal between the impeller and the casing H. Shaft seals-Shaft seals can be a stuffing box or a mechanical seal. The stuffing box is stuffed with packing, which is a soft compressible material. It is held in place with the packing gland

Explain the following positive displacement pump classifications: A. Single/Double acting B. Simplex/Duplex/Triplex/Multiplex

A. Single/Double acting-• 1-Single-acting pump - The single-acting pump discharges fluid only on the forward stroke of the piston. The return stroke is a cylinder-loading stroke and does not discharge any fluids into the discharge line. Pumps of this type, therefore, discharge fluids in pulses. 2-Double-acting pump - Discharges fluid on both strokes of the piston. As the piston travels to one end of the pump, fluid is discharged from that end. While this is happening, liquid is drawn in on the other side of the pump piston. When the piston reverses its travel, the side of the pump that just drew in fluid discharges that fluid and the other side of the pump then draws in fluid into the cylinder. Even though double-acting pumps are more efficient than single-acting pumps, there still is a slight pulsation in the flow of fluid as the piston reaches the end of its stroke. Figures 22A and 22B show a double-acting reciprocating pump. B.Simplex/Duplex/Triplex/Multiplex- 1-Simplex pump - A single cylinder pump. Although there are both driving and pumping ends to the pump, the single cylinder description refers to the liquid pumping end only. 2-Duplex pump - A two-cylinder pump that usually consists of two simplex pumps mounted side-by-side in a common housing. (look at lesson plan)

Describe the following hazards and safety precautions associated with compressed air systems: A. Stored Energy B. Leaks C. Noise D. Contamination (foreign material)

A. Stored Energy- 1.Stored Energy - Pressurized air can do the same type of damage as pressurized water. Treat all operations on compressed air systems with the same care taken on liquid systems. Closed valves should be slowly cracked open and both sides should be allowed to equalize prior to opening the valve further. Systems being opened for maintenance should always be depressurized before work begins. B. Leaks- 1.Small leaks or breaks in the compressed air system can cause minute particles to be blown at extremely high speeds. Safety glasses should be worn when working in the vicinity of any compressed air system. Safety goggles are recommended if contact lenses are worn. C. Noise 1.Noise - Compressors can make an exceptional amount of noise while running. The noise of the compressor, in addition to the drain valves lifting, creates enough noise to require hearing protection. The area around compressors should normally be posted as a hearing protection zone. D. Contamination (foreign material) 1•Foreign Material - Great care should be taken to keep contaminants from entering air systems. This is especially true for oil. Oil introduced in an air compressor can be compressed to the point where detonation takes place in a similar manner as that which occurs in a diesel engine. This detonation can cause equipment damage and personnel injury.

Explain the following centrifugal pump classifications: A. Vertical/Horizontal mounted B. Single/Double-suction impeller C. Open/Closed impeller D. Single/Double/Multi-staged E. Radial flow F. Axial flow G. Mixed flow

A. Vertical/Horizontal mounted-Vertical and horizontal refer to the position of the shaft during normal operation B. Single/Double-suction impeller-Single-suction and double-suction refers to the number of suction eyes of the impeller C. Open/Closed impeller-Impellers can also be classified as open or enclosed impellers. Open impellers are good for pumping fluids containing solids, since these impellers do not clog easily. Enclosed impellers tend to be more efficient than open impellers although more expensive. The enclosed impeller vanes also wear less, because there is less erosion D. Single/Double/Multi-staged-A pump can have multiple impellers for the purpose of increasing discharge pressure of the pump. Each impeller is considered to be a "pressure stage". Multi-stage pumps can provide high flow rates and high discharge heads. E. Radial flow-In radial-flow pumps, for example, the impeller is designed to direct fluid out from the shaft at a 90° angle F. Axial flow-axial-flow pumps, Figure 13A, are able to move tremendous volumes of fluid but at relatively low discharge pressures. The impeller of an axial flow pump is basically a propeller, moving the fluid along a path parallel to the shaft (axis) of the pump G. Mixed flow-to some degree, the functions of radial-flow pumps and axial-flow pumps. Mixed-flow impellers are designed to discharge fluid at an angle greater than 0 (axial-flow pumps) and less than 90 (radial-flow pumps) from the shaft

Define the following pump operating characteristics: A. Capacity B. Pump head terms C. Pump lift terms D. Net positive suction head available (NPSHA) E. Net positive suction head required (NPSHR)

A.Capacity-The rated volumetric flow rate for a specific set of parameters is the capacity of the pump. B.Pump head terms- 1.Static Head: The static head is a difference in fluid levels (elevation head). It is normally stated in feet (feet of water column). 2.Dynamic Head: This is the energy required to set the fluid in motion and to overcome any resistance to that motion (velocity head and friction head). Dynamic head is also normally stated in feet (feet of water column). 3.Total suction head is the amount of pressure, typically expressed in feet (feet of water column), that is available at the suction of a pump. The total suction head is the static suction head minus the dynamic suction head of the pump. 4.The static suction head is the elevation difference between the source fluid level and the centerline of the pump. 5.Total discharge head is the sum of the static discharge head and dynamic head of the piping downstream of the pump, also commonly expressed in ft (ft of water column). 6.The static discharge head is the elevation difference between the centerline of the pump and the fluid level on the discharge of the pump. 7.Total head is the total pressure difference between the total discharge head and the total suction head of the pump. C.Pump lift terms D.Net positive suction head available (NPSHA) 1.Net positive suction head (or available NPSH) is the absolute pressure at the suction of the pump minus the vapor pressure of the fluid at the same point. E.Net positive suction head required (NPSHR) 1.Required NPSH is the required pressure above the vapor pressure necessary to prevent cavitation for some given volume flow

Describe the following failure mechanisms and symptoms (including methods of prevention and correction) of centrifugal pump operation: A. Cavitation B. Deadheading C. Runout D. Gas Binding

A.Cavitation-Cavitation (or loss of NPSH) occurs when pump suction pressure approaches saturation pressure of the fluid in the pump. 1-Several different methods (or combinations of methods) are employed to prevent cavitation: •Use a head tank to create a static pressure at pump suction. •Use a booster pump to increase pressure at suction of next pump. •Use a large diameter suction pipe to convert fluid KE to fluid Pv energy, causing pressure to increase. •Subcool liquid to lower required NPSH (lower vapor pressure ) •Pressurize the entire system. B.Deadheading-Deadheading refers to operating a pump at high head with little or no flow through the pump. 1-Providing a flow path that meets the manufacturer's suggested minimum safe flow rate can prevent "deadheading". This is sometimes called "minimum flow recirculation" since the path provided usually returns (recirculates) back to the pump suction C.Runout-Pump Runout refers to the maximum flow rate at the lowest anticipated system head. 1-Runout can be prevented by system design (choose correct pump for system), throttling pump discharge to prevent high flow rates, by creating a minimum static head the pump must always discharge to and with alarms if flow rates become excessive D.Gas Binding-Gas binding of a centrifugal pump is a condition where the casing contains gases or vapors to the point where the impeller is no longer able to contact enough liquid to function correctly 1-A steady stream of liquid from the casing vent during filling must be observed to verify proper filling and venting. Other system vents must also be observed to emit a solid stream of liquid during filling to ensure all gases have been removed.

Describe the theory of operation of the following types of positive displacement pumps: A. Reciprocating pumps (piston, plunger, diaphragm, etc.) B. Rotary pumps (vane, screw, gear, etc.)

A.Reciprocating pumps (piston, plunger, diaphragm, etc.)-A reciprocating pump may be defined as a pump that operates using a back and forth, straight-line motion. Frequently an air or steam reciprocating piston drives the reciprocating pump. Reciprocating pumps can be piston-type, plunger-type, and diaphragm-type models. B.Rotary pumps (vane, screw, gear, etc.)-Defined in its most basic terms, a rotary pump is a positive displacement pump employing rotary motion. Rotary type pumps include gear, screw, and vane pumps.

Describe the operation of centrifugal pumps to include: A. Starting a centrifugal pump B. Control of flow rates (including minimum flow) C. Safety precautions D. Series and parallel alignment

A.Starting a centrifugal pump-The driver should be tested for its direction of rotation. The arrow on the pump casing indicates the proper direction for rotation. It should be possible to rotate the shaft by hand. This starts the flow of oil to the bearing surfaces. (look at page 22 for more information) B.Control of flow rates (including minimum flow)-Mini-flow recirc valve controllers usually sense the flow downstream of the pump discharge and open the recirculation valve if the flow is not at some minimum value. C.Safety precautions-A centrifugal pump should be shut down immediately if it becomes excessively noisy. Cavitation will cause excessive noise and can result in damage if the pump is not stopped and the cause corrected. Other sources of noise that may require pump shutdown include bearing failure, loss of lubricating oil or cooling water, and shaft alignment problems. D. Series and parallel alignment parallel-This type configuration is useful in systems requiring large variations in flow rate. Series- series operation typically results in a significant increase in head with a smaller increase in flow (high pressure)

Describe the operation of positive displacement pumps to include: A. Starting a positive displacement pump B. Control of flow rates (including deadheaded) C. Safety precautions

A.Starting a positive displacement pump- 1.A positive displacement pump should never be started with the discharge blocked or the discharge valve closed. Severe damage to the pump or piping downstream of the pump can occur. Additionally, the discharge valve should never be closed with a positive displacement pump running. If the discharge valve is inadvertently closed, the pump should be stopped immediately. B.Control of flow rates (including deadheaded) 1.The capacity of a positive displacement pump cannot be controlled by throttling its discharge valve. Instead, flow is controlled in several different ways, depending on the design of the pump and how it is used. The volume of the cylinder can be changed in some pumps by varying the length of the stroke. Another would be an adjustable speed drive as in the reciprocating water pump. The flow rate of the pump depends on the volume of the cylinder and the speed of the pump's prime mover C.Safety precautions 1.Ensure that the bearing areas are free from of dirt and moisture, and check for adequate lubrication. Dirt and moisture can accelerate the wear of bearing in the pump.

Identify the three common types of air compressors.

Air compressors are similar to pumps. They impart energy to a gas so the gas can do work as it is directed through components and piping systems. Air compressors come in many designs. Some of the most common are: 1. Reciprocating 2. Centrifugal 3. Rotary

State why air compressors use cooling systems.

Coolers are used to minimize the problems caused by heat and moisture in compressed air systems. Coolers used on the discharge of a compressor are called aftercoolers. Their purpose is to remove the heat generated during the compression of the air. The decrease in temperature promotes the condensing of any moisture present in the compressed air. This moisture is collected in condensate traps that are either automatically or manually drained.

Describe the operation of jet pumps.

Jet pumps are static (static in this use means no moving parts) devices that convert high pressure developed by a centrifugal pump into a high velocity jet flow at low pressure. The high velocity jet is submerged in the fluid to be moved. The low pressure at the jet nozzle draws the surrounding fluid into the throat or mixing section, where the low pressure suction flow mixes with the drive flow (Figure 32). The mixed fluid flows into a divergent diffuser, where the expanding area converts the velocity back to high pressure. This results in a high pressure, high volumetric output pump.

Identify the two main classifications of pumps.

Kinetic (dynamic) and positive displacement.

Describe the changes in velocity head and pressure head from the inlet to the discharge of a centrifugal pump.

Motor -Electrical -Mechanical Impeller -Mechanical -Kinetic Volute -Kinetic -Pv Look at drawing on page 23 of lesson plan

Explain the characteristic curve for a centrifugal pump, including the effects of system changes on pump operation.

The capacity of a centrifugal pump decreases as the pressure at the pump discharge increases. Look at Figure 15 is a plot for an ideal centrifugal pump. The red curve shows discharge head versus capacity for a given pump speed. This is often called the pump characteristic curve. The blue curve depicts the effect of operating the same pump at a higher speed.

Explain the characteristic curve for a positive displacement pump, including the effects of system changes on pump operation.

The pump characteristic curves covered so far have dealt with centrifugal pumps in various configurations. PDPs have simpler "curves" due to their design. The capacity remains virtually constant for any discharge head. The pump supplies enough pressure or head to overcome friction losses.

Explain the three centrifugal pump laws.

These laws state that the volumetric flow rate or capacity is directly proportional to the pump speed, the discharge head is directly proportional to the square of the pump speed, and the power required by the pump motor is directly proportional to the cube of the pump speed. VERY HARD PROBLEMS 1,2,3

Calculate changes in volumetric flow rate, pump head, pump power, and/or pump

VERY HARD PROBLEMS 1,2,3