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116 Cards in this Set
- Front
- Back
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What are the applications for pumps |
A pump is a machine that moves fluid |
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What are the two basic classifications of pumps |
Dynamic and positive displacement |
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How does a dynamic pump move fluid |
Centrifugal force |
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How do centrifugal pumps react when pressure builds beyond their ability to overcome it |
They allow the fluid to slip. Slip is caused when the centrifugal force created by the impeller is the same as the resistance in the discharge pipe |
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What are the four categories of centrifugal pumps |
Radial, mixed, axial, peripheral |
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Define pump head |
Is the pressure that a pump has to overcome to be able to move liquid through the system |
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Static suction lift |
The vertical distance from the liquid supply level to the pump center line when the liquid supply level is below the pump center line |
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Static suction head |
The vertical distance from the liquid supply level to the pump center line when the liquid supply level is above the pump center line |
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Static discharge head |
The vertical distance from the pump center line to either the surface of the liquid in the discharge tank or to the point of discharge |
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Total static head |
The vertical distance from the liquid supply level to the surface of the liquid in the discharge tank or to the point of discharge |
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Frictional loss |
The pressure needed by the fluid to overcome friction as it moves through the piping, valves and fittings in the system |
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Velocity head |
Velocity head is the force causing the fluid to flow through a chamber which is due to the velocity of the fluid |
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Dynamic suction lift |
This is equivalent to the static suction lift plus the velocity head plus all the frictional losses in the suction pipes and fittings |
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Dynamic suction head |
This is equivalent to the static suction head plus the velocity head and minus all the frictional losses in the suction pipes and fittings |
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Dynamic discharge head |
This is equivalent to the static discharge head plus the velocity head and all the frictional losses in the discharge pipes and fittings |
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Total dynamic head |
For pumping systems which have suction lift the total dynamic head equals the dynamic suction lift plus the dynamic discharge head For pumping systems which have suction head the total dynamic head equals the dynamic discharge head minus the dynamic suction head |
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Describe vapour binding and the reasons for it |
If pressure on the suction side of a pump drops below the vapour pressure of the liquid, vapour forms. This could partially or completely stop liquid flow into the pump. The pump is then said to be vapour bound. Reasons for the pressure drop could be: insufficient suction head, high suction lift, excessive friction head or high liquid temperature |
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Describe cavitation and its results |
If pressure inside a centrifugal pump drops below the vapour pressure, vapour bubbles form. The bubbles flow with the liquid until they reach an area of higher pressure (normally at the outer area of the impeller) they then collapse, producing a shock wave. The bubbles collapse, liquid fills the space, hitting and eroding the surface, causing vibration and noisy operation...if continued the erosion causes the impeller to become unbalanced and destroys the bearings in the pump |
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How are vapour binding and cavitation prevented |
Suction pressure must be greater than the vapour pressure of the pumped liquid. This required pressure at pump suction is called net positive suction head (NPSH) |
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How is a pumps capacity determined |
Determined by the volume of liquid delivered per unit of time |
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How is the slip factor and the pump’s volumetric efficiency expressed |
As a percentage of theoretical capacity |
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How is the pumps rating and size expressed? |
Pumps are rated according to the capacity at a given head and speed (RPM) |
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Describe the operating principles of radial flow volute pumps |
The rotating impeller discharges the fluid into a spiral shaped cavity called a volute, because this chamber widens, the velocity of the fluid decreases and part of the velocity head is transformed into pressure |
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Compare diffuser pumps to volute pumps |
Diffusers are used in pump casings to create multiple volutes, they are stationary curved vanes in the casing which redirect the flow of the liquid. The vanes direct the flow outwards thus forcing the liquid toward the discharge nozzle. |
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Describe the operating principles of axial flow and mixed flow pumps |
In an axial flow pump the impeller moves liquid through the casing without changing its direction. The impeller has vanes like a ships propeller. The pump develops its head by the lifting action of the vanes on the liquid. The liquid moves through the casing parallel to the shaft. They are usually mounted vertically, but there are some that mount horizontally. A mixed flow pump combines characteristics of radial flow and axial flow pumps. It develops its discharge head by using centrifugal force and lifting action of the vanes on the liquid. This pump can be mounted vertically or horizontally. Used for low-head, high capacity applications |
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How is greater pressure developed through multiple stages |
By using several impellers connected in series |
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Describe the operating principles of a regenerative turbine pump |
It is a type of peripheral pump. The impeller of this type of pump has a double row of vanes cut in its rim. The impeller is then centered in a machined groove in the casing. These pumps create high pressure for their size and are suited for high pressure low capacity service Liquid enters at the outer edge of the impeller As impeller rotates the vanes travel in a machined channel in the casing giving the liquid a forward motion As the liquid speeds up, centrifugal force throws it into the channel Because of the shape of the channel the liquid returns between the vanes The process repeats several times causing the liquid to follow a spiral path around the outer wall of the casing. Each time the liquid renters a vane it receives an impulse, these impulses increase the pressure gradually from suction to discharge |
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Compare the discharge pressure of a regenerative turbine pump to a similar radial flow pump |
The regen turbine pump can develop a discharge pressure several times larger than a radial flow pump can with the same impeller diameter and speed |
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Describe the types of casings used to encase pumps |
Split casings - axially split casings are split along the axis of the shaft. Suction and discharge nozzles are usually in the lower half of the casing. Upper half of casing is easily lifted for inspection Radially split casings are split at right angles to the shaft. Barrel casings- an inner casing is fitted into an outer casing called a barrel |
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What pump casing materials would you order to pump each of the following liquids |
Water- cast iron casing with bronze fittings Mild acids-bronze Moderate alkalis- ni-resist, stainless steel Concentrated solids in a slurry- chrome steel, ni-hard, maganese steel |
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What type of impeller has |
-a partial shroud on one side -open impeller -shrouds on both sides- closed, single inlet impeller Inlets on both sides- closed double inlet impeller A mechanical screw- screw style impeller |
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How are impellers mounted and held on the pump shafts |
Mounted either on the end of the shaft or mid shaft When mounting is on the end of the shaft the impeller -is screwed onto a threaded shaft and butting against a shoulder, the hand of the thread must have a tightening action as the shaft rotates -has a parallel bore with a sliding fit on the shaft. It is held in position by a shoulder or sleeve on one side, and a keeper (retainer) plate and nut (with a locking device) on the inlet side. A key is needed for positive drive -is installed on a tapered shaft, a key is also used for driving, a nut with a locking device and a keeper plate is used to hold impeller on the taper Mid Shaft Mounting -the impeller is driven by a key and is held in place by -a sliding fit against a shoulder retained by sleeves and a nut -a sliding fit against sleeves and retained by nuts on both ends of the shaft |
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What pump and impeller type would you use for the following applications |
Water at moderate temps-single or double suction, closed Hot hydrocarbons- single suction, often special refinery pump/closed with large inlets Pulpy solids-single suction pump, closed impeller |
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How is internal leakage prevented between the discharge and suction sides of a pump |
By keeping the clearance between the casing and the suction passage of the imperilled to a minimum, this seal is provided by the fit formed by the rim around the impeller eye and the casing. If the wear in the pump exceeds three times the initial clearance the pump loses too much efficiency, wear plates or rings are incorporated into the design of the pump so that they can be replaced when necessary |
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How are seized sleeves removed from the pump shaft |
Grind two grooves with a small hand grinder. Grooves should be 180 degrees apart, axially along the sleeve. Split the sleeve with a cold chisel being careful not to scar the shaft |
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What are the functions of bearings in centrifugal pumps |
To support the shaft carrying one or more impellers To allow the shaft to rotate with minimum friction To keep the rotating shaft and impellers in correct position within the stationary parts of the pump |
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What two basic kinds of bearings are used in centrifugal pumps |
Friction and anti-friction bearings |
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How are friction bearings lubricated on horizontal and vertical pumps |
Horizontal pumps used either drip feed oiling or if the housing has an oil reservoir an endless chain or a ring riding on the shaft can supply oil to the bearings Vertical pumps- use shaft driven pumps to supply oil under pressure to the bearings |
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Where are axial and radial rolling element bearings located in axial split and radially split pumps |
Axial split both ends of the shaft Radially split pumps use radial load bearings at the impeller end and combination (both radial and axial load) bearings are used at the drive end |
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Describe a suitable base to mount a pump and drive source |
Both pump and drive source must sit on a secure base. May be made of cast iron or fabricated steel base is bolted to a solid foundation to absorb vibration |
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What size of channel iron( base width) would be suitable for Type CL Bingham Willamette pump 3X4x9 |
54” |
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Compare base mounting pumps to center line mounting pump |
Base mounted-have mounting lugs on the bottom of the pump casing. Any change in temp of the pump while operating can cause the pump to lift and become misaligned with the coupling -center line mounting - the pump is carried on lugs extending from the center of the pump casing which rest on the base. Because the pump casing expands in both directions from the shaft center line during operating temperature, there is very little effect on coupling alignment |
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Describe close coupled pumps |
The motor shaft extends through the pump casing. The impeller is then mounted directly onto this shaft. The pump casing is normally mounted directly onto the motor casing |
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what checks should be made prior to starting a pump |
-the unit will turn over freely by hand -the pump is driven in the direction shown on the casing -all bearings are properly lubricated -the pump is primed -all air from the seal housing is vented -plenty of quenching fluid is flowing to the seals |
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What happens when the wear rings in a pump wear out |
The pump loses efficiency |
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What safety precautions should be followed when working on a pump |
Always lockout and tag all electrical controls Shut off lock and tag all main valves to and from the pump including the seal fluid supply Drain the pumps. This is important with suction head mounting Flush the pump if it has been pumping acids or any other substance that could injure workers |
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List the preventative maintenance procedures for maintaining centrifugal pumps |
-Volume and temperature of liquid leaking past the packing -oil level -bearing temperature and noise (vibration analysis) -joints and seals for leaks -flow rates at operating conditions |
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What are the routine maintenance procedures carried out on centrifugal pumps |
Consists of changing worn parts without major downtime -replace the compression packing -inspect and if necessary replace the shaft sleeve (not regularily) -change the oil |
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Describe what a pump overhaul usually consists of and where the information needed for this is obtained |
-inspecting/replacing the impeller -inspecting/replacing the wear rings or plates -inspecting/replacing the shaft and shaft sleeve -inspecting the stuffing box and replacing the compression packing or mechanical seal -replacing all bearings and seals **pay attention to the condition and size of fit in things such as spigots, sleeves, impellers and bearing housing. Also check the shaft and wear ring runout before and after tightening the impeller |
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What symptoms would occur if the impeller were running in the wrong direction |
Failure to deliver liquid |
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What symptoms would occur if air were leaking through the stuffing box |
Reduced capacity or pressure |
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What are the possible reasons for a pump driver to be overloaded |
Speed is too high Viscosity of the liquid is different then recommended for the pump Mechanical resistance in the pump |
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What are the causes of pump vibration |
Misaligned coupling Insecure foundation Unbalanced impeller due to a chipped blade Unbalanced impeller due to cavitation Bent shaft Worn bearings |
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what corrections should be made if an unbalanced impeller is due to cavitation |
Repair and replace impeller and increase suction pressure |
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What corrections are required if the pump casing wears |
Repair casing by means of welding or installing an insert. Replace the pump casing with a more suitable material for the pumped liquid |
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How are the wear rings fastened in a pump |
Shrink fit, a spigot groove or pins, screw threads |
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What corrections are needed if there is excessive packing wear due to overheating |
Ensure cooling supply to the stuffing box is operational Ensure gland nuts are not too tight |
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What are the usual causes of casing damage |
Impact Uneven base Freezing |
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Where are positive displacement pumps used |
Where a constant flow or a measured amount of flow is critical |
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What are the two classifications of displacement pumps |
Reciprocating Rotary |
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Define volumetric efficiency of a displacement pump |
As the system pressure increases so does the internal leakage. The degree to which this happens is called volumetric efficiency |
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What are the two types of reciprocating pumps and what type of flow is produced |
Piston/plunger Diaphragm Best for low flow rates and high suction lifts but are not suitable for dirty or viscous fluids |
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How are the wear rings lubricated |
By the pumped liquid |
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Describe wearing (cheek) plates |
Used with open impellers in radially split casings, wear plates, cheek plates are used instead of rings, they protect the from and/or back faces of the casing. Clearance between the plate and impeller can be adjusted by moving the shaft axially, usually done by adding shims |
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Describe how hydraulic axial thrust is controlled using opposing impellers, holes in impellers, and balancing drums/disks |
Any excess pressure built up in the back face of the impeller is allowed to pass through the radial clearance between the balancing drum and the balancing drum head. This pressure then returns to the suction side of the pump |
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What methods are used to control leakage between the casing and the shaft |
Mechanical seals or compression packing |
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Describe a mechanical seal |
The mechanical seal acts as a check valve to prevent liquid under pressure from leaking out of the pump or from drawing air into the pump when under vacuum conditions |
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Define volumetric efficiency of a displacement pump |
As the system pressure increases so does the internal leakage. The degree to which this happens is called volumetric efficiency |
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How is shaft wear and corrosion at the pumps stuffing box controlled |
On smaller pumps the shafts are usually made from corrosion resistant and wear resistant materials. larger pump shafts are usually protected by renewable sleeves made of satellite, stainless steel or chrome plated brass/bronze |
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What does the volume of liquid per stroke depend upon |
The cross sectional area of the piston and on the length of stroke |
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What is the difference between plunger and piston pumps |
The plunger pump has its plunger sliding inside packing The piston pump has its packing sliding with its piston |
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Describe the operating principles of a single-acting plunger/piston pump |
Has a piston which slides inside a cylinder. The cylinder acts as a chamber and as the piston moves in the cylinder it displaces most all the fluid in the cylinder. Single acting refers to only one side of the plunger piston doing the pumping
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Describe the operating principles of a double acting plunger/piston pump |
In double acting both sides of the piston moves fluid. The piston discharges at each stroke |
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What types of packing are used to promote efficient operation of plunger/piston pumps |
V ring or U ring |
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Describe the operating principle of external vane pumps |
Has a oval rotor ring rotating centrally in the housing. One sliding vane separates the inlet and discharge ports, as the rotor rotates it carries fluid from the inlet port to the discharge port, the vane maintains a seal between the rotor and the housing |
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Describe the operating principles and state the applications for flexible tube pumps, flexible liner pumps and flexible vane pumps |
-flexible member pumps use a flexible tube, liner or vane to carry fluid from the inlet to the discharge port Flexible tube pumps-uses a rotor with two lugs mounted on the periphery, 180 degrees apart, these lugs compress the tube against the housing, it forms a seal that prevents the liquid from returning to the inlet port. As the rotor rotates it forces the liquid around the housing to the discharge port. Rotation is slow about 200 rpm with pressures to 100 psi. Discharges liquid every 1/2 revolution Flexible liner pumps-uses an eccentric rotor to force the internal walls of a flexible liner outwards against the housing. It discharges liquid once per revolution. The liner has a divider between the inlet and discharge ports, preventing the liquid from returning to the inlet port Flexible vane pumps-has a rotor with flexible vanes, the vanes carry liquid around the housing from the inlet to the discharge ports, an insert is mounted between the discharge and inlet ports it compressed the vanes and forces the liquid out, used for transferring liquids such as coolants |
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Describe the operating principles of lobe pumps |
Lobe pumps have two rotors each with one two or three lobes. These rotors are placed in a casing with a set of external timing gears which synchronize the lobes. The liquid is trapped in the pockets formed by the lobes and the casing. The motion of the lobes carries the liquid around the casing to the outlet |
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How is proper timing assured for reassembly of lobe pumps |
Check the timing gears for mate marks, they are often put on at the factory to aid in reassembly. If there are no mate marks be sure to put some on before taking the gears apart |
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Describe the operating principles of single screw, two screw and multiple screw pumps |
Single screw-(progressive cavity) has one rotor (screw) inside a stationary lobed casing called a stator. Much like a lobed pump the cavity is produced between the inside surface of the rotor with the stator, while the outside surface of the rotor remains in contact with the stator to prevent the fluid from moving back to the inlet Two screw-has two rotors each with opposing screw threads one left and one right hand. One rotor is the drive and stays in proper mesh by means of timing gears Multiple screw-has multiple rotors, the center drive screw thread has one hand and the other screw threads have the opposite hand. As the screws rotate , the liquid is carried between the threads and the casing, axially towards the outlet. The threads are in constant mesh with each other restricting the fluid from returning to the inlet |
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Describe the operating principles of axial piston pumps |
Has its pistons positioned axially in the pump |
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What pumps are diaphragm pumps similar to in action |
Plunger/piston pumps |
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List the types of check valves used in conjunction with reciprocating pumps and state the application for each type |
Ball check valves-used where free opening of suction and discharge is needed Stem guided check valves-are used for low pressures Wing guided check valves- are used for moderate or high pressures (high pressure, clear liquid) Flap check valves-are used for low pressures and free flow of semi solids. Primarily found in diaphragm pumps |
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What type of flow does a rotary pump produce |
Continuous flow and smooth discharge |
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What are some applications for rotary pumps |
Used for fuel, lubricants, hydraulic oil, liquid viscosities including gases and liquified gases |
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Define fixed delivery and variable delivery |
Fixed delivery always delivering the same volume at a given speed Gear, vane and piston types are all used in these systems Variable delivery-delivering volumes varying from zero to a given maximum. Vane and piston types only |
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Describe the construction and action of external and internal gear pumps d |
External gear pumps have two oppositely rotated, externally cut gears inside one casing Internal gear pump have one internally cut gear and one externally cut gear they are separated on one side by a crescent shaped partition |
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Describe the construction and action of sliding vane pumps |
Sliding vane pumps have a rotor set slightly off center in its casing, vanes in the rotor are free to slide in channels pushed outwards by centrifugal force as the motor rotates. Because of the offset the vanes create chambers of different sizes as it rotates around the casing. They are bigger near the intake and smaller near the outlet |
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Compare unbalanced vane pumps to balanced vane pumps |
Unbalanced vane pumps-the pumping action is only on one side of the pump Balanced vane pumps- has a elliptical case with two inlets and two outlets |
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Describe the operating principles of a variable capacity vane pump |
The rotor may be centered or off centered in various directions. This is done by moving the pressure chamber ring. Automatic controls with a spring loaded governor are built into the pump. They vary the flow to meet demand; levels are preset. If the discharge rate is seldom changed, it is adjusted manually. These systems sometimes rely on pump action rather than relief valves to limit pressure |
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What types of packing are used to promote efficient operation of plunger/piston pumps |
V ring or U ring |
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Describe the operating principle of external vane pumps |
Has a oval rotor ring rotating centrally in the housing. One sliding vane separates the inlet and discharge ports, as the rotor rotates it carries fluid from the inlet port to the discharge port, the vane maintains a seal between the rotor and the housing |
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Describe the operating principles and state the applications for flexible tube pumps, flexible liner pumps and flexible vane pumps |
-flexible member pumps use a flexible tube, liner or vane to carry fluid from the inlet to the discharge port Flexible tube pumps-uses a rotor with two lugs mounted on the periphery, 180 degrees apart, these lugs compress the tube against the housing, it forms a seal that prevents the liquid from returning to the inlet port. As the rotor rotates it forces the liquid around the housing to the discharge port. Rotation is slow about 200 rpm with pressures to 100 psi. Discharges liquid every 1/2 revolution Flexible liner pumps-uses an eccentric rotor to force the internal walls of a flexible liner outwards against the housing. It discharges liquid once per revolution. The liner has a divider between the inlet and discharge ports, preventing the liquid from returning to the inlet port Flexible vane pumps-has a rotor with flexible vanes, the vanes carry liquid around the housing from the inlet to the discharge ports, an insert is mounted between the discharge and inlet ports it compressed the vanes and forces the liquid out, used for transferring liquids such as coolants |
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Describe the operating principles of lobe pumps |
Lobe pumps have two rotors each with one two or three lobes. These rotors are placed in a casing with a set of external timing gears which synchronize the lobes. The liquid is trapped in the pockets formed by the lobes and the casing. The motion of the lobes carries the liquid around the casing to the outlet |
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How is proper timing assured for reassembly of lobe pumps |
Check the timing gears for mate marks, they are often put on at the factory to aid in reassembly. If there are no mate marks be sure to put some on before taking the gears apart |
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Describe the operating principles of single screw, two screw and multiple screw pumps |
Single screw-(progressive cavity) has one rotor (screw) inside a stationary lobed casing called a stator. Much like a lobed pump the cavity is produced between the inside surface of the rotor with the stator, while the outside surface of the rotor remains in contact with the stator to prevent the fluid from moving back to the inlet Two screw-has two rotors each with opposing screw threads one left and one right hand. One rotor is the drive and stays in proper mesh by means of timing gears Multiple screw-has multiple rotors, the center drive screw thread has one hand and the other screw threads have the opposite hand. As the screws rotate , the liquid is carried between the threads and the casing, axially towards the outlet. The threads are in constant mesh with each other restricting the fluid from returning to the inlet |
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Describe the operating principles of axial piston pumps |
Has its pistons positioned axially in the pump The pistons connect to a drive shaft which rotates A cylinder block houses the pistons, it rotates against a stationary valve plate which houses the intake and outlet ports. The driveshaft is at an angle to the cylinders. The angle is called the housing angle. |
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Describe the operating principles of a constant displacement , radial piston pump |
Constant displacement radial piston pumps have a rotating, eccentric shaft rather than a cylinder block. The piston cylinders are contained in the fixed housing of the pump. Each piston has a check valve for fluid to enter and another for fluid to exit. -as the eccentric shaft rotates (180) from the high to low point, the piston cavity fills with fluid. -as the eccentric shaft rotates the other 180, the piston cavity discharges the fluid. -this cycle acts on every piston in sequence |
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How is capacity regulated in a positive displacement pump |
It is regulated by varying their speed. |
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Why is excessive pressure relieved with positive displacement pumps |
It is relieved by using a pressure relief valve that redirects the fluid after it reaches a set pressure limit. Without this pressure relief valve a blocked line could damage the motor or break the pump |
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What pumps are diaphragm pumps similar to in action |
Plunger/piston pumps |
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List the types of check valves used in conjunction with reciprocating pumps and state the application for each type |
Ball check valves-used where free opening of suction and discharge is needed Stem guided check valves-are used for low pressures Wing guided check valves- are used for moderate or high pressures (high pressure, clear liquid) Flap check valves-are used for low pressures and free flow of semi solids. Primarily found in diaphragm pumps |
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What type of flow does a rotary pump produce |
Continuous flow and smooth discharge |
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What are some applications for rotary pumps |
Used for fuel, lubricants, hydraulic oil, liquid viscosities including gases and liquified gases |
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Define fixed delivery and variable delivery |
Fixed delivery always delivering the same volume at a given speed Gear, vane and piston types are all used in these systems Variable delivery-delivering volumes varying from zero to a given maximum. Vane and piston types only |
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Describe the construction and action of external and internal gear pumps d |
External gear pumps have two oppositely rotated, externally cut gears inside one casing Internal gear pump have one internally cut gear and one externally cut gear they are separated on one side by a crescent shaped partition |
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Describe the construction and action of sliding vane pumps |
Sliding vane pumps have a rotor set slightly off center in its casing, vanes in the rotor are free to slide in channels pushed outwards by centrifugal force as the motor rotates. Because of the offset the vanes create chambers of different sizes as it rotates around the casing. They are bigger near the intake and smaller near the outlet |
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Compare unbalanced vane pumps to balanced vane pumps |
Unbalanced vane pumps-the pumping action is only on one side of the pump Balanced vane pumps- has a elliptical case with two inlets and two outlets |
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Describe the operating principles of a variable capacity vane pump |
The rotor may be centered or off centered in various directions. This is done by moving the pressure chamber ring. Automatic controls with a spring loaded governor are built into the pump. They vary the flow to meet demand; levels are preset. If the discharge rate is seldom changed, it is adjusted manually. These systems sometimes rely on pump action rather than relief valves to limit pressure |
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What are two important factors in the installation of positive displacement pumps? |
Should be mounted on a strong rigid base and aligned with the power source |
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What does the allowable wear for a pump depend on |
The amount of demand put on it |
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Are positive displacement pumps repairable |
Yes |
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What correction is needed if the pump is leaking around the shaft seal |
Inspect the bearings and replace if necessary and replace the shaft seal as specified |
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What is the symptom and the correction needed if the oil viscosity is too high for the pump to pick up and prime |
Use thinner oil following recommendations for temp and service |
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What corrective action should. Be taken if oil is freely re-circulating to the tank through the system |
Check directional control valves, the return line may be open |
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How would you test for a small air leak on the pump suction line |
By pouring pumped fluid on the joints while listening for a change in the sound of operation |
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What are the symptoms of a partially clogged intake line or filter, or restricted intake pipe and what corrective measures should be taken to repair it? |
Clean the lines & filter to prevent cavitation, pump makes unusual noise |
