Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
101 Cards in this Set
- Front
- Back
|
when inspecting or overhauling vertical centrifugal pumps, never rely on what type of coupling to support the total pump rotor weight?
|
FLEXIBLE COUPLING
|
|
|
what should be used to protect shafts or shaft sleeve areas of the supporting devices when working with vertical centrifugal pumps?
|
PADS OR WRAPPINGS
|
|
|
before opening the steam end of turbine-driven pumps, what should you ensure is done?
|
ensure that drains are open, and steam and exhaust root valves are wired shut.
|
|
|
what are centrifugal pumps used for?
|
used for teh majority of nonviscoous liquid services on ships.
|
|
|
what are the advantages of using a centrifugal pump?
|
simplicity, compactness, weight saving, and adaptability to the highspeed prime mover
|
|
|
what are the disadvantages of using centrifugal pumps?
|
lack of suction lift, sensitivity to variations in the head and speed
|
|
|
how is the bearing used with centrifugal pumps
|
supports or positions the shafts on which a rotor is mounted.
|
|
|
what two ways may a bearing be used for centrifugal pumps?
|
internal or external
|
|
|
explain internal bearings
|
lbearing is ubricated by the liquid being pumped
|
|
|
explain external bearings
|
bearing is isolated from the liquid being pumped
|
|
|
name two types of bearings used
|
anti-friction (roller or ball bearing), or fluid film (sleeve and journal)
|
|
|
name two types of anti-friction bearings
|
roller bearing and ball bearing
|
|
|
name two types of fluid film type bearings
|
sleeve and journal
|
|
|
what is the bearing bushing?
|
the removable portion of a sleeve bearing in contact with the journal
|
|
|
what is the bearing housing?
|
a body in which the bearing is mounted
|
|
|
what is the casing as applied to the centrifugal pump?
|
the portion of the pump which includes the impeller chamber and volute or diffuser
|
|
|
what is the casing wearing ring?
|
a stationary replaceable ring. protects the casing at a running fit with the impeller.
|
|
|
what does the wearing ring do?
|
provides an easily and economically renewable leakage joint between the impeller and the casing.
|
|
|
how does wear occur on the wearing ring?
|
occurs due to pressure differential across the leakage joint
|
|
|
what is the cyclone separator?
|
a mechanical device designed to eliminate foreign matter from the seawater (seal flushing water) supplied to the mechanical seal faces.
|
|
|
how is the cyclone seperator integrated into the pump?
|
integrally connected to the pump through tubing and fittings on the suction and discharge piping and on the stuffing box
|
|
|
what is the deflector (flinger)?
|
a flange or collar around a shaft which rotates with it to prevent passage of liquid, grease, oil, or heat along the shaft
|
|
|
what is the diffuser?
|
a piece, adjacent to the impeller exit, which has multiple passages of increasing area for converting velocity to pressure
|
|
|
what is the gland?
|
a follower which compresses packing in a stuffing box or retains the stationary element of a mechanical seal
|
|
|
what is a grease cup?
|
a receptacle for containing and supplying lubricant
|
|
|
what is the impeller?
|
the bladed member of the rotating assembly of the pump which imparts the centrifugal force to the liquid being pumped
|
|
|
what is the lantern ring?
|
an annular device used to establish a liquid seal around a shaft, to lubricate the stuffing box packing, and to prevent the leakage of air into the stuffing box during suction lift conditions
|
|
|
what is the mechanical seal?
|
a mechanical device located in the pump stuffing box.
|
|
|
what does the mechanical seal consist of?
|
a stationary element and a rotating element. each has a smooth flat face that prevents the flow of a lilquid or gas into our out of the pump casing
|
|
|
what is the nozzle?
|
the portion of the centrifugal pump casing between the pump and piping connection that is designed to convert fluid velocity to pressure
|
|
|
what is the packing?
|
a pliable lubricated material used to provide a seal around that portion of the shaft located in the stuffing box
|
|
|
what is the polymeric compound?
|
polymer-based material consisting of a thermosetting base (usually epoxy) with an addition of metal, ceramic, or other material
|
|
|
what is the shaft coupling?
|
a mechanism used to transmit power from the drive shaft to the pump shaft or to connect two pieces of shafting
|
|
|
what is the shaft sleeve?
|
a cylindrical piece fitted over the shaft to protect the shaft through the stuffing box, and which may also serve to locate the impeller on the shaft
|
|
|
what is the specific speed?
|
a dimensionless number which is defined as the number of revolutions per minute at which a geometrically similar impeller would run if it were of such a size as to discharge one gallon per minute against one foot of head
|
|
|
what is the stuffing box?
|
a portion of the pump casing through which the shaft extends and in which a mechanical seal or packing and a gland may be placed to prevent leakage
|
|
|
what is the stuffing box, auxiliary?
|
a recessed portion of the gland and cover of a mechanical seal sub assembly designed to accomodate two or more rings of emergency backup packing
|
|
|
what is the stuffing box, auxiliary, also known as?
|
the "back-up" stuffing box
|
|
|
what is the throat bushing?
|
a renewable lining for a pump casing at a shaft penetration or throat.
|
|
|
what is the purpose of the throat bushing?
|
provide a solid surface against which packing seats. provide a fairly tight clearance to the rotating shaft sleeve, so the packing doesnt extrude into the fluid system through the bushing-to-shaft sleeve gap, and be replace-able in case the tight clearance opens up due to wear
|
|
|
what are the types of centrifugal pumps?
|
overhung impeller type. impeller between the bearings type. turbine type.
|
|
|
explain overhung impeller type of centrifugal pump
|
mounted on the end of a shaft which is cantilevered or overhung from its bearing supports. these pumps are further categorized as either close-coupled, where the impeller is mounted directly on the driver shaft: or separately coupled where the impeller is mounted on a seperate pump shaft supported by its own bearings
|
|
|
explain impeller between the bearings type
|
mounted on a shaft with bearings at both ends. is mounted between the bearings. these pumps are further categorized into single stage and multistage configurations
|
|
|
what two categorizations are there for the impeller between the bearings type?
|
single stage and multistage configurations
|
|
|
explain the turbine type of centrifugal pump
|
pumps which are built mostly with internal, liquid lubricated bearings and diffuser casings, which are convenient for multistage construction, and which discharge through a supporting column pipe.
|
|
|
centrifugal pumps are also grouped by hydraulic geometry of their impeller designs. name these types of flows
|
radial flow, axial flow (propeller pump), and mixed flow
|
|
|
explain radial flow
|
liquid enters the impeller axially at the hub and flows radially to the periphery. develops pressure by action of centrifugal force.
|
|
|
what is the specific speed of radial flow?
|
specific speed below 4200 for single suction impellers, and below 6000 for double suction impellers. produce a low flow rate capacity at a high head
|
|
|
explain axial flow
|
a single inlet impeller with the flow entering axially and discharging nearly axially. evelops most of its head by the propelling or lifting action of the vanes on the liquid.
|
|
|
what are the specific speeds for axial flow?
|
specific speed above 9000. produces a high flow rate capacity at a low head
|
|
|
how is specific speed expressed?
|
Ns=n(Q) 1/2 / H 3/4
|
|
|
how is specific speed defined?
|
revolutions per minute at which a geometrically simpilar impeller would run if it were of such a size as to discharge one gallon per minute against one foot of head
|
|
|
what is specific speed indicative of?
|
the shape and characteristics of an impeller.
|
|
|
what pump is used for priming of centrifugal pumps, and occassionaly used as air ejectors or air compressors
|
vacuum pumps
|
|
|
most vacuum pumps are of what design?
|
liquid ring wet vacuum design, commonly referred to as centrifugal displacement pumps or rotary centrifugal compressors.
|
|
|
what does the rotor of a vacuum pump consist of?
|
series of blades projecting from a hollow cylindrical hub through which the shaft has been pressed
|
|
|
what do the blades form?
|
blades are shrouded at the sides and thus form a series of chambers
|
|
|
what kind of shape does the pump body of a vacuum pump usually have?
|
a crcular shape or an elliptical shape.
|
|
|
for circular pump casings, where is the rotor positioned?
|
eccentrically within the circular pump casing
|
|
|
what are Canned Motor Pumps?
|
close-coupled pumps with the motor rotor and stator sealed in separate cans.
|
|
|
how does the canned motor pump contain all pumped fluid?
|
they are completely sealed
|
|
|
what do canned motor pumps not contain?
|
they do not contain mechanical seals or packing.
|
|
|
what is used to lubricate the bearings and cool the motor?
|
pumped fluid
|
|
|
where are canned motor pumps used?
|
where containment of the pumped fluid is essential.
|
|
|
what collects liquid leaving the impeller at a high velocity?
|
a progressively expanding viral casing (volute). velocity is reduced and converted to the pressure head.
|
|
|
what are the stationary guide vanes that surround the impeller called?
|
diffusion vanes.
|
|
|
what do diffusion vanes do?
|
they change the flow direction and conversion of velocity head to pressure head
|
|
|
what are the classifications for centrifugal pumps?
|
service application, number of stages, shaft position, impeller type, and casing type, puping correction arrangement, and materials, and drive type and other classifications
|
|
|
what are the number of stages for centrifugal pumps?
|
single stage, two stage, multistage
|
|
|
what are teh shaft positions of the centrifugal pumps
|
horizontal, vertical, inclined
|
|
|
what are the impeller types for centrifugal pumps?
|
single suction or double suction. open, semiclosed, or closed. radial flow, mixed flow, or axial flow.
|
|
|
what are the casing types for centrifugal pumps?
|
volute. diffuser. or turbine. axcially split, radially split, or barrel.
|
|
|
what are teh piping connection arrangements for centrifugal pumps?
|
side, end, top, or bottom.
|
|
|
what are the materials for definining centrifugal pumps?
|
nodular iron, bronze fitted, all bronze, steel, stainless steel, titanium, nickel aluminum bronze, copper nicker alloy, monel, non metalic composities, ceramics, and other special allows
|
|
|
what are the drive types for centrifugal pumps?
|
flexible coupled. rigid coupled. close coupled. or gear or belt driven.
|
|
|
what types of pumps are seldom used in shipboard service because of shock proofing problems and rapid corrosion when handling sea water?
|
cast iron and bronze fitted pumps
|
|
|
available NPSH means?
|
represents the amount of energy (head) available at teh pump suction to get liquid to flow into the pump.
|
|
|
required NPSH means?
|
determined by the pump manufacturer and depends on the type of impeller inlet, impeller design, pump flow, rotational speed, and nature of the pumped liquid. usually based on an actual test of nearly identical pumps.
|
|
|
suction lift means?
|
exists when the total suction head is below atmospheric pressure. is equal to the static lift plus the friction losses in the suction piping.
|
|
|
what is cavitation of pumps?
|
pumps cavitate when teh absolute static pressure in liquid drops below the liquids vapor pressure.
|
|
|
what will occur when cavitation of pumps is present?
|
vapor bubbles will form
|
|
|
what will severe cavitation do to a pump?
|
in an impeller pump the severe cavitation will remove material from the impeller.
|
|
|
what can cause cavitation?
|
improper pump design, excessive suction lift, improper pump selection for the specific suction conditions, and improper piping arrangements.
|
|
|
what else can result from pump cavitation?
|
results in pump noise and vibration, reduced capacity and efficiency, and pitting of pump parts, especially the impeller.
|
|
|
how is cavitation characterized?
|
by pitting on the back side of the impeller van and on the inside of the back shroud, downstream of the suction edge of the vane.
|
|
|
recirculation means what when dealing with centrifugal pumps?
|
a small amount of recirculation occurs at all capacities from the impeller discharge to the suction through the impeller and casing wear ring clearance.
|
|
|
what will wear cause to the clearance of an impeller pump?
|
will cause the clearance to increase over time and the pump capacity to decrease.
|
|
|
where else can recirculation occur?
|
can also occur in the eye of the impeller of the centrifugal pump when the pump capacity is reduced to about 1/2 to 1/3 of the pump capacity (at the best efficiency point).
|
|
|
how is recirculation damage characterized?
|
by wear on the inside of the front shroud of the impeller where the vanes begin.
|
|
|
what are system curves?
|
a pump operating in a system must develop a total head which is made up of several parts, each stated in feet.
|
|
|
what are examples of SERIES OPERATED PUMPS?
|
potable water booster pumps, diesel engine circulating water pumps (booster pump located below water line) to supply the engine attached pump on a higher deck, and feed booster pumps installed between deaerating feed tanks and feed pumps.
|
|
|
important principle for the BOOSTER PUMP (acting as the first stage)
|
should have the same or slightly greater capacity rating and a lower required NPSH than the pump it feeds. booster pump should always be started first and secured last
|
|
|
how should the BOOSTER PUMP be started and secured?
|
started first and secured last
|
|
|
how can operating conditions be varied by operating pumps?
|
varied by operating pumps in series or in parallel the head capacity curve or two pumps operated in series is constructed by adding the heads of the individual pumps at any capacity
|
|
|
what is PARALLEL OPERATION?
|
pumps may be installed to operate in parallel to handle varying capacity demands over a wide range or when maximum reliability is required
|
|
|
what are examples of parallel operation pumps?
|
main and auxiliary condensate pumps, feed booster pumps, fire pumps, and boiler feed pumps.
|
|
|
operation of several pumps, in parallel, at very low capacities should be avoided for what reason?
|
to prevent overheating
|
|
|
when pumps of different capacity ratings are to operate in parallel (such as main and auxiliary condensate pumps), the shutoff head of the smaller pump should be what in relation to the shutoff head of the larger pump?
|
the shutoff head of the smaller pump should be slightly in excess of the shutoff head of the larger pump
|
|
|
describe MAIN FEED PUMPS
|
feed pumps usually are the high speed, multistage type driven by steam turbines.
|
|
|
MAIN FEED PUMPS may be of what type?
|
HORIZONTAL, VERTICAL, STEAM TURBINE, MOTOR DRIVEN
|
|
|
last card made on page?
|
27
|
