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Text MARINE PUMPS

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Title: Text MARINE PUMPS


1
  • Lesson 15
  • Text MARINE PUMPS

2
  • The pumps employed on board ship can be divided
    into two main categories

3
  • (i) positive displacement pumps(????)
  • and (ii) centrifugal pumps(???)?

4
  • They can be broken down into three classes
  • (1) reciprocating(???),
  • (2) rotary(???)
  • and (3) centrifugal.

5
  • Under reciprocating are the direct acting(???),
    power, and crank-fly-wheel types.

6
  • Under rotary are the gear, vane(???),
    cam-and-piston and screw types(???).

7
  • Under centrifugal are the volute(???),
    diffuser(???,???), mixed-flow, axial-flow and
    turbine or regenerative types(???).

8
  • Displacement pumps are those where the volume of
    the pump chamber is alternately(???) increased to
    draw the liquid in from the suction pipe and then
    decreased to force the liquid out into the
    delivery pipe.

9
  • Centrifugal pumps are those wherein an
    impeller(??) rotating at high speed throws(???)
    the liquid by centrifugal force from the center
    to the periphery of the impeller where the liquid
    is discharged through the delivery outlet.

10
  • Gear pumps consist of two or more meshing(??)
    gears spur(???), single or double helical teeth
    (???) enclosed in a close-fitted housing.

11
  • These are used extensively for pumping fuel oil,
    lubricating oil and hydraulic oil.

12
  • When gears are unmeshed on the inlet side, a
    pressure drop occurs that helps the atmospheric
    pressure acting on the surface of the oil in the
    reservoir to force it up the pipe to fill the
    void(??),

13
  • the oil is then transferred around the periphery
    of the pump housing.

14
  • As the gear teeth mesh again on the outlet side,
    they form a seal that prevents oil from backing
    up to the inlet, the oil in the void is then be
    forced out into the discharge line.

15
  • All vane pumps have a rotor driven within a ring
    (camring??????) by a drive shaft coupled to a
    prime mover.

16
  • A cylindrical rotor with sliding vanes,
    generally in radial slots(?), rotates within the
    ring.

17
  • In a simple vane pump(??????), the centre of the
    rotor is offset(??) from the centre of the ring,
    leaving a crescent(????) shaped chamber between
    rotor and the ring.

18
  • As the rotor turns, the vanes are forced outward
    against the inner surface of the cam ring by
    centrifugal force.

19
  • This outward radial movement of the vanes and
    turning of the rotor causes the chamber between
    the vanes to increase as the vanes pass further
    away from the inlet port.

20
  • This increase in volume results in a lowering of
    pressure until the atmospheric pressure is
    sufficient to force oil from the reservoir into
    the inlet chamber.

21
  • Oil from the inlet is swept away by the vanes
    toward the outlet port through a decreasing
    (volume) series of chambers until it is forced
    through the outlet port.

22
  • A vane pump of balanced design has an
    elliptical(???) cam ring so that two pumping
    chambers are formed.

23
  • This pump is in hydraulically balance, since the
    two intake ports and two outlet ports are
    diametrically opposed(?????) to each other.

24
  • Therefore the side loads exerted on the rotor
    cancel out(??), thereby increasing bearing life
    and permitting high operating pressure.

25
  • According to their piston arrangements,
    rotary-piston pumps are classified either axial
    or radial type.

26
  • The pistons in an axial pump operate along the
    axis of the pump drive shaft. The cylinder block
    has a series of cylinder bores with pistons that
    move in and out.

27
  • Rotation of the drive shaft causes the pistons
    and the cylinder block to rotate at the same
    speed.

28
  • As the block rotates, each piston moves in and
    out of its cylinder, the length of stroke depend
    on the angle of the cylinder block with reference
    to the drive plate or swash plate(???) according
    to the designs.

29
  • As each piston moves outward, oil is drawn into
    the cylinder bore through the valve plate(???).

30
  • On the return stroke, the oil is forced out
    through the valve plate under pressure.

31
  • Reciprocating pumps and rotary pumps are
    positive-displacement type because they discharge
    a near constant amount of liquid regardless of
    pressure.

32
  • If the discharge valve is closed, they build up a
    bursting pressure or stall(???) their
    motor(????).

33
  • Centrifugal pumps are nonpositive and a fairly
    low pressure unit. Here a close discharge valve
    will not cause excessive pressure to build up.

34
  • The simple centrifugal pump consists of a
    rotating impeller within a stationary(???)
    casing.

35
  • The fully shrouded(??), single entry impeller is
    the type most widely used.

36
  • The impeller is mounted on a shaft driven by a
    prime mover.

37
  • It consists of a number of vanes backward from
    the direction of the rotation between the
    shroudings.

38
  • Water enters the rotating impeller through the
    entry, known as eye(???)', at the centre.

39
  • Due to the circular motion given it is thrown by
    centrifugal force to the open periphery of the
    impeller where it leaves tangentially(??????) and
    enters the space in the casing, and then directed
    to the outlet branch.

40
  • Unlike the reciprocating displacement pump, the
    centrifugal pump does not have a positive suction
    action(????) and must be primed by flooding
    before it will draw water from a lower level.

41
  • An air pump (???) or a central priming system may
    be used for this purpose.

42
  • In general, reciprocating pumps are suitable for
    delivering small quantities at high pressure,
    rotary pumps are used for moderate quantities at
    moderate pressure, and centrifugal pumps are more
    suitable for large quantities at low pressure.

43
  • Centrifugal pumps, however, can be designed with
    a number of impellers in series(??) to attain a
    high final delivery pressure.

44
  • They are popular because they are very simple in
    construction, and can produce smooth, constant,
    nonpulsating( ???) discharge.

45
READING MATERIAL
  • A. INSTALLATION AND MAINTENANCE OF CENTRIFUGAL
    PUMPS

46
Installation (installation on site)
  • 1. Foundation
  • The foundation of marine pumps is a steel
    base frame (plane parallel alignment(???????) is
    essential).

47
  • Ensure the foundation has set hard before
    mounting the pump set. The surface must be smooth
    and flat.

48
  • Position the pump on the steel base frame or
    foundation, then align(??) and bolt in position.

49
2. Alignment of Pump and Driver
  • After fitting and bolting on the driver, centre
    (?????) it in the flange.

50
3. Connecting the Piping
  • Never use the pump as an anchorage point(???) for
    the piping.

51
  • The pipes must be supported very near the pump
    and connected to the pump without transmitting
    any stresses or strains(??) to it.

52
  • Make sure the pump does not bear the weight of
    the piping. The nominal(????) bore of the pipes
    should be the same as or greater than that of the
    pump nozzles(??).

53
  • Thermal expansion of the piping must be
    compensated for by suitable means, so as not to
    impose any additional load on the pump.

54
  • The suction pipe must not have any valves,
    fittings etc., which might interfere with the
    flow, at a distance of not less than 5 times the
    suction pipe bore from the pump, to ensure
    uniformity(??) of flow to the impeller.

55
4. Auxiliary Connections
  • The size and locations of connections for leak
    fluid and venting, if applicable, are shown in
    the dimension sheet and the lines should be
    connected up accordingly(??).

56
5. Coupling Guard(????)
  • Safety regulations specify that the pump can only
    be operated if the coupling has a guard. The
    coupling guard must be fitted before startup.

57
6. Final Check
  • It must be possible to rotate the rotor easily by
    manually turning the coupling through 360o.
    Ensure all auxiliary lines are correctly
    connected up.

58
Maintenance
  • 7. The pump must run quietly, smoothly and free
    from vibrations at all times. Rough running can
    cause damage to the bearings and shaft seal.

59
  • 8. The pump must never run dry. Avoid prolonged
    operation against a closed shut-off valve(???).

60
  • 9. The temperature of the ball and roller
    bearings may rise to 50oC above ambient
    temperature but must not exceed 80oC.

61
  • The shut-off valves in the various supply lines
    must not be closed during operation.

62
  • 10. Standby pumps must be started-up from time to
    time to ensure that they are in a state of
    constant readiness also rotate the shaft by hand
    at frequent intervals.

63
  • 11. A sealant reservoir for the mechanical seal
    should always be filled with water containing a
    washing up liquid.

64
  • Rapid water level fluctuation(??) points to a
    damaged mechanical seal or shaft seal ring.

65
  • 12. Lubricate the pump as described in the design
    and operating instructions, inspect the pump
    carefully during every grease change and replace
    any worn out parts.

66
  • 13. Before working on the pump and driver, switch
    the set off and ensure it cannot be accidentally
    switched on. Switch off and lock off the main
    switch.

67
  • 14. If work is interrupted, ensure that the set
    is still completely disconnected before-starting.
    Drain the pump and flush it out if necessary.

68
  • Use the general arrangement drawing, which shows
    the part numbers, and the parts list to help you
    when working on the pump.

69
  • 15. If it is likely that handling and storage has
    caused the grease to become contaminated,
    solidify, drain or form condensed water, make
    sure the pump is repacked(????) before startup.

70
  • The pump must also be repacked every time the
    bearings are dismantled.

71
  • 16. Wash and clean the bearings, bearing housing
    and bearing cover-plate using petrol, benzol
    (???,?) or similar, then completely remove all
    traces of washing agent(???).

72
  • Pack the spaces between the balls/rollers with
    30 to 50 grease and the bearing coverplate with
    about 30 grease.

73
  • 17. Check the mechanical seal every day for
    overheating. A leaking seal should be removed,
    checked and replaced, if necessary.

74
  • B. BILGE AND BALLAST SYSTEM

75
  • The bilge system(??????) and the ballast
    system(?????) each have particular functions to
    perform, but are in many ways interconnected.

76
Bilge system
  • The bilge main is arranged to drain any
    watertight compartment(????) other than(??)
    ballast, oil or water tanks and to discharge the
    contents overboard.

77
  • The number of pumps and their capacity depend
    upon the size, type and service of the vessel.

78
  • All bilge suctions must be fitted with suitable
    strainers, which in the machinery space would be
    mud boxes(??) positioned at floorplate(??,??,????)
    level for easy access(??).

79
  • The emergency bilge suction or bilge injection
    valve is used to prevent flooding of the ship.

80
  • It is a direct suction from the machinery space
    bilge which is connected to the largest capacity
    pump or pumps.

81
  • An emergency bilge pump is required for passenger
    ship but may also be fitted as an extra
    (stand-by) on cargo ships.

82
  • It must be an independent unit capable of
    operating even if submerged(??).

83
  • A centrifugal pump with a priming device is
    usually used, driven by an electric motor housed
    in an air bell(???).

84
  • The power supply is arranged from the emergency
    generator.

85
  • The various pumps and lines are interconnected to
    some extent so that each pump can act as an
    alternative or standby for another.

86
Ballast systems
  • The ballast system is arranged to ensure that
    water can be drawn from any tank or the sea and
    discharged to any other tank or the sea as
    required to trim(??) the vessel.

87
  • Combined or separate mains for suction and
    discharge may be provided.

88
  • Where a tank or cargo space can be used for
    ballast or dry cargo then either a ballast or
    bilge connection will be required.

89
  • The system must therefore be arranged so that
    only the appropriate pipeline is in service

90
  • the other must be securely blanked or closed off.

91
  • Where tanks are arranged for either oil or
    ballast a change-over chest(????) must be fitted
    in the pipeline so that only the ballast main or
    the oil transfer main is connected to the tank.

92
C. Domestic water systems
  • Domestic water systems(??????) usually comprise a
    fresh water system for washing and drinking and a
    salt water system for sanitary(???????) purposes.

93
  • Both use a basically similar arrangement of an
    automatic pump supplying the liquid to a tank
    which is pressurized by compressed air.

94
  • The compressed air provides the head(??) or
    pressure to supply the water where required.

95
  • The pump is started automatically by a pressure
    switch which operates as the water level falls to
    a predetermined level.

96
  • The fresh water system has, in addition, a heater
    which is heated usually with steam.

97
  • Fresh water supplied for drinking purpose must
    meet purity standards.

98
  • Water produced from most evaporator/distillers(???
    ) will not meet these standards and must be
    treated to ensure it is biologically pure and
    neutral(???) or slightly alkaline(???).
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