DESCRIBE SOME TYPE OF EMERGENCY BILGE PUMP AND HOW IT IS CONSTRUCTED
This pumps function is to drain compartments adjacent to damaged compartments. The pump is
capable of working when fully submerged. The pump is a standard centrifugal pump with twin
reciprocating air pumps or rotary air pumps the motor is enclosed in air bell as that even with
the compartment full of water the compressed air in the bell will prevent water coming into
contact with the motor. The air bell is tested to withstand a water pressure equivalent to 70 feet
head. The motor is usually DC operated by a remote controlled electric circuit which is part of
the vessels emergency power.
The pump is designed to operate for long periods without attention and is also suitable for an
emergency fire pump. This design is particular suited for use in large passenger vessels giving
outputs of 60 kg/sec. In the ordinary centrifugal pump priming usually required to facilitate
good pumping. In the emergency bilge, pump this process is taken care of by properly designed
reciprocating twin air pumps geared to the pump motor and sucking the air from the pump
chamber. The air when mixed with water rises to the top of the suction chamber where it is
withdrawn by the twin air pumps through a float operated valve. When the air is extracted from
the suction chamber the chamber becomes full of water causing the bell float to rise and close
the valve between the suction chamber and the air pumps. This permits the pump a continuous
flow of suction and discharge.
The pump consists of:
PUMP CASING:
Unless otherwise stated the pump casing is made of cast iron, with renewable impeller
clearance rings made of brass. The casing is of the divided type with suction and discharge
branches arranged in the back portion so that the front part can be removed and the impeller
and spindle can be taken out without breaking any pipe joints. An extension is provided for
taking the driving motor. This pump casing is provided with a hand hole giving access to the
impeller eye.
IMPELLER:
The impeller is made of bronze, so arranged as to pass any solid material which can come
through the suction strainers and mud boxes. The impeller is of the sided type so designed that
the upward thrust tends to balance the weight of the rotating parts of the pump and motor but
in addition a double thrust bearing is provided in the motor, capable of taking charge of any
unbalance thrust and weight of those rotating parts.
SPINDLE:
This is usually a very large diameter, fitted with an impeller of special hard bronze finished by
grinding. An external bearing is provided of suitable dimensions and of the divided type for case
of overhauling. A grease lubricator is fitted to this bearing.
STUFFING BOX:
This is fitted with special metallic packing rings, and is pressure sealed from the pump through a
central cock. Where specified a filter may be fitted
AIR PUMP:
The air pump has a cast iron crank case with detachable top arrangement for bolting to facing
on the pump casing to cylinders, valve plates and piston are of highest quality gunmetal alloy,
the latter being fitted with special piston rings and stainless steel gudgeon pins. Reversible
monel metal discharge valves with phosphor bronze spindle and cast iron valves covers are
incorporated, so design as to give ready access to the valves for cleaning and overhauling.
The air pump pistons are driven from a high tensile steel crankshaft carried in two split
gunmetal main bearing. The crankshaft is driven through worm reduction gearing (case
hardened steel worm and phosphate bronze worm wheel) by the main pump spindle. The air
pump has no suction valves, the pistons uncovering the inlet ports during their travel. The air
pump has been found in service to give satisfactory results over long periods without wear or
adjustment. The air pump can be removed from the main unit for overhaul by the removal of
four nuts and is divided in place to ensure correct alignment of gearing. Lubricating of air pump
bearings is by a mechanical pump feeding the drips in proportion to the speed of the pump,
from a box of ample capacity.
AIR BELL:
The air bell is of the best quality welded steel painted with betumactic solution, and is water
tested to a pressure equivalent of 70 ft head. A hand hole with an air tight joint is fitted near the
top of the air bell so that the commutators and bushing of the motor can receive attention,
without the unseal of the air bell. Suitable handles are fitted for convenience of removing or
turning the air bell.
ELECTRIC MOTOR
The electric motor is of the vertical spindle mica insulated, shunt wound type fitted with series
stability windings. All windings are thoroughly impregnated to withstand dampness. The thrust
bearing are of the roller type and the double thrust bearing of the heavily rated ball type. When
the motor is running non-submerged fresh air is drawn in around the motor and discharged
again by an air fan mounted on the armature shaft of the motor. When the motor is submerged,
this fan causes the entrapped air to imping on the sides of the air bell which is kept cool by the
surrounding water. The rating of the motor is such that it can be run continuously of the water
rises sufficiently high to seal the bottom of the bell but not submerge it. To facilitate rapid
charging a non-return valve is fitted on the delivery side of the pump.
