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Hydraulic systems for deck machinery and cargo equipment onboard
Hydraulic systems provide a means of distributing power and of obtaining it
from a constant speed and constant direction drive such as an a.c. electric
motor. The oil pressure can be used to provide variable speed drives through
hydraulic motors and power for actuating devices. Hydraulic power is used
extensively for deck machinery and remote control of valves.
Hydraulic systems:
The three essential components for a hydraulic circuit, are the hydraulic fluid
held in a reservoir tank, a pump to force the liquid through the system and a
motor or cylinder actuator to convert the energy of the moving liquid into a
working rotary or linear mechanical force. Valves to control liquid flow and
pressure are required by some systems.
Hydraulic fluid:
Water was the original hydraulic fluid and is still used for heavy duty such as
operation of lock gates or moving bridges. The disadvantages with water are
that it promotes rusting and other forms of corrosion, it is not a good lubricant
and it has a limited temperature range.
Hydraulic oils may be straight mineral or special additive oils. Properties of
these, enhanced by additives, include oxidation stability, film strength, rust
prevention, foam resistance, demulsibility and anti-wear characteristics to
enable the fluid to stand up to the higher operating temperatures and pressures
of modern systems. Pour point depressants are used to prevent freezing in low
temperature conditions. Other fluids used in hydraulic systems may be
synthetics or emulsions.
Emulsions have been used in systems such as the
telemotor, where force is applied and received by pistons. Oils are preferred for
systems using rotating pumps and motors, where good lubrication is essential.
In an emergency where short term expediency is the criterion, any thin oil
could be used in a system.
Deterioration of hydraulic oils:
Hydraulic fluids which are basically mineral oils, will degenerate very slowly
over time due to oxidation. The factors which encourage oxidation are the
heating and agitation of the oil in the presence of air and metal, particularly
copper.
The process of oxidation is accelerated by overheating and also by contamination with products of corrosion or the presence of metal wear
particles. Oxidation products, both soluble and insoluble, increase the oil's
viscosity and cause sludge to be deposited. Oxidation tends to encourage the
formation of emulsions with any water from leakage or condensation. Acidic
products of oxidation will cause corrosion in the system.
Contamination of oils:
Water promotes rusting of steel and must be excluded from hydraulic systems.
Rust can be detached and when carried around a circuit can cause the jamming
of those valves with fine operating clearance, as well as hastening deterioration
of the oil. Sea water can enter through the shaft seals of deck machinery and via
system coolers. Condensation on the cold surfaces of reservoir tanks which are
open to the atmosphere, is a common source of contamination by water.
Tanks
should not be constructed such that cold hull plating forms one wall
Metal wear is inevitable and fine filters are installed to remove these and
corrosion particles together with any other grit or dirt that finds its way into
the system. Care is necessary with hoses, funnels and oil containers used for
filling and topping up reservoir tanks, to ensure that they are clean.
Fine metal wear particles can act as abrasives causing further wear. All
particles could cause blocking of small passages or the jamming of valves.
Summarized below some of the basic operation of deck machinery and maintenance guide :
- Powering deck machinery -Systems and components
Pump and motor systems are used for powering deck machinery such as
winches and windlasses. Pump and actuating cylinders are normally employed
for hatch covers. One or more pumps will be used to supply the volume of fluid
at the pressure required to operate one or more motors.
......
- Mooring equipment for general cargo vessel
The operation of mooring a vessel has traditionally required the attendance of
a large number of deck crew fore and aft. Supervision of the moorings was also
necessary to maintain correct tension through changes due to the tides and the
loading or unloading of cargo.
......
- Hydraulic systems for deck machinery and cargo equipment
The three essential components for a hydraulic circuit, are the hydraulic fluid
held in a reservoir tank, a pump to force the liquid through the system and a
motor or cylinder actuator to convert the energy of the moving liquid into a
working rotary or linear mechanical force. Valves to control liquid flow and
pressure are required by some systems.
......
- General cargo ship deck machinery electric drives
Electric motors on vulnerable deck areas may be protected against ingress of
water by being totally enclosed in a watertight casing. Vents are provided on
some winches, which must be opened when the motor is operating in port.
......
- Handling deck machinery- Anchor windlasses,Anchor capstan & mooring winches
The windlass cablelifter brakes must be able to control the running anchor
and cable when the cablelifter is disconnected from the gearing when
letting go'. Average cable speeds vary between 5 and 7 m/s during this
operation.
......
- General cargo ship deck deck crane
A large number of ships are fitted with deck cranes. These require less time to
prepare for working cargo than derricks and have the advantage of being able
to accurately place (or spot) cargo in the hold. On container ships using ports
without special container handling facilities, cranes with special container
handling gear are essential.
......
- Mechanically operated steel hatch covers
Hatch cover equipment like the other deck machinery, has to exist in a very
hostile environment and the importance of regular maintenance cannot be
over-emphasized. Drive boxes and electrical enclosures should be checked
regularly for water-tightness.
......
- Derricks and cargo winches -Ship cargo handling gears
The duty of a deck winch is to lift and lower a load by means of a fixed rope on
a barrel, or by means of whipping the load on the warp ends, to top or luff the
derricks, and to warp the ship.
......
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