Section 3.3 Hydraulic Systems Flashcards
What are the safety aspects of hydraulics operation?
Hydraulic oil pressure can be used to drive hydraulic motors on deck machinery such as the windlass or winches.
It may be used to operate machinery requiring a change in pitch on variable-pitched propellers or the steering system rams.
- (i) Power produced by a power pack.
(ii) One power pack can act as a prime mover for a number of systems. - Power packs for specific uses having various types of pumps for the pressure delivery.
- The understanding of schematic drawings and the basic symbols in use with the system is crucial.
What is the basic operation of hydraulics?
- The use of hydraulic fluid pressure and flow can transmit energy from one point to another.
- Pressure is applied to the end of a shaft.
- It could be used to adjust the pitch setting on a variable-pitched propeller.
- It could be used to lift hatch covers or release the brake on a towing winch.
- Ram steering systems:
(i) The ram is attached to the tiller arm.
(ii) As the rams travel, the power is transmitted to the pivot on the connection.
(iii) This changes the rudder angle. - Utilising the pressure and fluid flow can be used to drive a hydraulic motor, as in the case of the windlass.
- The slewing motor on a hydraulically operated crane.
- The steering motor on an azimuth drive system.
What are the basic system components needed?
A uni-flow hydraulic positive displacement pump delivers oil in just one direction.
- The pump is driven using an electric motor direct coupled to the pump.
- The pump delivers oil at pressure to a directional control valve, drawing oil from a reservoir.
- Because it is a positive displacement pump, the system has a pressure relief valve that will open if the set pressure is exceeded. (This is essential to protect the pump that may be destroyed.)
- The direction of flow with the control valve will either raise the rams or lower the rams or operate while the rams are stationary.
- The ram or cylinder is fitted with a double-acting piston. This means that the piston could have oil delivered at the top to lower the hatch cover, or if oil was delivered under the piston, it would raise the hatch cover. Thereafter, the oil would then return to the reservoir.
- A filter is always fitted to the low pressure or return side of the circuit to give assurance of the oil condition.
- The other item on the return side is that because hydraulic oil has been placed under pressure and work has been done, there is a rise in temperature. Often this will require the use of a heat exchanger. These can be either shell and tube or plate exchangers. The cooling medium can come from numerous sources but sea water is in common use.
Details for hydraulic fluid or oil
- Hydraulic fluids are specified for the duty they are involved with.
- Different grades of hyrdaulic fluids depending on the system it is used for, is exposed to external elements, temperatures and pressures involved.
E.g. Hydraulic fluid for the CPP is different than for the windlass.
Details on hydraulic pipes
- Should be able to handle in order of 300 bar (atmospheres).
- The high-pressure side of a system requires that hoses, steel pressure pipes and fitting can withstand the pressures.
- The system should be able to resist vibration, corrosive effects of the environment as well as very high pressures.
Details on hydraulic control
- Operates with a combination of hydraulic power and either electric solenoid operation, lower-pressure oil or air circuitry.
- An electrical operation if exposed to weather should be double insulated to prevent earth leakage, which can cause problems.
E.g. The steering gear operation is operated by a low-pressure tele-motor system shifting the position of a shuttle valve, directing the flow of high-pressure oil to complete the circuit.
Details on hydraulic motors
The use of a directional valve employed with the pressure system to raise or lower the hatch cover.
- The uniflow pump delivers oil to a directional valve that provides the pressure and fluid to operate a hydraulic motor.
- The centre section of the directional valve allows the fluid to bypass the motor will neither raise nor lower.
- By directing the flow of oil either up or down will raise or lower the motor when the brake is released.
- A brake is often fitted with a delay and releases once the pressure is able to support the load.
Examples of deck machineries that are operated by hydraulic.
- The hatch covers.
- The operation of windlass and mooring winches.
- The operation of cranes.
- The bow and stern doors and deck ramps.
- Pilot ladders and gangway hoists.
How does the valve operate on the ballast and fuel systems?
- Hydraulic valve actuators are used on ballast and fuel systems.
- The reason for selecting these valves is that the movement from fully closed position to fully open is 90 degrees of movement.
- The use of potential energy for the operation is a a simple movement.
Operation of Variable/Controllable Pitched Propeller Systems (CPP)
- Remotely controlled from the Bridge, Bridge wings and from the main engine console in the engine room.
- The operation could be using a tele-motor hydraulic control system to remotely position the propeller blades.
- An oil pressure being maintained on a piston.
- Maintains the position of the control rod and crosshead in the propeller.
- The oil pressure is maintained operating against a very heavy spring that if the loss of pressure did occur, then the tendency of the system will locate the propeller blades in the full ahead position.
Loss of pressure on some types can be mechanically moved to position the blades, but generally, the hydraulic pressure is supported by stand-by pumping arrangements.
How would you safety operate the hydraulic system?
- If a leak is seen, NEVER use your hands to try and stop the leak. Pressure could be above 400 atmospheres (bar). High-pressure oil can pierce the skin and enter the bloodstream.
- If a leak does occur, the operator should, wherever possible, stop the machine and isolate the problem. Report the problem for immediate attention by engineering staff.
- Hoses are flexible and the new system hoses are often reinforced with stainless steel mesh and fittings, but leaks do occur still. Remember the problems with oil pollution MARPOL Annex 1.
