Fault diagnosis and maintenance of marine hydraulic equipment_ Hydraulic steering gear failure

Fault diagnosis and maintenance of marine hydraulic equipment_ Hydraulic steering gear failure

When sailing and berthing and leaving the wharf, the ship shall be able to turn or maintain the course according to the intention of the pilot, so as to ensure the safety of ship navigation. The method of controlling the course of a ship varies with the type and purpose of the ship. The most common method is to turn by the deflection of the rudder at the rear of the ship. The steering gear is an important mechanical equipment to control the rudder deflection. The following are the faults of electro-hydraulic steering gear widely used in large and medium-sized ships.

(1) Steering gear does not move

The root cause of the fault is that the main pump does not supply oil to the rudder mechanism or the rudder mechanism cannot return oil, and the impact rod has no reciprocating motion. The main reasons why the hydraulic pump does not supply oil to the rudder mechanism are as follows.

① The power supply of the hydraulic pump motor is open, the hydraulic pump is idling, the main oil circuit is not reversed, or the inlet and return oil circuit of the rudder mechanism is bypassed. The idling of hydraulic pump and non reversing of directional valve are mainly related to the control system.

② The working oil pressure of the control oil circuit is too low or the oil pressure cannot be established, the transmission parts of the remote control mechanism are stuck or the fasteners are loose, broken or fall off, the storage spring tension of the follow-up mechanism is too small or the reversing valve is stuck, etc., which will lead to the idling of the variable displacement pump due to the variable displacement mechanism still in the middle position Because the directional valve cannot be reversed, the oil discharged from the directional quantitative pump is directly bypassed to the oil tank through the directional valve.

③ The main factors affecting the operating oil pressure are the valve parts in the system, such as the opening of bypass valve and limit bypass valve, the adjustment pressure of overflow valve is too low, or the valve core and orifice are blocked by dirt.

④ The main reason why the rudder mechanism cannot return oil is that the hydraulic check valve on the main oil circuit cannot be opened, or the control oil is not introduced, or the control piston is stuck.

(2) You can only turn the rudder in one direction

The main causes of such failures are as follows.

① It is caused by the abnormal unilateral operation of the control system. For example, the traffic valve of a transmitter is normally open, the unilateral operation oil pressure cannot be established, the variable mechanism of the variable displacement pump cannot change direction, and the pump idles.

② When a limit bypass valve is pressed by an external object, the operating oil circuit on this side loses pressure, or the directional valve is stuck at one end, the directional valve controlling the main oil circuit cannot be reversed, and the oil discharge of the directional quantitative pump cannot be supplied to the corresponding steering hydraulic cylinder.

③ A safety valve in the main oil circuit leaks or the hydraulic check valve on the oil return side cannot be opened.

(3) The rudder speed is too slow

The speed of the rudder depends on the moving speed of the striker, that is, the amount of oil supplied to the hydraulic cylinder of the rudder mechanism. Large oil supply flow and fast rudder speed; On the contrary, the rudder speed is slow. Therefore, the fault is mostly caused by insufficient displacement of the main pump. If the pump is not selected improperly, it may be due to the low voltage and the decrease of pump speed; Or the oil level in the make-up oil tank is too low, the suction filter is blocked, the suction stop valve is not fully opened, or the suction pipeline of the pump is not tight, which destroys the suction conditions of the pump, and the relevant parts of the pump are worn too much, resulting in serious internal leakage; It is also possible that the maximum displacement limit of the variable displacement pump is not adjusted properly.

The leakage of main oil pipeline or hydraulic parts and the lax closure of bypass valve and safety valve will also reduce the rudder speed. If air is accumulated in the control oil circuit, the traffic valve is not closed in time, or the reversing speed of the reversing valve is adjusted too slowly, the time when the main pump starts to supply oil to the rudder mechanism will be delayed, making the rudder speed slow.

(4) Empty rudder

① Due to air accumulation in the hydraulic system, leakage or excessive opening of the traffic valve of the transmitter. If there is air accumulated in the control system, the air must be compressed before starting to rotate the steering wheel. The actuator will not act until the pressure of the system rises to a certain value, that is, the action of the actuator lags behind the transmitter for a certain time, resulting in the steering wheel idling for a certain angle. It can be seen that the process of compressed air is the process of steering wheel idling. The more air accumulated, the more serious the phenomenon of empty rudder.

② Because the control system and power system adopt closed circuit, when there is leakage, the hydraulic pump (the transmitter is also a manual pump) absorbs oil from one side of the actuator (actuator or steering mechanism). If some oil leaks on the high-pressure pipeline discharged by the pump, the oil entering the other side of the actuator will push the hydraulic cylinder or ram to move the swept volume, It is not enough to fill the volume of oil sucked out by the pump, resulting in "holes" on the oil return side of the actuator. If the oil level of the make-up oil tank is too low, the make-up oil pressure of the system is too low, or the make-up valve cannot be opened, so that the make-up oil is not timely, when the steering wheel returns to the rudder in the reverse direction, the oil delivered by the hydraulic pump must first fill the "cavity", and the hydraulic cylinder or striker of the actuator can be pushed, resulting in the phenomenon of rudder idling.

③ If the opening of the transmitter traffic valve is too large, its closing is bound to be delayed. When starting to rotate the steering wheel, the pressure oil will either bypass through another traffic valve or drain back to the oil tank through the traffic valve and safety valve until the traffic valve is closed, and the actuator will not act, resulting in the phenomenon of empty rudder.

④ If the bypass valve or safety valve in the main oil circuit is not closed tightly, it will also produce empty rudder, which can not be ignored in management.

⑤ Air in the system may accumulate due to incomplete removal, or may penetrate due to packing leakage of transmitter, actuator and rudder mechanism. In case of leakage of hydraulic cylinder packing, it is often useless to tighten the gland. If conditions permit, it is best to take it out and replace it, or trim and cut it flat, so that it can be flat and tight after reassembly.

(5) The actual rudder angle is inconsistent with the steering angle

① The following mechanism is not adjusted properly, so that when the rudder turns to the rudder angle required by the steering, the variable mechanism of the hydraulic pump has not returned to the center, the rudder will continue to deflect due to the failure of the hydraulic pump to stop oil supply, resulting in rudder flushing; Or the rudder has not turned to the required rudder angle, the following mechanism has pulled the variable mechanism of the hydraulic pump back to the middle position, and the rudder stops running because the hydraulic pump stops oil supply, resulting in insufficient rudder. In case of this phenomenon, the following mechanism should be repositioned. Two points shall be noted during positioning: A. when the rudder is in the middle, the displacement of the hydraulic pump shall be adjusted to zero; b. When the rudder is in the middle, ensure the perpendicularity of the following rod and the connecting lever.

② For directional electro-hydraulic steering gear, if the driver is not skilled, it is easy to rush the rudder. This is because when the rudder turns to the required rudder angle, the directional valve of the main oil circuit does not return in time, and the rudder will continue to rotate due to the non-stop oil supply of the hydraulic pump, resulting in rudder flushing. This depends on skilled operation.