Description
Function and Composition
Function
The manual control valve directly drives the valve core movement through manual operation (such as a handle, handwheel, or lever), thereby controlling the fluid flow in the hydraulic or mechanical system, and achieving the lifting or rotating of the lifeboat davit.
There are two independent manual control levers. One controls the lifting and lowering of the boat hoist wire, while the other controls the extension and retraction of the door crane arm.
Composition
It usually includes the valve body, valve core, handle, seals, etc. The rotation or movement of the valve core can change the state of the flow passage, achieving on-off or directional control of the fluid.
Operation Method
Standard operation
When the electrical or hydraulic system is functioning normally, the manual control valve is typically in a closed state. When manual operation is required, the valve spool position is directly controlled by rotating the handle or pulling the lever, thereby releasing or locking the hydraulic pressure to achieve the slow descent or ascent of the lifeboat.
Emergency operation
In the event of a power loss or hydraulic system failure, the manual control valve serves as the ultimate safeguard for the release of the lifeboat. For instance, by operating the manual pump or accumulator to drive the hydraulic cylinder, coupled with the operation of the manual valve, the release of the lifeboat can be completed.
Operation Procedure
Operation process of launching a boat
• After starting the hydraulic pump station, operate the control lever to gradually raise the crane jib out of the water.
• During the hoisting process, it is advisable to slightly loosen some of the boat hoisting wires to keep the lifeboat close to the slideway.
• After raising the crane arm out of the water, continue to operate the control lever to lower the lifeboat to the surface.
Release decoupling control
• Conventional decoupling: Rotate the manual pump switch clockwise to close the hydraulic valve, and then operate the manual pump handle (moving it back and forth at an angle of about 45° for about 8 times) to complete decoupling.
• Emergency decoupling: In the event of a hydraulic system failure, rotate the emergency decoupling handwheel clockwise to directly decouple through mechanical propulsion.
Recovery operation
• First, operate the control lever to raise the boat hoisting wire to a certain height.
• Operate the control lever to retract the crane jib. During the process, loosen the wire for lowering the lifeboat while retracting it, so that the lifeboat can be gradually drawn in close to the track.
Scenarios and Precautions
Manual control valves are widely used in ship's lifeboat davit systems, especially in emergency situations, to ensure the safe launching of lifeboats.
Precautions
1. Before operation, it is necessary to confirm the valve status to avoid misoperation that may cause system pressure abnormalities.
2. Regularly maintain the sealing and flexibility of manual valves to prevent failure due to corrosion or wear.
3. During drills or actual operations, crew members need to be familiar with the operating steps of manual valves to ensure quick response.
Maintenance
• Visual inspection: Conduct a weekly visual inspection of the control valve and the entire hydraulic system to ensure there are no external leaks, rust, or damage.
• Connection tightness: Check whether the mounting bolts of the control valve and the pipeline joints are loose, ensuring they are firmly fixed.
• Hydraulic system inspection: Check whether each component of the hydraulic system is working properly, and whether there are any abnormal leaks, vibrations, or noises.
• Lubrication and maintenance: Apply lubricating grease to all lubrication points (grease nipples) on the davit. Pay special attention to key moving parts such as the bottom shaft of the hydraulic rod. Lack of lubrication can easily cause the shaft and hydraulic rod to rotate simultaneously, resulting in damage to the external limit stop plate or deformation of the shaft.
• Functional test: Under safe conditions, conduct a no-load operation test to verify whether the control valve can smoothly and accurately control the boom extension/retraction and the boat hoist wire lifting/lowering.
Annual inspection
• Hydraulic oil inspection: Check the oil level and quality of the hydraulic oil tank, replace the hydraulic oil every 12-18 months, and clean or replace the oil filter.
• Seal inspection: Inspect the valve core, valve body, and all seals of the control valve. If the seals are aged or fail, resulting in internal/external leakage, they should be replaced promptly.
• Stress test: Check whether the system's operating pressure is normal and whether there are any abnormal pressure fluctuations.
• Overall operation test: Conduct an annual operation test of the boat to verify the functional integrity of the entire release and recovery system, including the control valve.
Common Faults and Solutions
• Operation is stuck/not working: This is usually caused by lack of lubrication, internal contamination, or rust. Cleaning and lubrication should be performed. If the valve core is worn, it needs to be repaired or replaced.
• Leakage: Inspect and replace failed seals (such as O-rings, gaskets).
• The handle cannot rebound: check whether the reset spring is failed or broken, and replace it in time.
