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A leaking overboard valve is a nuisance in port and a danger at sea. Because these valves sit on the Hull, a repair has traditionally meant a dry dock. Underwater valve and pipe repair in Nagoya allows many of these jobs to be done while the ship is at the berth.
The key to changing a valve afloat is to close the opening on the outside so that water cannot enter. The Diver fits a blanking plate or cover over the hull opening, held by bolts or magnets and sealed with a gasket. Once the opening is closed, the engine room can open the valve, remove it and fit a new one. The blank is then removed and the valve tested.
Typical jobs include overboard discharge valves, sea chest valves, cooling water valves, ballast system valves where they connect to the hull, scupper non-return valves and short pipe sections at the shell. Flange gaskets that leak can often be replaced. Cracked pipe spools can be removed and replaced.
Valve work depends on a close link with the chief engineer. The system must be isolated, drained and made safe. If the valve serves several systems, the plan needs to show how they will be supplied during the work. Spare parts must be ready on board before the Diver blanks the opening. We ask for the valve data, the hull opening size and drawings if they are available.
Pressure from outside can be strong, especially at depth. A badly fitted blank can leak or fail. Our blanking plates are designed for the pressure at the opening and tested before use. A second barrier is often added in the form of the ship's own valve, closed and locked, while the work proceeds. The supervisor does not allow the dive to start until the engine room confirms isolation.
Blanking and valve replacement often take 4 to 8 hours, depending on the valve size and access. Larger valves, or those in awkward positions, can take longer. Weather and visibility also play a role.
After the work, the valve is tested by the engine room and, where required, witnessed by the surveyor. The Diver films the area, and the report records what was fitted. This gives the owner a clear record of the repair and the date.
If the hull opening or the surrounding plating is badly corroded, or the valve is too large to blank safely, dry-docking may be necessary. We tell the owner clearly if this is the case.
A cooling water overboard valve that will not close fully is a common case. Another is a cracked flange on a sea chest valve. A third is a leaking non-return valve on a discharge. In each case, the plan is similar: isolate, blank, repair, test. Our team has done many of these, and the sequence is well practised. Spare gaskets, bolts and a spare valve should be ready before we arrive.
Send the valve type and size, the pressure rating, the position on the Hull, and any drawings or photographs. If the valve is hidden behind a sea chest, tell us. The more we know, the faster we can prepare the blank and the plan.
Q1. How is a valve changed without dry-docking?
The Diver fits a blanking plate over the hull opening from outside, sealed with a gasket. The engine room then removes and replaces the valve and the blank is removed.
Q2. How long does a valve replacement take?
Blanking and replacement often take 4 to 8 hours, depending on valve size and access.
Q3. What must the engine room do first?
Isolate and drain the system, confirm it is safe, and have the new valve and spares on board before the Diver fits the blank.
Q4. When is a dry dock required instead?
When the hull opening or surrounding plating is badly corroded, or the valve is too large to blank safely.
