Fuel valve of marine engines play a very important role in deciding the quality of combustion inside the engine cylinder. The penetration and atomization of fuel, governed by the condition of the fuel valve, ensures efficient combustion in the engine.
Fuel valves are an integral part of ship’s planned maintenance system and are therefore overhauled and cleaned at regular intervals of time.
Maintenance work for fuel valves needs to be done with utmost care in order to prevent damage to the valve and also ensure proper cleaning.
Following are the important points that must be considered while overhauling marine engine fuel valves:
1. Check the Valves: Before opening the fuel valve for overhauling, ensure that the engine is isolated; fuel inlet and outlet valves are shut and fuel valve cooling water line is isolated.
2. Cover the Cylinder Head: When the fuel valve is removed from the cylinder head, ensure to cover the opening with a big cloth to avoid any tool or parts from falling inside the cylinder.
3. Check Testing Machines: Before testing the fuel valve, ensure to check the diesel oil, hydraulic oil and other electrical systems of fuel valve testing machine (Depending on type of valve testing machine- Electrical, manual or hydraulic). Also, check the rated opening pressure of the valve in machinery manual
4. Loosen the Pressure Setting Screw First: Before opening the fuel valve for overhauling, tightly hold the valve body in a vice and loose the pressure setting screw before attempting to open the needle holder.
5. Keep All Overhauled Parts in Diesel/ Kerosene: Ensure to keep and clean all the opened parts in diesel or kerosene. Clean the fuel valve body with diesel and remove all heavy fuel oil deposits from the inside.
6. Inspect the Spring: Check the spring for it’s length, elasticity or any breakage or cracks. Also check spring quarter/ holder for breakage.
7. Check Surface of Valve Needle: Check the surface of valve needle holder and lap it with fine lapping paste if pitting or scratch marks are seen. Do this until the surface is smooth. Measure the face width and if it is less than required, replace the holder.
8. Check Needle Movement: Check the surface of needle tip and movement of needle inside the holder guide.
9. Clean Nozzle Holder Atomization Holes: Clean the nozzle holder atomization holes with micro wire (or gas torch hole cleaning wires).
10. Check Valve Properly After Overhauling: Once the fuel valve is overhauled and assembled back, check the opening pressure, atomisation and dripping of the fuel in fuel valve testing machine. Ensure to use eye glass and gloves while performing the tests. Check the opening pressure in manual and increase or decrease the opening pressure with the help of pressure setting screw provided on the top of the valve.
Some marine engine fuel valves with zero sac volume are not recommended for pressure testing. and hence should be used directly in the engine after overhauling.
Do you know any other important points to consider during fuel valve overhauling? Let us know in the comments below.
Checkout the video on fuel valve overhauling: