This article deals in the overhauling of the starting air valve of the main engine and the common parts that this have inside it.
Starting air valve as it name suggest is used in the main engine. It comes in use when engine is being run on air, before it can attain being driven by the combustion pressure of the fuel.
Why We Need To Start Engine On Air?
As we all know that all the internal combustion engines work on the principal of burning fuel under high pressure of air and then using that force to push piston down. For example, you have a car. But it is stopped. So, to start the engine, you need to give it some revolutions, before the fuel actually starts to get ignited. You can either turn the engine with hand or you can just connect a electrical motor.
But marine engines are quite big, they cannot be started with hand. And you will need a big electrical motor to turn it. Very big though. So easy way is to pump high pressure air approx. 30 bar, in to it and then turn it. But you cannot just pump air from starting air valve in to the cylinders. There has to be a sequence for that.
Starting air valve is pneumatic controlled valve. And each unit of main engine have its own.
Starting Air Valve Maintenance and Parts (General)
Well like another machinery, it also needs some kind of maintenance. Usually maintenance involves the opening of valve and cleaning all parts and then putting the new ones. Below is the diagram which shows the parts of starting air valve. The valve that being mentioned here is from a sulzer RT FLEX engine. But more or less the valves are same for every engine maker.
The main areas where the engineer should focus while maintenance:
1) The seating surface of the valve should not have any kind of dents on it. If dents are visible, it needs to be removed by lapping or filling.
2) The surface between the spindle and its seat, should lapped. The lapping needs to be gradual. Start from a coarser lapping paste to finer one.
3) All the piston rings need to be checked.
4) The distance between the spindle and guide needs to be also taken in account. Otherwise the exhaust gases from the combustion chamber will come in.
After overhaul checks.
1 put oil in the space, mentioned with blue color. And check if the oil leaks to another end. If it leaks, then you have to lap the seat again.
Opening and closing test. Put the control air valve and then open and close the starting air valve. Opening and closing should be smooth.
Checks for the dents on the seat.
So this was all related to the overhauling the starting air valve and checks that needs to be done, once you are finished overhauling it.