Construction & Working
The construction of the master air starting stop valve is shown clearly in the diagram below which shows the cut section of the valve and all the internal parts and passages are clearly shown and legibly marked for the benefit of the readers.
The inlet and outlet for the starting air are shown in the diagram as well as the drain and the control air path. It must be understood that there is a difference between the control air and the starting air. The starting air actually goes inside the cylinders and makes the engine start, while the control air is used to control the timing of the main starting air and cutting it off at an appropriate time.
The arrangement consists of a spring loaded non-return valve which is used for safety purpose and to prevent blow back of the gases to the engine aided with the flame trap which is also provided there.
There is also an arrangement to operate this valve manually in case it does not open or close automatically due to some problem. Now suppose the control air line suddenly gets faulty so the starting air pressure could keep the valve open, but because of the stop valve it gets shut when blow back gases try to escape to the other side.
It is important to note that the main starting air line is kept in vented position when not in use. This is important to prevent any build up of pressure due and also to remove any condensate in the line which could cause knocking in the line when the compressed air at high pressure whizzes past it. Next to the starting air master valve are the individual cylinder valves which deal with different cylinders, as well shall see in our next article.