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Starting air system for diesel engine - how it works
Function of starting air system Diesel engines are started by supplying compressed air into the cylinders in the appropriate sequence for the required direction. A supply of compressed air is stored in air reservoirs or 'bottles' ready for immediate use. Up to 12 starts are possible with the stored quantity of compressed air. The starting air system usually has interlocks to prevent starting if everything is not in order.
A starting air system is shown in Figure below. Compressed air is supplied by air compressors to the air receivers. The compressed air is then supplied by a large bore pipe to a remote operating non-return or automatic valve and then to the cylinder air start valve. Opening of the cylinder air start valve will admit compressed air into the cylinder. The opening of the cylinder valve and the remote operating valve is controlled by a pilot air system. The pilot air is drawn from the large pipe and passes to a pilot air control valve which is operated by the engine air start lever.
When the air start lever is operated, a supply of pilot air enables the remote valve to open. Pilot air for the appropriate direction of operation is also supplied to an air distributor. This device is usually driven by the engine camshaft and supplies pilot air to the control cylinders of the cylinder air start valves. The pilot air is then supplied in the appropriate sequence for the direction of operation required. The cylinder air start valves are held closed by springs when not in use and opened by the pilot air enabling the compressed air direct from the receivers to enter the engine cylinder. An interlock is shown in the remote operating valve line which stops the valve opening when the engine turning gear is engaged. The remote operating valve prevents the return of air which has been further compressed by the engine into the system. Lubricating oil from the compressor will under normal operation pass along the air lines and
deposit on them. In the event of a cylinder air starting valve leaking, hot gases would pass into the air pipes and ignite the lubricating oil. If starting air is supplied to the engine this would further feed the fire and could lead to an explosion in the pipelines. In order to prevent such an occurrence, cylinder starting valves should be properly maintained and the pipelines regularly drained. Also oil discharged from compressors should be kept to a minimum, by careful maintenance. In an attempt to reduce the effects of an explosion, flame traps, relief valves and bursting caps or discs are fitted to the pipelines. In addition an isolating non-return valve (the automatic valve) is fitted to the system. The loss of cooling water from an air compressor could lead to an overheated air discharge and possibly an explosion in the pipelines leading to the air reservoir. A high-temperature alarm or a fusible plug which will melt is used to guard against this possibility.
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I have a question about the interlocks on a MAN B&W engine: What are the start interlocks next to the three interlocks that are in the manoeuvring system(start air distr., turning gear) ????
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Member: kestrel5915
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Post Date: 5/25/2011
I think the interlocks are: 1. 2. 3. 4. 6.
Turning Gear Lube Oil pressure Running Direction (same as Starting Air Distributor) Spring Air Auxiliary Blower
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Member: anonymous
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Post Date: 8/31/2011
The last one -aux blower -is not an interlock in some engines like the one I am sailing right now. 6S 60MC B&W
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Member: anonymous
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Post Date: 11/4/2011
emergency stops activated from anywhere are also interlocks
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Member: RolloTomkins
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Post Date: 6/10/2003
If an MAN B&W MC engine is required to start in the opposite direction, an air signal moves the fuel pump cam follower from the ahead to the astern position (as the engine starts turning on air). I always understood that if an individual fuel pump follower failed to move into the correct position (due perhaps to corrosion in the servo cylinder) then an air signal prevented the puncture valve on the fuel pump from venting on that particular cylinder. However on studying the air start control diagrams, I cannot see how this is achieved (if indeed it is). Can someone enlighten me please?
The manouevring system of MAN B&W two-stroke engines does not prevent the puncture valve from closing if the reversing link in question is in an incorrect position. If the engine is starting with one or more reversing links in the wrong position an alarm for too high exhaust gas temperature deviation will occur shortly thereafter. If the wrongly positioned reversing links cause the engine to start in the wrong direction a wrong way alarm occurs. There is no alarm provided for wrongly positioned reversing links, but an AHEAD and ASTERN indication in the engine control room and at the local control stand is specified by MAN B&W Diesel A/S. The indication is given by proximity switches on the air cylinders, connected in series. If one or more air cylinders fail to move to the wanted position there will be no indication that all reversing links have changed to the wanted position. Lars G. Jacobsen MAN B&W Diesel A/S Copenhagen
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Member: rizwansaeed123
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Post Date: 2/24/2006
i have got the got the querry regarding reversing of SULZER RND or other lost motion reversing engine that when the cam shift or do lost motion then why this is not effecting other cylinders timing on the entire cam shaft
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Member: puneet1313
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Post Date: 11/15/2009
dear mr lars r u still in MAN.I have also joined b@w
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Member: Marto
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Post Date: 12/9/2009
If a signal missing from any pump the starting air valve is blocked by mean of the safety system. more explanation u have to look inside the control system diagram which is provided on board.
