vacuum door locks and other things - Mercedes-Benz Forum

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post #1 of 5 (permalink) Old 03-16-2010, 03:04 AM Thread Starter
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vacuum locks

what advantages are there over electric

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post #2 of 5 (permalink) Old 03-19-2010, 09:29 AM
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Not sure, but it's quieter and the lines are larger, they carry air instead of electricity.

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post #3 of 5 (permalink) Old 03-19-2010, 10:21 AM
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Vacuum controls

In a previous life, I worked on a research ship that was converted from an Antelope-class (PG-84) patrol gunboat. That ship had an LM-1500 gas turbine and two big diesel engines. The three engines fed a common transmission wherein any combination of power could be selected. Bitch could do 42 knots on diesel fuel instead of the JP-4. All engine and transmission controls were vacuum operated.

Thanks for stimulating memory.
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post #4 of 5 (permalink) Old 03-23-2010, 09:17 AM
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Vac systems

My knowledge of the engineering system on the boat is somewhat limited since I was an electrical/acoustics engineer but I can tell you this.

As you may know, a diesel engine produces no vacuum so requires an engine-driven vacuum pump and reservoir if vacuum is to be used for control systems. In our diesel cars, the vac pump is belt-driven, on that boat there was an additional auxiliary diesel that provided "housekeeping" functions such as vacuum and electrical power. The auxiliary was also run through the Combined Diesel and Gas Turbine (CODAG) transmission so that if the aux engine failed, housekeeping power could be provided by one of the main propulsion diesels.

As an OT aside, since the boat started life as a Naval asset, the turbine and diesels were designed to run off of JP-4. We ran all engines on diesel fuel and found the boat ran faster since diesel is sea-level fuel and has a higher specific heat hence energy content per pound of fuel. The conversion simply consisted of an additional stage of filtering plus changing filters more often. All pumps and injectors were perfectly happy to drink diesel.

We surprised a lot of so-called fast cabin cruisers when we blew past them as though they were dead-in-the-water.
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post #5 of 5 (permalink) Old 03-23-2010, 10:25 AM
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I am old enough to remember classes I took in technical school about air powered logic systems.
Yes you can build pneumatic equivalent of electronic computer, but transistors went long way in last 20 years.
The vacuum system was build in MB when electronic chips didn't exist yet and electric motors were heavy and unreliable. Vacuum is coming for free in gas engines and vacuum pump on diesels is not an expensive item.
I did own W123 that used vacuum from engine pump and when aged tubings leaked accumulated vacuum -opening all locks get pretty annoying. That is probably why MB made designated electric vacuum pump to solve that issue. Mind that shut off valves on old 300 diesels were vacuum operated.
It worked well for last 50 years, why change it?
Human lungs can't produce any significant vacuum, nor pressure.

Last edited by Kajtek1; 03-23-2010 at 10:32 AM.
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