Diesels and vacuum....

[llong66]

Im not sure if this is the right place for this, but seeing as I have a M1008, Id start here. Why dont diesels have the vacuum to run stuff like power brakes like a gasser? Vacuum in a gasser is the result of the piston pulling in air during the down word intake stroke, right? If this is correct, a diesel should have the same situation as far as vacuum goes, I would think anyway. So why cant you run vacuum operated accessories off a diesel? Could someone please explain this to me? Thanks!!

Greg

 

[Warthog]

Diesels don't create a vacuum because they don't have a carburetor/throttle body. It is the Venturi effect that actually creates the vacuum.

That is why a vacuum pump is required for the TH400 transmission and also a hydroboost brake system is required.

You can actually run a diesel without the intake manifold installed.

 

[alburms311]

Thanks for that last part Warthog, I was going to ask if that could be done for future reference. Had I started my vehicle without the manifold on it would have saved me a lot of trouble this weekend with my leaking injector line.

 

[llong66]

Thanks for your explanation Warthog, so if I understand correctly then, the vacuum is caused by a differance in the density of the air in the intake vs he air outside?

 

[Tow4]

In a gasoline engine you have either a carburetor or throttle body that acts as a valve to restrict the air flow into the engine. The pistons drawing against this restriction to the air flow is what creates the vacuum. If you open the throttle, the vacuum will go down. At wide open throttle the vacuum level is zero and the intake manifold is at atmospheric pressure.

Diesel engines have no throttle body to restrict the air flow, so a normally aspirated diesel engine's intake manifold is always at atmospheric pressure.

 

[Keith_J]

(most) gasoline engines regulate power by regulating manifold pressure using a throttle valve. At part throttle, the engine is literally choked off. This reduces the amount of fuel going into each cylinder.

At idle, most gasoline engines develop about 18" of vacuum. That is 18" of mercury on a manometer. Since air pressure at sea level is about 29.9 " of mercury, you can get an idea of how much the engine is choked to idle.

Airplanes with gasoline engines use manifold pressure as a measure of engine output. Of course you have to understand the difference between manifold vacuum and manifold pressure. Just realize vacuum is the absence of pressure.

 

[doghead]

But, how does a home vacuum work, with an electric motor?

 

[phil2968]

But, how does a home vacuum work, with an electric motor?

I bet Amy knows.

 

[kawkev]

But, how does a home vacuum work, with an electric motor?

The motor spins at a high rate of speed using inertia to convert electrical energy into suction and noise.

 

[MarcusOReallyus]

If it's like my vacuum at home, there's a lot more noise than suction.