VACUUM PUMP FAILURE! Are you neglecting yours?? - Page 6 - PeachParts Mercedes-Benz Forum

Diesel911 · #76 06-23-2012, 10:44 AM

Quote:

Originally Posted by kerry

I've seen contradictory charts about what loss occurs at what altitudes. But if Beagle's claim is correct that it takes 25" of vacuum to park the pump, it couldn't occur above a certain elevation and pumps would be working full time.

What happens in the real World often differs from calculations and statistics.
Well, I am learning something. I have lived most of my Life in the LA CA Basin aea and not given much thought to what happens at higher up with Gauges and pressures.
I learned in my Respiratory Therapy Classes that a Gauge reading of Zero is not really Zero because there is always Atmospheric Pressure.
But, I had not thought what happens to Vacuum readings at altitude.

qwerty · #77 06-23-2012, 10:46 AM

Quote:

Originally Posted by kerry

I've seen contradictory charts about what loss occurs at what altitudes.

In the lower part of the troposphere, a reduction of 1" Hg per thousand feet of elevation increase is a common rule of thumb.

Air Pressure and Altitude above Sea Level

Except for the "daily" variations in atmospheric pressure that differ from the scientific "standard" air column, there is little room for "contradiction." You are not going to pull 30" in the eye of a huricane, for example.

Quote:

Originally Posted by kerry

The most the gauge will read in Denver is about 18" due to the altitude since the measured is correlated to atmospheric pressure. Not sure what the pump 'would think' it is. Would it act as if it were measuring 25" at sea level or would it keep thinking it needed to pump more?
The whole issue is more dubious in my mind all the time.

The vacuum pump is not regulated, so it does not "think" anything. If the actual (NOT sea-level adjusted) barometric pressure in Denver is 24" Hg, then no vacuum pump can generate a differential greater than 24".

Stevo · #78 06-23-2012, 04:20 PM

Quote:

Originally Posted by funola

How did ypu test it?
Did you make the special Tee per the FSM?

I just tested mine using that special "t" which I made up from odds and ends, works pretty slick

kerry · #79 06-23-2012, 04:31 PM

Quote:

Originally Posted by qwerty

In the lower part of the troposphere, a reduction of 1" Hg per thousand feet of elevation increase is a common rule of thumb.

Air Pressure and Altitude above Sea Level

Except for the "daily" variations in atmospheric pressure that differ from the scientific "standard" air column, there is little room for "contradiction." You are not going to pull 30" in the eye of a huricane, for example.

The vacuum pump is not regulated, so it does not "think" anything. If the actual (NOT sea-level adjusted) barometric pressure in Denver is 24" Hg, then no vacuum pump can generate a differential greater than 24".

I'm not saying there is a real contradiction, just differing chart of vacuum level changes correlated with elevation on the internet.

The reason is used 'think' is that Beagle said the pump parked at 25" so metaphorically it 'thought' it was done with its work, according to that analysis.

qwerty · #80 06-23-2012, 05:21 PM

Quote:

Originally Posted by kerry

The reason is used 'think' is that Beagle said the pump parked at 25" so metaphorically it 'thought' it was done with its work, according to that analysis.

And that would serve as a form of regulation, if it actually worked that way. We just need Beagle to explain how 3-4 square inches worth of atmospheric pressure (12 psi differential, more or less) is going to overcome that 57 Kg return spring.

Diesel911 · #81 06-23-2012, 06:10 PM

Quote:

Originally Posted by qwerty

And that would serve as a form of regulation, if it actually worked that way. We just need Beagle to explain how 3-4 square inches worth of atmospheric pressure (12 psi differential, more or less) is going to overcome that 57 Kg return spring.

Isn't there also Crankcase Pressure on the Engine side of the Vacuum Pump Piston?

whunter · #82 06-23-2012, 06:46 PM

Quote:

Originally Posted by Diesel911

Isn't there also Crankcase Pressure on the Engine side of the Vacuum Pump Piston?

YES.

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whunter · #83 06-23-2012, 06:47 PM

Diesel Injection Pump Timing Device threads
Diesel Injection Pump Timing Device threads

whunter · #84 06-23-2012, 06:49 PM

In Detroit my 300SD vacuum pump reads 28 inches mercury.

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qwerty · #85 06-23-2012, 07:16 PM

Quote:

Originally Posted by whunter

In Detroit my 300SD vacuum pump reads 28 inches mercury.

.

That pretty well shoots down the "parks at 25 inches" theory.

qwerty · #86 06-23-2012, 07:22 PM

Quote:

Originally Posted by Diesel911

Isn't there also Crankcase Pressure on the Engine side of the Vacuum Pump Piston?

On the piston pump, there is (effectively) crankcase pressure on both sides of the piston.

mach0415 · #87 06-23-2012, 07:44 PM

I am pretty sure that 29 in. Hg is considered "perfect" vacuum at sea level. So, 28 is pretty dang on the money

whunter · #88 06-23-2012, 07:55 PM

Quote:

Originally Posted by jbach36

W124
Any maintenance to be done on those?

Email me if there is, as I probably will not get back to check this thread.

NO.

The later 60x vacuum pumps where superseded many times due to failure issues.

There are NO repair kits for any of them.

the current valid part number is:
Vacuum Pump
MB# 000 230 31 65

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