Electric Vacuum Pumps

[dazmans3]

Hi

Can anyone tell me how I can find out what the required Vacuum pressure is in order to operate the brake servo, carb management & heater vents?

I know this was brought up fairly recently, however I saw no solution given for a good replacement. And they seam to be in sort supply at the moment.

I am in the middle of my S3 Turbo HC conversion and the final stumbling block is the brake servo. I would like an electric Vac pump, because of the improvement it offers to the brake system. I think I may have found one for the job, however I need to make sure its up for the job in hand.

The Vac Pump I have seen produces a Vac of -0.65 bar, & the version I am looking into with achieve 0.5 bar to a booster tank in 6 sec. I was told that if my brake vac system uses a standard vac level (about 18" Hg) then the pump will be ok. I am not sure what the 'Hg' refers to, if any one can help me here please?

If this works out then I can see it a good upgrade for all you fellow

[Bibs]

Moved from General Chat - Please read the forum description before posting.

[98GT3]

18" Hg is 18 inches of mercury, which is about 0.61 bar. I assume when they say 18" Hg they mean Minus 18", so on your figures it looks OK.

Phil

98GT3

[superdavelotus]

Hi Daz, can you please pm me and tell me which pump you are using?

Dave Walters

[dazmans3]

Hi Phil

Thank you, looks like I am on the right track at least. Yes it is minus 18 Hg. I assume then that this is a standard for all/or most cars brake servo systems?

Dave, have sent PM.

Daz

[98GT3]

Hi Phil

I assume then that this is a standard for all/or most cars brake servo systems?

Daz

Daz, a perfect Vacuum is described as 30" or 760mm of mercury (Hg) meaning that if you had a long tube plonked into a tub of mercury at sea level and started drawing the air out of the top you could draw the mercury up it 30" and there it would stop........draw as much as you like and it would go no further! This is because as you reduce the pressure at the top, the air pressure acting on the surface of the tub pushes the mercury up the tube. At 30" the weight of mercury in the column is exactly countering the air pressure acting on the surface of the tub at the bottom ie. 1 atmosphere.

Anyway to cut a long story short, the price of a pump starts to rise very sharply the nearer it gets to vacuum perfection, so I would assume that the .61 bar is the best compromise, price vs performance......but I am only assuming!!!!

Phil

98GT3