# vacuum tank or no vacuum tank?



## TTmartin (Feb 7, 2012)

Hi all,
just getting parts together for vac power brakes, Audi pump, festo switch,etc but not sure if tank is really needed?
It seems some do and some dont, has anyone had experience of with and without tank? advice appreciated.


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## Woodsmith (Jun 5, 2008)

I have only had bench testing experience on this.

Without a tank the compressor will run every time the pedal has been pressed, and take a finite time to produce full vacuum. How long that is depends on the pump. If your pump can pull a vacuum very quickly then that's ok. But if your pump failed then you are back to manual brakes, possibly without warning.

With a tank your pump will run less frequently but for longer each time to pull a vacuum from a larger volume. You will be able to pump the brakes a few times without loss of assistance, depending on your tank size.
If the pump failed you will still have assisted braking but with less assistance each time so there is some warning that the pump is not running.

When I set up a bench test for my aborted MR2 conversion I found that I could get vacuum in the servo in about 2-3 seconds without a tank.
With a tank it took about 8-10 seconds, IIRC, to pull full vacuum in the tank but I could get 2-3 presses on the pedal before assistance was trivial. The time to vacuum the tank wasn't expected to be an issue as it is less time then it take me to belt up, check mirrors and put on some music.

I opted to use a tank, made from a small dry powder fire extinguisher bottle and added a vacuum gauge in the dash so I could see if I was low or losing vacuum.


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## Joey (Oct 12, 2007)

For many pumps, turn on wears more than steady state operation. A buffer tank will reduce the number of turn ons and increase the on time for each cycle. Woodsmith also bring up a very good point about detecting if a pump fail occurs. In other projects, I've used these as buffer tanks: http://www.sierratradingpost.com/15l-fuel-bottle-by-sigg-of-switzerland~p~99207/


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## TTmartin (Feb 7, 2012)

Thanks guys,

tank it is then, plus secondary low vac warning pressure switch with warning light


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## FarFromStock (Mar 16, 2009)

I used a length (~18") of 1 1/2 pvc pipe. Glued on end caps. Drilled holes in each end cap to accept threaded/barbed fittings. Threaded the fittings with teflon tape into the end caps. Then connect the pipe to the vaccum hose between the pump and brake vaccum assist.


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## Woodsmith (Jun 5, 2008)

Here's my extinguisher tank.

The hose attached to it is a standard 22mm reducer to 15mm flexi plumbing hose.


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## kerrymann (Feb 17, 2011)

Joey said:


> For many pumps, turn on wears more than steady state operation. A buffer tank will reduce the number of turn ons and increase the on time for each cycle. Woodsmith also bring up a very good point about detecting if a pump fail occurs. In other projects, I've used these as buffer tanks: http://www.sierratradingpost.com/15l-fuel-bottle-by-sigg-of-switzerland~p~99207/


I like it! I was going to make mine out of PVC but didn't like the style but didn't want to weld one up either. Too bad they are out of stock at that price it would have been cheaper then the PVC fittings.


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## Woodsmith (Jun 5, 2008)

I didn't even pay for mine. I picked up 6 out of date dry power extinguishers as scrap in a pile of rubbish I was clearing out and decided to keep them. The powder was a bit messy when I tipped it out but the aluminum bottle is light and easy to use. Came complete with a wall mounting bracket too.

The plastic nozzle handle assembly was cut down and turned on the lathe to fit a 22mm plumbing compression joint to provide an easy connection.


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## kerrymann (Feb 17, 2011)

Woodsmith said:


> I didn't even pay for mine. I picked up 6 out of date dry power extinguishers as scrap in a pile of rubbish I was clearing out and decided to keep them. The powder was a bit messy when I tipped it out but the aluminum bottle is light and easy to use. Came complete with a wall mounting bracket too.
> 
> The plastic nozzle handle assembly was cut down and turned on the lathe to fit a 22mm plumbing compression joint to provide an easy connection.


So I started tearing down my Miata today and I decided I will be reusing the AC accumulator and lines for the vaccum system. It will make a good reservoir for the electric vacuum pump. It's a little small (~.5l) so it will probably only work for one stop if the pump dies. But it's light, has fittings and a mount already, and it was free.

​


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## Woodsmith (Jun 5, 2008)

Given it was all there and can be put back in use it is a good way to reuse stuff and save some cash.
I was planning on reusing the AC plumbing in the MR2 too as I intended to use the old AC compressor driven from the motor tail shaft to draw the vacuum. The electric clutch on it would have been controlled by the vacuum switch so it would only have run when needed.

It was a weighty solution but, again, free.


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