Monday, September 22, 2008

Finished the vacuum reservoir

When you take out the petrol engine, you lose the vacuum that makes the brakes work. So EV conversions need to install a separate vacuum pump. Many trucks have these installed anyway, and it's a fairly easy process to make it work.

The vacuum pump itself is quite noisy and even though it doesn't chew a lot of power, there's no need for it to be running all the time. What you do is make a reservoir so the brakes can access the vacuum when you need it, and then the pump only has to run to top it up.

I asked Gav at KiwiEV about his reservoir (which you can see here) and he said it was about 2 litres, and if he was doing it again he would make it 5 litres, just so he can show off the stopping and acceleration power of his EV. So I decided to stand on the shoulders of giants and make mine 5 litres.

Hmmm - problem...How do you calculate the volume of a cylinder? Was I digging out my old maths textbooks? No way - I just did a google search for "volume of a cylinder" to get the formula, then divided by 5,000 to get my dimensions:

Volume = (Radius x Pi) squared x length. So (2.5cm x 3.142)^2 x 80cm = 4.9 Litres

So, for about $20 at my local Bunnings Hardware I got 1 metre of 50mm PVC tube, two end caps, 4 washers, 2 brass hose nipples and 2 brass locks for the inside. 3m of vacuum hose cost me $12 at the local auto parts store. I cut the tube down to 80cm, as this will give me about 5 litres of vacuum.

Then when I got home I learned that the thread on the brass nipples is about 1/2 inch - a lot larger than the largest drill bit in my kit. Back to Bunnings for a drill bit and I also picked up some silicone sealant and a gun. I drilled a hole in the end caps, fitted the washers and nipples to the locks and sealed all around them, then left it to cure overnight. Pushing the vacuum hose onto the nipple was a bit of work, but then tightening up the hose clamps was the easiest part of the job.

So: here's my finished setup. I've checked that it will fit in the car in front of the radiator, using cable ties to secure it to the body.

Now all I've got to do is afford the vacuum pump from ZEVA. Please donate! If you own a business, ask me about sponsorship/advertising.


Anonymous said...

Hi Justin, I found your blog thru Gav's might be interested that I'm doing the same thing, but with a Ford Capri down here in Sydney. I've been blogging at - with vids and all. Drop me an email sometime...i'm sure we could share heaps of info!

David Harrington said...

Have you considered getting a vacuum pump from eBay? I just bought a 12 volt Thomas Vacuum pump capable of 23 HGs of vacuum for $98 USD + shipping. All I need now is a vacuum switch and resevoir. Way cheaper than a pump from the US EV suppliers, and it has a 6 month warranty.