Friday, January 14, 2011

Vacuum Pump part 2 - Parts list discussion continued


PART 5 - The microswitch that is used in the regulator. You can buy these from Jaycar Electronics, Dick Smith... Instead of having just the button they have a 3cm lever over the top.

This worked out to be ideal for using in the regulator because by having the armature from the vacuum pump contact between the button and the fixed end of the lever on the mocroswitch you get very rapid actuation of the button and so a nice clean shut off and turn on. Originally I had the armature contacting at the other (free end) end but the vacuum advance armature had to travel twice as far to depress the button fully compared to having it directly on the button. As the movement is slow this meant that the button was partially depressed for a couple of seconds. The result was audible arcing inside the switch which in turn caused the compressors overload protection to kick in. When this happens you have to unplug the compressor and let it cool and reset - a big problem if you are leaving the job unsupervised while the resin cures.

PART 6 - The Vacuum Gauge. This is optional as you could probably manage the clamping visually and by listening to the compressor labouring. However, this is a cheap addition that takes a lot of the guesswork out of it.

Boost gauges for turbo chargers are ideal as they only measure less than 1 atmos pressures and so don't waste the scale on pressures greater than 1 atmos which we wont make use of. I found this one at 'RacerTech' for $14. In SuperCheap Auto they're about $80, I guess because they are higher precision and bling.

This one came with the tubing and T piece needed to add it to the pneumatic circuit and so you need to take this into account when picking the size of the tube to use elsewhere in the circuit.

Part 8 - the regulator spring. Don't underestimate how much force the vacuum advance will apply when you pick the spring to use. The vacuum advance I got had a diaphragm area of about 4 sq inches which at 14.7 psi ( 1 atmos) this is about 60 lbs or about 25kg of force it will exert against the spring. I salvaged a spring from an old metal bed base which turned out to perfect. In addition, the bed base turned out to be great for making the rocker table so if you can track one down , in fact 2 is even better, then it would be handy.

..... next instalment will cover the construction of the vacuum pump.

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