David Jenkins
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| posted on 3/1/07 at 08:45 PM |
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Vacuum pipe
I'm currently setting up my Megajolt, but have a bit of a problem - I need to run a bit of pipe from the MAP sensor (a pressure sensor) to an
outlet on the case. Ideally I would use the sort of pipe used between the carb and the dizzy as that doesn't collapse under low pressure, but
it's much too stiff to use inside the MJ case - I'm worried about snapping the plastic neck off the sensor.
The stuff I've got is 1/8" inside, and 3/8" outside, but made of quite a stiff material - quite a hard rubber.
Is there any sort of thinner stuff available, that won't collapse when the pressure drops?
cheers,
David
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graememk
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| posted on 3/1/07 at 08:46 PM |
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i used air pipe from a pet shop used for fish tanks
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paulf
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| posted on 3/1/07 at 09:14 PM |
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Windscreen washer pipe works fine, its unlikely that you will get enough vacuum to collapse it. Ive used it in a few units ive built with no poblems
at all.I tend to use a short length onto the sensor and then use 4mm bulkhead fittings for industrial nylon airline to take it out of the box. The 4mm
airline will push into the washer tube and not come out easily.
I have used the rubber tube also but it tends to be a bit bulky to fit in the unit but is good under the bonnet.
Paul.
Paul.
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David Jenkins
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| posted on 3/1/07 at 09:16 PM |
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Some good ideas there - I made my own bulkhead fitting with 3mm ends - I'll have to find the right-sized pipe! 
David
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martyn_16v
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| posted on 3/1/07 at 09:43 PM |
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I wouldn't use windscreen washer pipe anywhere near the engine, it softens enough when it warms up to collapse (I know, I did it on my first
install). It'll be fine for a short run away from the engine though.
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Jon Ison
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| posted on 3/1/07 at 09:53 PM |
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David, if you want some 4mm fittings & pipe I can post you some, the 4mm pipe fittings I have require a tapped M5 hole too screw into, they are
designed for vacuum.
That sounds double dutch, the pipe is 4mm external dia but the fitting require an M5 threaded hole ? Still clear as mud.
Can go larger if you require up too 12mm.
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David Jenkins
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| posted on 3/1/07 at 10:04 PM |
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Thanks Jon - but I think I'll be OK (but I'll keep your offer in mind, if things go pear-shaped).
Martyn - it'll be 4" of pipe in an ali box under the dash!
cheers,
David
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David Jenkins
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| posted on 4/1/07 at 01:44 PM |
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LAST QUESTION! (for now...)
OK - I've made my bulkhead fitting, and connected it to the MAP sensor with a nice bit of thick-wall silicon tubing courtesy of my local model
shop.
Now that it's all ready to go, I have one last question - the carb vacuum connector (and now, my bulkead fitting) has a diameter of fractionally
over 5mm (0.2" to be precise - good Italian measurement!). Having just found out that the previous 3mm i.d. pipe had split where it was pushed
onto the connector, I'd like to get the next bit of pipe the correct size. The plan is to buy some Samco silicone vacuum pipe for a bit of
under-bonnet bling, but I need to know whether I should buy 4mm i.d. and make it stretch over the connector, or 5mm i.d. with a risk of it being too
slack - or do I get 5mm and some hose clips to be absolutely sure?
Oops - one more question - should I fit an oil trap in the vacuum line?
cheers,
David
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paulf
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| posted on 4/1/07 at 05:23 PM |
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Hi David .
I would fit 5mm and a hose clip to hold it on, you should ideally fit a fuel trap. I found that when first connected without one the pipe work filled
with petrol after a short while. I made one using a co2 bulb and some brake pipe one tube going to the bottom and connected to engine and the other
one from the top to the megajolt.
Paul.
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David Jenkins
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| posted on 4/1/07 at 06:26 PM |
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That makes sense - thanks!
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