Sorry, hit the wrong button before finishing the ASCII art. This
is my plan for the valve design. View in mono-spaced font like
Courier.


Atmosphere

-- -- lip to retain spring and form seal with disk
|===========| --- disk between spring and lip
|o o|
| o|--- pipe with spring inside. spring pushes disk
against lip
|o |
| o|
|o |
| o|
|o |
| o|
|o |
| o|
|o |
| o|
|o |
| o|
|o o|
-- -- lip to retain spring

Inside of bin


When the pressure drops enough inside the bin, the disk will be
pulled down and air allowed to go through the pipe.

Obviously the disk needs to be a bit smaller than the pipe to
allow air past its edges. The spring tension will also need
playing with so that air is not admitted under normal conditions
but the valve does its job when the pressure drop is sufficient.

I will post back when I have something working.

W.






"Woodspoiler"
wrote in message ...
In response to various posts:

Galvanised bins: good idea. I'll look into that if I destroy
the
plastic one.

Static: never noticed any! Maybe using hose designed for dust
extraction has helped. I got that and the step-down adaptor to
connect to my jigsaw from www.axminster.co.uk.

Mesh on inner bucket:: blockages occur in the inlet hose
between
the business end and the cyclone bin, so that wouldn't help.

Spring catches: neat idea, but crude and involves spending
money.
This is a low budget project and I'm using found items where
possible.

Screwfix springs: hadn't noticed they sold them, but I think
that's the wrong sort of spring (my valve idea requres the
spring
to compress and push back, rather than stretch and pull back)

A ferret around my garage has turned up a suitable looking
spring. It looks like the return spring from an ancient car or
bike throttle linkage (or perhaps brake or clutch). It fits
nicely up a bit of scrap copper pipe I have, so all I need is
to
cobble together the valve end.

I shall post back when I've got someting usable, but the plan
is
to have a lip at the bottom of the pipe to retain the spring
but
allow air through the pipe. The spring will be compressed
inside
the pipe. The inlet end will be like the outlet, with the
addition of a plastic or rubber disk. This will be sucked in
whent he pressure is great enough, and allow air in.


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This was my original post: http://tinyurl.com/m9j3

(http://groups.google.com/groups?q=wo...one&hl=en&lr=&

ie=UTF-8&safe=off&as_qdr=all&selm=bbi4hc%24jnm%241%40tita n.btinte
rnet.com&rnum=1 )

W.