If you are on BCC list I think you MAY have usefu=
l
comment to make (be kind)).

EE seemed closer than TECH.

I have a requirement for 1 or  2 (maybe 3) vacuum pumps capable of providin=
g
a vacuum of slightly over about 0.5 atmosphere / 50 kPa / 7 psi / 14 inches
of mercury / at a flow rate (if vacuum flows :-) - of say 1.8 litres /
minutes or about 3cc/second. That's a very modest requirement by most
standards.

This is for a proof of concept demonstration that may get replaced by a
"proper" solution in due course or may be used indefinitely if I make it to=
o
good.

But I'd prefer it to be quiet in operation and moderately low priced. If it
could be light and small, so much the better. (I'll be taking the system it
drives in my luggage to China - if the pump was less than say 1kg it could
come along for the ride.)

The intended use is a leakage tester for sealed object with a volume of
about 150 cc (Probably more like 100cc)..
Internal pressure is lowered to 50 kPa absolute and then held for some
seconds while pressure is monitored for leaks.
Test rate is say 6 to 10 per minute (probably 6 or even less)
Worst case =3D 10 x 150cc =3D 1.5l of air to 50% evacuate.
More likely =3D 6 x 100 =3D 0.6l/min to 50% evacuate.

All sorts of pumps suggest themselves with various fits to the requirement.

- Commercial motor driven vaccum pumps - vane/scrtew/piston ... - probably
overkill.
-  'Fridge  compressor - OK but messyish and  heavyish
- Suction side of various small pumps made for pressurising - fish tank /
tyre inflator / electric breast pump (don't laugh) ...
All possible but eg fish tank pump suction probably to low due to crude
design and battery powered type pressure pumps  would work but are noisy an=
d
life time is questionable.

The best sounding suggestion so far is a peristaltic pump - a series of
rollers force a volume of trapped space along a flexible tube. Sealing
should be OK enough. Volume can be calculated. Available commercially. Can
be DIY'd if desired.

Commercial small units are often medical or specialist. Large ones for slug=
e
pumping and similar are inappropriate. Roll your own is possible but tome
rushes onwards with much to fill it.

this is too small but shows people who haven't met them what they look like
and how they work and how simple they are

      http://www.anatech.co.nz/includes/display_media.php?media_id=3D51

SO:

Any other good suggestions for a suitable vacuum pump?

Any experience with using peristaltic pumps for gas-vaccum use (ie as
opposed to liquids which is their more normal use)? (Pressure attainable,
practical issues, ...?)

____________

A just maybe thought is an air eductor or water eductor using either
compressed air of water. In the latter case it may be possible to use mains
water pressure to produce enough vacuum. Water runs to waste which is
wasteful but may be a cheap  demo solution.
_____________

I must say that as I write this I'm thinking that a 12V car tyre compressor
solution would be good enough for demonstration purposes. Quick mental-BOTE
calc suggests that they should be have  least 10 x  the capacity needed
(based on car tyre volume, pressure needed and time taken to inflate a tyre
(forever it seems). If so, duty cycle of <=3D 6 minutes/hour. Quick calc
suggests that a substantial reservoir would be needed to run a whole day so
only a modest one is required. (A 1 m^3 tank  at 50 kPa vacuum could be a
very exciting object).

["Playful" thought: Could use a TV CRT / picture tube as a 1 atmosphere
rated vacuum reservoir :-). Drill or knock out stem in centre of base to
"safely" de-vacuumise and add a vacuum hose. But, presumably such things ar=
e
readily enough available.



                  Russell
--=20
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