Porosity testing machine?

[riggerrob 643]

Does anyone know where to buy a porousity testing machine for canopy fabric?

New or freshly over-hauled are both good.

[mark 107]

Bench-type: http://www.frazierinstrument.com/products/category/porosity/porosity.html

The standard pressure difference for testing canopy fabrics is 0.5" of water, which is not very much.

Portable: the Aerostar balloon fabric tester is not very expensive, but tests at 10" of water, so not useful for parachute canopy fabric.

Home-made: There are designs that use an skydiving altimeter and a variable speed vacuum cleaner.

Mark

[tdog 0]

http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=3191905;search_string=porosity%20;#3192322

[g-bomb 0]

If it is only 0.5'' of water of pressure - you can make a pressure regulator from a glass jar or a Coke bottle (yes in this case Coke and Pepsy are treated the same).
These regulators are used in medicine for chest tube vacuum aplication. Basically you take a half-full container (or is it half-empty?) with 3 holes in lid:
1- to canopy
2-to source of vacuum with greater power than what you'll need.

The ports 1 and 2 need not protrude from the lid too much - few mm will do

In 3rd port you put a tube that is open to atmosphere and by submerging the tube below the water surface you create a pressure regulating device that adjusts to your needs - keep the end at 1/2 inch below and you get EXACTLY 1/2 inch of water pressure

The attachment to fabric is out of my realm of expertise.

If you need a picture - I could probably muster something later, so let me know...

[safetyjim 5]

Rob,
If you were doing rigorous fabric checks or canopy manufacturing, you'd probably want a commercial device.

If, instead, a rigger simply wanted to measure permeability to compare fabrics or canopies, track their degradation, or just establish a baseline measurement when someone brings a canopy for inspection, a homemade set-up should work just fine. You would also have greater flexibility in how you choose to make the measurements -- you wouldn't be restricted to 0.5" H2O, or 100 mm, or a single standardized value.

When I saw your post, I immediately knew at least one way to piece together a simple setup. (At work this would take about 20 minutes with high-school chemistry parts on hand; at home, I'd first have to go to the hardware store.) The 4 basic components you'd need are 1) a cell for holding the fabric, 2) a source of air pressure or vacuum, 3) a means for determining & controlling the differential pressure across the fabric, and 4) a means for measuring the air flow (okay, a watch or stopwatch might be #5). I haven't thought about #1, but #2,3,4,5 are straightforward, and I would think the whole thing could be assembled for less than $40 or so (maybe less than $20, if someone is really creative).

I could attempt a legible sketch, if you're interested. Unless I travel somewhere warm, I won't be doing much jumping during winter...