Help with Rupture Disc/Relief Valve

[bill70j]

We have completed a separator using a 30 gal galvanized steel trash can ahead of a HF 2HP collector and have retained the 4" HF wye feeding the separator.  We now want to add protection to avoid collapsing the can should there be a suction blockage.

For permanent protection, we plan on building the relief valve described by johncarl in his 6/24/09 post.  It apparently works, and is quite sexy.  And maybe we will add stiffening rings as well.

But in the interim, we were thinking of adding a simple rupture disc-type device.  It would simply be a thin membrane that would replace the end cap on one of the wye ends feeding the separator.  Maybe nothing more that plastic wrap (with a few pinhole starter holes) attached with a rubber band like shown in the image below.

Do you think this would work? Or is this a dumb idea?  Has anyone tried it and come up with a membrane that is proven to work?  Would appreciate any and all input and ideas.

[Vodkaman]

I have read the post that you mentioned, a while back. It is a beautiful piece of engineering: http://www.jpthien.com/smf/index.php?topic=198.msg1161#msg1161

I like your temporary solution. I just did a quick test on a small shop vac. The hole thing worked, but without the holes, you would lose your can. Test it with too many holes and work your way back. Pressure or vacuum has a nasty habit of catching us out.

My solution would be a simple plug and leaf spring arrangement, but I have not built anything yet.

Dave

[bill70j]

Dave:

Thanks for the input.  Appreciate your test.  And great idea to start out with too many holes.  I had not thought of that. 

So I am going to go out and start some testing on my setup.  Using a blast gate to vary pressure, I'll hook up a manometer of some sort and also rig up a dial indicator to measure can deflection.  At varying pressure levels, I'll decrease the number of holes in the membrane until it fails.

Also, I think I'll consider your rupture disc design vs. the relief valve for a permanent solution.  Sounds a lot more simple.  Have you given any thought to size?  Maybe I can get some design info from my test data.

Bill

[DavidcGrimes]

Maybe this will work for you.  I have ordered one and will report results in a few weeks, but here is the link for your review:

http://shop.centralvacuumfactory.com/vacvalve-relief-valve-central-vacuum-systems-p-954.html

[Vodkaman]

Dave:

Thanks for the input.  Appreciate your test.  And great idea to start out with too many holes.  I had not thought of that. 

So I am going to go out and start some testing on my setup.  Using a blast gate to vary pressure, I'll hook up a manometer of some sort and also rig up a dial indicator to measure can deflection.  At varying pressure levels, I'll decrease the number of holes in the membrane until it fails.

Also, I think I'll consider your rupture disc design vs. the relief valve for a permanent solution.  Sounds a lot more simple.  Have you given any thought to size?  Maybe I can get some design info from my test data.

Bill

You are welcome Bill.

As for disk size, you will be able to do some simple sums, once you have your pressure readings. Convert the numbers to Lb/sq ins or metric and calculate the area of various size plugs and work out the load that the spring will have to hold. I was thinking around 3 - 5cm diameter, but that is just gut feeling.

Again, this can be determined by experiment. Build a flat plate with a piece of 2" drain pipe. Use it to restrict the flow at end of hose and observe the can for effects. Restrict the area further, to find the critical area.

Space is probably not a problem, so no need to go micro with this. Build it big and let people admire your engineering skills, LOL.

Dave