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Mackinac Movies 05-31-2010 09:59 PM

Pressure relief valve
 
1 Attachment(s)
Going to share my weekend science project.

I am a little worried about my 1HP b-Air blower and my CB 16x8 screen. So I have been thinking about an easy home-made device to vary the pressure inside the screen without using the zipper, which I am worried could fail being 1/2 unzipped.

I used a salvaged 3" gate valve, a 4" (3") T, and a 5" to 4" rubber fermco coupler.

I thought the gate valve would dump enough air out the T that the screen would partially deflate, and that I could slowly close it until the screen was at a good working pressure, without building up too much pressure. My results were a little interesting.

The construction was straight forward. Since schedule 40 PVC has several hundred working psi, I was not worried about even gluing the parts together for this test. It turn out the fermco coupler will actually tighten onto the rectangular blower opening with the band clamp.
Attachment 88
As you can see, the gate valve is all the way open. When I inflated the screen I was running about 4 1/2-5 " of pressure, where I previously established that operating should be about 4 ".
OK, so maybe the 3" T opening isn't venting enough air. I removed the gate valve and tried blowing up the screen again. This is the interesting part: The screen inflated properly without any air coming out of the open hole! After the screen inflated, the air vented, and established about a 4 1/2 " pressure rating as before.

I don't have access to a 4" gate valve to test, and I think the cost is too much to justify the experiment. But I am kinda thinking now, that I may run my little contraption with the open hole to lower the max psi rating on my 16x8 screen. I figure it has to be a little better then just unzipping the vent and putting the stress on the stitching.

Doug Miles 06-01-2010 07:42 PM

Your picture is exactly what I was imagining that type of relief valve system would look like.

Quote:

Originally Posted by Mackinac Movies (Post 370)
OK, so maybe the 3" T opening isn't venting enough air. I removed the gate valve and tried blowing up the screen again. This is the interesting part: The screen inflated properly without any air coming out of the open hole! After the screen inflated, the air vented, and established about a 4 1/2 " pressure rating as before.

I'm just guessing, but could the blower be pushing so much air straight ahead that there was no reason for it to come out the open hole?

I forget what you said the max pressure was without the zipper open. Was it 6"? Seems like it works pretty good if it reduces it by 1 1/2 ".

Quote:

Originally Posted by Mackinac Movies (Post 370)
I don't have access to a 4" gate valve to test, and I think the cost is too much to justify the experiment. But I am kinda thinking now, that I may run my little contraption with the open hole to lower the max psi rating on my 16x8 screen. I figure it has to be a little better then just unzipping the vent and putting the stress on the stitching.

Yes, I would use it if I were you. Remember, you get the added advantage of being able to attach the valve and close it a little in order to create more pressure if you need it (windy night for example).

Mackinac Movies 06-01-2010 09:38 PM

Quote:

Originally Posted by Doug Miles (Post 376)
I'm just guessing, but could the blower be pushing so much air straight ahead that there was no reason for it to come out the open hole?

Yes and no. Yes it is 'zooming' past. But no, if there is no back pressure in teh screen, there is no reason for the air to stop at teh T until the screen is full and there is back pressure
Quote:

Originally Posted by Doug Miles (Post 376)
I forget what you said the max pressure was without the zipper open. Was it 6"? Seems like it works pretty good if it reduces it by 1 1/2 ".

6 1/2" Yes it did reduce it quite a bit, just not quite enough. Maybe 4 1/2" would be OK. I could also use it, and unzip too.

Quote:

Originally Posted by Doug Miles (Post 376)
Yes, I would use it if I were you. Remember, you get the added advantage of being able to attach the valve and close it a little in order to create more pressure if you need it (windy night for example).

Ya, since I have the valve, I will shorten up the connections to reduce teh weight, and length and put it in the tool box for use.

Also forgot to mention: Fermco coupler= $22, T= $19, the rest salvage material, so under $50

Also forgot to mention, the above info was for the 16x8 screen, but the 20x12 way very very similar outcome.

Doug Miles 06-02-2010 10:20 PM

This is definitely worth $50, that's for sure! Could actually save your screens over the long run too.

Too bad the 4" valves are so expensive. I understand why they are, they're made for water tight seals (and water pressure). Do you think a 4" would work a lot better?

Mackinac Movies 06-03-2010 11:52 AM

I am gonna get a 4" T and try it sometime. I am guessing that with a 4" opening, I can actually get the screen to start to deflate. I am gonna keep my eye out for a 4", but I will use it this way, for now.

Being so new to the inflatable screen thing, I just want to baby them as much as possible (for now).

Doug Miles 06-03-2010 01:16 PM

When I first got my CB screens I was worried about the quality, whether the seams would hold up, etc. I think the first few parties I did with them I ran with the zippers partially open. After a few parties though, I honestly forgot about opening the zipper, and I have never done it since.

I think running at 4.5 inches of pressure is good. Assuming your screens are made as well, if not better, than mine, they can withstand pretty high pressure. I use the ToolKing blower on my 10' CB screen without the zipper open, and it creates 8-8.5 inches of pressure in that screen. I've basically been doing it this way for 2 years.

I'm not recommending anyone else do this, but it gives you an idea of the legroom you have. I would still like to make a similar relief system for myself, just not sure when I can get to it.

Doug Miles 07-07-2011 09:21 PM

I never got around to making one of these. Are you still using yours? If so, do you think it helps?

Mackinac Movies 07-08-2011 09:46 AM

Doug, I sure am, with every job, on both my 16 and 20' screens now. Only one change, I have removed the actual valve, and I am just using the PVC Y pipe. I just put it in line, and the air blows right by the opening while filling the screen, and once filled, the extra pressure seems to come out of the open hole. Stupid proof! In all of the times that I have used it, I only closed it off once. Last year I posted about the winds really coming up on me during an event, the top tube was bending down, and I taped over the opening to increase the screen pressure (and I sat on the rear tube to keep it down) But I would say it was a success.


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