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I need a small, variable pressure relief valve

I need a small, variable pressure relief valve

I need a small, variable pressure relief valve

(OP)
I need a small, variable pressure relief valve to protect the plastic bottle from which air is removed.

The vacuum is up to 4.5 bar. This causes the 4 L bottle to implode. I need a pressure valve to pop open when the vacuum is too high. This must fully open, let a sudden rush of air into the bottle, almost instantly. It may stay fully open until reset. The pressure release settings must be adjustable between 0.5 and 4.5 bar. I need 6 of these to test on my prototype.

I make food vacuum packing machines. Will you recommend a low-cost, variable, small, pop-off valve that will open fully when triggered by vacuum level.

Can you recommend a small PVC or plastic pop-open valve to do the above?

Kindly,
Hank(dot]ensing(at]gmail(dot]com
 

RE: I need a small, variable pressure relief valve

4.5 bar of vacuum?????  Are you sure of your units?  A perfect vacuum (i.e. the total absence of all mass) is reached at -1 atm(gauge).  If you are near sea level and zero bar(g) = 1 bar(a), then the best vacuum physically achievable is 1 bar.  In Death Valley and other sink holes below sea level you can get up to around 1.1 bar below zero.  Reaching 4.5 bar of vacuum would be a bit of a stretch.  I would expect the earth to implode if you reached that kind of negative pressure.

David

RE: I need a small, variable pressure relief valve

Well, he has a test case: Maybe the vacuum-rated "pressure vessel" (the one being tested) is inside a larger pressure vessel:  Perhaps he is raising the pressure in the outside vessel to create a DP from outside vessel to inside vessel - for whatever process he is actually testing! - and so the internal pressure on the inside vessel could be anything fro a "perfect vacuum" to 12 bar.  Outside pressure vessel would be 16 bar.   DP = 4 bar "negative"

Of course, if so, I'd hate to have a safety feature such as a relief valve be a "manually adjustable" automatic trip, relying on the reset of the valve to protect my vessel from blowing up and hurting people.  .    
   

RE: I need a small, variable pressure relief valve

(OP)
I've attached a PDF showing the motor models and specs.
I am using the 240V AC supply with the 20-RNS and 25-RNS models. See attached PDF.

The bottle imploded in my face. I was looking directly at it. Very loud bang. Ears ringing for 15 minutes. Shock to me. Needed a hot drink and a sit down to recover. No cuts.

Here's the plan. I want to create a vacuum in a 2 L jar full of grain. It has a sealing lid. I put the 2L jar inside a larger plastic bottle. Then create a vacuum in the larger bottle. The inner 2L jar burps out air to equalize. Then, suddenly, I break the vacuum. The lid on the inner 2 L jar sucks shut with a vacuum retained inside. The outer large bottle must go from a vacuum to room air pressure instantaneously for this to happen. I want a valve to protect the outer bottle from imploding. It must open fully to let all the air rush in.

Mike, the valves you recommend at  http://www.plastomatic.com/vbl.html don't suddenly open fully, suddenly, so this valve will not work .

Can anyone help me find a small valve to do this? Or how I can make a simple one?

 

RE: I need a small, variable pressure relief valve

What you're saying is that your outer, large plastic jar is resistant to SOME vacuum, ENOUGH to provide the amount of vacuum packing that you need in your inner jar, but not enough to avoid collapsing when the vacuum gets too large.

Assuming the above is correct, I suggest you stop trying to find a self-operated multifunction device to replicate your manual process. A better solution would be to choose a thicker jar which is fully vacuum resistant, or to install a conventional vacuum relief valve or preferrably a backpressure regulator on your pump suction line, to limit the maximum vacuum you can draw to something your jar can reliably resist- if that's even possible.  A backpressure regulator will allow air to flow into the suction line of the pump smoothly, rather than suddenly disturbing your vacuum level like a vacuum relief valve might do.  Then all you need is a quick-opening solenoid valve with a large Cv, to break the vacuum suddenly after some period of time, or on a signal from a pressure switch etc.

Note that your jar is probably not reliably vacuum-resistant to the desired level- it just takes time for it to collapse.  The thicker-walled jar is probably necessary.

RE: I need a small, variable pressure relief valve

Please heed molten's words, especially if you intend to sell the end product -- unless, of course, you're rich enough to handle the law suits for when the valve fails and the bottle implodes on a customer and he has a heart attack from the shock.

Patricia Lougheed

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RE: I need a small, variable pressure relief valve

(OP)
Patricia, I don't want a heart attack. :)

Moltenmetal, You recommended I use "a conventional vacuum relief valve or preferrably a backpressure regulator". Is that a simple spring operated device that opens 'a bit' to let air in when the vacuum gets strong enough to open it? It is a great idea. All this time I've tried to fit it to the flask. But of course you are right, I can fit it to the suction line inside the box that houses the vacuum motor. Then nobody can tinker with it.
Three questions:
1. Could I then have a manually operated vacuum breaker as "nothing could go wrong"? :) FAMOUS LAST WORDS ...
2. How do I find one that will be the exact specs for my application?
3. What triggers the solenoid valve to open?

 

RE: I need a small, variable pressure relief valve

Sorry kahakura, I'm not going to design it for you.  If you can't figure out how to get a pressure switch to open a solenoid valve, I'm afraid you're out of your depth.

RE: I need a small, variable pressure relief valve

(OP)
That's fine.
I didn't put that clearly. The 3 questions are not just for you. Advise from anyone who visits this forum is appreciated, as was your excellent advice. Thank you.

To my understanding, there are people who like to share their expertise and experience with others who don't and forums are ideal to enable this. Design ideas too. Any ideas from anyone else?

1. How do I find a vacuum relief valve that will be the exact specs for my application?

Do I need to install a vacuum gauge, measure the desired vacuum, then seek a vacuum relief valve for this value, or are variable ones available. Anyone else know?

 

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