high pressure shutoff valve?

[colwem]

Hi, we have a system that cycles from high pressure (~80 bar) to low pressure (~1 - 2 bar). We want an automatic air release valve. We are finding that they don't make such things that can handle 80 bar of pressure. So we're trying to figure out a solution to this. In my head I am imagining a valve that works just like a regulator except it simply closes the valve when the upstream pressure is above a set value and then opens it when the pressure drops. This way we can collect trapped air during the high pressure cycle and store it right under the pressure shutoff valve. Then when the pressure drops the valve opens and the air bubbles up and reaches the automatic air-release valve.

The problem with regular regulators is that they respond to downstream pressure and not upstream pressure. So when it closes during the high pressure cycle how is it going to open during the low pressure cycle? The downstream side has no outlet and is hopefully pressure tight. So it will remain above the regulators threshold and the regulator will remain shut right? We don't want this. We want it to open when the upstream pressure drops below the downstream pressure. One thing we could do is put the regulator in backwards right? So now the flow goes backwards through the regulator but at least the "sensing element" is on the right side. So now the regulator should close when the pressure rises and open when it drops. But this is not what it's designed for right? Can we do that? Is this standard practice?

I'm just confused about why I can't find a device that is designed for this purpose? Something that disconnects one part of your system from the other part in the event of overpressure but then opens back up when the pressure drops. We do not want to use a PSV for this purpose because this is not a "safety" event. This is an intended part of the process.

I am also welcome to any advice on how to solve our actual problem without resorting to expensive control elements. Meaning, how do people vent air out of a high pressure system? Like I know we could put in a pressure sensors and a control valve but It just feels to me like we should be able to do this without a control system.

Sorry, I am woefully unqualified for what I've been asked to do so sorry if my ignorance is painful for you.

 

[EdStainless]

They do make 'back pressure regulators' that sense on the HP side.
Of just use your pressure signal to sense low pressure and then open the vent valve.

 

[jhnblgr]

What fluid is being pressurized?
How is the system to work? What is the general process?

 

[colwem]

The

What fluid is being pressurized?
How is the system to work? What is the general process?

The fluid is water.

We are doing a filtration process. We pressurize the water to push it through a filter. We have a recirculation system that is constantly running the high pressure water over the filter and not just through the filter. Once the water has been squeezed out the remaining dirty water must be flushed and then the system is refilled. This is done at low pressure. So the loop not stay pressurized all the time. During the low pressure flush and refill cycle we would trapped air to be able to reach the automatic air release valve. But during the pressurized stage we do not want it to do that.

We could of course have an actuated valve. This just seems to me like a more complicated solution than we should need. I would think a valve that works with the same principles as a regulator but is even simpler should be sufficient. When the pressure rises above some value the piston/spring gets compressed, the piston pushes on a plunger that plugs the valve. When the pressure drops the spring pulls the plunger up opening the valve.

 

[colwem]

They do make 'back pressure regulators' that sense on the HP side.
Of just use your pressure signal to sense low pressure and then open the vent valve.

As I understand it though those backpressure regulators open the valve when the pressure rises right? We want the opposite. I want it to close the valve when the pressure rises. So it would in practice operate like a regular regulator except plumbed backwards.

Yes, we could definitely use our pressure signal to control a shutoff valve leading to the vent. This is our fallback solution. I just can't believe there isn't a non-actuated valve that exists that could make this simpler and cheaper.

 

[georgeverghese]

From what I gather, you want this valve to open at the end of the low pressure refill step. If so, then this is a sequence operated valve that gets its open and close command from the backflush / refill sequence controller for this filter.

 

[colwem]

From what I gather, you want this valve to open at the end of the low pressure refill step. If so, then this is a sequence operated valve that gets its open and close command from the backflush / refill sequence controller for this filter.

No I want it to open at the end of the high pressure step.

Yes, we can absolutely use an actuated valve. As I posted above I understand that that is the default method we will fall back on. But my question is why not use a regulator backwards as long as it's rated to 83 bar. Or if not, isn't there a valve that works this way? I mean why add a controller when the change in pressure is directly readable right there and a "spring" does a pretty good job of reading it. Isn't that simpler and cheaper than an actuated valve?

Or my other question is, how do people normally handle situations like this. We are in general having issues finding components that can handle the 80 bar pressure. What do we do when we want to put an analyzer into the process to see how the filtration is going but the analyzer can't handle 80 bar? It would be nice if we could tap the process and drop its pressure so we can analyze it then repressurize it. But then this sounds like we need a regulator then another pump.

 

[georgeverghese]

You could most likely find a self operated regulator that opens at low upstream pressure, but then, it would remain open all through the time when pressure in the filter is low - this is probably not what you want either.

Many analyser loops are complicated, feedstream "conditioning" is often required, and you'd be lucky if you could set up this analyser with just a letdown regulator, PSV and re pressurisation pump.

 

[colwem]

You could most likely find a self operated regulator that opens at low upstream pressure, but then, it would remain open all through the time when pressure in the filter is low - this is probably not what you want either.

No that's exactly what I want. The valve should be open the entire time it's not under high pressure. Closed tightly when the pressure is high. Tightly enough to prevent the build up of pressure on the other side for 3 minutes or so. Then wide open during low pressure.

 

[georgeverghese]

Well then, that seems like a self operated press regulator, set up the "wrong way" round.

 

[Snickster]

I think that in this case the simpler the system the less safe it is going to be. Any self-actuated device you could find dumping into a lower pressure system has the potential to fail open causing the lower pressure system, including the air release valve, to be over-pressured by a lot causing a hazardous situation. Even if it don't fail it still will leak and build up pressure on the low pressure side.

I would consider at the high point installing a large diameter pipe in vertical with level sensor to open a smaller solenoid vent valve at top when the liquid level reaches a low point and close the vent valve when the liquid level reaches the high point, all rated for the higher system pressure.

 

[LittleInch]

Just get a standard pressure regulating valve and connect the sensing line to the upstream side.

Nothing wrong or complicated there.