gas detection system

[John harry]

I am working on my new project and need some gas detection system which detect multiple leakage of gas. Currently i am using multi pro rae . Please suggest me some good gas detectors.

 

[davenn]

Hi there
welcome

what is a multi pro rae ?

 

[John harry]

Thanx.
It is a gas detector to detect the multiple gas leak.

 

[shrtrnd]

I'm not familiar with systems designed for this. I'm assuming you're talking about a pressurized gas, and not a gasoline fuel system.
If so, what about a pressure sensor for your system? A digital display (or attached to a process control system) should tell you when you have a leak.
If this is just for a test, I use 'snoop' which is a liquid 'soap' that bubbles when a leak occurs, and shows you the points of leakage.
If this is a system in use that cannot be monitored for test conditions, I think a pressure sensor is the way to go.
It would tell you if there is a drop in the pressure within the system.
Do we need more information from you about what exactly the gas is, or the pessure you're working with?
Is this a test bench issue, or a system that will be in constant use?

 

[davenn]

Thanx.
It is a gas detector to detect the multiple gas leak.

OK so what is wrong with this one that you have ?

 

[hevans1944]

Which gasses do you want to detect? What is the minimal detectable concentration? What is the maximum detectable concentration? Do you need on-board data logging or just a visual display of the concentration? Do you need wireless (remote) data readout? How much are you prepared to spend? Is human safety impacted by the measurement results? More details, please.

 

[davenn]

I'm not familiar with systems designed for this. I'm assuming you're talking about a pressurized gas, and not a gasoline fuel system.

no, as he stated its for detecting leaks, so that infers it would be detecting air/gas ratios outside or in a room from leaking pipes/cylinders etc

he still hasn't answered why the one he has doesn't do what he wants

 

[hevans1944]

... he still hasn't answered why the one he has doesn't do what he wants

Maybe the one he has does do what he wants, but he also said this was a new project. The one he has is a little pricey at $6000 or so. So I think he is looking around for a less expensive alternative. JMO, but it would make sense to explore options. Youse guys would not believe how much I had to pay for a "sniffer" to detect SF6 gas leaks. My tax dollars hard at work.

 

[davenn]

which is why I asked him the Q and he still hasn't responded

 

[John harry]

I need some other detectors and the one i use is working fine but i don't know that is this detector detecting accurate gas leak or not, i.e i have put this question davann

 

[hevans1944]

I need some other detectors and the one i use is working fine but i don't know that is this detector detecting accurate gas leak or not, i.e i have put this question davann

Please answer my questions in post #6.
There are calibration kits available for gas detectors so it is easy to find out "is the detector detecting accurate gas leak or not".

 

[John harry]

I want to detect the multiple leakage of the gas like co2, natural gas, LPG gas and nitrogen gas.

 

[hevans1944]

I want to detect the multiple leakage of the gas like co2, natural gas, LPG gas and nitrogen gas.

Thank you for answering part of my questions in post #6.

I can understand you want to detect leakage of CO2, natural gas, and LPG (liquified petroleum gas)... but nitrogen? The air we breathe is 80% nitrogen. How do you expect to detect a nitrogen leak (presumably from a cylinder of gas or a Dewar of liquid) into the atmosphere when there is so much nitrogen already present? That is one of the reasons I asked you to specify minimum and maximum detectable concentrations, which so far you have failed to do.

What do you mean by your statement "I want to detect the multiple leakage of the gas like..."? Does this mean there are other gasses you want to detect (in addition to the four you mentioned) such as hydrogen, hydrogen sulfide, ammonia, whatever?

Can you reveal what you want to do with your "new project" and explain why you need to detect gas leaks, other than the obvious reason, i.e., stop the loss of the gas. Sometimes posters here are reluctant to reveal "what" they want to do and already have a pre-conceived (quite often ill-conceived) notion of how to do it. That isn't the way we work here. You explain the "what" and the "why" and we will try to help you with "why not?" alternative solutions. When you post that you need a gas detector without revealing much more detail, it broadens the field of possible answers to such an extent that a specific answer is impossible... we would just be guessing. Here is my guess: You purchase a gas chromatograph/mass spectrometer, hire a chemist who knows how to use and interpret the results, then put it on a cart with a battery power supply and truck it around in the field looking for gas leaks with a sniffer probe.

 

[davenn]

I looked at the owners manual for the detector he already has
there's a huge list of gasses it detects

I really cannot understand what else he is trying to do ... it doesn't make sense


D

 

[hevans1944]

Yeah, the Multirae Pro is quite the thing for gas detection... and gamma rays, too! Every prepper needs one. However, it's sensors are only sensitive to the particular gasses they are designed to detect. If you need to detect a gas that your current sensor isn't sensitive to, you need to change sensors, or have several of these instruments with different sensor heads.

The only instrument that I am aware of that does not have this sensor-specific limitation is the gas chromatograph/mass spectrometer or GC/MS. Unfortunately most commercial GC/MS are laboratory instruments, not field instruments. They also require an operator, usually a physical chemist, to operate and interpret the data, although.much of the interpretation of late can now be done with the aid of a computer and a data-base of known chemical "signatures". None of this is cheap. There have been many attempts over the past ten years or so to shrink the GC/MS and mate it with a computer. The bottom line always revolves around interpretation of the data, which IMO is best left to a competent human being.


If the OP wants to investigate field-portable GC/MS solutions, perhaps he should visit this link.

 

[John harry]

Thanx hevans,
Actually i am not expert in this field i.e i have put this question in this forum.
So hevans we can't detect the nitrogen leak?. Please tell me some other way because i want to detect the leakage of co2, nitrogen, natural gas, and LPG gas and concentration doesn't matter. I want to detect even it is a small leak.

 

[davenn]

there are detectors like the one you have for detecting nitrogen dioxide NO2 and one other variation

but detecting straight nitrogen in the air would be difficult since it is already there in sich hi concentration, as heavens said

Dave

 

[hevans1944]

Small nitrogen leaks are virtually impossible to detect because of its strong background presence in the air. You would need to get a "sniffer" probe that sucked in the nitrogen leak with a vacuum pump and then the detector would have to suppress the background nitrogen level the sensor would "see". In other words, you would hold the "sniffer" probe up in the air, away from any suspected leak, and "zero" the sensor output. Then, when you move the "sniffer" probe over the leak, the sensor should "see" a greatly increased concentration of nitrogen. All of this requires an appropriate sensor and vacuum system and "sniffer" probe of course. It is possible your Multirae Pro can do this, but I have no experience with this instrument or other instruments that might be similar in function.

This "sniffer" method of leak detection is commonly used with helium as the sensor gas and a helium leak detector (a form of mass spectrometer tuned to respond only to helium) to detect defects in hermetically sealed containers. You pump helium into the container at a few psi and then go over it with the "sniffer" probe looking for leaks. Since helium is not normally present in the atmosphere, and the instrument responds only to helium, background gas is usually not a problem... unless the leak is so large that you fill the room with helium!

Theoretically, the same principle could be used with nitrogen, but helium leak detectors do not respond to nitrogen. The next best thing is a different type of gas spectrometer called a residual gas analyzer or RGA. The RGA is always operated in a very good vacuum and its original purpose was to determine just how good the vacuum was by detecting trace amounts of gas remaining in the vacuum system after it was pumped down and baked out for a few days. Anyone working with very high vacuum systems usually has an RGA plumbed into the system somewhere for quality control purposes. But you could put the RGA to use as a leak detector. Again, it requires someone who understands its operation to determine what is being detected, but they are quite sensitive.

 

[John harry]

Thanx hevans, You provide a very good description, This will be very helpful for me.

 

[hevans1944]

Sometimes, someone hands us an "impossible" problem to solve with the expectation that we will fail. And sometimes we do fail because no solution to the problem exists. But detecting a nitrogen leak in the presence of atmospheric nitrogen is just very difficult, not impossible. One possible way to get a detection advantage, if the source of the leak is from a pressurized nitrogen supply, is to deliberately mix a small quantity of helium into the nitrogen gas to allow its detection with a helium leak detector. You of course are not detecting nitrogen with this procedure, but it does detect where nitrogen (or any other gas) is leaking from a sealed system. Since helium is an inert gas, there is no permanent effect to admitting even a large quantity of helium to the system to check for leaks.

A minor disadvantage is helium will eventually leak through anything, even glass and solid steel. There are calibrated helium "leaks" you can purchase to calibrate the sensitivity of a helium leak detector, and these have a valve, but the valve is only there to vent the helium, not stop it from escaping through the calibrated leak. You connect the calibrated leak to a vacuum system (like the input test port of a helium leak detector) with the valve closed. After pumping down the system to a good vacuum, you open the valve to admit helium at a calibrated flow-rate into the vacuum system.

You state that concentration doesn't matter, but usually it does. Concentration determines the sensitivity of the leak detector to real leaks. Concentration determines the smallest leak that can be detected. And concentration affects the generation of "false positives" if all you are looking for is the mere presence of a leak, rather than trying to measure its magnitude. A sensor operating close to the lower limit of the concentration it can detect will generate a lot of "false positive" leaks that aren't leaks at all... they are background noise that the sensor interprets as a leak. And that is the problem you will encounter trying to detect a nitrogen leak: you need to suppress the atmospheric background nitrogen by reading the sensor output in air and subtracting it to produce zero output. Then you need enough sensitivity to see a very small increase in concentration when your probe is passed over the leaking area. I think it can be done, but I don't think it will necessarily be easy. Good luck with that!