Compressor humidity indicator

Sutty · 1st January 2007, 17:21

Genesis mentioned an "eyball" with a humidity indicating card which enabled a compressor operator to check that the air being produced was dry, in this post.
Does anyone know of a similar product in the UK?

Thanks,
Neil

divetheworld · 2nd January 2007, 01:35

Quote: (Originally Posted by Sutty)

Genesis mentioned an "eyball" with a humidity indicating card which enabled a compressor operator to check that the air being produced was dry, in this post.
Does anyone know of a similar product in the UK?

Thanks,
Neil

I've always used drager tubes. Cost a few quid but then again, you dont need to use them that often.

Genesis · 2nd January 2007, 02:33

Aerocon Systems Aqua Environment

Cheap enough for them to ship. That device accepts the humidity cards from here:

Humidity Indicator Plugs, Cards & Desiccators

You want the 0.95" 3-section 10/20/30% cards.

And no, checking once in a while is NOT good enough. You need continuous monitoring - when the 20% indicator just starts to turn your dessicant (molecular sieve) is shot and within minutes you will have oil vapor in the product gas.

divetheworld · 2nd January 2007, 13:54

Neil, check it every three months in accordance with the HSE guidlines (DVIS9) if your pump is maintained correctly.
Maintain less than 35mg/m3.

Quote: (Originally Posted by Genesis)

And no, checking once in a while is NOT good enough. You need continuous monitoring - when the 20% indicator just starts to turn your dessicant (molecular sieve) is shot and within minutes you will have oil vapor in the product gas.

Yeah, right O. You have fun with that one then.

Genesis · 2nd January 2007, 14:05

Quote: (Originally Posted by divetheworld)

Neil, check it every three months in accordance with the HSE guidlines (DVIS9) if your pump is maintained correctly.
Maintain less than 35mg/m3.

Anyone see the contradiction here?

No?

Go read it again.

Now tell me how you "maintain" something you are only measuring once every three months.

Then justify your position when the appliance to measure conitinually costs about $50, the cards are $3 each and last a year or more (they revert back to blue when dried) and you now KNOW that your gas is dry all the time - and thus that your purification system is working all the time.

The "test every three months because that's what the government says" guys have sold me several tanks of bad gas over the last few years. But I'm quite sure that once every quarter they had a test that says their gas is ok.

The certificate on the wall says so.

divetheworld · 2nd January 2007, 14:49

Quote: (Originally Posted by Genesis)

Anyone see the contradiction here?

No?

Go read it again.

Now tell me how you "maintain" something you are only measuring once every three months.

Then justify your position when the appliance to measure conitinually costs about $50, the cards are $3 each and last a year or more (they revert back to blue when dried) and you now KNOW that your gas is dry all the time - and thus that your purification system is working all the time.

The "test every three months because that's what the government says" guys have sold me several tanks of bad gas over the last few years. But I'm quite sure that once every quarter they had a test that says their gas is ok.

The certificate on the wall says so.

Neil,

Attached stuff you might find helpful. Unfortunately it doesnt say you can go out and buy a £1.50 packaging indicator that shows your under 5-10% RH but I'm sure you will sift through it and find what you need.

Brent.

Genesis · 2nd January 2007, 15:25

Yes, yes, quarterly monitoring is important, and so is meeting dew point standards to prevent free water condensation (especially with regards to steel cylinders!)

However, quarterly monitoring cannot possibly determine that during the entire period you are pumping acceptable quality gas!

There are two separate issues here:

1. If the dew point of your gas is too high, at working pressure in your cylinder, free water can condense and this causes severe problems (e.g. corrosion in steel cylinders) which must be avoided. As pressure rises the amount of water expressed in absolute terms (mg/m^3) falls precipitously. Likewise, temperature is a significant factor, since warm gas holds more water vapor than cold gas. This is what the Draeger tubes are checking for, and what the quarterly air check does as well. In addition, if you dive (particularly open circuit) in cold water, there's a second problem in that temperatures can fall radically during expansion in the first stage. If the gas is not sufficiently dry you can get icing inside the regulator's internal mechanism which will cause a first-stage freeze with resulting malfunction. This is unlikely on a CCR due to the much lower volume of gas delivered (and thus the lower adiabatic cooling load) but happens all the time with open circuit gear.

2. However, what I am referring to here is a way to monitor, in real-time, whether or not your purification stack is actually working. Since "online" air testing for hydrocarbon content is impractical, and quarterly monitoring does not tell you whether or not you are pumping clean gas all the time, a proxy is helpful for determining whether or not your filter stack is expended and needs service.

The "eyeball" indicator with a 10/20/30% RH card in it, on the high pressure delivery side, is an effective means of determining the latter circumstance.

When the 10% card has "turned", you have a 10% RH in the high side of the system at delivery pressure and temperature. By the time the 20% card has started to turn, your purification stack is no longer effectively removing moisture from the gas stream, and you are at severe risk of hydrocarbon bypass.

Since the question originally asked (and from which this thread was derived) was asking specifically about compatability of product gas with oxygen for the use of blending, moisture, while troublesome, isn't the issue under consideration.

Compressor and filter manufacturers all cite "expected service life" numbers, usually in cubic feet of gas processed. However, those ratings all require that one know the temperature of the inlet gas - and that is quite difficult to measure accurately. Ambient temperature does not provide a reasonable guide to stack inlet temperature. Inaccuracy here leads to belief that you have working filtration when you in fact do not.

Checking quarterly only tells you that the filters are working at the time of the check.

I note from your own quoted documents that HSE recommends:

Quote:

2 A more reliable method is to monitor the air quality on-line. One technique of monitoring on-line is to measure the moisture content.

n

Filter cartridges are usually designed so that the drying element becomes saturated before there is any deterioration of the other elements. Therefore, monitoring the moisture content of the air at the filter outlet can indicate when the filter has reached the end of its life.

n On-line moisture content measurement equipment can be:

- built into the filter element;

- a separate measuring device;

- a simple visual indicator.
n

The provision of on-line moisture content measurement equipment will be of particular

benefit where the air is for sale, as it will provide visible assurance to the user of the gas.
n

Before fitting such devices the views of the compressor and/or filter manufacturer should be sought.

Which, of course, is what I recommended.

You might want to read your cites before using them, as in this case they backed up my position rather than yours!

divetheworld · 2nd January 2007, 15:36

La la la la.. All I can hear is La la la la.

Dispite the self opinionated arrogant tossers continuous ranting of pages and pages of bollocks, 5-10% is not good enough.
If your stack is maintained and logged, a periodic check is sufficient.

Now, where is that ignore button.

Sutty · 2nd January 2007, 15:37

Thanks guys.
For the small volumes of air I'm pumping quarterly testing is a bit OTT, so I'll be logging fill volumes. That is one of the reasons I was considering in-line monitoring for humidity. I've not worked out how a relative humidity indicator at pressure correlates with mg/m3 yet though.

Neil

Genesis · 2nd January 2007, 15:49

To get an ACCURATE correlation you need both the pressure at the time of the measurement AND the temperature of the gas at the measurement point.

The former is pretty easy, but the latter is not (accurately.) Without the temperature you cannot correlate the RH to an absolute (mg/m^3) value.

Monitoring online does not tell you that you are within dewpoint specs generally (the big risk here is taking a tank filled in the middle of summer, and letting it sit until winter, then diving with it - you could have free condensed water in the tank, and thus have corrosion problems if that's a steel cylinder, or have problems in cold water with a regulator first-stage freeze)

What it does tell you is that your dessicant is working and thus your activated carbon is still effective in removing hydrocarbons.

That is the point of online monitoring with an "eyeball" - to know that you are still effectively removing contaminents from your product gas.

Note that a lot of the "compressor guys" will sell you 20/40% cards. Those are completely worthless as once the 20% one turns your stack is already rubbish and by the time the 40% one turns you're not only pumping water-laden gas but LOTS of oil vapor as well!

For those who say "that doesn't work" - yes it does. I've verified my setup with a montoring test and meet OCA (Mod-J) air quality standards just as my indicator card says I need to change the primary filter stack. Most "commercial" shops change the filters and then test for their "certificate." That, of course, is backwards - they should be testing with used filters at maximum life so they see the worst case - not the best case!

The shop is concerned with getting sued if they are out of complience. I'm concerned with not blowing up or killing myself while underwater due to contaminated breathing gas.

Try diving in the Caribbean sometime if you want to breathe truly foul "air". I just got back from there a week or so and found it basically impossible to find air that didn't have a "taste" to it. I'm not sure I want to know what a test would have shown......

1st January 2007, 17:21	#1 (permalink)
Sutty Classic Kiss diver Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Jun 2005 Location: Glossop, Derbyshire, UK Posts: 802	Compressor humidity indicator Genesis mentioned an "eyball" with a humidity indicating card which enabled a compressor operator to check that the air being produced was dry, in this post. Does anyone know of a similar product in the UK? Thanks, Neil __________________ Never forget that life is a finite resource.
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2nd January 2007, 01:35	#2 (permalink)
divetheworld Dive porn pimp Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Inspiration Vision Classic Kiss Other CCR Join Date: Mar 2005 Location: Leeds, England Posts: 1,585	Re: Compressor humidity indicator Quote: (Originally Posted by Sutty) Genesis mentioned an "eyball" with a humidity indicating card which enabled a compressor operator to check that the air being produced was dry, in this post. Does anyone know of a similar product in the UK? Thanks, Neil I've always used drager tubes. Cost a few quid but then again, you dont need to use them that often. __________________ Attitude and self praise is no reccomendation. Dont try to be a great man, just be a man and let history be the judge of you. CHECK OUT OUR INTERWEBS FOR CUSTOM REBREATHER UPGRADES *WWW.NARKEDAT90.CO.UK* *http://www.grpservices.com/pursuit/* Supporting Shearwater Research Products in Europe
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2nd January 2007, 02:33	#3 (permalink)
Genesis Bubbless Box of Death Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Oct 2005 Location: Sunny Florida Posts: 1,396	Re: Compressor humidity indicator Aerocon Systems Aqua Environment Cheap enough for them to ship. That device accepts the humidity cards from here: Humidity Indicator Plugs, Cards & Desiccators You want the 0.95" 3-section 10/20/30% cards. And no, checking once in a while is NOT good enough. You need continuous monitoring - when the 20% indicator just starts to turn your dessicant (molecular sieve) is shot and within minutes you will have oil vapor in the product gas. __________________ "A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American." http://www.denninger.net http://www.diversunion.org/liability.htm - Fix the Diving Cert racket
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2nd January 2007, 13:54	#4 (permalink)
divetheworld Dive porn pimp Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Inspiration Vision Classic Kiss Other CCR Join Date: Mar 2005 Location: Leeds, England Posts: 1,585	Re: Compressor humidity indicator Neil, check it every three months in accordance with the HSE guidlines (DVIS9) if your pump is maintained correctly. Maintain less than 35mg/m3. Quote: (Originally Posted by Genesis) And no, checking once in a while is NOT good enough. You need continuous monitoring - when the 20% indicator just starts to turn your dessicant (molecular sieve) is shot and within minutes you will have oil vapor in the product gas. Yeah, right O. You have fun with that one then. __________________ Attitude and self praise is no reccomendation. Dont try to be a great man, just be a man and let history be the judge of you. CHECK OUT OUR INTERWEBS FOR CUSTOM REBREATHER UPGRADES *WWW.NARKEDAT90.CO.UK* *http://www.grpservices.com/pursuit/* Supporting Shearwater Research Products in Europe Last edited by divetheworld : 2nd January 2007 at 14:09.
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2nd January 2007, 14:05	#5 (permalink)
Genesis Bubbless Box of Death Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Oct 2005 Location: Sunny Florida Posts: 1,396	Re: Compressor humidity indicator Quote: (Originally Posted by divetheworld) Neil, check it every three months in accordance with the HSE guidlines (DVIS9) if your pump is maintained correctly. Maintain less than 35mg/m3. Anyone see the contradiction here? No? Go read it again. Now tell me how you "maintain" something you are only measuring once every three months. Then justify your position when the appliance to measure conitinually costs about $50, the cards are $3 each and last a year or more (they revert back to blue when dried) and you now KNOW that your gas is dry all the time - and thus that your purification system is working all the time. The "test every three months because that's what the government says" guys have sold me several tanks of bad gas over the last few years. But I'm quite sure that once every quarter they had a test that says their gas is ok. The certificate on the wall says so. __________________ "A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American." http://www.denninger.net http://www.diversunion.org/liability.htm - Fix the Diving Cert racket
(Offline)

2nd January 2007, 15:25	#7 (permalink)
Genesis Bubbless Box of Death Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Oct 2005 Location: Sunny Florida Posts: 1,396	Re: Compressor humidity indicator Yes, yes, quarterly monitoring is important, and so is meeting dew point standards to prevent free water condensation (especially with regards to steel cylinders!) However, quarterly monitoring cannot possibly determine that during the entire period you are pumping acceptable quality gas! There are two separate issues here: 1. If the dew point of your gas is too high, at working pressure in your cylinder, free water can condense and this causes severe problems (e.g. corrosion in steel cylinders) which must be avoided. As pressure rises the amount of water expressed in absolute terms (mg/m^3) falls precipitously. Likewise, temperature is a significant factor, since warm gas holds more water vapor than cold gas. This is what the Draeger tubes are checking for, and what the quarterly air check does as well. In addition, if you dive (particularly open circuit) in cold water, there's a second problem in that temperatures can fall radically during expansion in the first stage. If the gas is not sufficiently dry you can get icing inside the regulator's internal mechanism which will cause a first-stage freeze with resulting malfunction. This is unlikely on a CCR due to the much lower volume of gas delivered (and thus the lower adiabatic cooling load) but happens all the time with open circuit gear. 2. However, what I am referring to here is a way to monitor, in real-time, whether or not your purification stack is actually working. Since "online" air testing for hydrocarbon content is impractical, and quarterly monitoring does not tell you whether or not you are pumping clean gas all the time, a proxy is helpful for determining whether or not your filter stack is expended and needs service. The "eyeball" indicator with a 10/20/30% RH card in it, on the high pressure delivery side, is an effective means of determining the latter circumstance. When the 10% card has "turned", you have a 10% RH in the high side of the system at delivery pressure and temperature. By the time the 20% card has started to turn, your purification stack is no longer effectively removing moisture from the gas stream, and you are at severe risk of hydrocarbon bypass. Since the question originally asked (and from which this thread was derived) was asking specifically about compatability of product gas with oxygen for the use of blending, moisture, while troublesome, isn't the issue under consideration. Compressor and filter manufacturers all cite "expected service life" numbers, usually in cubic feet of gas processed. However, those ratings all require that one know the temperature of the inlet gas - and that is quite difficult to measure accurately. Ambient temperature does not provide a reasonable guide to stack inlet temperature. Inaccuracy here leads to belief that you have working filtration when you in fact do not. Checking quarterly only tells you that the filters are working at the time of the check. I note from your own quoted documents that HSE recommends: Quote: 2 A more reliable method is to monitor the air quality on-line. One technique of monitoring on-line *is to* *measure the moisture content. n Filter cartridges are usually designed so that the drying element becomes saturated before there is any deterioration of the other elements. Therefore, monitoring the moisture content of the air at the filter outlet can indicate when the filter has reached the end of its life. n On-line moisture content measurement equipment* can be: - built into the filter element; - a separate measuring device; - a simple visual indicator. n The provision of on-line moisture content measurement equipment will be of particular benefit where the air is for sale, as it will provide visible assurance to the user of the gas. n Before fitting such devices the views of the compressor and/or filter manufacturer should be sought. Which, of course, is what I recommended. You might want to read your cites before using them, as in this case they backed up my position rather than yours! __________________ "A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American." http://www.denninger.net http://www.diversunion.org/liability.htm - Fix the Diving Cert racket
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2nd January 2007, 15:36	#8 (permalink)
divetheworld Dive porn pimp Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Inspiration Vision Classic Kiss Other CCR Join Date: Mar 2005 Location: Leeds, England Posts: 1,585	Re: Compressor humidity indicator La la la la.. All I can hear is La la la la. Dispite the self opinionated arrogant tossers continuous ranting of pages and pages of bollocks, 5-10% is not good enough. If your stack is maintained and logged, a periodic check is sufficient. Now, where is that ignore button. __________________ Attitude and self praise is no reccomendation. Dont try to be a great man, just be a man and let history be the judge of you. CHECK OUT OUR INTERWEBS FOR CUSTOM REBREATHER UPGRADES *WWW.NARKEDAT90.CO.UK* *http://www.grpservices.com/pursuit/* Supporting Shearwater Research Products in Europe Last edited by divetheworld : 2nd January 2007 at 15:38.
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2nd January 2007, 15:37	#9 (permalink)
Sutty Classic Kiss diver Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Jun 2005 Location: Glossop, Derbyshire, UK Posts: 802	Re: Compressor humidity indicator Thanks guys. For the small volumes of air I'm pumping quarterly testing is a bit OTT, so I'll be logging fill volumes. That is one of the reasons I was considering in-line monitoring for humidity. I've not worked out how a relative humidity indicator at pressure correlates with mg/m3 yet though. Neil __________________ Never forget that life is a finite resource. Last edited by Sutty : 2nd January 2007 at 15:42. Reason: clarity
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2nd January 2007, 15:49	#10 (permalink)
Genesis Bubbless Box of Death Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Oct 2005 Location: Sunny Florida Posts: 1,396	Re: Compressor humidity indicator To get an ACCURATE correlation you need both the pressure at the time of the measurement AND the temperature of the gas at the measurement point. The former is pretty easy, but the latter is not (accurately.) Without the temperature you cannot correlate the RH to an absolute (mg/m^3) value. Monitoring online does not tell you that you are within dewpoint specs generally (the big risk here is taking a tank filled in the middle of summer, and letting it sit until winter, then diving with it - you could have free condensed water in the tank, and thus have corrosion problems if that's a steel cylinder, or have problems in cold water with a regulator first-stage freeze) What it does tell you is that your dessicant is working and thus your activated carbon is still effective in removing hydrocarbons. That is the point of online monitoring with an "eyeball" - to know that you are still effectively removing contaminents from your product gas. Note that a lot of the "compressor guys" will sell you 20/40% cards. Those are completely worthless as once the 20% one turns your stack is already rubbish and by the time the 40% one turns you're not only pumping water-laden gas but LOTS of oil vapor as well! For those who say "that doesn't work" - yes it does. I've verified my setup with a montoring test and meet OCA (Mod-J) air quality standards just as my indicator card says I need to change the primary filter stack. Most "commercial" shops change the filters and then test for their "certificate." That, of course, is backwards - they should be testing with used filters at maximum life so they see the worst case - not the best case! The shop is concerned with getting sued if they are out of complience. I'm concerned with not blowing up or killing myself while underwater due to contaminated breathing gas. Try diving in the Caribbean sometime if you want to breathe truly foul "air". I just got back from there a week or so and found it basically impossible to find air that didn't have a "taste" to it. I'm not sure I want to know what a test would have shown...... __________________ "A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American." http://www.denninger.net http://www.diversunion.org/liability.htm - Fix the Diving Cert racket
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