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Discussion Starter · #1 ·
Does anyone have any ideas how I can make an air purity tester? Ideally for use with the Draeger test tubes so must have a variable flow rate. Also ideally must be able to test direct from compressor filling whip DIN/INT and direct from a cylinder valve...

I have a few ideas but, as great minds think alike I would like your input please!!

BTW, yes, I know I can buy one, however the cost is the slight problem. I work as a tech abroad and have been tasked to make one while back at home.
 

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Nigel Hewitt
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I bought this thing second hand but it's really just a first stage in a box, a needle valve, the usual ball in a tapered tube flow rate meter, a Dräger tube holder and a timer working the gas valve.
The only bit you can't get cheaply off the shelf is the tube holder but it wouldn't be too hard to fabricate as it just pinches the tube between two O-rings top and bottom.
 

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Discussion Starter · #3 ·
Thanks Nigel,

Some years ago for company I was working for had the same unit I think - I am fairly sure that is one of the old Draeger units and also if I recall had around a £1000 price tag about 12years ago!

So far I have found flow meters on ebay and of course an old diaphram first stage to drop the pressure is no problem... Think it might be a trip to the workshop though to get all the necessary adapters made up.

As far as being able to connect to a compressor whip, the best method I can think of is to have made a female G 5/8 to female G 5/8 on a HP hose so the male DIN fittings on 1st stage and compressor whip will screw straight in... Similar-ish to your unit which has a female DIN (G 5/8) on a HP microbore hose coming out the back of the box... Then, fitting from the 3/8" LP port on the first stage to flow meter, then flow meter to test tube holder...

It is going to be adapters-a-plenty but can't think of any other way of simplifying it or without splashing out on a new off the shelf unit.

Shaun
 

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I have done this myself by using a personal oxygen medical regulator for less than $50. It was a Pin Index fitting, so I just got a pin index to 1/4 BSP fitting, then put a 1/4 BSP to 300 bar DIN fitting on the other end. This allows me to screw it into the supply tank. I also have a female DIN to DIN adapter, so I can put it into the whip. The regulator will do variable litres per second, 1/2, 1, 2, 3, and 5 from memory, so was perfect. Undersea make all the bits you need and you should be able to get a regulator from ebay quite cheap. oxygen 02 regulator 0-275 bar | eBay something like this was what I got, but you'd need to check that it has the variable flow rates you need.
 

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Interesting idea, what tubes are you using at the moment?

The oil in your compressor is critical as some oils use olefins
and this will mask any CO reading depending on the tube used

The flowmeter is also critical, the one on Nigel's post is from Brooks flowmeters
Its a good brand, flow is most accurate at around 70% of full flow calibration
A good 2% or 3% accurate flowmeter should be OK

Watch the max pressure some are only 100psi such a the Dwyer flowmetrers

It would be helpful if Nigel lifted the lid, but theres not much inside

Easy to make your own using an industrial regulator to the flowmeter and the stain tube
can be attached to the regulator by simply using some rubber tubing 7mm ID from memory
(must be soft rubber not the hard clear plastic PVC stuff)

IMHO these oxygen regulators are simply not accurate enough if you are reliant on the
"click flow" adjustment. A better idea is an industrial BOC welders type cost about £60,

We us a small Tescom regulator 42 or 44-2214 series cant remember, more expensive
than the BOC type but much better quality. At a guess £150

The tube choice is a battlefield, the 10 pump hand pump tubes are the easiest but not the
most accurate for some gases why oh why they don't make an air test pack I will never
know pack of 10 and a 2 years shelf life is rubbish. They will last half a century sealed in glass.

CO 2.5 to 150ppm part 6728 511
CO2 100 to 3000 ppm part 6728 521
Water 2-450 mg/m3 part 6728 531

H2S (hydrogen sulphide) 0.2 to 5ppm part 8101461 (10pumps)
SO2 (sulphur dioxide) 0.5 to 25ppm part 6728 491
OIl 0.1 to 1 mg/m2 part 6728 371

I would like to have posted a photo of the one we made but I cant find it (typical) somewhere
in the workshop I guess unless out on loan in which case if your reading this and have it,
return it forthwith.

Also you wont be able to connect directly to your compressor as it will quickly fill up the charging lines and stop, hopefully
or relieve pressure or just blow up. So you may need a by pass, but the female DIN in the pic is around £10 (the black thing)
each end. The stainless joint in the middle is more at £15, the Stainless DIN male connector £25 and the flowmeter around £30 I think
Added the gauge £12.50 and it's rubber cover £1.50

Not shown is the fitting to the rubber tube called a "hose barb" Say 1/8NPT male to say 6mm OD hose in brass about £2
Just made it up quickly with parts around the workshop but gives you an idea


Iain Middlebrook
 

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Discussion Starter · #6 ·
Many thanks for your detailed reply Iain...

I have previously used the Draeger tubes, but for the last 3 years have had a 3rd party do air purity tests. The other tubes I have seen and might consider are the Kitigawa tubes... Any experience with these?

I think the best idea is not the o2 regulator, down to the fact of accuracy, as you pointed out, and possibly reliability - I have come across a few faulty clickers before on used and abused o2 kits.

To keep the adjustable flow meter happy, a diaphram 1st stage with the IP cranked right down to 2 or 3 bar / 30 - 45psi should be ok, or as you pointed out a welding regulator but TBH am steering towards a DIN diaphram 1st stage as I have a load sitting around in the workshop. Probably wise to fit an OPV to it also, but finding one to go as low as 100psi might be tricky... Dwyer is gucci stuff and quality assured - my favourite, especially their magnahelics! :)

Soon will start to collect together the components I need... Want to get it right first time.
 

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Kitigawa? sounds like something big with feathers and flies LOL

Kitagawa are OK I guess again a minefield of how many pumps or how much LPM for how long
But at 25 quid a box they are much cheaper now that Draeger jacked there price

With a scuba regulator you could also look at changing the spring rate in the 1st stage we used to do this with the Conshelf XIV for an underwater gun we used to build but not sure
if you could do this with other brands now mind.

The 30 quid Dwyer I showed was a VFA Visi-float model there just cheap and nasty but work OK offshore no one bothers nicking them for E bay at least. The Brooks unit Nigel showed is much better, glass graduated tube stainless float that must be 70-80 quid at a guess, maybe more.

If I ever get ours back or find it I will post a photo you can work from, cant think where it is it's an age thing I guess. Iain
 
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