Compressed air humidity measurement

sagalout

sagalout

Member Extraordinaire
Joined
Jul 6, 2022
Messages
9,030
Reaction score
19,405
Location
Ross on Wye
How do you measure the moisture content in the output of a compressor?

There a 9 billion compressor/filter threads on the airgun forum but I have a little devil whispering in me earhole "How do you now how dry the compressor output is?" quickly followed by "How do you measure it?"

I have never seen any signs of moisture in any of the guns that have been filled by my compressors and the bottles that have been filled by me and tested have past their 5 year inspection (that's 2 or 3 bottles now).

Is that a good enough test?

Playing with the Hill EC3000 the other day :
  • 170mm gold filter filled with cotton filters >> small filter filled with self indicating silica gel >> empty small blue filter on end set to leak at 275 bar. Run for 12 minutes (6 minutes under pressure, 2 minute cool down, 3 minutes under pressure, 2 minute cool down, 3 minutes under pressure). Result was first 3mm of silica indicating.
  • 170mm gold filter filled with 3A molecular sieve >> small filter filled with self indicating silica gel >> empty small blue filter on end set to leak at 275 bar. Run for 12 minutes (6 minutes under pressure, 2 minute cool down, 3 minutes under pressure, 2 minute cool down, 3 minutes under pressure). Result was first 3mm of silica indicating 50% less than with cotton filters.
  • Just the small filter filled with self indicating silica gel. Filled to 300 bar and left at 300 bar for 4 hours. Silica indicating a lot but not saturated.
Don't have a liner for the 170mm gold so not keen on using the molecular sieve in there because of corrosion.
 
inline humidity meter that you can connect to the whip so the compressed air flows over it
would that work
alternately fill a container with a humidistat in it with air from the compressor and see what that gives
admittedly the 2nd option may be inaccurate but should give a ball park figure
 
gdsm10airgunner said:
alternately fill a container with a humidistat in it with air from the compressor and see what that gives
Click to expand...
Good thinking that one. I could put a plastic bottle of the leaking little blue filter and stick me cheap pin moisture meter through the plastic. That might work.
 
No experience with this but the link below makes sense to me. Do the cheaper filters have a moisture drain tap?

 
On the smaller expensive and lower costs Compressors
I found just filling some of the filters available themselves is simply putting excessive wear and pressure on the compressor itself before gun starts to fill takes a lot longer that’s for sure
But where do you draw the line over potential cost damage from moisture 😞
 
PETEB22 said:
Do the cheaper filters have a moisture drain tap?
Click to expand...
No, but the compressor has a condensate filter and traps a lot of moisture before the external filters.

I will watch that video soon. Have watched lot's of videos on the subject but would lke to be able to test mine. The pin type meter doesn't work poked through a bottle. I will have a look for a cheap suitable meter.
 
If you're feeling flush, these kits are for diving air compressor tests and one of the tests is water vapour.
tempImager0zrLC.png
tempImage57d8ge.png
 
"Don't have a liner for the 170mm gold so not keen on using the molecular sieve in there because of corrosion."

On this matter, has anyone sourced a liner/sleeve that will fit in the 170mm gold filters?
 
Will be reading this thread with interest.

Starting to look at compressors as alternative to pump/bottle.

FWIW never noticed any moisture in my pumps inline moisture trap.....maybe rubbish trap, lol.
 
Dodgyeye said:
Will be reading this thread with interest.

Starting to look at compressors as alternative to pump/bottle.

FWIW never noticed any moisture in my pumps inline moisture trap.....maybe rubbish trap, lol.
Click to expand...
I’ve definitely felt moisture when loosening the bleed off screw on our Hills Mk4 and did regularly change the media
IT’s recently died so will eventually strip down and replace valve parts
Last time I done this there were signs of moisture corrosion
300bar pumping 😆
 
Interesting thread and something I'd like to be able to quantify too; if only to definitively test the Hills "Dry Pac" as, while I love their pumps generally, I'm dubious of the claims relating to this unit.

PETEB22 said:
No experience with this but the link below makes sense to me. Do the cheaper filters have a moisture drain tap?

Click to expand...

Interesting video with some salient points - particularly that about the "pressure maintaining valve", as presumably you want the air to be at as higher pressure as possible in the condensation tower to force the water to condense out in here, rather than in the gun as pressure builds. Not something I'd considered before..

In principle I don't think it'd be hard to make your own condenser, but it does raise some interesting questions. Generally I like steel for pressure vessels, however this wouldn't be great from a corrosion perspective. Ally would be good to promote condensation as it has a very high thermal transfer coefficient, but doesn't like cyclic loading and will corrode in the presence of moisture. Stainless is probably a good bet but is expensive and would mean you'd have to go bespoke on the tower, rather than perhaps re-purposing something from an existing airgun application.

When it comes to design bigger is going to be better as regards moisture removal efficiency, however this is all lost volume that needs to be filled. That said, if you had a (PM as above) valve on the output end that would only open at say 200bar, along with a check valve on the inlet, you could effectively keep the tower pressurised all the time and only drain it down periodically for inspection / maintenance.. so you'd only need to fill the volume of the condenser once for numerous fills..

No doubt something else I'll get half way through designing then forget about!
 
Ade C said:
There's your answer
Click to expand...
I know, but the devil on me shoulder likes to make look deeper into things. It would be nice to get a better idea of what is worthwhile and what ain't. would a £75 tuxing filter be loads better than 4 big cotton filters? Certainly my playing the other day suggests the sieve is better than the cotton but by how much?
 
Usable numbers would be great, I did the whole compressor output into a bag with a humidistat thing a while back, it seemed like a flawed exercise, not least because the air has decompressed at that point and in terms of condensing, it's all about the RH/temp/dew point - I think @BallisticBill chucked a link to how that and pressure interact on a previous post.

Stu.22 said:
On the smaller expensive and lower costs Compressors
I found just filling some of the filters available themselves is simply putting excessive wear and pressure on the compressor itself before gun starts to fill takes a lot longer that’s for sure
But where do you draw the line over potential cost damage from moisture 😞
Click to expand...

Filter size should be proportionate to the compressor type and the volume of what is being filled/run time. This is why anything other than the smaller tube filters isn't recommended in the compressor FAQ for the 12v compressors, you could probably get away with a pencil style filter on a pistol due to the low volume/run time, but they get saturated on extended fills.
 
Avalon said:
not least because the air has decompressed at that point and in terms of condensing, it's all about the RH/temp/dew point
Click to expand...
Ah, yes, bugger.

The big Tuxing filter and the Coltri MHC6 filter appear to be a very similar design. 😁
 
Humidity in my area is pretty high at the moment, noticed a bit of dampness when i took the hose off the mini compressor so decided to give the pump a quick purge. Sadly a drop or two of water came out which really displeased me so I decided to try and sort it.
Filtering and measuring the output was going to be pricey so I decided to go the opposite way. I DIY'd a filter and monitoring system for the compressor inlet air instead. My line of thinking could well be flawed but in my head, if 15% RH air is going in, then the resultant compressed output should remain at 15% (it's not going to "gain" moisture in the compression phase). Whilst some of the water content may well still condence to a liquid post compression, it's going to be a much smaller amount that the whip filter should be able to deal with.

20230121_121408.jpg
 
Gilly said:
monitoring system for the compressor inlet air instead
Click to expand...
I like the idea of monitoring the current ambient humidity and then the output humidity.

Can the cotton filters extract anything form the high pressure side since the moisture is in vaour form not droplets. I am getting in well over my pay grade now.
 
You must log in or register to reply here.
Back
Top