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  1. #16
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Pumpkinate View Post
    I bet the desiccant makes a big difference
    yeah the bloke at Uni I got the desiccant from was using it in a similar situation - drying nitrogen for a lab application. At least I feel confident about measuring it or something, although it won't surprise me if the moisture goes down below my detection limit.

  2. #17
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    Morning Bob,

    Interesting as always.

    I think I see an issue you haven't addressed.(or more likely, you have thought about it and haven't mentioned it or I missed it)
    Isn't the air just going to take the shortest route though the filter? As the filter is unlikely to get blocked to any great extent the air will keep taking the same short path through the very top of the filter/desiccant, this will saturate quickly leaving the rest dry?
    Perhaps wrap something around the filter to force the air to travel down through more of the desiccant?

    How about a check valve on the inlet or you might end up with a desiccant cannon

    Regards

    Stu

  3. #18
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Stustoys View Post
    Morning Bob,
    Morning.

    Interesting as always.
    Thanks

    I think I see an issue you haven't addressed.(or more likely, you have thought about it and haven't mentioned it or I missed it)
    Isn't the air just going to take the shortest route though the filter? As the filter is unlikely to get blocked to any great extent the air will keep taking the same short path through the very top of the filter/desiccant, this will saturate quickly leaving the rest dry?
    Perhaps wrap something around the filter to force the air to travel down through more of the desiccant?

    How about a check valve on the inlet or you might end up with a desiccant cannon
    All very Good points Stu and I have indeed been thinking about them.

    In the first instance I will leave the spun polyester water sediment filter in place and pack desiccant around that - this will prevent any desiccant and desiccant dust from leaving the filter and entering the rest of the pipes etc. There is a small pressure difference across the water sediment filter and while this pressure difference is small it will be much greater than any caused by the desiccant so that will tend to spread the flow out - I guess I will find out how much by making some measurements.

    Then I will measure a AH I/O profile over time. ie how long does it take for the O air to become the same as the I air.

    Your suggestion of wrapping something around the filter to force the air to travel through more of the desiccant is one I have been contemplating and is what I will probably try next. Again measuring an AH I/O profile over time.

    There are lots of other things I could try. If I made the water sediment filter slightly conical (I wonder if they can be turned?) this will reduce the pressure drop across the filter along its length so if the narrowest part of the cone is located at the furthest path this will promote flow in that direction.

    Perhaps a combo of the filter wrap plus conical shape might optimise things further.

    The water sediment filter does take up a long of space so ultimately I'll be looking to find something that is thinner so I can pack more desiccant into the filter holder. If I can turn the filter down I could maybe turn it into a thinner cone?

  4. #19
    BobL is online now Member: Blue and white apron brigade
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    This morning I did a trial run with some desiccant.

    As a precaution against blowing desiccant into the downstream rectic pipes I decided to leave the water sediment filter in and pack desiccant into the remaining space around the sediment filter.
    As you can see there's bugger all room to fit much desiccant in around the sediment filter so the shortest pathway through the filter does not need to travel through many dessicant beads but nevertheless some 600g of beads managed to squeeze in there.
    600gSIgel3.jpg
    The ragged looking end of the filter is because this filter is about 3 mm too long to fit inside the CUNO filter housing so I cut it to length on the bandsaw. The circular indentation (orange arrow) in the end of the filter is where the knife edge seal of the top of the filter housing bites into the sediment filter. There's even a strong likely hood of air bypassing the beads altogether because the area outside the knife edge seal line on the top/end of the sediment filter is not sealed. I will have t think about how I will seal this. After seeing all this I was not expecting too much or anything from such a short air pathway through the beads from this arrangement but though I would give it a shot anyway.

    I then connected every thing back up and set up a measuring regime to measure and record the absolute humidity (mg/L) of
    a) the enclosure air, b) the filter input air, and c) filter output air .

    Measuring a) is easy as there is a dedicated sensor in the enclosure for that measurement.
    However, because I only have one test chamber/sensor to measure b & c I have to alternate between b&c and wait for the new air to flush old out of the chamber and if the chamber has picked up moisture it needs to dry out (this is why SS is usually used as a chamber instead of plastic). These measurements require at least a minute between them so I went for 3 minute intervals to make sure.

    Despite these limitation I got some useful info.

    600gSIgel2.jpg
    The blue line shows the enclosure air - it's a warm day here in Perth, BM shows RH at 47% my enclosure meter showed 45%

    Green dots show pre filter AH, (~2.5 mg/L) or about a factor 3 less than enclosure air - this water removal is the effect of the auto drain valve - it really does do the heavy lifting during light compressor use. Of course if the compressor runs continuously it's not as good as shown here - the compressed air simply does not get enough time to cool down and allow the water to condense and then drain.

    The red dots are the effect of that thinning layer of Silica gel crystals around the sediment filter. As you can seen the AH was still slowly dropping dropping as all the surfaces inside the filter, the sediment filter itself and the plastic tubing would have a film of water all over them and this need to be desorbed to make proper measurements - the lowest reading after some 45 minutes was 0.6 mg/L of water. So from about 8 down to 0.5 mg/L or a 16 x reduction - I admit to being surprised.

    [New problem: at these low levels of absolute humidity the DTH22 sensor is reading only ~4% RH and given its only good to +/-2% anyway, measuring anything at this level may not be that valid.]

    Now these are only spot or bleed tests (~1L/min) and are unlikely to be indicative of the water removal capacity during high volume flows. To test what happens in a more realistic situation I performed 2 blast tests. ie release a 30, and the later a 60s, highish volume air releases.

    The blue dots show the AH starting at 0.6 mg/L at before the 30s blast at the 20 minute mark, with readings every 30 seconds after the blast - the highest it went up to after the blast was 0.8 mg/L and then it went back down to 0.6 mg/L over 7 minutes.

    The 60s blast was at the 29 minute mark and this time the AH rose to 1.1 mg/L. This time the blast triggered the compressor to recharge - note slight rise in enclosure air humidity as new air is sucked into the enclosure. it also took 12 minutes to come back to 0.6 mg/L, again surprising considering the thin layer of desiccant in use.

    I though these results were quite encouraging given the piddling short air flow path way available through the desiccant

    Because it is easy to do the next thing I will try is to cover up the outside top half of the sediment filter and repeat the above. This will force the air to go through a longer pathway.
    Suggestions for ways of covering up would be useful. I was thinking cling wrap.


    I want to optimise the desiccant layer and sort out the other filter issues before measuring the effect of some long runs of continuous compressor use.

    Ultimately I will need a thinner sediment filter so can pack more desiccant into the filter holder but I think I will run out of measurement sensitivity well before I reach maximum water absorption.

  5. #20
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    Quote Originally Posted by BobL View Post
    I was thinking cling wrap.
    Same.

    I assume(what could go wrong there lol) that air flow through the filter is never going to be an issue.(I figure if you can run 40 odd litres of water a minute through it, air isn't going to be an issue at any flow rate you're likely to be talking about??) If so perhaps going forward you could cut the filter in half(or even less)and replace the top section with a pipe of some description? Heaps more desiccant over a much longer distant....
    A test with cling wrap sounds easier.

    The check valve was in case you have your reticulation system full and disconnect the tank side of your filter. Wouldn't be the end of the world but I smashed a 2" x 2" x 1" container of desiccate in the kitchen one time, was finding bits for months, that didnt go down so well lol. Maybe I'm over thinking things and you're less likely to do something that stupid .

  6. #21
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Stustoys View Post
    Same.

    I assume(what could go wrong there lol) that air flow through the filter is never going to be an issue.(I figure if you can run 40 odd litres of water a minute through it, air isn't going to be an issue at any flow rate you're likely to be talking about??) If so perhaps going forward you could cut the filter in half(or even less)and replace the top section with a pipe of some description?
    Yep - same wavelength here.
    I have already located a piece of 50 mm ID SS tube that (~15 mm smaller than the sediment filter diameter) that will sit neatly outside the filter end knife edge seal on the inside of the filter housing.
    My plan is to turn down about half the length of the sediment filter and slide a piece of the SS tube about half the length of the sediment filter onto the turned down section of the sediment filter. This will force the air to go right down into the desiccant to get around the SS tube.

    Heaps more desiccant over a much longer distant....
    A test with cling wrap sounds easier.
    Yep will do that in the first instance

    The check valve was in case you have your reticulation system full and disconnect the tank side of your filter. Wouldn't be the end of the world but I smashed a 2" x 2" x 1" container of desiccate in the kitchen one time, was finding bits for months, that didnt go down so well lol. Maybe I'm over thinking things and you're less likely to do something that stupid
    .
    I wouldn't bet on it.

  7. #22
    BobL is online now Member: Blue and white apron brigade
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    SUCCESS!!!!!

    Just tried the cling wrap.

    1) From an outside AH of 7.5 mg/L, and an air filter inlet AH of ~2.5 mg/L, the filter outlet AH decreases about 5 times more rapidly than without using the cling wrap.
    2) The minimum AH displayed is 0.2 mg/L. However, I strongly suspect it's lower than this because at the current temperature the RH display is 1% and the sensor will not read less than 1% so am basically limited by the bottom end sensitivity of the sensor.
    3) Did a couple of 60s air release/blasts and the filter outlet AH does not change during the blast or thereafter - it sits on 0.2 mg/L

    Thats a reduction of absolute humidity of at least 97% - I'm calling that a win!

    The next thing I need to check are some longer repeated air releases to see if I can get the filter inlet AH up and then see what it can do.

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  9. #24
    BobL is online now Member: Blue and white apron brigade
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    Got stuck inside with the heat yesterday so decided to whip up a new Arduino sensor micro controller box for the temp/humidity monitoring of the comp air.

    5Sensor.jpg


    The old micro controller had 2 sensors ie inside and outside air.
    This new one has built in wiring/sockets/ports for up to 5 sensors (S1 to S5).
    The sensors inputs are set up as 3 digital for (DTH22 on S1 - S3) and 2 analogs on S4 - S5, but the sensor inputs can easily be swapped around on the Arduino Board for added flexibility

    S1 currently monitors the compressor enclosure air.
    S2 the pre or post sides of the compressed air filter .
    S3 the air inside the shed.
    My plan is to use S4-S5 for the 2 analog air pressure sensors I have ordered that will go pre or post filter.

    The "knob" switches/togges between LCD display pages/screens for
    Temperature
    Relative Humidity
    Saturated Water Vapour pressure
    Absolute Humidity
    Air Pressures

    It turns out the DHT22 does have an extra significant digit for its RH readout but its lowest RH output reading is still 1.0% whatever its reading, ie any less than this is still shows 1.0% RH.
    I have no idea how meaningful the second digit is but assuming it has some value I decided to display and play with it.

    The smallest AH reading that can be calculated from a minimum value of 1.0% RH is temperature dependent but so far this translates into a minimum of 0.17 mg.L
    From a compressor enclosure air starting AH of 10.75 mg/L, a 0.17 mg/L is a 98.4% reduction in absolute humidity.

    I went back and played around mathematically with the rate of change of the AH after I switch the air feed to the sensor from pre to post filter.
    As I said the AH values drop quite rapidly and and starts to change in an inverse exponential pattern before all of a suddenflat-lining after about 90s.
    Using a bit of maths and small amount of extrapolation it's possible to see how the AH will be even lower that what is disputed, maybe even as low as 0.05 mg/L.
    If that is the case then its effectively removing at east 99.5% of the water.

    When I GRTI I will do some more large volume air release tests, the extra significant digit in the AH should at least be useful to more clearly detect any changes in AH while air is being released.

  10. #25
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    It may be more useful rather than sensing the pre-filter pressure (which after all is going to be pretty much atmospheric??) to get a differential pressure across the filter. At least that way you will have a ready reckoner on when the filter needs to be changed/ cleaned.

    Michael

  11. #26
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Michael G View Post
    It may be more useful rather than sensing the pre-filter pressure (which after all is going to be pretty much atmospheric??) to get a differential pressure across the filter. At least that way you will have a ready reckoner on when the filter needs to be changed/ cleaned.

    Michael
    Sorry that's what I meant I'll be measuring the pressure difference across the filter but the cheap ($8) pressor sensors I've ordered measure relative to atmosphere so I'm going to be using two of them and comparing them.

    The prefilter pressure is the same as the air pressure at the compressor 135 v 133 psi after recharge. The water sediment filter and Silica gel filter look like the lose another 5-6 psi.

  12. #27
    BobL is online now Member: Blue and white apron brigade
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    I purchased a couple of cheap (~$13 each) 10 bar pressure sensors from ebay and decided I would try them on my compressed air filter/dryer.
    Screen Shot 2019-02-17 at 8.05.03 am.png

    https://www.ebay.com.au/itm/1-8NPT-S...0fbf%7Ciid%3A1

    At that price I was not expecting too much but they each came with a reasonably rugged water resistant plug and socket that would cost that much alone here in Oz.

    The first thing I did was to calibrate them to suit my Arduino micro controller so I set up the following Xmas tree on my portable compressed air supply (An old BBQ gas bottle).
    BV is a bleed valve, Sensors are S1 and S2 and M is a 150 psi rated gauge.

    The BV is connected to a Nitto style plug so can easily be removed and replaced with a oneway valve with Nitto style plugs on each end. Connecting up my compressor to the oneway valve and opening the valve on the gas bottle allows compressed air to enter the bottle. Then the bottle valve is closed, compressor disconnected and the one way valve is replaced by BV.

    PTestercalibr.jpg

    With the micro controller running and displaying the Analog/digital Converted outputs (ADC's, numbers between 0 and 1023) of the sensors I slowly open the bleed valve so it loses ~5psi a minute and as the pressure drops simultaneously record the gauge pressure and the ADC's for each sensor ever minute or so. Then plot up a graph of Gauge pressure versus ADC for each sensor. The allows me to generate a calibration curve which is then programmed into teh micro controller so that it can display pressure (sorry for switching to kPa)

    Screen Shot 2019-02-16 at 5.17.28 am.png

    I was really surprise at how linear their response is and how close together (<0.5%) their response slopes are, especially given I could really only read the gauge to +/- 1 psi and accuracy wise who knows where this really is.

    Then I fitted a sensor either side of the filter/desiccator but the one on the downside stopped working after a few minutes. Given the burst rating is at least 2X the max pressure I doubt it was the problem. I did drop that sensor just before I installed it but I am thinking that maybe the moisture in the pre-filter side of the air might have had something to do with it n longer operating. The ADC output it gives at all pressures is "zero" which is similar to a shorted signal to ground response. This is odd because the sensor to ground resistance is ~15kΩ which is still the same as the working sensor.

    I have tried a few things like sucking on the sensor with a vacuum pump and leaving it in the sun to see if it dries out but no change. Whether this is is just the vagaries of purchasing a cheap sensor or mistreatment or . . . .

    Anyway not to worry too much as I already have small gauges on either side of the filter and the real reason for a pressure sensor is to see if I can calibrate the Humidity sensor under pressure with the aim of measuring the compressed air humidity while retaining it within the compressed air system compared to the current setup where the compressed air used to measure the humidity is lost from the system.

  13. #28
    BobL is online now Member: Blue and white apron brigade
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    Just to round things out for the foreseeable future the low volume (0.1 to 3.0 L/Min) flow rate regulator came today and was installed as shown in the photo below.
    It's the green coloured acrylic cylindrical object with the black adjustment knob on it similar to an Ar regulator.
    The flow is indicated by a floating black bead hovering around the 1 L/min mark
    Fnal1.jpg
    Accurate absolute humidity measurements have to be performed at low (<1 L/min) flow rates which turns out to be a faint whisper of air leaving the regulator exit.

    Another photo of the whole shebang.
    final2.jpg

    For the first time I am starting to see the relative humidity of the air coming out of the filter going above the minimum reading of 1%. Today its 3% suggesting the desiccant is starting to load up, It will be interesting to see how long it takes to get to intake levels. I have been doing a lot of testing which consumes a lot of compressed air and probably does not help the readings..

  14. #29
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    Default The low tech fix

    The low tech fix for reducing water content in compressed air lines is to put at least 10 meters of copper between the compressor and the water trap.
    The arduino looks far more sexy than plumbing.
    Mark
    Attached Images Attached Images
    I've become a tool of my tools.

  15. #30
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Poloris View Post
    The low tech fix for reducing water content in compressed air lines is to put at least 10 meters of copper between the compressor and the water trap.
    The arduino looks far more sexy than plumbing.
    Mark
    I actually have a finned copper heat exchanger similar to the one you show in the photo.
    Cufinmedpipe2.jpg

    Two Issues -
    1) no spare area of wall large enough to hang it up on inside shed although I could hang it on an outside shed wall
    2) No taps - would have to work out a way of removing the fins and leaving a smooth enough surface for tap junction. If I could work out way to get a smooth surface I could use two elbows, a Tee and a tap at the bottom of every U bend.

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