GTA
Support Equipment For PCP/HPA/CO2 and springers ,rams => Support Equipment For PCP/HPA/CO2 => Topic started by: Taso1000 on April 27, 2018, 02:08:46 PM
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Hi All,
In my quest to ensure I have dry hpa air for my pcp guns I had some questions concerning pressure maintaining valve set points. In my search, pretty much from scuba forums, I found that the recommended set points were between 140 and 160 bar, 2030 - 2320 psi.
A couple weeks ago when I charged my first scba cylinder the pmv valve on my Alpha filter opened at about 1700 psi. I thought that maybe I should set the pmv higher and that maybe a higher set point would have benefits.
So today I found an article that answered some of my questions. http://thedecostop.com/forums/showthread.php?10085-Understanding-SCUBA-Compressors-and-Filtration (http://thedecostop.com/forums/showthread.php?10085-Understanding-SCUBA-Compressors-and-Filtration)
This is an excerpt from the article concerning water filtration:
First on the list is water.
On an analysis for Scuba air (grade E) and OCA (Oxygen Compatible Air) water is expressed
as a dew point and should be -50 degrees Fahrenheit or below or 67 ppm (parts per million).
For those not familiar with the term dew point, this is the temperature at which moisture in
the air condenses to water droplets. If you can visualize 67 parts per million of anything, your
doing better than me. In the last segment, I explained that water was not compressible and
there are filter media that will reduce the percentage in the air. We will talk about which
media to use later. For now the important thing to understand is that we must remove as
much moisture as possible before it gets to the filters.
The first step is to force the air through the last moisture separator at as high a pressure as is
practical. The higher the pressure, the more moisture will separate out in the separator for a
given temperature. How high should we go? When we run air through the separator at 58.8
psi (5:1 compression), the air will have near 100% humidity since some moisture will have
fallen out. At ambient pressure this air will have 20% humidity. In a house this would be
considered dry. If we crank the back pressure valve up to 279.3 psi (20:1 compression), after
the separator we will still have 100% humidity, but the ambient pressure humidity has
dropped to 5%. You’re off the scale as far as houses are concerned. If we crank the back
pressure valve up to 1,455.3 psi (100:1 compression), the ambient pressure humidity has
dropped to 1%. The Sahara desert would be envious. At a back pressure of 2,925.3 psi (200:1
compression), the ambient pressure humidity has dropped to 1/2%. Nothing in nature is this
dry. At a back pressure of 4,395.3 psi (300:1 compression), the ambient pressure humidity
has dropped to 1/3%. While 1/3% humidity is impressive, it’s not worth running your
compressor at 4,395 psi all the time to achieve. In my book ½% of anything is nothing. So my
back pressure valve is set at 3,000 psi and has been for the last 20 years (8,000+ compressor
hours). If you want to set you valve at 1,455.3 psi, go ahead, but your filter will have more
moisture to contend with and your compressor runs more than 60% of the time above this
pressure anyway.
The second step is to reduce the dew point in the separator. A lower dew point means more
moisture condensing and falling out in the separator. The best possible scenario would be to
submerge the third stage inter cooler coil in a bucket of ice water. This unfortunately isn’t
practical. So, keep your compressor clean. Run it outside in open air. Pump high pressures if
you can, when the temperature is coolest, early morning and late evening. Fill your banks
completely on cool days. Enough about water.
From this article I learned that the higher you set the pmv the more moisture is squeezed out. I also stumbled on the information, from another thread: https://www.gatewaytoairguns.org/GTA/index.php?topic=120428.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=120428.0) , that molecular sieve needs to be above 1590 psi to perform its best.
So I have a different question now: are there any cons to setting the pmv set point to 2,925.3 psi or higher?
Also would it be better to place the molecular sieve filter after the pmv, to separate it from the pre set point moisture, instead of before it? I could put a shutoff or one way valve after the Alpha to keep the molecular sieve from being contaminated by atmosphere while not in use.
I think the pmv it a great find for water removal. There have been suggestions of mimicking a pmv with a shutoff and letting the system build pressure then intermittently letting the hpa pass to your cylinder. That's would be lot of time wasted sitting in front of my Shoebox when an adjustable set point pmv only costs $90.
Thank you!
Taso
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I assume the concept of a "pressure maintaining valve" is to have the oil/water separator running at a high pressure ALL the time, so that the saturated air on the output side is at a higher pressure, and hence contains less water vapour per unit volume.... If you had this setup, and it was tight with no leaks, then you would have the added advantage of not losing the HPA in the separator, except when you bleed it.... Of course any leakage backwards into the compressor would defeat the purpose....
If you also had a dessicant filter on the output side, then yes, that should be on the downstream side of the PMV.... This is so that it has less water to remove from the saturated air.... If you are filling a tank to 4500 psi, and you had the PMV set at 3000 psi, you would only need to remove 1/3 of the remaining water to bring the humidity below the saturation point at 4500 psi (at constant temperature)....
If you are using a dessicant filter on a ShoeBox between the shop compressor and the inlet of the ShoeBox, then it is likely that a PMV would have no advantage, other than to keep a separator on the output side pressurized to conserve air between fills.... However, that would keep the O-rings in the ShoeBox pressurized all the time, and may increase leakage and/or shorten their life....
I suppose a PMV may be as simple as a spring-loaded check valve that only opens when the inlet pressure exceeds the set point.... There might be an advantage to running it at 5000 psi, if the compressor and the separator were safe at that level.... because then when you fill a 4500 psi tank you would be filling it with air saturated at 5000 psi, so only about 90% humidity at 4500 psi (at constant temperature).... During use, the PMV would "chirp" open on each compressor pulse, allowing a small amount of 5000 psi air to pass, expanding to whatever the tank pressure was at that moment.... Just a thought....
Note that with such a setup, pressure sensing for any auto-shutoff for the compressor would have to be on the outlet side of the PMV.... If it was before it, the compressor would shut off at 4500 (assuming that is the setpoint), and no air would reach the tank.... OR, if you increased the auto-shutoff above 5000 psi so that the compressor kept running, it could overfill the tank until the switch eventually shut off the compressor (at 5500 or whatever you had it set at)....
Bob
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Mr. Sterne,
Thank you for your response. It's taken me a long time to wrap my brain around all this. Dew points, relative humidity are hard to understand. Parts per million is a little easier. To me it's like remainders, if that makes sense.
The way that I understand it the higher the pressure the less moisture air can hold. The same goes with temperature. The higher the temperature the more moisture air can hold.
Lets take my Shoebox setup as an example. I initially thought that removing moisture between the shop compressor and the Shoebox would have the most benefit. The membrane drier I stumbled upon researching refrigerated air driers will remove moisture to a -4°F dew point. At 75°F that's 4.25% relative humidity. This is before I knew what a pressure maintaining valve was and how it could be used. But I will get to that later.
I still feel, in my situation, that the ~100 psi moisture removal is beneficial because I don't have the capacity to capture the condensate on the output side of the Shoebox. I created a water trap on the output of my Shoebox to collect condensate out of hpa fittings. Lloyd created a thread on how to estimate how much water was in compressed air and I used enough fittings, a couple ounces per my estimate at my 4% rh input, to hold this condensate. If I wasn't removing moisture on the 100 psi line I would need a larger high pressure vessel to collect it. A vessel of this type recently popped up from China. I had asked the self anointed airgun scientist if he could sell me one from the Carette compressor he sells. He never responded. So I went with my fitting route.
After I bought my Alpha filter I researched what the pmv did and it became clearer what member Guy Kuo was saying in my Shoebox thread. The high pressure wringing of the air is very effective and not as expensive as I thought. That's what happens when one doesn't grasp what is going on.
So the pmv, set at 3000 psi, bringing down the relative humidity to .5% is pretty good in my opinion. A concern it still have is, is it still low enough to not have water and corrosion in my scba cylinders at 4500 psi?
So since molecular sieve has such little capacity, I knew to protect it from ambient air. Then I thought if I ran the pmv before the Alpha I could extend the life of the molecular sieve on the input side. I was puzzled as all the scuba compressor schematics showed the pmv after the molecular sieve.
So in answer your 5000 psi set point thought: I guess it's possible but like the author of the article inferred, there's a point of diminishing returns.
As for safety I would have to verify every fitting if it was ok to work at 5000 psi. I know I made sure of at least 4500 psi and I know some fittings were rated at 6000 psi. I don't know what pressure the Alpha is rated or if my pressure switch can be set that high.
Do you think there would be enough benefit to change the set point to 5000 psi?
Thank you Bob!
Taso
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If the air is saturated at 4500 psi when the tank is filled, and the tank is then stored at a lower temperature, then at least in theory SOME liquid water will condense out in the tank.... However, as soon as you use some of the air and the pressure in the tank drops, that water will once again "evaporate"....
I only know of one way to guarantee no liquid water is in your tank.... You must reduce the ABSOLUTE humidity to less than what would be 100% relative humidity at 4500 psi at your lowest storage temperature.... The best thread about this is by AlanMcD....
https://www.gatewaytoairguns.org/GTA/index.php?topic=139845.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=139845.0)
The table attached to the bottom of the first post shows you exactly what is required.... At 4500 psi at 20*C (68*F) you must have less than 0.06 g/m3.... That is the equivalent of a dewpoint of -48*F at ambient conditions.... Reading through Alan's thread should answer all your questions....
Bob
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Bob,
Your idea was so elegant, I couldn't see the forest for the trees. lol I apologize. If we compress to 5000 psi and remove the condensate, filling a scba cylinder to 4500 should not produce any liquid water as long as the temperature is kept similar and not much colder.
My thinking is that the electronic pressure switch on my Shoebox would need to be set higher that the pmv setpoint. So if we set the pmv to 4900 psi and the compressor cutoff to 5000 psi that should work.
I have seen in the Shoebox Max user manual that the mechanical shutoff will initiate between 4000 and 5000 psi. This makes me think the Shoebox can handle going to 5000 psi safely.
I think you could fill an scba cylinder this way but would have to manually shut off the cylinder valve when it's pressure reaches 4500 psi.
I do have a gold regulator I use for tethering to the cylinder to shoot and I have one of the blue Ninja fill stations. If I had to I could
change fittings and connect the gold regulator or I could use the Ninja if it can be made to work. The Ninja doesn't work like the gold regulator, or I'm not using it right, so I don't know if it could be integrated.
Another thought that I had is if I get this idea to work do I still need the Alpha filter? There was a graph I saw about desiccants that showed that molecular sieve and the others don't work well under about 5% relative humidity. I may be confusing relative and absolute humidity again so maybe it would still provide more drying?
Thank you,
Taso
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You aren't worried about the relative humidity, but the absolute humidity.... On the output side of any compressor, the relative humidity will usually be 100%, unless the air going in is VERY dry.... Look at that chart in AlanMcD's thread and try and wrap your brain around absolute humidity and how that relates to the dew point.... If you can get the dew point to below -50*F you will never see any liquid water in your tank....
Bob
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Bob,
With all due respect, I get what absolute humidity is. I am not saying that in a snarky tone, just clarifying.
What will the resultant dew point be from compression to 4900 or 5000 psi? I expect the absolute humidity to be less than .06 grams/meter³ and the dew point to be less than -48°F as in Alan's chart.
I had a calculator that i can't seem to find now. I tried this one, www.howelllabs.com/resources/dew-point-conversion-calculator (http://www.howelllabs.com/resources/dew-point-conversion-calculator) but I can't get the right results for some reason. On top of that I can't figure out how to reset all the fields. :-[
So if we compress past 4500 psi to 5000 psi, we trap and bleed all the condensed water out and our "Hot air charge out of "hot" Shoebox" air temp is 120°F. Once the scba cylinder cools to room temperature, say 70°F, would the extra 500 psi we temporarily compressed to give us enough leeway to keep and moisture from condensing?
If yes, there is no need for the molecular sieve right before the air cylinder. Correct?
Why has no one done this before? I get that the scuba guys have been compressing are for the most time and are the experts. Maybe it's because they only compress to 3500 psi and are also concerned with air that is breathable.
That was my original question. Why are pmv set points only 140 - 160 bar and are there any cons for us air gunners to setting the pmv to 2,925.3 psi or higher?
Thank you,
Taso
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Here are the specs on different classes of breathing air....
Class 1 = -70*C (-94*F).... This is 2.6 PPMV, or 0.002 g/m3.... Dew Point at 4,500 psi = -22.6*C (-9*F)
Class L (SCBA) = -53.8*C (-65*F).... This is 24 PPMV, or 0.02 g/m3.... Dew Point at 4,500 psi = 2.8*C (37*F)
Class D = -45.5*C (-50*F).... This is 67 PPMV, or 0.05 g/m3.... Dew Point at 4,500 psi = 18.2*C (65*F)
Class 2 (SCUBA) = -40*C (-40*F).... This is 127 PPMV, or 0.1 g/m3.... Dew Point at 4,500 psi = 28.8*C (85*F).... but at 3,000 psi typical for SCUBA, DP = 22*C (72*F)
I wrote a bit about this in Reply #9 of this thread.... https://www.gatewaytoairguns.org/GTA/index.php?topic=140456. (https://www.gatewaytoairguns.org/GTA/index.php?topic=140456.) .... You can see that I concluded in that thread that a dew point of -50*F at STP is "dry enough" for our use.... Using the calculator I linked in that thread.... http://www.dew-point.com/dew-point_calculator.asp (http://www.dew-point.com/dew-point_calculator.asp) ....
If we input 5000 psi at 20*F, we get 67 PPMV, which is 0.05 g/m3, or a dew point at 1 atmosphere of -45.4*C.... If we then reverse the calculation, and use 4500 psi at 67 PPMV, we get a dew point at 1 atmosphere of almost the same at -45.5*C, and at line pressure of 18.2*C.... If I understand that correctly, cooling the 5000 psi air just 2*C while expanding to 4500 psi would mean it is still saturated.... If that is the case, then we would not be getting the desired result.... In fact, expanding it to 3000 psi only drops the dewpoint at line pressure to 11.9*C.... What this means is that temperature drop is more important in the formation of liquid water than a drop in pressure....
As we often find, a little knowledge is a dangerous thing.... It would appear that my suggestion of setting a PMV to 5000 psi and then expanding the air to 4500 would only work at constant temperature.... Even a few degree drop in temperature in the 4500 psi tank would still cause water to condense out.... As Alan stated, it is the absolute humidity, in PPMV or g/m3, that is important....
Bob
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After a little more research and conferring with member GuyKuo I have decided to add another pmv set at 3000 psi before my Alpha filter to wring more moisture out of my compressed air before it hits the molecular sieve. The molecular sieve is staying in the loop as it's still needed.
I will report my findings once I have integrated the pmv and I fill another tank. Hopefully I will have some captured water for all my efforts. ;D
Thanks,
Taso
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LOL ... you guys are making this too hard. Who cares what the dew point is as long as you are doing your best to remove as much moisture as you can?
ANY compressor is going to be able to compress the air. And, since water or oil isn't compressible, it becomes a bigger "chunk" of the air that gets pumped out. So, to get air out, we put a gizmo inline that makes the air change direction a LOT which makes the uncompressed chunk of moisture fall free from the air flow. There are two things that can increase the amount of moisture that is knocked free.
1. Increase the air flow - the faster the air is flowing across the deflectors, the more moisture is going to get knocked loose.
2. Increase air density - the thicker the air is before going into the separator, the easier the moisture will come loose
Once you have purchased your compressor, you are pretty much locked in to the air flow rate so nothing you can do for #1. But changing #2 is easy ... install a pressure maintaining valve. A simple PMV will restrict the air flow until pressure gets up to about 1800 psi.
To further process air, we add a filter chamber that is filled with a real fine filter medium called molecular sieve. Basically, they are little balls of material that has micro pores that trap moisture molecules that get past the moisture separator. To increase the efficiency of THIS filter we need to:
1. Increase the dwell time - this allows the air to spend more time flowing across the media, increasing the chance of moisture getting trapped
2. Increase air density - denser air means the moisture chunk sticks in the media better
So, assuming you don't have an adjustable size filter tower, the only other adjustment you can add is a PMV.
So ... this is really a no brainer ... install one PMV on the outlet of your filter so that it can maintain back pressure on the entire filtration system.
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Ray,
What you say is basically true, but you are comingling two different things in your one term of "moisture": 1) condensed water, or droplets, no mater how small (including at least three water molecules stuck together via a hydogen bond - the thing that makes water a liquid instead of a vapor once more than two are bonded together; two are referred to as a water dimer) and 2) free water molecules, or what most people call water vapor (individual water molecules not held together via hydrogen bonds).
And yes, the two things you are referring two do work to "dry" the air - first, physically removed the droplets/liquid via spearators, and then reduce the remaining water vapor to level below any anticipated future condensation level for the compressed air. Once that water vapor is removed from the air, it does not come back at any point in time - it maintains that level of absolute humidity (but do note that if the air tank temperature falls below the dew point for that air charge, small amounts of water vapor will condense to liquid, but having no where to go it will evaporate back into the air when the temperature later rises - the amount fo water molecules does not change as it is a closed system). So once the air is "dried" to the desired level, it will maintain that level of dryness.
I do agree that for the use of a Shoebox compressor, many including Tsao is making it more complicated than it need be. In his system, he is doing both things twice - once before the Shoebox, and then again after it. I contend that once is enough, and that it can be done properly before the air enters the Shoebox. And I have proved, at least to my satisfaction that this is true, by checking my Guppy tank for signs of condensed water after having had more than 350 cubic feet of air compressed into it and found none https://www.gatewaytoairguns.org/GTA/index.php?topic=139773.msg1407075#msg1407075 (https://www.gatewaytoairguns.org/GTA/index.php?topic=139773.msg1407075#msg1407075)
But it does matter that we "dry" the air to the right level, and knowing and understanding the relationship between dew points and absolute humidity levels is important for figuring this out. Of course once somebody has figured it out and "showed a way" that works, all one needs to do is to follow a proven path - understanding the path is optional. After all, we don't all need to know how do design, build, and program a computer to use one . . .
All that said, we all have hobbies, and we all go overboard on them from time to time, so more power to Tsao! Keep experimenting!
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heres a screenshot on one of the scuba forums why pmv are set at around 2000 psi
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Eumel,
Thanks for that. Can you provide the web link?
Taso
EDIT: Disregard Eumel. I found it: https://www.scubaboard.com/community/threads/rix-sa-6-needs-priority-valve-owner-needs-guidance.540338/page-2 (https://www.scubaboard.com/community/threads/rix-sa-6-needs-priority-valve-owner-needs-guidance.540338/page-2)
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I'm confused. Where does the PVM go in the food chain? between the filters and the tank? On the alpha, it looks like it goes before the filler. If you left it like this it seems like it would keep the pressure on the compressor. This would, in turn, put added stress on the compressor if you left it under pressure. What am I missing?
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No matter where you put it on the output side of the compressor.... if you don't bleed it off when you are finished, it will keep the compressor under pressure.... at least back to the check valve on the output side of the last stage of the compressor (there has to be one).... As long as that seals, and there are NO leaks, the pressure between the check valve and PMV should stay at the PMV setpoint.... Chances are the compressor itself will leak down past the rings or seals.... I would be concerned with a ShoeBox that the final O-ring might stay under pressure and deform.... which might cause it to leak prematurely....
Bob
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Mark,
I've attached two pictures of my "experimental" setup. Circle #1 in the second picture is the pmv on the Alpha filter as it came from Airtanks for Sale. As I read up on what the pmv does I thought about installing a pmv with a higher setpoint in the area of circle #2 before the Alpha filter.
Taso
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Thanks for the clarification on the location. Do you have a source for the PVM?
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I ordered this one and it should be arriving tomorrow.
https://www.nuvair.com/store/1-4-npt-6000-psi-back-pressure-regulator-pressure-maintaining-valve.html (https://www.nuvair.com/store/1-4-npt-6000-psi-back-pressure-regulator-pressure-maintaining-valve.html)
Taso
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I am just dropping a handy shoe box tip, I prefer to keep the cover on mine while it is running ,, to ease the removal of it I ran one of the cover screws on each side on the bottom holes in from the inside , so the threads stick out, leave the top screws out,, then I just slip the cover over the holes and it snaps in place 8)
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Thanks, Taso. Did you order any fittings from them? I am planning on installing a drain valve on the bottom of my gold filter and gauge and hose on the top with the PMV.
It wouldn't allow me to quote you because of the link? Maybe because I'm a noob?
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Hey Mark,
Yeah, I ordered the pmv, 2 couplers, 2 nipples, a tee, a plug, a filter cartridge and two bleed valves with hose barbs. I compared prices from Nuvair, August Indutries and Northshore Compressor because shipping is kinda high. I guess I'm spoiled by Amazon Prime 2 day shipping that's no charge.
The two bleed valves I have just have a hole that blows moisture everywhere. With the barbed bleeds I can capture the moisture and possibly measure it to quantify what I'm removing.
Then I saw Steve Scialli's Daystate compressor review, https://www.youtube.com/watch?v=vSs0d_nTZNc (https://www.youtube.com/watch?v=vSs0d_nTZNc)
and he was bleeding off lots of moisture so I'm glad I'll be able to direct it into a container.
I did fail to notice that the barbed bleeds are 1/8 npt. I had emailed Nuvair about the working pressure but didn't think to ask about the thread size. I assumed they were 1/4 npt like my other bleeds. I'll see if I can find some reducers from Grainger locally.
I keep adding stuff to the Shoebox and I'm not liking all the weight hanging off the front. Once I figure out the final setup I may remote mount the filtration with a 6000 psi jic ended hose I have. We will see. ;)
Thanks,
Taso
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Taso, Thanks for the info. I ordered mine and should be here next week. I planning on putting on the top of my gold filter. Going to start looking for a tee and valve to mount on the bottom to purge in addition to the one on the AV compressor.
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Hi All,
I added the new pmv in my loop today. I still need to pressurize the system and set the pressure point once the thread sealer cures.
By next weekend I should have the pressure point set and hopefully catch some water as I have a cylinder almost at 3000 psi that needs topping up. ;D
Once my testing is done, pretty soon, I think I will remote mount the pmv and Alpha filter because I don't like how everything is hanging of the original Shoebox outlet. The new pmv has mounting holes that will be a big help.
Thanks,
Taso
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Taso I understand why you need the 1/4"x1/8" bushing....but why do you have all the other fittings!?! (http://www.cafehusky.com/smilies/eek.gif)
Are you looking for extra water collection space??? Or did I miss something??? (http://www.cafehusky.com/smilies/excuseme.gif)
(https://i.imgur.com/ZyOLqny.jpg?1)
Found another site for a PMV or priority valve
1310 Back Pressure Regulator (https://valvesandregulators.aquaenvironment.com/item/ard-flow-back-pressure-regulators-priority-valves-/1310-back-pressure-regulator/1310) (Non adjustable pre set 1900psi) $67.00
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Dave,
Yes. I didn't know how much water would be collected in the first drip leg you marked. Most of the water will collect here in the first leg.
I don't expect much, if any to collect in the second drip leg under the Alpha but I did need a bleed there if I wanted to take the Alpha apart to change the molecular sieve cartridge out.
I can always remove couplers and nipples later if I have more than enough capacity. That's why I intend to capture whatever water collects there. I don't plan on bleeding every 15 minutes like Steve S. but after the cylinder is topped off.
Yes, it's like the pmv on the output of the Alpha filter is the one that came with the filter. It is non adjustable and opens around 1700 psi.
The big gold pmv is new and is adjustable.
Thanks,
Taso
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Tasso,
What is the black thing on the bottom of the alpha.
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Mark,
The black cylinder is a moisture indicator.
https://www.augustindustries.com/visual-indicator-ind-mois.asp?bc=no (https://www.augustindustries.com/visual-indicator-ind-mois.asp?bc=no)
And I have installed the 20 - 40 - 60 relative humidity disk.
https://www.augustindustries.com/moisture-indicator-disk-kit-mois.asp?bc=no (https://www.augustindustries.com/moisture-indicator-disk-kit-mois.asp?bc=no)
Thanks,
Taso
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Mark,
The black cylinder is a moisture indicator.
https://www.augustindustries.com/visual-indicator-ind-mois.asp?bc=no (https://www.augustindustries.com/visual-indicator-ind-mois.asp?bc=no)
And I have installed the 20 - 40 - 60 relative humidity disk.
https://www.augustindustries.com/moisture-indicator-disk-kit-mois.asp?bc=no (https://www.augustindustries.com/moisture-indicator-disk-kit-mois.asp?bc=no)
Thanks,
Taso
Taso,
Thanks for those links. I think I am going to put an extra gauge I have on the opposite side of the PVM outlet to my fill hose as another verification of correct pressure between all three gauges. Any thoughts on that?
Mark
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Mark,
It can't hurt. :)
I also have the big gauge right at the Shoebox outlet. I don't know how often these high pressure gauges fail or read wrong. My firefighter scba tanks have built in gauges in the valves that I double check with too when the Shoebox stops at 4500 psi. All 3 gauges should agree. ;)
Taso
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It just dawned on me, but if you never empty your tank, is it not in essence a pmv until you open it?
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Mark,
Could you elaborate? I don't understand what you are trying to say. :)
You want to separate and remove the condensate before it gets to your tank. That's what my drip legs are for. They're water traps that work via gravity.
If your air is not dry enough water will condense as the tank gets colder and/or has more pressure. If you warm the tank and or decrease the pressure in the tank any condensate will evaporate into the tank air.
That's why a lot of people think they don't have a problem when they relieve the pressure form their tanks and don't see any water in the tank. The moisture could have been in liquid form at 1000 or 2000 or 3000 or 4500 psi depending on the moisture content.
I hope that makes sense.
Taso
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I understand what you are saying, and I am installing a PMV on the top and a drip leg on the bottom of my filter. What I am saying in theory is that if I do not lower my tank below 3k psi and I do not open the valve until I hit say 3.3k on the compressor, the tank has by default become a PMV until I open the valve. The only time the PMV will have any real benefit is when I completely drain the tank or go below whatever I set the PMV pressure. Does that make sense?
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What pressure are you going to set your pmv to?
Taso
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I was thinking 3k
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I understand what you are saying, and I am installing a PMV on the top and a drip leg on the bottom of my filter. What I am saying in theory is that if I do not lower my tank below 3k psi and I do not open the valve until I hit say 3.3k on the compressor, the tank has by default become a PMV until I open the valve. The only time the PMV will have any real benefit is when I completely drain the tank or go below whatever I set the PMV pressure. Does that make sense?
Yes, but how are you going to remove the water that condensed out in your molecular sieve filter and fill adapter? Once you open your cylinder you're just going to blow that water into it. You don't want liquid water coming in contact with molecular sieve as it causes an exothermic reaction and will cause a pressure spike in your system.
If you put the pmv right after a water trap you can remove the condensed water and everything downstream will see drier air.
My understanding is this, Putting the pmv after the molecular sieve filter exposes the media to moisture unnecessarily. If you put it before the molecular sieve it will see less moisture. Molecular sieve is really only beneficial to getting already dry air a little drier. My reasoning is to not have to regenerate the molecular sieve as often.
I could leave the 1700 psi pmv after my Alpha filter off, I think. With the scba tank valve closed, if I were to pressurize the whole system and let the Shoebox shut off at 4500 psi I don't think opening the valve on a 3000 psi cylinder would cause the pressure to drop to a little over 3000 psi. There may not be the same amount of dwell but the molecular sieve would be in its optimal pressure range.
If I was filling an empty tank then the second 1700 pmv would bring the molecular sieve to the optimal working pressure and I would have more dwell.
The Shoebox flow is so low that dwell may not be a huge issue. I have the 1700 pmv already. I don't see any downsides leaving it in place only benefits. So it's staying in the loop.
Thanks,
Taso
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Yes, but how are you going to remove the water that condensed out in your molecular sieve filter and fill adapter? Once you open your cylinder you're just going to blow that water into it. You don't want liquid water coming in contact with molecular sieve as it causes an exothermic reaction and will cause a pressure spike in your system.
Taso
Not sure I follow your logic. I am not using a shoebox. I am using an AV compressor that already has one filter stage. After the first couple of blow-offs that is always dry. Now I am going to the bottom of the gold filter which has another drain valve installed. On the top is the PMV. Right now it is set to open at the default of 1800 PSI. The PMV forces the air to dwell in the sieve until it reaches pressure and then onto the closed valve on the tank. The Tank will have about 3000 PSI. My point is that the tank is acting as a PMV before I open it. If I never go below 3000psi I really didn't need the PMV. Now if I empty the tank, I'm good to go for a refill. Picture below
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Not sure I follow your logic. I am not using a shoebox. I am using an AV compressor that already has one filter stage. After the first couple of blow-offs that is always dry. Now I am going to the bottom of the gold filter which has another drain valve installed. On the top is the PMV. Right now it is set to open at the default of 1800 PSI. The PMV forces the air to dwell in the sieve until it reaches pressure and then onto the closed valve on the tank. The Tank will have about 3000 PSI. My point is that the tank is acting as a PMV before I open it. If I never go below 3000psi I really didn't need the PMV. Now if I empty the tank, I'm good to go for a refill. Picture below
Mark,
Tell me what you don't follow and I will try to explain, if I can. You never mentioned you were using an Air Venturi compressor and I have no idea what filtering it is doing.
So I will start at the point in your system beyond your compressor and at your trap, molecular sieve and pmv. To explain I will use the humidity percentages from the quote in my original post.
At your stated pmv setting of 1800 psi the humidity percentage of the air after the pmv will be slightly below 1%, per my estimate, taking account that the molecular sieve removing some moisture and the higher pmv setting above 1455 psi will also squeeze some moisture out.
So now you keep on compressing air to 3000 or 3300 psi before you open you tank valve. This is your theoretical pmv question. At any pressure above 1800 psi you will have water condensing out into you fill hose. From your picture there is no way to remove this condensate. So it will be pushed into your cylinder right?
Say you don't compress past 1800 psi and you open your 3000 psi cylinder. Your fill hose pressure will fall to about 2800 psi or less. That air will be as dry as you've previously made it. Then when you turn your compressor on and complete the fill you're still filling with ~1% humid air.
If you're fine with that humidity and regenerating your molecular sieve more often then you're golden.
Or you can put the pmv set at 3000 psi before the molecular sieve and have .5% humidity going past the pmv and have the molecular sieve deal with that. You will then be presenting the molecular sieve with half the humidity than your configuration. It will definitely produce less than .5% humidity going into your tank and the molecular sieve will last longer before it needs to be regenerated.
I don't know how much humidity molecular sieve absorbs but its a fixed weight. If you overwhelm it and use it up in 5 minutes what's the point in having it?
Taso
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I think I may kick it up a bit, but at this point, I think I'm trying to crack a nut with a sledgehammer ;D
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Mark,
You're going to be making drier air than the vast majority. I am testing out ideas in my setup and presenting the results, successes and failures ;), in my Shoebox thread. My ideas and setup have changed many times as I learn more.
I like maximizing the performance of the different components. No method is more right as long as we recognize that we need to keep water out of out airguns and cylinders. I am very glad that I have not read or heard about a corrosion failure under normal use.
Taso
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Mark,
You're going to be making drier air than the vast majority. I am testing out ideas in my setup and presenting the results, successes and failures ;), in my Shoebox thread. My ideas and setup have changed many times as I learn more.
I like maximizing the performance of the different components. No method is more right as long as we recognize that we need to keep water out of out airguns and cylinders. I am very glad that I have not read or heard about a corrosion failure under normal use.
Taso
I'm thankful that there a people like you that blaze the trail so that I don't have to think so much. 8) The problem I am thinking on now is the money I wasted on this: https://www.pyramydair.com/product/air-venturi-dry-air-intake-filter-for-air-venturi-4500-psi-compressor?a=7906 (https://www.pyramydair.com/product/air-venturi-dry-air-intake-filter-for-air-venturi-4500-psi-compressor?a=7906) If I had read more I would have figured out that this is a total waste of money. Now I am thinking about how to filter the input air without another compressor.
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Thank you Mark! I like experimenting and trying out ideas.
The stuff that I don't need anymore I will list on ebay or the classifieds here.
That filter you linked to looks like it could be used in the intake of a hand pump or a Yong Heng because it doesn't seem it will present much restriction.
Taso
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Thank you Mark! I like experimenting and trying out ideas.
The stuff that I don't need anymore I will list on ebay or the classifieds here.
That filter you linked to looks like it could be used in the intake of a hand pump or a Yong Heng because it doesn't seem it will present much restriction.
Taso
Taso,
It is made for the AV Compressor but I don't think it is effective since the sieve is not under any pressure to increase the dwell time. It may remove some moisture, but I doubt much. I don't think it will be any more effective than the spongy material in the original filter. Just my thoughts.
Mark
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Yeah, molecular sieve works best at high pressure but it will work in that canister. Silica gel should work better in your situation because it works better in higher moisture conditions and has a little more capacity
that than molecular sieve.
I assume the AV compressor has a high flow rate. You could make a silica gel moisture filter with a long length of clear hose/tubing and fill it with indicating silica gel. That should give the intake air more contact time with the silica gel.
A home made canister would be easier to fill but less dwell time. You could make or buy something like this but larger:
https://www.ebay.com/itm/New-Clear-RO-DI-Inline-Refillable-filter-Housing-Cartridge/142790279756?hash=item213ef6c24c:g:01MAAOSwGzhaKKq3 (https://www.ebay.com/itm/New-Clear-RO-DI-Inline-Refillable-filter-Housing-Cartridge/142790279756?hash=item213ef6c24c:g:01MAAOSwGzhaKKq3)
The only issue you may have is with restriction on the AV compressor intake. The compressor may be able to handle some or none at all. So whatever filter you use has to be as free flowing as possible. Optimally the longer your filter is the larger internal diameter you should have.
Just some ideas for you to build on. :)
Taso
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I plumbed one of these into the intake of my yong heng and it made a noticeable reduction in the moisture bled after the first stage.. the threading matches up with intake filter thread so I took some nylon fittings and some hose and have it hanging off to the side..
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I plumbed one of these into the intake of my yong heng and it made a noticeable reduction in the moisture bled after the first stage.. the threading matches up with intake filter thread so I took some nylon fittings and some hose and have it hanging off to the side..
I like it! Where did you source it?
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harbor freight for 8 bucks
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Using the smallest filter you can get on the inlet side where the volume is the greatest will remove a bit of moisture, but about the least efficient way to do it....
Bob
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This evening I attempted to top off one of my 30 minute scba cylinders. Everything started well. The Shoebox quickly pressurized everything up to the first pmv. The gauge read that the pmv was holding around 3600 psi of pressure. Then the Alpha filter was pressurized and my fill adapter gauge rose to about 2500 psi and started falling.
So I turned both compressors off and found two leaks on either side of a coupler that was just added for the second drip leg. I bled off all the pressure in the systems and tightened the leaking fittings more.
It didn't fix the leak.
I dug through my fittings and I had a spare coupler. I replaced the old one and pressurized the system again. The leak on the top had stopped but the one on the bottom still leaked. It's a reducer and I think it was threaded wrong. It's almost entirely in the coupler.
Tomorrow I'll go to Grainger and get a new reducer and a coupler since I'm there.
One curious thing though. I still have not seen one drop of water. I think there's two explanations for that. The first is that there isn't a lot of humidity in the house at the moment. It's around 40%.
Also I think the pressurized air from my membrane drier and my bleeds is dropping in pressure and vaporizing into my dry house air when released to atmospheric pressure.
The large amount of water that was blowing out of Steve Scialli's Daystate compressor review was very dramatic. ;D
I am feeding my Shoebox pre treated air with the dew point of -4°F so that has to be part of it.
Does anyone have an explanation? Or all my filters aren't doing squat! lol :o
Thanks,
Taso
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Taso
Is it possible to take a pic and show where you found these leaks?
It's been brought to my attention that the gold filter is taped 10x1 metric female.
I threaded the 10m x1 male x Foster adaptor into a 1/8" bleed vlv, pumped it up to 3500psi and left it over nite...it did not leak down.
For lack of finding a 10m x 1 male x 1/8" npt male adptor (https://www.mscdirect.com/product/details/84433465) that is made for 5000psi. And will ship to Canada...(http://www.cafehusky.com/smilies/excuseme.gif)
Edit: Sorry got excited there ::)...thought you were using the gold filter....
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Dave,
It's ok. :) No gold filter.
In reply #23 where you marked my pic in yellow, it's the 1/4 npt to 1/8 npt reducer bushing on the shorter drip leg.
I had a crazy headache that would not go away today. I took care of my appointments and went back home and just took one Tylenol. If it doesn't help I'll take a second one.
I wasn't in the mood to play around with it tonight so I'll go to Grainger tomorrow for the reducer bushing.
Thanks,
Taso
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@HuskyDude, I was able to source two 10mm male to 1/8"NPT in San Antonio. I just stuck with NPT after that. Taso turned me on to these folks:https://www.augustindustries.com. The guy I dealt with was very helpful. Nuvair never returned my call and when I gave the reception person my number they acted like it was an imposition.
Mark
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Tsao,
Here is the simple explanation why you aren't getting any signs of moisture in your traps after the Shoebox: the Drierite filter upstream of your Shoebox is drying the air to the point that there is not enough vapor left to condense in any of the conditions you set up after compression.
Drierite can dry the air as well as molecular sieve - I am not sure why you think your input air to the Shoebox has only been dried to an equivilent ambient dew point of -4F. Untill it becomes saturated, everything after the Shoebox is just fancy plumbing (and as you found out, a source for leaks too). Personally, I think your "input" setup is all you need . . . .
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Alan,
The Drierite canister fill full of silica gel has been removed. All that's left on the low pressure side is the membrane drier, it's prefilters and 2 regulators.
The membrane drier makes the dew point of -4°F
I've attached a picture of the current low side since I made changes around May 8th.
Taso
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I installed the new 1/4 npt to 1/8 npt reducer and the leak is gone. I guess I have been lucky as that is the only leak I've ever had.
I had the Shoebox pressurize the whole setup and fill adapter up to the closed scba bottle to 4500 psi just fine.
I cracked open the first bleed and there was no water. Either there is no water condensing there because it's dry or there is very little water that vaporizes at atmospheric pressure.
Tomorrow I will top off my cylinder and report my findings.
Thank you,
Taso
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Be wary.. you only may have water bleed once the sieve in the alpha filter is saturated.
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Be wary.. you only may have water bleed once the sieve in the alpha filter is saturated.
Daniel,
My bleeds are before the Alpha filter except for the bleed to relieve pressure so I can disconnect the fill adapter quick disconnect.
I think the Alpha will see extremely small amounts of moisture with the 3600 psi pmv in my current setup.
Taso
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I forgot to add Daniel, if the molecular seive gets saturated the moisture will go into my cylinders. Not good.
Once I finalize my setup the moisture indicator will go on the output of my Alpha filter to indicate when it is time to swap change out the molecular sieve cartridge. :)
Thanks,
Taso
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I topped off the 30 minute cylinder last night. The moisture indicator disk after the 3600 psi pmv and before the Alpha filter registered 20% relative humidity. I don't know what that figures out in absolute humidity or parts per million but I think that's pretty good.
I am not positive but I think I the humidity is low enough to not really need the Alpha filter. I admit I have a hard time understanding the humidity amounts. The indicator disk is the ultimate decider. So if the experts can confirm my conclusions that would be great.
I've wanted to to better than just removing liquid water as that leaves the air saturated at about 100% humidity. Things in our everyday life rust without having direct contact with water. If I recall correctly corrosion stops at about 45% relative humidity. Obviously lower than that is better but that 45% is the minimum.
Thanks,
Taso
EDIT: I forgot to attach the pictures of the moisture indicating disk and pink is the level versus blue.
https://www.augustindustries.com/moisture-indicator-disk-kit-mois.asp?bc=no (https://www.augustindustries.com/moisture-indicator-disk-kit-mois.asp?bc=no)
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Taso, I have ordered the humidity indicator and plan to install between my PMV and the fill hose. In my mind, this is the only way to verify the amount of moisture entering the tank/gun. You make me think too much. ;D
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Mark,
Tell your wallet I'm sorry. ;)
I've burnt myself out lately overthinking this stuff. So I step back for a break and shoot or tune an air gun and then jump back in.
I started my Shoebox thread January 23, 2017. If it wasn't for my car accident March 8, 2017 I would have finished all this sooner. I honestly think I'm close to the final configuration.
I'd like to watch the disk for a couple more top offs to confirm everything is working consistently and the 20% reading is not some fluke. Then I will remote mount the pmv, water traps and Alpha filter. I also plan to switch over to ultimox grease lubrication for the Shoebox pistons as it's non flammable, doesn't have a flash point or auto-ignition point.
I hope the gurus will post comments with formulas to confirm what the indicator disk is showing. ;D
Thanks,
Taso
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I installed the moisture indicator after the PMV and then the hose. The indicator did not change at all. I installed the 20-40-60 indicator disk. I also have the 10-20-30 indicator and may install it on my next top off. Feeling pretty good about minimal moisture in the tank.