Clearing up misunderstandings on water vapor and compressors / tanks

[Trigger_Finger]

What is the best recommended and cost effective way to do this low pressure side filtering?

I think most will say, "the bigger, the better".   Certainly, if you are filling large bottles or using a compressor that needs higher flow rates, big ones are better. 

Alan posted a nice set-up that works well with SB compressors.   It is larger than what I use.

I use this: https://www.harborfreight.com/38-in-desiccant-dryer-with-oil-removal-filter-69923.html  about 3' from my CAT first stage compressor.  I have a coiled line from the output of that filter, with two disposable filters, just prior to SB input.  When I see the first one of the disposables change color, I swap out the desiccant on all three.  I save the old, to bake out at a latter time.   When I get 3/4 way through the current bag, I'll bake out the used.

I only fill guppy and 90ci tanks.

I went to Harbor Freight last Sunday to check that specific dessicant /dryer but I thought it's really small and wonder if I can find a little bigger since I'm using a Great White tank 90 cubic feet.so I'm still in the search.

[Trigger_Finger]

Will this work. If you hook up like 3 or 4 of these in series?

https://www.a2zozone.com/products/silica-air-dryer?utm_medium=cpc&utm_source=googlepla&variant=574447973&gclid=Cj0KCQiAq6_UBRCEARIsAHyrgUy2kFmX7TW83gx5NMvPdQryWt__47nDZBhcvdsFX8dpspRLXFwdMB0aAp0qEALw_wcB

[FuzzyGrub]

For a 60 minute tank, then would look seriously at what Alan and Dan are using.  if you mount it where it is not easily visible, then maybe add one of those inline at the input to SB. 

[Taso1000]

Will this work. If you hook up like 3 or 4 of these in series?

https://www.a2zozone.com/products/silica-air-dryer?utm_medium=cpc&utm_source=googlepla&variant=574447973&gclid=Cj0KCQiAq6_UBRCEARIsAHyrgUy2kFmX7TW83gx5NMvPdQryWt__47nDZBhcvdsFX8dpspRLXFwdMB0aAp0qEALw_wcB

I don't see a pressure rating for those filters.  Make sure they can handle the pressure.

Taso

[FuzzyGrub]

Will this work. If you hook up like 3 or 4 of these in series?

https://www.a2zozone.com/products/silica-air-dryer?utm_medium=cpc&utm_source=googlepla&variant=574447973&gclid=Cj0KCQiAq6_UBRCEARIsAHyrgUy2kFmX7TW83gx5NMvPdQryWt__47nDZBhcvdsFX8dpspRLXFwdMB0aAp0qEALw_wcB

I didn't see a pressure rating.  You want one that can withstand 125psi.  It looks like it would hold a decent amount of desiccant, but didn't see that listed.  Wondering if it is like the inline disposables, where the beads only fill a thin layer vs the whole cylinder.   

PS: With shipping, Amazon Prime might be a better option at $20.

[Trigger_Finger]

I emailed the seller if that plastic case will hold 125 psi. I will look at those Gold filter at Ali express. Or have those contents poured into the gold filter instead.

[FuzzyGrub]

I emailed the seller if that plastic case will hold 125 psi. I will look at those Gold filter at Ali express. Or have those contents poured into the gold filter instead.

The gold filter is way overkill (psi wise) for the input side and then you would want a visible inline one downstream. 

[Trigger_Finger]

How about this? Just replace the inside with the desiccant?



https://www.aliexpress.com/item/PCP-oil-water-separator-30-mpa-4500psi-310bar/32815274871.html?spm=2114.10010108.1000014.1.7cb13ae39ib21t&traffic_analysisId=recommend_3035_1_83054_iswinstore&scm=1007.13338.83054.0&pvid=ce25fa18-04f2-46ee-a659-acaa15b9f80a&tpp=1

[FuzzyGrub]

That looks like the standard gold filter vessel that many have been using for the high side filter.  For using it on the low side, to me, it is not worth the savings over what Dan and Alan are using.  You are giving up the visual inspection capability and need to convert fittings to low side type.

[dgwren]

So I started digging to find the threads where we discussed:

https://www.gatewaytoairguns.org/GTA/index.php?topic=123325.0

https://www.gatewaytoairguns.org/GTA/index.php?topic=135521.0

Taso

Thank you Taso! I got my Altaros used, and it came with extra fittings for boosting from a tank. I never thought about using a second air compressor. Good stuff!

[rsterne]

Alan, I have a question for you.... Let us assume for a moment that the air in your 4500 psi SCBA tank is saturated at 68*F.... which means it contains 0.06 grams water per Cubic Metre.... Now, let's use that air to fill a PCP to 3,000 psi.... The pressure in the SCBA has now dropped slightly, depending on the volume of the reservoir on the gun, and you haven't added any water to the system, so does that not mean that the air in the SCBA tank can hold more water?.... So, if there was a trace of liquid water in the tank, should it not evaporate, at least partially, to re-saturate the air in the SCBA tank?....

More importantly, the reservoir you filled to 3,000 psi can hold much more water (50% more?) than the saturated 4,500 psi air you filled it with.... So, as long as you don't invert the SCBA tank, and blast liquid water into your PCP, shouldn't it be well below the saturation point at 3,000 psi.... I have heard people claim that as you fill your PCP, you are gradually accumulating water inside the reservoir.... I don't believe that to be the case if you are filling from a tank at a higher pressure, because my understanding is that air "dries" as it expands.... so even if your source air is saturated with water vapour, filling anything from that tank results in less than saturated air.... and zero chance of condensation, providing the storage (equilibrium) temperature is the same?.... Specifically, what would be the Dew Point of air at 3,000 psi that contains 0.06 g/CM water?....

Am I "all wet"?....

Bob

[AlanMcD]

Bob,

You have it correct.  Even if water does accumulate in the tank as the air charge cools, no liquid water will end up transferring to our guns.  While that is good news, we still need to keep the water out of the tanks to avoid corrosion there.

Unfortunately, the reverse is also true - when we begin filling our tanks up, if the air is not dried to the level we want at the highest pressure / lowest temperature situation for our tanks, the air charge entering the tank can carry more water vapor into the tank.  Assuming we start filling the tank at 3000 psi, then at 68F that air entering the tank can carry 0.09 grams of water per cubic meter, leaving some to condense out as the pressure rises.  But it is worse than that, because if the air is not dried before going into the tank, it will carry water vapor at whatever the temperature and pressure allows.  At 3000 psi and 100F (probably typical coming out of most compressors, unless cooled very actively) the air will carry 0.2 grams of water per cubic meter, which leaves a lot to condense out when the tank is full.

Bottom line - we need to dry our air before it gets to the tank (or gun if filling directly).  It can be dried anywhere in the airflow path through compression, but we need to get it dried.