Inexpensive Oxygen Fill Cart

Any DA42 related topics.

Moderators: Rick, Lance Murray

User avatar
ultraturtle
4 Diamonds Member
4 Diamonds Member
Posts: 300
Joined: Fri Mar 31, 2017 2:46 pm
First Name: Rob
Aircraft Type: DA62
Aircraft Registration: N62KZ
Airports: KAAF
Has thanked: 64 times
Been thanked: 180 times

Inexpensive Oxygen Fill Cart

Post by ultraturtle »

On the DA42 VI (and similarly the DA62 and DA40NG), the advantage of cruising at higher altitudes is significant. 18,000 rather than 8,000 means 15 knots more true airspeed at the same fuel flow (180 vs 165 kTAS, at 75%, 13.2 gph). No wind, that means for any given leg at the same fuel flow, a 9% greater cruise speed, 9% greater range, 9% less fuel burn, 9% less airframe time, 9% less engine time, 9% less oil change/gearbox/high pressure fuel pump swap reserves. Not counting airframe time and depreciation, operationally I save about $8 per hour flying high while spending about $0.44 per hour per person on oxygen. ~1,800% ROI ain’t bad. Generally smoother ride and generally better visual situational awareness of weather are but icing on the cake.

When fighting headwinds, it would take a difference of greater than 15 knots to compel me to fly at 8,000 rather than 18,000. Tailwinds are when flying high really pays off, as they typically increase with altitude. A few months ago, a 50 kt tailwind at FL180 netted me an 18% savings in time and dollars over the 30 kt tailwind at 8,000.

My only option to resupply my built in oxygen tank on airport locally was a $90 charge to "fill" with no guarantee they could top it off to 1850 psi for what ends up costing me less than $8 for the same amount purchased in bulk from the local gas supplier (assuming a full fill from 500 psi when doing it myself). I estimate that ~9 aircraft refills (only 3 runs to the gas store to swap cylinders) will be the breakeven point to cover my equipment costs, but that is not the primary appeal. The instant availability to fill up in my own hangar at my convenience rather than taxiing across the field and waiting at their convenience made the decision easy.

I purchased a 3 cylinder cascade manifold, the FBO-3 from http://www.aviationoxygen.com/aviation- ... stems.html

A more sophisticated system that you can specify part by part, at a commensurately higher price is available from Mountain High: http://www.mhoxygen.com/index.php/groun ... ansfillers

I cannot recommend strongly enough that you purchase an “Oxygen Cleaned” transfill manifold from a reputable dealer assembling it for the sole purpose of Oxygen use, as the consequences of even a small amount of petroleum lubricant or any other compound that reacts explosively in a pure oxygen environment anywhere in the system could be catastrophic.

In addition to the 3-tank transfill manifold, I bought three 125 cu ft cylinders, and built a cart to haul them to the fill port in the nose. I would have preferred to purchase a 3-tank cart ready made, but the cheapest I could find was $3,500. I built mine for a little more than $210, modifying an inexpensive 2 tank cart:
Small tanks, yes, but they are the largest I can purchase and swap for full tanks with the local gas supply company. Larger tanks would require leasing which would be insanely expensive. The gas supplier remains responsible for hydrostatic testing of my purchased tanks regardless of how often I swap them. Also, the sweet spot cylinder count of 3 for a cascade system makes the total cart weight just shy of 200 lbs, making the weight and bulk safer to maneuver than it would be for a system with larger cylinders.

I spent a week or so nosing through every bit of oxygen tank handling safety information I could get my hands on, then cobbled the bits together:
3 Tank Oxygen Cart 01.jpg
Oxygen Fill Cart 03.jpg
3 Tank Oxygen Transfill System 02.jpg
Be smart and aware, and the fill process is easy and safe:

1. Ensure that there are no petroleum lubricants or any other compound that reacts explosively in a pure oxygen environment anywhere on your hands, person, or near the fill site. It would be wise to use wrenches cleaned with 409, then alcohol, that are dedicated for this purpose only.
2. Check that the bleed valve is closed.
3. Uncover the fill port in the nose and attach the PB3 fill connector using a 7/16 wrench to steady the tank fitting, while using another 7/16 wrench to tighten the fill adaptor slightly tighter than hand tight.
4. Identify the lowest pressure tank of the three, and open the tank valve very slowly. Feel for heat, and back off the flow if heat starts to build.
5. As the pressure between the lowest pressure tank and the aircraft tank equalizes, note the pressure, write it down on a piece of tape stuck to the tank, and then close the valve.
6. Identify the next lowest pressure tank of the three, and open the valve very slowly. Again, feel for heat, and back off the flow if it starts to heat up.
7. If this tank is capable of filling to 1850 psi, close the valve as it reaches that pressure and write “>1850” on a piece of tape stuck to the tank. If not, as the pressure between this tank and the aircraft tank equalizes, note the pressure, write it on the tank, then close the valve.
8. Use the highest-pressure tank to top off the fill.
9. Close all tank valves, open the bleed valve to depressurize the manifold, then disconnect the fill adapter from the aircraft fill port. Close the bleed valve and cover the adapter and fill port.
10. Once the highest pressure tank cannot fill to 1850, it is time to replace the lowest pressure tank with a freshly filled cylinder, to now be used as the highest pressure tank, dropping the other two down in fill sequence.
User avatar
ultraturtle
4 Diamonds Member
4 Diamonds Member
Posts: 300
Joined: Fri Mar 31, 2017 2:46 pm
First Name: Rob
Aircraft Type: DA62
Aircraft Registration: N62KZ
Airports: KAAF
Has thanked: 64 times
Been thanked: 180 times

Re: Inexpensive Oxygen Fill Cart

Post by ultraturtle »

A couple of notes to add to the previous post:

The AMM states that
The refilling of a fully depleted oxygen cylinder takes approximately 3.5 min.
If your total time filling from 600 psi is less than 2:20, you are filling too quickly.

Also, if the ambient temperature is warmer than 45 deg F (7 deg C), you will need to fill to a pressure greater than 1850 psi:
Filling pressures will vary due to the ambient temperatures in the filling area and the rise of temperature resulting from the compression of the oxygen. Due to these factors merely filling the cylinder to 1850 PSI will not result in a properly filled cylinder. Fill oxygen cylinders to the pressures indicated in the table shown below, based on the filling area's ambient temperature.
Screen Shot 2017-07-25 at 12.15.32 PM.png
User avatar
Colin
5 Diamonds Member
5 Diamonds Member
Posts: 2006
Joined: Sat Aug 21, 2010 8:37 pm
First Name: Colin
Aircraft Type: DA42
Aircraft Registration: N972RD
Airports: KFHR
Has thanked: 319 times
Been thanked: 527 times

Re: Inexpensive Oxygen Fill Cart

Post by Colin »

That's some great information and a lot of research, Rob. Thanks for putting this up here. As soon as I have a hangar I will build a similar system.
Colin Summers, PP Multi-Engine IFR, ~3,000hrs
colin@mightycheese.com * send email rather than PM
http://www.flyingsummers.com
N972RD DA42 G1000 2.0 s/n 42.AC100 (sold!)
N971RD DA40 G1000 s/n 40.508 (traded)
User avatar
CFIDave
5 Diamonds Member
5 Diamonds Member
Posts: 2678
Joined: Wed Nov 07, 2012 3:40 pm
First Name: Dave
Aircraft Type: OTHER
Aircraft Registration: N333GX
Airports: KJYO Leesburg VA
Has thanked: 231 times
Been thanked: 1473 times

Re: Inexpensive Oxygen Fill Cart

Post by CFIDave »

Great info; I've always wanted to install an O2 tank in my hangar.

What would be the disadvantage of using only 2 tanks if you didn't want to modify the standard cart? Couldn't you similarly fill from the lowest pressure tank and then top off with the highest?

Also, how much does a single tank weigh for hauling it to/from the local gas supply company? (Gotta protect my back.)
Epic Aircraft E1000 GX
Former DA40XLS, DA42-VI, and DA62 owner
ATP, CFI, CFI-I, MEI
User avatar
ultraturtle
4 Diamonds Member
4 Diamonds Member
Posts: 300
Joined: Fri Mar 31, 2017 2:46 pm
First Name: Rob
Aircraft Type: DA62
Aircraft Registration: N62KZ
Airports: KAAF
Has thanked: 64 times
Been thanked: 180 times

Re: Inexpensive Oxygen Fill Cart

Post by ultraturtle »

CFIDave wrote:What would be the disadvantage of using only 2 tanks if you didn't want to modify the standard cart? Couldn't you similarly fill from the lowest pressure tank and then top off with the highest?
Here's a really good article explaining why each tank added to a cascade system exponentially increases its utility. Skip to the bottom section on Oxygen Filling: http://www.myrv10.com/tips/accessories/oxygen/

Here is what the pressure of each cylinder in my 3 tank system would be after each fill from 500 to 1850 psi:
Screen Shot 2017-07-22 at 6.53.06 PM.png
With three, I should be able to get almost 4 fills from 500 psi to 1850 psi before the max pressure I can fill would be 1686. If I only had two tanks, I would not be able to fill to even this pressure on the second fill. I would be swapping the lowest pressure tank with 1251 psi (60% capacity remaining) rather than 849 psi (40% capacity remaining). One less tank would mean more runs to the gas store, and 50% higher gas costs to fill to the same capacity. By the way, the chart is conservative. I actually get 2200 psi in the tanks, and plan to refill at 600 psi, so I should be able to get a full 1850 fill up to the 4th refill.
Also, how much does a single tank weigh for hauling it to/from the local gas supply company?
For 125 cu ft, 72 lb empty tank + 13 lb oxygen = 85 lb.
User avatar
CFIDave
5 Diamonds Member
5 Diamonds Member
Posts: 2678
Joined: Wed Nov 07, 2012 3:40 pm
First Name: Dave
Aircraft Type: OTHER
Aircraft Registration: N333GX
Airports: KJYO Leesburg VA
Has thanked: 231 times
Been thanked: 1473 times

Re: Inexpensive Oxygen Fill Cart

Post by CFIDave »

I'm not crazy about hauling 85 lb tanks around. Did you look into whether the local gas supply company would deliver a leased tank? If so, would they typically deliver a single larger tank? Our new DA62 has a larger 77 cu ft capacity instead of 50 cu ft in our previous DA42-VI so we might need more or bigger tanks from which to fill.

Also as an alternative to creating/operating your own filling system, using the Mountain High O2D2 pulse-demand system adapted to our plane's built-in O2 system (with a $250 pressure regulator that plugs into any one of the plane's outlets), 2 people flying in the plane each consume only 1/3 as much O2 as before and thus we only need to refill the plane's tank 1 or 2 times/year. (The O2D2 also has the huge advantage of automatically regulating each user's individual O2 consumption based on altitude so you're not repeatedly adjusting O2 levels while in flight.) So for us the typical $80/fill by an FBO isn't that often.
Epic Aircraft E1000 GX
Former DA40XLS, DA42-VI, and DA62 owner
ATP, CFI, CFI-I, MEI
User avatar
ultraturtle
4 Diamonds Member
4 Diamonds Member
Posts: 300
Joined: Fri Mar 31, 2017 2:46 pm
First Name: Rob
Aircraft Type: DA62
Aircraft Registration: N62KZ
Airports: KAAF
Has thanked: 64 times
Been thanked: 180 times

Re: Inexpensive Oxygen Fill Cart

Post by ultraturtle »

Don't know about delivery options, but the requirement to lease any tank larger than 125 lb was a deal-breaker for me. Cost to lease for less than a year was more than the cost to purchase.

Height to the top of the valve of these smaller 125 cu ft tanks is less than 4', keeping the center of gravity low and the cart easy to maneuver. Filled tank weight varies from 74 to 85 depending on source, and never need to be lifted more than an inch or so - tilt slightly and they roll easily. Swapping cylinders is as easy as releasing the bracket and rolling the old one out and the new one in.

The physics of filling from a single tank don't really pan out. If you wanted even a single refill of your 77 cu ft aircraft tank from a single cylinder, you would theoretically need a massive tank of at least 300 cu ft, weighing at least 170 lb, full. A single aircraft fill from 500 psi would drop the big tank pressure from 2200 to 1850, so you would need to replace the 300 cu ft tank every time you wish to top off the aircraft tank. You would only be using 16% of the oxygen in the big tank, making it pretty expensive. Contrast that with a 3 tank cascade system, where you would be using approximately 60% of the oxygen in the tank to be swapped, while still getting a full aircraft tank. You'll also be making fewer runs to replace a much lighter tank.

A cascade fill system for several hundred bucks, or an oxygen boost pump system fed from a single cylinder for many thousands of dollars are your two best options.

We use the Mountain High O2D2 and love it. We get about 40 man-hours of oxygen at 18,000 on the F1 setting from our 50 cu ft tank before the pressure drops to 600 psi. We fly high whenever possible, so have had to refill the tank already after a little over 3 months of flying.
User avatar
CFIDave
5 Diamonds Member
5 Diamonds Member
Posts: 2678
Joined: Wed Nov 07, 2012 3:40 pm
First Name: Dave
Aircraft Type: OTHER
Aircraft Registration: N333GX
Airports: KJYO Leesburg VA
Has thanked: 231 times
Been thanked: 1473 times

Re: Inexpensive Oxygen Fill Cart

Post by CFIDave »

ultraturtle wrote:Height to the top of the valve of these smaller 125 cu ft tanks is less than 4', keeping the center of gravity low and the cart easy to maneuver. Filled tank weight varies from 74 to 85 depending on source, and never need to be lifted more than an inch or so - tilt slightly and they roll easily. Swapping cylinders is as easy as releasing the bracket and rolling the old one out and the new one in.
My concern is lifting an 80 lb tank into/out of a vehicle to drive it to/from the gas supplier; I don't have a truck with a ramp that would allow use of a wheeled cart.
Epic Aircraft E1000 GX
Former DA40XLS, DA42-VI, and DA62 owner
ATP, CFI, CFI-I, MEI
User avatar
Colin
5 Diamonds Member
5 Diamonds Member
Posts: 2006
Joined: Sat Aug 21, 2010 8:37 pm
First Name: Colin
Aircraft Type: DA42
Aircraft Registration: N972RD
Airports: KFHR
Has thanked: 319 times
Been thanked: 527 times

Re: Inexpensive Oxygen Fill Cart

Post by Colin »

But with two unmodified carts you could have four tanks...
Colin Summers, PP Multi-Engine IFR, ~3,000hrs
colin@mightycheese.com * send email rather than PM
http://www.flyingsummers.com
N972RD DA42 G1000 2.0 s/n 42.AC100 (sold!)
N971RD DA40 G1000 s/n 40.508 (traded)
User avatar
ultraturtle
4 Diamonds Member
4 Diamonds Member
Posts: 300
Joined: Fri Mar 31, 2017 2:46 pm
First Name: Rob
Aircraft Type: DA62
Aircraft Registration: N62KZ
Airports: KAAF
Has thanked: 64 times
Been thanked: 180 times

Re: Inexpensive Oxygen Fill Cart

Post by ultraturtle »

CFIDave wrote:My concern is lifting an 80 lb tank into/out of a vehicle to drive it to/from the gas supplier; I don't have a truck with a ramp that would allow use of a wheeled cart.
Not really a big deal. I'm a feeble old man and can easily lean the tank against the loading lip of my Prius at nearly the tank's half height point, tilt, lift and slide it in without exerting more than a few pounds of force.

Strap it securely using ratchet tie-downs so it will not budge during transport.

Best advice ever came from the gas store guy who recommended that I not experience a collision on my way to the hangar. I took his advice.
Post Reply