On board oxygen transfill technique

[Geoff]

Looking for instruction/techniques people use to fill onboard oxy tank.

I have a two bottle 125 cf each cascaded mobile fill station and the transfill connectors but have never seen anyone do this before.  A video would be perfect.  Anyone done this themselves?

[aggiepilot04]

Hey Geoff,

I will try to record a video the next time I do this, but it's pretty straightforward.  2 most important things: keep your connections clean (especially petroleum products - you don't want to blow yourself up), and open the valves very gradually.  Connect your setup to the port on your airplane, and then slightly crack open the valve on the tank with lower pressure.  Let the pressure equalize (if you hear rattling, you're doing it to quickly...close the valve on the tank).  I may be overly cautious on this, but I barely crack the valve and let it equalize very slowly.  Then I gradually open it more after it stops hissing.  Once you have the tank fully open and it stops hissing, close that tank and gradually open the tank with more pressure in the same way.

When you exchange a tank, obviously exchange the one with lower pressure.  Then your previously high pressure tank becomes the low pressure tank, and your newly exchanged tank becomes your high pressure tank.  You'll get the most out of your tanks this way.

All of this being said, I never had anyone demonstrate this for me.  This came from research here on MS and elsewhere.  I'm sure there are plenty of other MSers out there that are happy to correct me if any part of this procedure is incorrect...hah!

[peevee]

125cf tanks won't last long. We use two 330CF and get several fills. Here are the instructions from our transfil rig.

o2 fill instructions.pdf

 

it's basically fill as slowly as you can and watch your pressures as already mentioned. I put an inline valve in between our tanks and the plane so I can close it off and see what my tank pressure is. Be sure to use clean wrenches, no oil on them.

[kortopates]

If you have the 115cf built in system, you won't even be able to fill it with two 125 cf tanks from near empty. 330's are two big for me to pick and move to refill so I use the 220's but 2 entirely full 125's starting from full without +P pressure will only get you to about 3/4 full. With +P pressure (~2200 psi) should get you near full. But I'd suggest getting larger tanks if able.

Recognize this is not owner approved preventative maintenance and so highly suggest reviewing and following the instructions in the Maint Manual for servicing your O2. Its not hard but their are limitations to observe: the maximum fill PSI based on temperature table and also note the tank must not be down to totally empty to refill - it must still be pressurized before refilling or technically they call for removal and cleaning before re-filling if air has been able to get in. Servicing O2 is considered maintenance and as such its suppose to logged but this is rarely done except when it's serviced with other maintenance. I track my fills in a spreadsheet where I put the Boyles law formula in it which shows me exactly what PSI I will end up with starting with tank psi and the starting PSI and ending PSI's of my 2 cascading tanks. More than you need but shows my refill history.

[Geoff]

Thanks for the responses so far.  I have a 75 cf onboard system.  Will I be ok with the 125 cf tanks or should I upsize?

[peevee]

Fancy, I just look at the chart and fill based on oat.

I don't know how to do the math to say how your 75cuft will fill but if you own the tanks airgas will let you pay the difference for 330s if you decide later you need more. Ours are on a big cart and I don't find them to be terribly difficult to move but it takes two people to lift if you need to 

[thinwing]

I use 4 330s in a cascade...first of all the 1/8 in copper infill line to most of our Mooney installed systems tends to act as it's own regulator as far as flow rate is concerned..my 115 cubic composite tank (which I just replaced last month)is rated at 1800 lbs working pressure and is hydro tested to over 3500.So as far as flow rate..open the valve all the way...I tend to refil my bottle when it drops to 500 or so.First trans fill takes it to 750 than 1100 than 1500 and last monitor aircraft gauge at 1800 or skip this stage altogether.This will last two people over 10 hrs at 17000 ft flow rate..

[DonMuncy]

Whether you are using 125 cf tanks, or larger ones, and depending on how much pressure you start with, you will never "fill" your on board tank. The pressure will equalize where it equalizes. A big FBO operation cascading with 6 tanks will get a pressure very close to what you would consider full. When you are doing it yourself, you will have to decide how many "fills" you will get by deciding what pressure you are willing to live with after filling it. It won't take you long to figure out how much pressure will last you how long at what altitude, and you get to decide. 

[larryb]

An alternative to fully filling the big installed tank is to need/use less. I have about a year with the Mountain High O2D2. At 13,500 feet for 6 hours, my wife and I used less than 500 psi out of a 22cu-ft portable bottle. That is less than 1 cu-ft/hr for the both of us. A 125 cu-ft built-in tank would last 125 hours, a year of flying. Now that I have a plane with a built-in system I can still use the O2D2 with an adapter, which is a secondary regulator that drops the pressure of the built-in system down to the level the O2D2 wants.

It seems the built-in system is incredibly wasteful of oxygen when used as the factory intended.

I also transfill my oxygen, both portable and built-in. Even if my big tanks are low and I only get 1000psi into the Mooney, that is still > 60 hours of flying and will last any conceivable trip.

Larry

[gsxrpilot]

6 hours ago, larryb said:

An alternative to fully filling the big installed tank is to need/use less. I have about a year with the Mountain High O2D2. At 13,500 feet for 6 hours, my wife and I used less than 500 psi out of a 22cu-ft portable bottle. That is less than 1 cu-ft/hr for the both of us. A 125 cu-ft built-in tank would last 125 hours, a year of flying. Now that I have a plane with a built-in system I can still use the O2D2 with an adapter, which is a secondary regulator that drops the pressure of the built-in system down to the level the O2D2 wants.

It seems the built-in system is incredibly wasteful of oxygen when used as the factory intended.

I also transfill my oxygen, both portable and built-in. Even if my big tanks are low and I only get 1000psi into the Mooney, that is still > 60 hours of flying and will last any conceivable trip.

Larry

That is unbelievable. I really need to look at that O2D2 system. I've got the 115 cu tank built in and it only lasts about a 6 hour trip.

[peevee]

26 minutes ago, gsxrpilot said:

That is unbelievable. I really need to look at that O2D2 system. I've got the 115 cu tank built in and it only lasts about a 6 hour trip.

So we flew from Co to ca to northern CA to or to ut to home, 2 of us at alts from 140 to 240. We left with 1500psi and landed with 1k psi. 10 or 12 hours of flying. Probably about 8 hours at 180-200