Using gravity to flush hydraulics

I put 2 gallons of gas in hydraulic oil. I'm on my third flush. This time I decided to use gravity to get some oil out of cylinders. I used outriggers to lift rear wheels, put jack stands under tractor, then raised outriggers. Curled front bucket and raised it all the way. Extended rear boom and curled rear bucket too. After draining oil, I had someone move the controls while I pulled down of buckets. Pushed down on outriggers and more oil drained out tank. Same when I dumped front bucket, lowered loader arms, moved rear bucket and boom. Then I removed filter and moved all control levers again. That helped drain some of the hoses back to tank. Wish I had thought of this earlier. I think this flush may be my last for a while. Will leave fill cap off and covered with a rag to let fumes out and keep dirt from getting in.

Good news is no major damage. I have a couple of cylinders that are leaking around the rod, but that's normal. If my 12 cylinders don't leak today, good chance they will leak tomorrow. There is really only 2 o-rings at rod end that are problematic. The rest of the o-rings in cylinder don't need replaced, they rarely wear out. I do most of my cylinder work. Really doesn't take that long.

You know, "if it wasn't for Gravity, monkey poop would never make it to the ground". ;^)

If it weren't for gravity, we wouldn't weigh anything. Then there would be no need to go on a diet.

I was gonna say something about women needing foundational support,but I won't.

Yeah and your bibs wouldn't be so tight in front.

Got that right. Danged gravity anyway. LOL

I've just opened the lines and put a shot of compressed air through them to clean them out. Do it away from anything you don't want oiled down though. If you take the lines loose you should be able to push or pull the cylinder to get the oil out of it and them use the air to clean the lines.

Impossible to remove lines without removing cylinders. My way is easier. Some lines drain with filter removed

George help me understand this a little better.
Let me use some numbers I pulled out my head to explain.

There is a tractor that holds a total of 5 gallons of hydraulic oil.
With the cylinders all the way closed there is 4 gallons in the sump and 1 gallon in the hoses and cylinders.
With the cylinders all the way extended there is 2 gallons in the sump and 3 gallons in the hoses and cylinders.

So I want to change my oil. I close all the cylinders. When I drain the oil I get to replace 4 gallons that was in the sump. There is still 1 gallon in the system that I can not drain because it is in the hoses and cylinders.

So I try something different. I extend all the cylinders. Now I drain the sump and get 2 gallons of oil. I then open the valve and physically force the cylinders closed forcing 2 more gallons into the sump that drains. I drained a total of 4 gallons now because 1 gallon is still in the hoses and cylinders.

So can you explain to me what I did different by starting with the cylinders all the way open or closed other than getting a little exercise by having to physically force the cylinders closed with brute force.

John in La,
I don't understand where you got your numbers. My hydraulic tank holds 12 gallons. I only put 10 gallons in tank, leave room for thermal expansion. The hoses, pump, transmission, torque motor and 12 cylinders hold 2 or 3 more gallons. I filled tank with 2 gallons of gas. Ran it for an hour, the hyd oil expanded when it warmed to about 145. Then it started running out of the tank on the ground. Then I discovered my mistake.

I've flushed the hydraulics 3 times now. The last time I discovered how to get most of the oil out of 8 cylinders and some of the hoses.

With the cylinders extended, there was only oil on one side of piston. When gravity pulls the lift arms, or buckets, the cylinders are compressed and the oil in cylinder is returned to the tank which you could easily see it returning to the tank. Therefore I was very easily got the oil out of 8 cylinders and a few of the hoses using gravity.

Next time you change the oil in backhoe, try it, you will see how easily it works.

I explained where I got my numbers from in my first post.
"Let me use some numbers I pulled out my head to explain."

I am trying to understand what you think you did by following your new procedure starting with the cylinders extended.

I fully understand what you did and are trying to do with your multiple flushes but can not understand why you think starting with the cylinders extended made any difference.

Yes if you start with the cylinders extended and then close them with gravity you will get more oil out of the hoses and cylinders. That's easy to understand.

But if you start with the cylinders closed this extra oil you got from the cylinders and hoses will still be drained because it will be in the sump to start with.

So in the end you are still gona drain the same amount of oil from the entire system no matter if you start with the cylinders open and close them with gravity or started with the cylinders closed.

Also moving the cylinders under engine power is gona flush the hoses the same as draining the system with gravity.

Maybe I am reading it wrong; so that is why I am asking; but it seems you are trying to say you were only able to drain 9 gallons of your 10 gallon system out the system because 1 gallon is stuck in the hoses in your first 2 flushes but are now able to get the full 10 gallons out.
I disagree. I bet you drained 7 gallons from the sump and then another 2 gallons by closing the cylinders with gravity. You still only got 9 of the 10 gallons out.

So I am trying to understand what you think you accomplished other than getting a little exercise closing the cylinders with brute force and gravity.

If they are double acting cylinders they are always full of fluid. When they are down the fluid is on one side, when they are up the fluid is on the other. By having all cylinders retracted he still had the back side of each full.

So he extends them all and shuts down the machine. Now if he can retract them manually the other side will be dry (pump not running). It puts air into each cylinder, but if they are all cycled when he puts in the new fluid they will fill.

On something that size it is doable and easier than cracking the hoses at each cylinder.

I have read your reply over and over trying to understand what you were saying.
I think I may understand now.

You are thinking that since the cylinders have power down to compress the cylinders under power fills the cylinders with oil on the top side of the cylinders. You can not drain this oil.
But since you started with the cylinders fully extended there is no oil on the top side of the cylinder and you are able to drain the oil on the lower side of the cylinder with gravity.
Since there is no oil in the sump and the pump is not running you now have cylinders with no oil on the top or the bottom of the cylinders.

Thanks notjustair

I figured it out and was posting my next reply as you were posting this.
I just could not understand what his thinking was till I thought about how hydraulic cylinders with power down work.

I had a small Kubota with loader that had water in the hyd. oil.
Drained it all out like you just did let gravity do it's thing. Then in addition I used a larger loader tractor to lift it back up and down a few more times to cycle it while holding the levers in the right position and got even more out.

I had to get some parts at local hydraulic shop this morning. I told him what I did. He smiled and said that's what we do all the time.

So the older I get, the dummer I feel. Why didn't I think of doing this a long time ago when I changed oil in my other terramite for the past 6 years?

Everyone thinks you have to remove hoses and cylinders to drain them, even terramite told me to do that.

After 3 flushes, I don't smell that much gas in hyd tank.

I think you got the idea. The hydraulic shop told me today that's what they do too.

Want to thank you for explaining this and clearing my mind up... wanting to change my fluid and was unsure exactly...