Question about All new Hydraulic line install "Bleeding"

blacknbart

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L3430DT with LA723 Loader
May 31, 2020
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I just bought all new Hydraulic lines for my LA723 Loader. The question I have after they are installed and connected with the Master cylinder will I have to then bleed those lines to remove all that air? Any suggestions tips and or tricks?

Bart
 

whitetiger

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To bleed them, start the tractor, raise and lower the loader several times. With the loader raised up some, cycle the bucket from a full dump to fully back several times.
Set loader on the ground, shut off the tractor and check/top of hydraulic fluid.
DONE.
 

bernhardine

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One more movement is necessary. Cycle the bucket to full dump (better without bucket) and lower the loader as far down as possible. Wait about 30 seconds so the air can go to the rear and now upper end of the two cylinders. Then fully curl in. Do so two or three times.
 

whitetiger

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One more movement is necessary. Cycle the bucket to full dump (better without bucket) and lower the loader as far down as possible. Wait about 30 seconds so the air can go to the rear and now upper end of the two cylinders. Then fully curl in. Do so two or three times.
That is not necessary as the air is expelled from the cylinder by the fluid filling the cylinder. What little air is left in the cylinder very quickly mixes with the oil, is returned to the hydraulic reservoir, and separates from the oil.
There is no sense in making a very simple procedure into a long-drawn-out process.
 

bernhardine

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That is not necessary ....
well, it is. - We do it with every new or repaired FEL and it makes a big difference.

If you cycle the bucket only with the FEL in a upper position, the air in the outcurl chamber of the cylinder stays in the opposit side of the hose connector.
Curling in, the air is the last volume that comes out of the cylinder. It than stays in the hoses and pipes and is pushed back into the cylinder while curling out.

You must't do anything of all that bleeding, but doing it removes the air much quicker and saves seals.
 

GeoHorn

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Firstly, I am not an experienced tractor-hydraulics mechanic. I’ve never bled a tractor’s hydraulics... Heck, I’ve never even serviced one.
But I do own one and I’ve operated hydraulic systems in various equipment from tractors to large airliners and supervised extensive maintenance operations on them. So here’s my opinion:

Trapped air can cause problems in hydraulics such as scoring, local over-heatings, lack of lubrication and cooling, and (rarely) “dieseling” such as when high pressure causes small explosions under high-pressure/heat conditions.

Hydraulic system maintenance (mx) can be very dangerous so think about what you are doing when you crack open a system.
There are basically 3 different types/ways air can be trapped in hydraulic systems, trapped air “bubbles”, entrained air, and dissolved air.
Dissolved air is the simplest problem.... It’s not a problem. Eventually it will coalesce out of the system when the hydraulic fluid eventually makes its way to the main reservoir and allowed to rest when the fluid cools.
Entrained air is usually in the form of “foam” or froth, and it will usually separate-out when the system is de-powered and allowed to rest for a period, and resort to trapped air capsules or pockets.
This last type of trapped air/capsules/pockets can sometimes be either moved to the main reservoir and allowed to return to atmosphere thru the vents when the system is shut down.... or can be “bled” via bleed valves or by using ad hoc techniques such as “cracking” open fittings while the system is at rest or at low activity. This last method can be DANGEROUS and can contaminate the area making clean-up hazardous. For this last reason, many hydraulics mfr’s and service-providers are reluctant to offer laymen instructions for bleeding the systems for liability reasons.
High pressure hydraulic systems can inject fluid into the skin, muscles, eyes, and penetrate organs and cause serious injury or even death. For that reason many entities simply refuse to issue instructions, considering it best to let the possibilities of degraded performance exist for privately-owned equipment.

The BEST method of avoiding the problem is to pre-fill components during installation/repair. When replacing a hose or line or cylinder... FILL it with fluid before installation and closing of the system. If that is done carefully then any remaining or captured air will be so small as to be of little influence and can be allowed to clear itself by ordinary usage.

If entrapped air pockets or large areas of air is suspected there are ways to get rid of it. One method, and likely the safest, is to. Position the equipment to allow the air to rise to the uppermost point near a fitting which can be cracked-open.... but this requires thoughtful consideration before doing it. Raising a FEL to it’s greatest height and opening a fitting up near the bucket..can actually CREATE or INCREASE the problem ... as the fitting is opened air can ENTER an unpressurized system as the fluid descends due to gravity. If the system is pressurized ... the danger previously mentioned of personal-injury and contamination exists. In such cases, it may actually be more beneficial to LOWER the FEL and crack open an UN-pressurized system at it’s highest point. Unfortunately this method allows the greatest spillage...and BE AWARE that cracking open ANY FITTING can and will suddenly release contained pressure and HEAVY EQUIPMENT/COMPONENTS CAN MOVE OR FALL ... a potentially dangerous result.

Sometimes living with the air and the associated risks is the better solution. After a while the air will either dissolve or work its way to the main reservoir and dissipate on its own... and that is why companies are reluctant to offer instructions which may place them into a liability/risk area.

Hope this helps.
 

SidecarFlip

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Gawd George, that is complex...lol I've never did any of that and I replace hoses all the time.

Least I don't have a 'master cylinder' on my tractor......:D
 

Bmyers

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On dad's tractor, we just replace the hoses (two of them), he used the tractor for about an hour, we stopped, checked the fluid and topped it off. Has been working fine, actually better since we replaced to the two leaky lines.
 

whitetiger

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well, it is. - We do it with every new or repaired FEL and it makes a big difference.

If you cycle the bucket only with the FEL in a upper position, the air in the outcurl chamber of the cylinder stays in the opposit side of the hose connector.
Curling in, the air is the last volume that comes out of the cylinder. It than stays in the hoses and pipes and is pushed back into the cylinder while curling out.

You must't do anything of all that bleeding, but doing it removes the air much
quicker and saves seals.

What loader manufacture recommends this when installing or servicing their loader?
What cylinder manufacture recommends this?
Every time you put the loader or backhoe on your tractor you have to go through this procedure? You induce air into the system every time you uncouple and recouple the disconnects.

In several applications, the cylinder lays horizontal with the oil ports pointing down.
There is no way to remove all the air initially. You just connect the hoses and cycle the cylinder.

The funny thing about a tractor that uses the same oil reservoir for the transmission, rear end, PTO is as the gears turn they induce air into the oil. This same oil is sent to every cylinder every time you stroke a cylinder.
By the nature of the design, there are always minuscule air bubbles in the hydraulic oil.
It is not necessary to do anything other than connect the hoses and cycle the loader.
 

GeoHorn

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Gawd George, that is complex...lol I've never did any of that and I replace hoses all the time.

Least I don't have a 'master cylinder' on my tractor......:D
Yeah, I was just trying to give the worry-warts some background-understanding of the issue .... and also why I ended the description with: “ living with the air and the associated risks is the better solution. After a while the air will either dissolve or work its way to the main reservoir and dissipate on its own...”