NH air in hydraulic lines

[jinman]

It appears that New Holland has at least two and maybe three mid-mount loader valve assemblies for our Class III tractors. The early model tractors like my TC45D (prior to 2004) used part 86400325 on the 16LA loader. After 2004 on the DA and A model tractors, the part changed to a different valve part no. 86403581. The latest model tractors including the Boomer 30xx, Boomer 8N, and 1530 tractors use a part number 87571203 which looks very similar to the 86403581 in appearance, but is less expensive in cost.

HCb, I'm guessing that your friend's TC40 which didn't exhibit the problem was a pre-2004 model. I say that because my loader shows no signs of similar symptoms. Also, you are the only member who has ever complained of the problem. You'd think someone else would notice it too if it was as prominent as you say. Your being "twice snake bit" is pretty incredible. I make no presumptions of why you are having these issues, but just point out that you seem to be alone in your complaint. That's puzzling. . .

 

[J_J]

Just some casual observations, You also said you had air in the BH cyl. I think that is a give-a-way for suction hose leak. After running the tractor, look in the reservoir and see if there are tiny bubbles in the fluid. The air bubbles will also make you think the reservoir is over filled. After awhile the bubbles burst/float, or whatever. The bubbles in the cyl, just form an air pocket, but usually can be expelled by operating all the cyl. It could do it on a third tractor if there is a suction leak.

About the only other way air can get into a cyl is by a high vacuum on the cyl rods/seals.

I also think that fluid being relieved, goes through a tiny orifice, and can generate bubbles, and increase the heating of the fluid. Do you hear the reliefs going off a lot?

Notes:

Another reason Relief Valves make noise as they pass fluid at pressure is from the expansion of air trapped and compressed in the fluid. This is seen in aeration at the valves outlet since the bubbles have decompressed to atmospheric pressure. The bubbles may be quite small but there are often lots of them.

 

[Transit]

HCB, if you have that much air in the system you should see a level change in the sump when the system is purged of the air.
You say that the hydraulic filter was changed, that filter should never be finer than 150 microns or you risk drawing air into the suction line between the filter and pump. Or you may cause cavitation, when hot oil boils and becomes oil-steam. In most cases, the oil-steam bubbles will collapse once they are on the high pressure side of the system.
Another cavitation problem can be caused when working the hydraulics hard and the oil is hot. With a load in the bucket and allowing the bucket to dump freely by the force of gravity, as the piston moves within the cylinder, oil is pushed out of the decreasing side of the cylinder and sucked into the expanding side of the cylinder faster than the oil lines will allow, the resulting low pressure will allow the oil to flash into steam [caveat] or draw air into the cylinder around week seals. Dont say it cant happen because I have had the problem until I figured out the cause. Now I dump with the engine at 1,200 rpms to feed oil into the expanding side of the cylinders instead of just idling the engine.

But with having the same trapped air problem with the backhoe I would suspect a suction side air leak.
Is the trapped air caused by the FEL or backhoe? Have you tried disconnecting the backhoe to see if the problem stays with the FEL?