BH75 Hoses a popin !

[riprap]

I have a BH75 that I have not used much (say less than 10 hrs) that is about 6 years old - it has been stored indoors, and is in like-new condition. I use it on my B2630, which is used all the time and has given me no trouble at all - the loader has about 300hrs on it.

The problem is that I have had several strange hydraulic hose failures (1/8 inch or so blowouts).

The first failure was in the line from the swing valve to the distribution block - this is a stationary hose, is totally protected under the deck, doesn't move at all. I chalked it up to a manufacturing defect and replaced it. The line failed after 10-20 minutes of use.

The second failure happened in another hose for the swing circuit, this time one of the hoses that goes from the distribution block to one of the swing cylinders. The blowout occurred after only 15 minutes of mild use, the hydraulic fluid and lines were still at ambient temperature (70 deg ). Again a well protected, new looking, basically stationary and non-chafed line. Both blow-outs were 1-2 inches from the crimp.

Anyone have any ideas what could be going on ?

So far I have been lucky that these are easy access lines. Am I correct that this can't be a pressure relief problem - the loader has never had a problem - and these are 3000psi rated hoses - with the relief supposed to be set around 420psi ? (haven't measured it yet) - it would be a serious and obvious problem to get anywhere near that hose failure limit?

Anything special about the swing circuit ? Bad batch of hoses years ago ?

Any ideas but keep replacing them ?

Thanks all.

 

[leonz]

Hydraulic fluid under pressure
is like electricity and water-
its lazy and will escape
wherever and when ever
it can.


To begin with, the hoses are
10 years+ of age.


The rubber hose covering is
affected by the ozone in the
atmosphere.

The wire weaving for the hose
reinforcement is two wire braid.

You might simply have a weak spot
in the wire braid that finally gave way
where the hose might have been nicked
by a forklift fork that missed the pallet
picking the pallet up or the braiding wire
had a bad spot when the wire was formed
or when the hose was woven when the
hydraulic hose was made.


UNLESS you have a main relief valve on the
control valves for the back hoe your using the
main relief valve for the tractor only and it is
entirely possible that you had a spike in pressure
that found its way out.

 

[Egon]

Was the loader made by Kubota?

Sometimes you will find Kubota attachments that are painted the proper orange with Kubota decals but are actually outsourced.

 

[Stonehaller]

Might be worth taking apart and cleaning the valves for the swing circuit. Swing circuits generally have two pressure relief valves. In addition to limiting swing force these valves relief pressure from inertia of the hoe when you stop the swing. Perhaps one of your relief valves is stuck closed so the momentum of the hoe is over pressurizing the lines when you stop the swing.

 

[Kubota 2007]

Another thing to check is the Quick disconnects, the return may not be open completely or may have something restricting it. Check the easy things first. Having the return line blocked or restricted would act as the relief not working.
Another easy test is to "T" a gauge in the Pressure line (at the Quick Disconnect) start the tractor and read the gauge not using any functions, that will show "back pressure". Back Pressure shows the restrictions in the system, hose kinked, quick disconnect not full opening or blocked, you may have a hose that has come apart internally. Back Pressure should be no more than 100 psi. The less back pressure the better, ever pound of back pressure takes a pound of working pressure away. This is where I would start.

 

[riprap]

The loader is an LA403.

Thanks for the ideas guys.

One tiny detail that I hadn't considered is that this is the first time I have used an extension on one of the hoe quick connections - Anyone who has this set up knows how short the rear hydraulic hose is that goes to the hoe (and normally is looped back) - so this time I made up a 12" extension with quick connects so that I can power up the hoe a bit farther away than the normal 3" for installation. After the hoe was installed, I left the extension in place (could have unplugged it and plugged in direct).

I can't imagine what difference it made - but since this problem started with the extension it is very very suspicious -

 

[JoelD]

As others have mentioned I'd first check the relief valve (s), pull apart and ensure not seized up.

Joel

 

[riprap]

Does anyone know if the bh75 has a relief valve as part of the control assembly ? or does it only use the tractors limit ?

Also, what is the relief set to for the B series ? I saw a post talking about something like 420 psi, but that seems much too low.

 

[CHDinCT]

Check your manuals but your tractor's relief should be somewhere around 2300 - 2500 psi for your B. Also, most BH's have a relief valve as part of the BH valve/block or perhaps even a separate one for your swing circuit.

 

[riprap]

Check your manuals but your tractor's relief should be somewhere around 2300 - 2500 psi for your B. Also, most BH's have a relief valve as part of the BH valve/block or perhaps even a separate one for your swing circuit.

Thanks, Yes, I have verified that the swing circuit has its own relief cartridges and I will verify the setting as soon as I get a pressure gage.

I think I am on the right track with the quick connect jumper being the problem. On close inspection I notice that the OEM Snap-tite ISO B connectors have a thin/pointy actuating tip on the check valves - the one I used has a broader conical tip that may very well be causing some problem under some flow conditions (the connectors seat/connect fine).

This is a set I bought from ebay and they do not show a manufacturer on them (they seem very well made otherwise) - this is actually the second set I received from the same supplier - and in looking at the last set, the male connector has the thinned down actuating tip, but the female has the conical tip like the new set - this set had been working fine on a 3pt splitter for a year or so.

I am not sure how closely the ISO spec regulates the shape of this valve tip, but I will experiment with this a bit with a pressure gage to verify if this is the problem.