Cat 299D2 XHP Blowing hydraulic hoses. Bad relief valve?

[Nige]

I'm not familiar with the 299 but if it's a closed loop circuit then the casedrain could very well return to the pump.

According to the hydraulic schematic the travel motor case drains return direct to the tank.

Apart from that it's already been established that the 2 hoses that have blown so far (which both come from the same tee) are either on the 2-speed or on the parking brake release cicruits. I'm just not sure which one's which based on the hose layout shown in both the illustration and the attachment in Post #4.

 

[mjones35]

Nige, Could you attach the hydraulic schematic? I see the the illustration that you posted and attached, but I don't see the schematic. Do the 2-speed and the parking break release circuits both go back to the pump? Is it surprising that the 2-speed travel lines are only 3/8" 2250psi lines? Are they only used when the rabbit speed is selected? I'm not using the rabbit speed btw. I may well be completely misunderstanding what the 2-speed lines are.

 

[mjones35]

If these are the parking brake lines, could it be that the Parking Brake Solenoid (Part number 278-8743) located on the pump near the point where the line returns from the T is not functioning and causing high pressure in the line?

 

[Nige]

Attached the hydraulic schematic.

If these are the parking brake lines, could it be that the Parking Brake Solenoid (Part number 278-8743) located on the pump near the point where the line returns from the T is not functioning and causing high pressure in the line?

There is only oil pressure in the parking brake lines when the solenoid is activated. The brakes are spring-applied and released by hydraulic pressure.

 

[mjones35]

I ordered a new hose along with the fittings necessary for me to hook up a pressure gauge and relief valve on the line. I'll get an extra hose long enough to mount the gauge and relief valve outside the cab so I can monitor it.

 

[mjones35]

Thanks for the hydraulic schematic.

 

[mjones35]

Does anyone have any documentation on that drive motor, part 442-5642? If I had something showing the function of each port, that will tell me the function of the line that is blowing. I know which port the line is connected to. It is also shown somewhat by the illustration that Nige posted. It just happens to be the only #15 labeled there on the left drive.

 

[heymccall]

 

[Nige]

Just be aware that the illustration posted by HMC above is oriented the opposite way in relation to the parts image in Post #4 on page 1. Physically on the machine the 2-speed and park brake release connections are at the top, the case drain connection & speed sensor at the bottom.

 

[mjones35]

Thanks Nige. And thank you heymccall for posting that very helpful doc. I'll take a look at the machine shortly and identify the exact port.

 

[mjones35]

Just looked and it is in fact the brake release port. I should receive the new hoses, pressure gauge, and relief valve this weekend. If the pressure exceeds the 2250 psi relief valve, does anyone have any suggestions on what could be causing the high pressure on this line?

 

[mjones35]

Nige previously pointed out that the brake solenoid is activated to allow pressure into the line to release the spring brake. I know nothing about valves, but does the valve controlled by this solenoid regulate the pressure that goes into the line. If so, could a defective valve allow too much pressure in?

 

[uglyguy]

When are hoses blew, it was because the hoses had rubbed against each other. When we installed the new hoses, we made sure to turn the elbows and then tighten them so the hoses did not touch each other. That's probably the reason your blew. When we removed the hoses, it was obvious that the hoses rubbed each other. You could not see the wear on the hoses when they where installed. Its tight.

 

[mjones35]

I think (and hope) that my problem is going to be the same problem experienced by uglyguy. The first hose was definitely worn where it went through the opening with the other hoses to the drive. The fact that the second hose that blew was hooked to the same t-connector and blew within an hour of replacing the first hose may mean that the problem is both worn hoses and that something changed slightly with that valve. Maybe a sudden slight increase in the pressure passed by that valve caused both worn hoses to blow within hours of each other. I believe the min burst pressure on those hoses when new should be 9000 psi even though the working pressure rating is 2250psi, so you would think that neither hose could have been healthy. I'm still waiting on the fittings for hooking up a pressure gauge to test the output of that valve.

 

[Nige]

Both are the smallest of the group of hoses leading to the drive motors on each side and are only rated at 2250 psi.

That's not quite correct. The tag on the hose says "WP 2250psi". That translates as the [expected] working pressure is 2250psi, not the rated pressure.

The 345-4633 Hose As is manufactured from Cat XT-3 hose. This type of hose has a maximum working pressure of 4000psi. The minimum burst pressure of XT-3 is 4 times the MWP, i.e. 16,000psi. The hose must not fail when impulse-tested to 133% of the maximum working pressure (so 6000 psi) for 1 million cycles at 250 DegF. I think it should stand up.

 

[mjones35]

Nige, would you say then that if I'm testing this with three new Cat hoses and a gauge, that I don't need to bother with a pressure relief valve? Is it even possible for that pump to output a pressure that would burst a new hose?

 

[Nige]

Is it even possible for that pump to output a pressure that would burst a new hose?

Remember that hose only has pressure when the parling brake is released.

would you say then that if I'm testing this with three new Cat hoses and a gauge, that I don't need to bother with a pressure relief valve?

I can't envisage how an additional relief valve attached to the test equipment, which I think is what you are proposing, would work under those circumstances.

 

[mjones35]

I'm just installing an extra T and mounting the pressure gauge and relief valve to the cab where I can see them when I release the parking brake. I'm trying to avoid spewing a huge amount of the hydraulic oil before I even realize there is a problem like the last 2 times.

 

[uglyguy]

I had the same issue and lost entire Hydraulic fluid (twice), before I took an hour to hand dig all the muddy oil out and took towels and cleaned it out really good. That way I could see where the leak was. I then lowered cab. and started skidsteer up for 2 seconds and then shut it back off. Then raised the cab and it was very clear where my leak was. Someone on the forum told me to do this, and I wanted to avoid cleaning, because I knew it was going to be a real pain since it was broke down in the woods.

I was thinking it was my pump! Glad I took the advice and cleaned it out.

 

[mjones35]

After the first leak, I was able to prop the cab up slightly and climb in and crank it up while someone looked in from the side to spot the leak which was very obvious. Mine is also sitting in the woods with a mulcher attached, but I have the new hoses now and will get it fixed if it ever stops raining.