Cat 257B blowing main pump suction line????

[watglen]

1000 hrs on unit. 2005 Cat 257B mtl.

About 2 months ago the unit blow the suction line off the main pump. At least I think its the suction line. Its the only soft sided hose going to the main pump. It originates at some sort of valve bolted to the belly pan.

Today, it blew the same line. There is enough pressure in that line to spray oil. Its the pressure that has me scratching my head. Is there a system that creates pressure on the suction side of the pump? I am thinking it is supposed to have a little pressure, but something is causing it to be to much for that hose.


I worry replacing the hose won't do it.

Ken

 

[fast_st]

what shape is your vent in? There would be static head pressure, for water it'd be about 1/2 psi per foot of elevation to the top of the fluid level to the point you're measuring.

 

[Nige]

Check the hydraulic tank breather. I'm not 100% sure about your machine but in the case of the C series machines the idea is that the breather generates a slight positive pressure in the tank when the oil is at operating temperature to help maintain flow to the pump without the pump cavitating. If the breather is plugged then when the hydraulic system gets fully up to temperature there will be no way of relieving it. This could be what's blowing your hose off.

 

[kshansen]

The 257B I looked up on SIS, the SLK prefix, shows a breather in a hose attached to the tank and a hose coming off the other side of the breather. Not sure what it actually looks like on the machine but in the drawing it looks like it could get a kink in it or maybe just plugged with dirt. It is circled in red in the picture below the one on the right is a close-up but not the best picture.

 

[watglen]

thank kshansen, that is exactly right.

I blew and sucked through it and it seems to be clear, but will remove and inspect more directly.

A plugged vent was my first thought as well.

That suction line doesnt come from the tank directly. It comes from a valve mounted to the belly pan. That, in turn, is fed from the bottom of the tank. Weird. I would love to know what that valve is for.


Will keep this thread fresh....thanks so far.

Ken

 

[Mark250]

hi, the valve you are referring to is the return manifold for the work tool hydraulic and hydrostatic drive system oil to the hydraulic tank.
the valve contains an oil cooler bypass valve and a eco drain valve you haven't included a serial number but this be pretty much the same for your model


Mark

 

[watglen]

Hey! Thats awesome! Thanks.

I wonder if its a bad hose then? or something blocking up that manifold?

 

[watglen]

Well, for lack of any better ideas, I replaced the failed suction line and will give it a try this week.

I pulled the vent tube apart, all clear. Can blow both ways through what appears to be a filter in the line.

I hope the hose was weak or something.

 

[watglen]

It happened again. Same hose blew a pinhole. Doing a little grading gravel part throttle.

1040 hours, so 40 hours on new cat hose.

Gotta be something wrong in the hydraulc return manifold. Would love to hear someone else had the same problem.

Going back to dealer this week.

 

[kshansen]

It happened again. Same hose blew a pinhole. Doing a little grading gravel part throttle.
1040 hours, so 40 hours on new cat hose.
Gotta be something wrong in the hydraulic return manifold. Would love to hear someone else had the same problem.
Going back to dealer this week.

Any chance of posting a complete S/N so better help might be given? Just want to be sure we are all talking about the same hose and parts. Also how about the part number of this hose that is failing?

And maybe even a picture of the failed hose pointing to the leaking spot!

 

[watglen]

The sn is slk05022

Pic is poor

Leak is at the white spot center image.

Pinhole crack spays oil like mad when the engine is running

Hose is the feed line to the main pump 275 0621

 

[DIYDAVE]

Burr/seam on the flange?

 

[kshansen]

Just so everyone is on the same page.
In the following picture is the leak in the area of the red circle or the green circle?

Going by the part number for the hose you posted I'm thinking it is the green hose.

 

[Mobiltech]

there was a changeup on that hose in 2006. You did get the new updated hose if it's a 2750621. The letter says it fails due to pressure in the return system so some pressure there is normal.

 

[watglen]

Yep the green one is the hose.

Intetesting info on hose update.

Stay tuned. Going to dealer today

 

[watglen]

Ok, machine is repaired.

Dealer installed a test port in that line and found a steady 100psi. He is of the opinion this is about what it should be. I have no idea.

He installed the new hose. It is the same part number as the one I installed myself, but he said his is much heavier, built in the USA. He is thinking that for whatever reason, the hose I installed had the updated part number but wasn't the updated hose. I guess stranger things have happened.

Didn't treat me too bad either. $600 included $100 hose and $200 worth of oil. After doing it myself last summer, I am happy to pay someone 300 to wreck themselves getting at that on. Next skid steer I buy I am checking how the cab comes off. On this CAT, rear engine access isn't too bad, and stuff up near your feet is nicely accessible, but the stuff in the middle is buried.