kobelco sk 130-8 main pump failure

[anwat]

Dear members,
I recently had issues with kobelco sk 130 - 8
the unit main pump tends to fail badly ,the piston shoes were lifted,causing major damage to the related components,this happened repetitively in a series of short period up to 4 times,the control valve had been checked for any anomaly or failure ,visually there wasn't any serious issue from it ,only one spool that had unsmooth stroke,but with a little fine abrasive paper it was gone,the main pump case pressure had also been monitored using pressure gauge,it indicated a normal value.
When disassembled the visual damage seen was in the cyinder and pistons,the pistons jammed in the bore and the shoes was lifted
Do anyone know what issues i am encountering?hope you all can help solving it,thanks

 

[uffex]

Good day anwat
Our experience of similar failures has been connected to the following issues - wrong grade of fluid (to heavy) - blocked suction filter - air pressurising filter malfunction - Extra ordinary equipment installed requiring excessive fluid filling. If we can be of further help you can find information at excatech.com.
Kind regards
Uffex

 

[anwat]

Dear uffex,
Thanks for your reply,about the oil grade i can make sure i use the proper one,then about the blocked in the suction filter ,i am sure i have double checked the cleanliness of the circuit,we also did not install any other attachment in the circuit,but about the air pressurizing filter malfunction could you explain to me,i do not have idea with such issue

 

[mikebramel]

If the face of the shoes are rounded that is evidence of the shoes coming off of the swash plate. If that is the case, like uffex is saying you would need to check the inlet pressure on the pump. The hydraulic tank is pressurized to help fill the pump on upstroke and to overcome the suction strainer and prevent the pump from having problems like this.

 

[uffex]

Good day Anwat
Please see attached.
Kind regards
Uffex

View attachment Tank positive air pressure.pdfView attachment Tank positive air pressure.pdfView attachment Tank positive air pressure.pdf

 

[anwat]

Dear mikebramel,thanks for your kind help
But one thing ,could you tell me what range of pressure gauge to monitor the inlet pressure,and also the standard value for inlet pressure
@uffex,that is the one i have not checked ,i would get it done,thanks anyway

 

[mikebramel]

http://www.amazon.com/2-1-Filled-Va...-fkmr0&keywords=Lower+Mount+-30HG/30PSI+gauge

30 in - 30 psi

Vacuum should not drop below 5 inches

If the oil is aerated replace the suction hose

 

[John C.]

Pressure in the hydraulic reservoir is as a general rule held at one atmosphere or 14 PSI. It is achieved by letting air into the tank when the level of the oil goes down and holding that volume in there when the oil level goes back up. That is why most manufacturers tell you to cycle the hydraulic functions first think in the morning at before putting the machine to work. I tell people to cycle the boom up and down a couple of times which usually enough. The other action that pressurizes the tank is thermal expansion but it doesn't work to a great affect.

There are other issues that can cause your problem as well. Dirty oil is usually the most common. Any debris in the oil will cause the pistons to stick in the bores and pull the pistons out of the shoes and off the swash plate. An oil sample would be very helpful to check this. Even if you have new oil it may have contaminants and you can never get all the old oil out of the system. In my experience once you trash a pump, the debris ends up in every part of the system and you have to remove and clean everything. Coolers, motors and cylinders will carry that stuff through hundreds if not thousands of cycles before all the junk is gone. If your pump prematurely has failed more than once I would suggest cleaning out the entire system before you install another pump. Probably the last concern is where you are getting your replacement pumps. I have seen plenty of aftermarket stuff that was just one step from being scrap metal when it was installed. Is your supplier working with you about the causes of the failure?

 

[anwat]

The supplier in this case was kobelco authorized dealer was in charge when the machine first pump failure prior to the operator report of noise heard around pump ,when the kobelco mechanic disassembled it they found one of the piston shoe had worn out ,so they make a whole set replacement of the piston as well as replacing the oil and filter,from this point after the first overhaul ,the pump did not make it long,around 100hrs of operation it failed even worst the shoe lifted in the rear pump ,when got it done ,after a work of one week the pump failed again with almost the same case,this time it hit front pump ,we made it again but this time we got thorough inspection of the main valve and pressure monitoring,and the pump failed only after 10 hrs of work,i really need help,the cost ,time,perspiration lost far beyond than expected.many thanks to you guys
this time i think i need to disassembled whole part and get them cleaned,and start it again,this time with inlet pressure monitoring

 

[mikebramel]

Please take a picture of the damaged parts and post them on this thread. That will tell most of the story

 

[John C.]

I have never heard of anyone trying to just replace a set of pistons. We have always replaced the the piston an barrel assemblies as a set.

 

[anwat]

Dear john,i missed telling that in the first case the piston only found to have worn out in the spherical joint ,there wasn't any scratch or unsmooth stroke of the piston and the barrel,the worn piston found was only one of the front and rear pump,the kobelco man suggested to replace whole part pistons for both pumps
And in the second and third case the pump failed with damaged pistons and related components,the damaged parts were replaced in set.and in this fourth happening we have not disassembled the pump,so we do not know yet what kind it has suffered from.

 

[anwat]

 

[anwat]

 

[anwat]

first group photo is the second case,the second is the third case
may this photo will give you sufficient information,thanks mike

 

[tctractors]

Did you drain the Hydraulic tank and clean it including the strainer filter on the pump supply, this damage to the rotating parts is not common, the usual thing is wear in the shoe pivot mounts, its ether something blocked off or the wrong oil causing this damage, is the shaft damaged or the thrust washers (Belvill0 fitted correctly
tctractors

 

[anwat]

Sure i did,the oil,return filter was replaced,the strainer was thoroughly checked for tear and residue,only one i didn't clean the whole circuit ,i drained the cooler control valve, hydraulic cylinder chambers and motor case,as it required dismantling the whole part for the hydraulic circuit,which was really hard and time consuming,the unit was in the worksite,along way from workshop,about the oil compatibility to the unit hydraulic component,i think i used the specified grade,and the same unit used this type of oil is running in good condition,thanks for your info ,tc

 

[John C.]

I think I'm seeing scoring on the piston and barrel assembly and I notice the pistons on the one photo with the feet broken off are all at the same level in the barrel. Both interpretations indicate foreign material in the system. Where that foreign came from is probably the question you need to solve. It could be from a component failure inside the pump which caused a cascading failure. I would suspect that if the suction strainer in the tank is still clean. In that case I'm looking to the manufacturer for same answers. If the suction strainer has shiny particles I'm probably looking outside of the pump for answers.

Here is another question that might pertain to the issue. Did anyone bleed the air out of the pump before start up the first time? I've seen a couple of pumps torn up when the machine started up and there was no oil in the pump. When the engine starts, the pump goes to full stroke and then back when the negative control function catches it. With no oil in the pump there is nothing to destroke the pistons so they are sliding the full length of the barrel.

 

[anwat]

Dear john,i do not get it clear,"with no oil in the pump there is nothing to destroke the piston"the pump distroke system using swashplate mechanism which is control by servo piston ,isn't it?could you please give me a clear on it as i am not good in hydraulic system,thx
And one thing ,the unit main pump case drain hose position in tank is higher than the pump itself,as compare to the other manufacturer ,the hose is usually below or abit below the pump,does it mean something to this failure?

 

[mikebramel]

The way the shoes look they are not making contact that is why they are rounded. The pistons are sticking in their bores with the scoring and the broken retainer plate in your pictures. If it were external contamination the valve plate would most likely be scored. If it were a lack of lubrication the valve plate and shoes would have a smeared look to them. What is all replaced on rebuild? To me it looks like the contamination started from inside of the pump. Maybe the shaft bearings or the control block?