BX24 blowing hydraulic filters

[Suki]

What bothers me is everybody is saying filter is in hydraulic circuit which I interpret as high pressure side.... Confused as to whether filter could stand 1700-1800 PSI... Would seem to me filter would be on low pressure return to tank side, or suction side....

You are correct

 

[Suki]

I ll keep you posted.

 

[TMGT]

Looking at the workshop manual page that was posted, I would start by checking the charge pressure for the HST, looks the relief for it might be sticking. The charge pressure should be fairly low, 1-200psi, but is run off a system that is capable of much more.

It's also a possibility that there is an issue in the HST that could be causing the excessive pressure, but the relief should prevent overpressure of the system.

I'm not sure where the test port is for it, but it will be listed in the WSM.

 

[rScotty]

What bothers me is everybody is saying filter is in hydraulic circuit which I interpret as high pressure side.... Confused as to whether filter could stand 1700-1800 PSI... Would seem to me filter would be on low pressure return to tank side, or suction side....

The high pressure side of a hydraulic ciruit doesn't always operate at high pressure. It only develops high pressure when it encounters a load....like moving a cylinder or a plugged filter. Otherwise, if there is no load then the fluid just circulates at very little pressure.

And some systems - like the loader - can move an unloaded bucket with a few hundred pounds and then automatically respond to a big load by allowing local pressure to climb up to 2000 to 3000 psi. Think of psi as being proportional to force. The hydraulic system automatically creates enough psi to move the load. The top psi is set by the relief valve.

Unlike Front end Loaders, Power Steering systems don't develop very high pressures. All PS has to do is turn the wheels. So although power steering is also in the "hydraulic side of the circuit, it operates at lower pressures. The power steering relief valve will often set a limit of 150 to 300 psi instead of the 2000 to 3000 psi for the FEL.

After leaving the power steering circuit, a portion of the fluid is still under a few hundred pounds of pressure and is diverted to the HST system. That is called the "charge pressure", and is a poor choice of a name. It comes about because larger tractors will have an additional small pump called the "charge pressure hydraulic pump" specifically to feed the HST. Larger Kubotas all have that. Your BX doesn't have that extra charge pressure pump. Instead, it just uses a little bit of the extra flow from the power steering. But unfortunately, that flow is called by the same name...it is still called "charge pressure".

But regardless of how that slightly pressurized charge flow gets to the HST, it should have only just enough pressure to drive fluid through the special filtration media in the HST filter so that ultra cleaned oil goes forward to the HST. The HST requires the cleanest oil possible. That is why the HST filter is the only hydraulic filter that operates under a slight positive pressure - usually the same pressure range as the power steering.

As you say, all other hydraulic filters are suction types and operate under negative pressure pulling flow under suction from the tank to the primary hydraulic pump.
I can't recall ever seeing a tractor design that allowed filtration on the return to tank side of a hydraulic system. I guess it would work if it had a super sized safety relief valve, but it is much simpler to just filter on the suction side to the pump. Then there is no complexity or hazard.

Yes, your whole problem could be a series of defective filters. You should keep them for your mechanic to inspect. He will want to. But it is more likely that the filters are ok, and there is some other form of an obstruction between filter and HST. The most common obstruction is caused by long term use of water-contaminated hydraulic fluid, but it could be anything that blocks the flow.

rScotty

 

[Suki]

Looking at the workshop manual page that was posted, I would start by checking the charge pressure for the HST, looks the relief for it might be sticking. The charge pressure should be fairly low, 1-200psi, but is run off a system that is capable of much more.

It's also a possibility that there is an issue in the HST that could be causing the excessive pressure, but the relief should prevent overpressure of the system.

I'm not sure where the test port is for it, but it will be listed in the WSM.

I will relay your message. The pressure relief valve has been tested and we even replaced it without adding shims, but seems that is after the filter and didn't stop the pressure. Next step is to see if there is a stuck valve.

 

[TMGT]

I will relay your message. The pressure relief valve has been tested and we even replaced it without adding shims, but seems that is after the filter and didn't stop the pressure. Next step is to see if there is a stuck valve.

The charge lines pressure relief or the main loader/3pt relief?

See item 3 on the diagram Scotty provided earlier.
View attachment 3631324

 

[oldnslo]

Excessive flow is going to hydraulic filter.

How did you determine that excessive flow is going to the filter?

If and I repeat if you are talking about the filter that screws onto the front of the transaxle that is filtering the priority flow that goes to steering first and then into the HST as “charge” flow to keep a positive pressure on the HST and replace leakage flow from the HST circuit. If this is seeing excessive flow then loader would operate slowly or possibly not at all especially at lower engine RPM.

Loader circuit should be totally separate circuit running at totally separate pressures.

Yes it is one common pump feeding both steering and implement but the priority valve separates them.

There is a system relief before the priority valve. Then Steering will have a relief valve, and that then feeds the filter, after the filter is the “charge” circuit relief. Everything between the filter and HST is suspect on what could cause the filter to fail. If it runs 10+ hours and then fails points towards something changes suddenly increasing this pressure.

Have you noticed any significant speed change on loader movement or steering suddenly being faster?

 

[TMGT]

How did you determine that excessive flow is going to the filter?

If and I repeat if you are talking about the filter that screws onto the front of the transaxle that is filtering the priority flow that goes to steering first and then into the HST as “charge” flow to keep a positive pressure on the HST and replace leakage flow from the HST circuit. If this is seeing excessive flow then loader would operate slowly or possibly not at all especially at lower engine RPM.

Loader circuit should be totally separate circuit running at totally separate pressures.

Yes it is one common pump feeding both steering and implement but the priority valve separates them.

There is a system relief before the priority valve. Then Steering will have a relief valve, and that then feeds the filter, after the filter is the “charge” circuit relief. Everything between the filter and HST is suspect on what could cause the filter to fail. If it runs 10+ hours and then fails points towards something changes suddenly increasing this pressure.

Have you noticed any significant speed change on loader movement or steering suddenly being faster?

And don't forget the pto circuit after the steering but before the filter and hst charge circuit, each with their own pressure relief valve!

 

[KWentling]

I will relay your message. The pressure relief valve has been tested and we even replaced it without adding shims, but seems that is after the filter and didn't stop the pressure. Next step is to see if there is a stuck valve.

You are picking on the wrong relief valve. I would really like to see a schematic of a BX24. There are changes between my BX22 and the BX23S posted. At any rate, you need to be checking HST charge pressure.

 

[rScotty]

And don't forget the pto circuit after the steering but before the filter and hst charge circuit, each with their own pressure relief valve!

Yes, important that there are relief valves everywhere. Each hydraulic circuit has at least one. On schematic diagrams, relief valves are the little box with a squiggly tail and a dotted line connecting one side with another. Their main function is to open up and return any overpressure back to the tank. That tank return path is sometimes shown and sometimes just assumed.

Relief valves are not always shown unless the view is expanded. For example, look below. We know that the steering priority valve must have its own relief valve, because every circuit does. But although we see the steering priority valve, its relief valve s not shown in the overall diagram. To find it we must dig deeper into the WSM. The same goes for the relief valves in every circuit. There are many. In fact, the HST has several internal ones. All are in the WSM if you look deep enough.

Relief valves are a simple one-way valve set to open at a specified pressure. Each one has a different operating pressure that is set by shims or an adjustment screw. Relief valves are deliberately easy to access, disassemble, clean, adjust and re-use. WHEN THEY OPEN THEY TEND TO MAKE A LOUD & CONTINUOUS SHRIEKING SOUND. Like any alarm, that is deliberate. Relief valvesare also considered "fail-safe" because in normal operation They cannot fail to open when their operating pressure is reached.

IF A RELIEF VALVE IS NOT OPENING, CHECK FIRST TO SEE IF THE PORT LEADING TO THE RELIEF VALVE IS PLUGGED. (ZERO PRESSURE ON GAUGE) . IT IS COMMON FOR A PHYSICAL OBSTRUCTION TO BE PREVENTING FLOW TO THE RELIEF VALVE. COMMON CULPRITS ARE GLOBS OF DEBRIS. DIG THEM OUT AND FLUSH.

rScotty

 

[rScotty]

You are picking on the wrong relief valve. I would really like to see a schematic of a BX24. There are changes between my BX22 and the BX23S posted. At any rate, you need to be checking HST charge pressure.

Kubota is an incredibly conservative company. There have been minimal technical changes in the BX hydraulic system from the BX22 (2002) to the BX80 (BX23S type) series of today.
Frankly I'd like to see an extra filter in their system like their larger tractors have, but it is hard to argue with the BX success.

There have been NO changes that would affect Suki's problem. We know what that problem is. There is an obstruction to flow - probably between the filter and the next series of relief valves which are in the HST itself. The charge relief valve is only one of those.
I'm hoping it is a blob of lube/water slime goo, rather than a furball of destroyed parts.

A part of what I hope to do here is try to interest people in hydraulic analysis. It's a wide-open job field throughout industry and throughout the world - at much higher than traditional mechanical wages. The wage makes it difficult to hire a tractor mechanic to work on hydraulics. A one year evening trade school education in hydraulics can sure open a lot of doors.
Yes, I'm biased.
rScotty

 

[ruffdog]

I'm hoping it is a blob of lube/water slime goo, rather than a furball of destroyed parts.

I have been wondering where all the debris from the destroyed filters is going. That can't be good for the pumps and HST.

 

[TMGT]

Scotty, I don't believe the relief in the priority valve is another relief not listed.

Going from memory, the priority valve is made into the back of the hyd pump. The relief shown in that diagram of the priority valve is the same as the main relief shown in the overview of the system (after pump, before everything else).

 

[rScotty]

Scotty, I don't believe the relief in the priority valve is another relief not listed.

Going from memory, the priority valve is made into the back of the hyd pump. The relief shown in that diagram of the priority valve is the same as the main relief shown in the overview of the system (after pump, before everything else).

Could be, that is the problem with schematics - sometimes devices are shown where they are hydraulically correct rather than where physically located. And the BX is an economy model, so it is entirely possible to use one relief valve for two functions. But
regardless of whether there is an additional one in the main system (in fact there are several more), there still has to be one in the priority valve.

One way to check a schematic against reality would be to look at the WSM for the recommended pressure in the priority relief valve and compare that with the setting at the loader control valve input or back on the 3pt.

However, sometimes an obvious relief is simply not shown in overviews. For example on the BX, we know that there are forward and reverse relief valves within the HST itself because a HST requires that they have to be there. But those are not shown until you look at one specific view of details within the internals of the HST. The charge relief serves both, so it is shown in intermediate views.

Good thinking,
rScotty

 

[dougtrr2]

For the OP could you please enlighten me as to exactly what is going on with the filters. You start out saying they are blown and then later talk about them being blown up internally. How do they blow up. Do they start leaking, where? From the gasket, the crimped seam, or a split in the side? How can you tell they are blown up internally? All I can see on a filter are the holes the fluid goes through, are you splitting them open? Some pictures would be nice.

To be clear, I do believe there is something going on, and I am not intending to belittle or troll you. I am just hung up and can't get past the failure mode. I have a BX 24, so I am learning a lot from this thread.

Doug in SW IA

 

[oldnslo]

Could be, that is the problem with schematics - sometimes devices are shown where they are hydraulically correct rather than where physically located. And the BX is an economy model, so it is entirely possible to use one relief valve for two functions. But
regardless of whether there is an additional one in the main system (in fact there are several more), there still has to be one in the priority valve.

Priority valve is a flow control with a totally separate valve for relief function. Priority valve would typically not have any pressure setting. Kubota clearly shows the relief in the schematic and then also as part of the priority valve assembly.
This relief protects the pump in this system.

One way to check a schematic against reality would be to look at the WSM for the recommended pressure in the priority relief valve and compare that with the setting at the loader control valve input or back on the 3pt.

However, sometimes an obvious relief is simply not shown in overviews. For example on the BX, we know that there are forward and reverse priority valves within the HST itself because a HST requires that they have to be there.

HST does not have forward and reverse priority valves. They do have forward and reverse relief valves for limiting the closed loop or drive pressure.

But those are not shown until you look at one specific view of details within the internals of the HST. The charge relief serves both, so it is shown in intermediate views.

Good thinking,
rScotty

 

[rScotty]

Priority valve is a flow control with a totally separate valve for relief function. Priority valve would typically not have any pressure setting. Kubota clearly shows the relief in the schematic and then also as part of the priority valve assembly.
This relief protects the pump in this system.

Look at the expanded view of the steering priority valve. There it is. Yes, it could serve several functions.

HST does not have forward and reverse priority valves. They do have forward and reverse relief valves for limiting the closed loop or drive pressure.

Good catch, my fault to use the wrong word. Priority valving there makes no sense, and it would be redundant since we are changing direction...even if it were there. I changed the original to read "forward and reverse relief valves" which makes sense with the rest of the text, even if you have to look deeply into the HST disassembly in the WSM to access them. .
rScotty

 

[Redlined0002]

Problem is in you loader valve

 

[oldnslo]

Problem is in you loader valve

Would you care to explain how the problem is the loader valve?

 

[dicktill]

Yes, important that there are relief valves everywhere. Each hydraulic circuit has at least one. On schematic diagrams, relief valves are the little box with a squiggly tail and a dotted line connecting one side with another. Their main function is to open up and return any overpressure back to the tank. That tank return path is sometimes shown and sometimes just assumed.

Relief valves are not always shown unless the view is expanded. For example, look below. We know that the steering priority valve must have its own relief valve, because every circuit does. But although we see the steering priority valve, its relief valve s not shown in the overall diagram. To find it we must dig deeper into the WSM. The same goes for the relief valves in every circuit. There are many. In fact, the HST has several internal ones. All are in the WSM if you look deep enough.

<snip>

rScotty

@rScotty: Sorry for the slight thread hijack, but can the steering relief valve be in the steering valve? I have looked at the hydraulic schematics and the workshop manual for my 2022 Massey Ferguson GC1723EB and cannot find a separate relief valve for the priority (dividing) valve within the housing that MF refers to as "the control valve", which also contains the valve for the 3-point. There is only one relief valve within it and that is set for 1920psi.

Thanks, Dick