What's up with dual oil filters on hydraulics

[Redbug]

I have a L3830 HST and my 50 hour mark is coming up right around the corner. I plan to do the servicing myself. I have already bought the Kubota UDT, engine filter, and hydraulic filter.

However, just crawling around underneith the tractor, I noticed yet another filter! Reading the manual...it says that it is for the transmission. The hydraulic filter is on the right hand side of the tractor, (as you sit on it), the transmission filter is on the left side under the steps. Both filters are different lengths and not the same stock numbers.

My question for you all...I thought the UDT services the hydraulics AND transmission from the same sump? That is, it's the same fluid source that runs both systems, right? If that's the case, why did Kubota engineer two separate filters running on the same body of fluid? One seems redundunt. What's up with that?...Enquiring minds need to know as they are buying that other filter...

 

[DVR]

one filters all the hydro fluid, the other filters the hydro fluid prior to going through the hst unit.

"it's sanitized for your protection"

 

[chrisjbell]

Volume. There wouldn't be ample flow with just one filter.

 

[J_J]

If you have a manual for your tractor, look at the schematic for the hydraulic circuit. Let us know what you found out.

I have noticed on a lot of hydraulic driven machines,that only one filter is used. There should be a filter on each circuit.

 

[Redbug]

Thanks Chris and DVR. JJ...that's a good idea I did not think of. I will get the manual out and follow the hyd/xmission paths and see where it takes me. I will post back...since I suspect other enquiring minds may want to know...

 

[Taiser]

I had to buy 3 for my7800 too, that also caught me by surprise. Can never have too many filters I guess?

 

[john_bud]

Volume. There wouldn't be ample flow with just one filter.

Not correct.

The HST filter is special. It filters all of the fluid from the pre-charge pump at 2-300 psi. You want the HST to last a long time, so it gets filtered well. That filter is also EXPENSIVE as it has to filter the higher pressures. It is also on at least the 3rd generation of filter due to them leaking on cold temperature start ups. (Wisconsin cold, -20F or so)

The hydraulic fluid filter is a low pressure filter that is on the suction side of the hydraulic pump. It filters the fluid for the loader, 3pt and any hydraulic power implements.

jb

 

[Redbug]

I looked in the service manual. The schematics have the transmission (HST), and hydraulics separated. However, an input line connects them together in the schematics.

After buying the filter today, (the transmission or HST filter), and looking at it, I believe John Bud is correct in his assessment. That filter is the heaviest filter I have seen. Made to handle some high pressure or volume. Not like the standard filters you normally use. Never seen one like it, before.

I figure it weighs about 5 pounds...Let's see that comes to a little over $10 a pound...

 

[J_J]

I looked in the service manual. The schematics have the transmission (HST), and hydraulics separated. However, an input line connects them together in the schematics.

After buying the filter today, (the transmission or HST filter), and looking at it, I believe John Bud is correct in his assessment. That filter is the heaviest filter I have seen. Made to handle some high pressure or volume. Not like the standard filters you normally use. Never seen one like it, before.

I figure it weighs about 5 pounds...Let's see that comes to a little over $10 a pound...

Those filters connected to the same input line, tells the story. They are low pressure, and one of them is probably 10 microns, and the other one might be a 1 micron bypass filter. On one of my machines, the 1 micron filter is much larger and heaver than the 10 micron filter.

A good high pressure filter cost between $75 to $195. I am talking about filters to handle pressure around 3000 psi.

 

[Rich P]

It is just filter changes at 50 hours (and clutch ajustment chect, at least for my 4240). You will only need a little new fluid when changing the filters. Also be prepared to have the HST filter on the machine VERY tight.