L2501 hydraulic

[domigold]

I bought a L2501 with 3rd function setup (true 3rd function, not diverter valve). I noticed that the 3rd function valve only has 4 ports: 2 going to the front for the 3rd function, one goes to the loader PB port, and the other goes to the PB port on the front hydraulic block.

I think the line from the loader PB port is the high pressure side and the 2nd line to the PB port on the block is the return to tank/PB line. Is that correct? In this set up, there is no dedicated return to tank line? I always thought that the return to tank (low pressure) is separate from PB line.

Comments?

 

[Dave_eng]

This 3rd function valve is already installed and you just have questions is this it?..

3rd function valves are designed to be in series with the power beyond loop and do not have a Tank port.

In general because I do not know your tractor, the hydraulic block supplies high pressure to the loader valve IN port.

Now because the high pressure is directed to the loader valve, the loader valve returns high pressure to the block using its pb port.

In the same way the hydraulic block does not have a TANK port, the 3rd function valve does not either

This marked up drawing of a hydraulic block is not your tractor but a bit larger one and is provided to help you understand what I am saying.

I think your tractor has a LA525 loader. Try asking a dealer for a copy of the LA525 assembly instruction manual. It shows in great detail how a third function valve is tied into a L2501. Bring a USB stick and hope...........

Dave

 

[lugbolt]

You don't fully understand an open center system.

Study up on it and you'll have a better understanding.

That's normal. BY normally goes from block to loader valve. U wanted a 3F valve so they remove the line from block to valve, then put the 3F valve in between and plumb it into the 3F, then out of the 3F. That's the only way the system can work.

backhoes are the same design. They remove the factory line from block to loader valve. Then a long hose goes from the block to the backhoe, then out of the backhoe to the loader. The backhoe goes in between the loader valve and the block. Similarly any rear remotes. You get the idea.

 

[kubotafreak]

To the OP, most functions in a open center setup divert/rob flow from the main artery. Unlike an aftermarket say, solenoid that diverts function from another function(switching/diverting) at the press of a switch(common for backhoe thumbs) the factory kits tie in to the circuit without taking away from one of the prior functions unless you steal max flow. The very nature of a open center is the "priority" of things. You still have a dedicated third function with the factory kit 4 ports, because the loader valve has a T port. In theory you can feather the loader and press the switch for your third function and both work.

I do believe there are cases where some of these land pride/kubota third function valves do not have an open/tandem center. The instructions on these kits usually start with not intended for use on a machine with a backhoe. This seems to work as a cost savings to some, at the detriment to not really knowing down the road when they want to add a rear remote/backhoe.

The separate return to tank allows the function to have the most flow possible from the pump, with the least restrictions/heat. Not really that common for some loader grapple functions. If you were running a hydraulic powered motor, that would be a different story. It all goes to cost, and really starting open center limits the system from the start.

Kubota does make some third function kits with a T return, like for the GL60.

 

[domigold]

Thank you all for taking the time to answer my question. My loader is LA525 and the 3rd function is dealer installed (I think it is Land Pride kit). The PB out from the 3rd function runs to the PB on the front hydraulic block to power the 3 point hitch.

The LA525 loader does have a return to tank line to the front hydraulic block. My confusion came from the fact that the 3rd function valve just use the PB out as the low pressure (tank) line.

I am thinking about adding a spool valve (2 spools, not Kubota part) for the rear remotes. The spool valve has a dedicated return to tank line that needs to be T off into the front hydraulic block existing tank line. I think the line is necessary but a friend thought it is not. Looking at the 3rd function valve, he might be correct because it works without a tank line.

However I read somewhere that the tank line is necessary to allow the relief valves to operate correctly since the spool valve also has one (set at 2650PSI from factory). I don't understand the reason why the tank line affects relief valves operation.

But according to Dave from his above post, the tank line is primarily to reduce heat/restriction to the system and therefore improve flow rate. I think his answer makes more sense. I'll probably just spend the extra tank line hose to be on the safe side.

 

[kubotafreak]

If the valve was designed for a dedicated tank line you need to use it. If the valve is designed like your 4 port third function you don't have need for it. There are usually a sleeve adapter to adapt for dedicated power beyond. This sleeve separates the return mixed flow into two paths. (PB, and T) If your new valve has its own relief, it will have a T port. You need a T (neutral) path for the relief oil to flow.

Envision the use, If it is made to drive a motor it needs a waste neutral flow back. If your only driving cylinders with constrained volume, a simpler valve may be used. Be careful how you tie into the power beyond circuit. Many times you cannot simply break the circuit with a non power beyond valve. Thus the reason for the additional sleeve adapter.

Here is the confusing part. Your 4 port uses the pb line to waste oil like a T port. The demand of the valve utilizes all the available P flow. (Solenoid, not lever) This is how the valve can operate without a dedicated neutral path, since it creates one. This is where at non use, the center matters. If it is tandem/open center, it creates a pb throughput from its source P. It is diverting the P source on use. It should still be called a diverter at the end of the day. The reason you don't, is because its not robbing you of another function in the sense.

The protection for a non relief valve comes from the one prior to it, and an overall system relief.

 

[kubotafreak]

Found this on market place....