# Can I "return to tank" hydraulic fluid via the drain plug?



## jflener (6 mo ago)

This is probably a dumb question but please bare with me. I have a front end loader valve that requires a return to tank line that does not run through the factory hydraulic block (pressure relief valve). I hate to take the hydraulic block off the tractor and have to put in a tee in the metal return line. Can I just return the fluid via the hydraulic drain plug at the mid mounted PTO? I can put in an adapter and connect the return to tank hose. Just not sure if it will drain into tank at the bottom. Thanks in advance for the help.


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## thedukes (Jan 9, 2022)

What tractor?

In general ....maybe...I bet there are other options maybe.


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## jflener (6 mo ago)

Thanks for the reply. The tractor is a 2001 Kubota L3010GS.


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## Fedup (Feb 25, 2014)

Regardless what make or model tractor you have, individual results may vary, but for the most part, the answer would be yes. Would it be the wisest choice? Absolutely not. The bottom side of any tractor is vulnerable to all manner of snags and overall damage to lines, wires, linkages, you name it. With homeowner tractors that risk is easily doubled due to typical inattention and quite simply the stupid things people do with a tractor. If you do that, you're on track to a major "I wish I hadn't done that" some day in the not too distant future. A hose or fitting down there will inevitably get busted off, all you oil will be in the weeds before you know it, and you could have major problems. 

Think it over, look at options and do it right. You won't be sorry.


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## thedukes (Jan 9, 2022)

I' agree with above.

I'd look for an entrance on side or top.
Maybe "T" into some other line.


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## Groo (Jan 17, 2020)

I would tee it into the other return as well. if for some reason, through the drain port is the ONLY realistic option, I would definately put an in-line filter on it.


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## LouNY (Dec 15, 2016)

My concern would be that the flow coming in the bottom of the case would stir up all the stuff that normally settles out in the bottom.


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## Just Wondering (Mar 25, 2018)

When my dad died, one of the itches I scratched over the next two years was changing all the filters on each of tractors and the backhoe.
In-line filter! Man I wish that the backhoe had one and that two of the bigger tractors had one.
The gunk that I had to scrape out of the filter assembly was awful.
The 'chocoloate milk' I removed -- simply amazing anything was actually running even close to normal.


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## Groo (Jan 17, 2020)

LouNY said:


> My concern would be that the flow coming in the bottom of the case would stir up all the stuff that normally settles out in the bottom.


that shouldn't be an issue. there is probably more flow sweeping the reservoir than you think.


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## NTSOG (Dec 13, 2021)

*Fedup*:_ "Would it be the wisest choice? Absolutely not. The bottom side of any tractor is vulnerable to all manner of snags and overall damage to lines, wires, linkages, you name it."_

I can't agree more!

I wrote a post recently that I called 'Sticks!' after a branch kicked up and jammed against the fuel filter and mounting bracket on my Fendt and snapped off the bracket. That fuel filter is tucked up and away against the chassis and _should_ have been safe from damage - I thought. Now I'm looking at a hydraulic hose that runs to the front 3 point lift arms and wondering how I can relocate that higher and closer to the chassis so as to avoid it being snagged.

Jim


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## LouNY (Dec 15, 2016)

Groo said:


> that shouldn't be an issue. there is probably more flow sweeping the reservoir than you think.


I don't know about that every transmission case/ reservoir that I've had to open up to work on had a bunch of sludge and grit and garbage in the corners and bottom.
They all took some brush scrubbing and diesel flushing to be cleaned up before being bolted back up, especially units with wet clutches or brakes.


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## thedukes (Jan 9, 2022)

Can you run it to the Fill plug or oil level plug on a side maybe if it has such a fitting.


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## Groo (Jan 17, 2020)

LouNY said:


> I don't know about that every transmission case/ reservoir that I've had to open up to work on had a bunch of sludge and grit and garbage in the corners and bottom.
> They all took some brush scrubbing and diesel flushing to be cleaned up before being bolted back up, especially units with wet clutches or brakes.


Could be. Most of my experience is with dedicated hydraulic reservoirs. The case I did split was clean inside, but the machine wasn't very old at the time.


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## John Liebermann (Sep 17, 2018)

jflener said:


> This is probably a dumb question but please bare with me. I have a front end loader valve that requires a return to tank line that does not run through the factory hydraulic block (pressure relief valve). I hate to take the hydraulic block off the tractor and have to put in a tee in the metal return line. Can I just return the fluid via the hydraulic drain plug at the mid mounted PTO? I can put in an adapter and connect the return to tank hose. Just not sure if it will drain into tank at the bottom. Thanks in advance for the help.


Do I understand this correctly? Are you saying the current system returns through the relief valve? That does not seem correct. Most systems are free flowing with open center valves and only use relief valves when flow is hydraulically blocked. 

If it is the way I understand your description the pump would be under max pressure all the time. That just does not sound right.


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## Groo (Jan 17, 2020)

John Liebermann said:


> Do I understand this correctly? Are you saying the current system returns through the relief valve? That does not seem correct. Most systems are free flowing with open center valves and only use relief valves when flow is hydraulically blocked.
> 
> If it is the way I understand your description the pump would be under max pressure all the time. That just does not sound right.


I think he is saying to not return it to the "A", "B" or "P" port of a valve, but instead Tee it into a "T" port.

Most return lines are actually through a relief because the relief opens when the differential pressure at the filter exceeds a set level.


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## John Liebermann (Sep 17, 2018)

Groo said:


> I think he is saying to not return it to the "A", "B" or "P" port of a valve, but instead Tee it into a "T" port.
> 
> Most return lines are actually through a relief because the relief opens when the differential pressure at the filter exceeds a set level.


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## John Liebermann (Sep 17, 2018)

Hi Groo, Well I guess I gotta let this play out as I dont understand the new hydraulic systems. Thank you for responding.


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## Groo (Jan 17, 2020)

there are often cast letters near a valve's ports.
A and B are work ports. it isn't a hard and fast thing, but usually B goes to the base of the cylinder and A to the rod.
P goes to the Pump
T goes to the Tank
LS with go to Load Sense line, on a Load Sense System. you might also get a dedicated Pilot Drain, or a Pilot Suply, and a few other less common port options.


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## thedukes (Jan 9, 2022)

I know nothing......that said:

There are open center hydro and closed center.

What this terminology means...IDK

I assume one is under pressure always everywhere..the other not?

Is there a simple explanation too the 2 types or is it way more complicated?

I can swap hoses..install fittings etc. Know the flow of basic stuff but the OC/CC
well I am confused on this.


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## LouNY (Dec 15, 2016)

Originally in this country there was one system, open center.
Then John Deere went with the closed center system.
The open center system the pump is a fixed displacement and the entire volume of fluid circulates through the system, 
when a valve is operated it closes off a portion of the main through flow and diverts it to the loop that the valve controls.
If the valve is operated fully it closes off the through flow and diverts all flow through the valve till the system can't take any more and the system relief takes the flow.

A closed center system uses a variable displacement pump, often during engine startup there will be a destroke system that eliminates pump operation till the engine is operating at which time the pump will go into operation it will pump fluid until the system pressure is reach at which time it will start de-stroking the pump until it is just pumping the amount to maintain system pressure.
The valves in this system are closed to flow until operated at which point fluid will flow through the valve until the pressure has reached the design limit or the valve is closed.

The current systems on most ag tractors has become a Pressure Compensated Closed Loop system, which operates as a low pressure closed loop system untill a valve is operated at which time the pressure sensing loop is dumped which puts the pump into full flow mode. The normal pressure on some of these system is around 600 PSI for a standby pressure.
The valves operate similar to closed center


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## Groo (Jan 17, 2020)

LouNY said:


> Originally in this country there was one system, open center.
> Then John Deere went with the closed center system.
> The open center system the pump is a fixed displacement and the entire volume of fluid circulates through the system,
> when a valve is operated it closes off a portion of the main through flow and diverts it to the loop that the valve controls.
> ...


Pressure compensated closed center is normally referred to as Load Sensing.

A simple closed center system will hold full pressure and modulate the pump displacement to maintain that pressure. A load sense system is the same, but instead of going to relief pressure, it only asks for 300-600 psi over what the functions are asking for.

The nice thing about the closed center systems is that various valve can be plumbed in parallel, where open center/fixed displacement hydraulic systems must be plumbed in series in a power beyond arrangement.


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## Always something (6 mo ago)

I am not familiar with the modern tractor pressure compensated closed loop .That louNY described .I need to check that out It .Don't like new tractors let me try to simplify. the weath of good info you have received. First let me explain hydrlic pumps .There are more than one type of pump .The 2 most used on tractors are gear flow pumps .Simply 2 gears that cirulate hydrlic fluid continously through the open center system.Then there are piston pumps that are used in closed centered systems .John deere Those operate like a piston sort of .With one exception .When the specified pressure is reached ,the pressure stops the piston from working .When there is a pressure drop .the piston goes back to work. That is how John deere works .Other piston pumps continue to move the piston up and down.Controlling pressure by releasing oil through through pressure relief valves. THE ONE THING YOU09 MUST CONSINIDER AFTER YOU FIGURE OUT WHICH YOUR TRACTOR HAS .DO YOU HAVE THE RIGHT TYPE OF VALES ON YOUR LOADER? Some valves can work either way by pluging a port .If you use the wrong valve the damage can be very costly. Plus haunt you for years .The next thing you have to consider is power beyond. That means are you deverting power away from something else that needs pressurized hyd oil to function properly .In a open centered system you should remove the pressure line go through the valve and back to the port where the pressure line was attached.This keeps the pressure moving correctly through the system. And that powers functions beyond the valve your installing.On a closed centered system ,you install a closed centered remote valve by using a T in a pressure line .Since it is closed centered and fluid stops moving when the valve is closed you can dump fluid anywhere there is a open unused port that returns fluid to the reservoir. OPEN CENTERED Fluid CIRULATES THUROUGH THE SYSTEM AT ALL TIMES EXCEPT WHEN A WORKING CYLINDERED IS APPLIED .The working pressure of the pump valve and cylinder are protected by the pressure relief valve.A closed center system is what your house water is. When you turn off the water if you are on a well there is a pressure switch that stops the pump when set pressure is reached . THE JOHN DEERE SYSTEM IS UNIQUE IN THAT THE PISTONS HAVE NO CONTECTING RODS .they are driven by a eccentric lobe on a shaft And controlled by a bunch of little springs check balls and ports.It is an amazing system designed to take load away from the engine when it isn't needed. Know your system Proper line plumbing is a must do right .I speak from experince .Not going to tell you what I did. Just that I did it and 40 years later it is still haunting me .Knoledage gaind at a very high price. Oh to be young and ignorant again.


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