hydraulic oil getting hot after new valve bank and relief valve installed

[quietrangr]

I replaced a five valve sectional bank with a three and a two valve monoblocks on a closed center system. The valves work fine, but when I run the machine down the road for 15 or 20 minutes, the hydraulic fluid gets hot enough to make water sizzle on the fittings. I also installed a 1500 pound relief valve before the valve banks. The loader manual calls for 1000 pounds on two of the valves, so I set it there originally, but it was way weak. I then set it up to max 1500, and is still not as strong as before, but it works well enough. I can hear noise at the relief until the oil warms up, then don't hear it anymore. It's a 2000 lb standby pressure system on a 440 C John Deere log skidder. The valve bank controls a Barko 40 log loader. Any ideas?

 

[davesl708]

Sounds like the new setup has restrictions heating up the oil. Your setup may not work if the flow cannot be cleared. That high of a temp will start damaging seals and gaskets.

 

[Tx Jim]

IMHO any relief valves on a CC system need to be set at or above stand-by pressure. If RV is lower than stand-by then it will unseated causing extreme heat to be generated. Technically CC system doesn't need or require a relief valve as stroke control valve controls psi

 

[quietrangr]

OK, thanks, guys. I was suspicious of the relief valve causing a restriction. I guess no relief valve needed for the closed center system is the reason the closed center kit for the Cross monoblocks included a no relief plug to replace the RVs in the monoblocks. Well, taking out that RV will at least uncomplicate my plumbing.

 

[dfkrug]

The loader manual calls for 1000 pounds on two of the valves, so I set
it there originally, but it was way weak. I then set it up to max 1500, and is still not as strong as before,
but it works well enough.

Sure sounds like your RV is opening too often, heating up the oil. If your manual calls for a 1000psi
max pressure for 2 of the circuits, then you need to put the RVs in the work ports, not the IN lines.
That may require work-port RVs on as many as all 4 of the work ports, assuming they operate
cylinders.

Of course, that's just my opinion, and I have little experience with closed-center systems.

 

[quietrangr]

I was mistaken about the manual calling for 1000 pound relief setting. The manual says "setting stamped on cap." The cap has a 1000 on it. That setting is probably a safety overkill for yahoos who might tip over the machine. You can tip it over if the blade's not down to stabilize it, or if you try, you might tip it over even with the blade down by reaching way out and picking up a heavy log. I took out the relief valve, and seems to be running nice and cool, though I haven't yet run it down the road. My gauge just before the control bank reads 2200 when not working. (Gauge could be a little bit off.) Thanks for all the replies.

 

[Tx Jim]

quietrangr
Simple test on CC hyd system is remove hyd valve bank return hose from tractor,with all control levers of valve bodies in ""neutral"" start engine and if oil comes out return hose then either control valve or relief valve in valve body is at fault.
Jim

 

[CJONE]

Sure sounds like your RV is opening too often, heating up the oil. If your manual calls for a 1000psi
max pressure for 2 of the circuits, then you need to put the RVs in the work ports, not the IN lines.
That may require work-port RVs on as many as all 4 of the work ports, assuming they operate
cylinders.

Of course, that's just my opinion, and I have little experience with closed-center systems.

I do a lot with closed center open loop systems and you are spot on with what you said. He is pushing all the oil across the relief in the main system at 1500psi. A relief in the main pressure line of a closed center system MUST always be set higher that the pump compensator setting or you will build a bunch of heat. The reliefs need to be in the work lines with either a inline or in the work section [high boy] of the control valve. CJ

 

[CJONE]

I was mistaken about the manual calling for 1000 pound relief setting. The manual says "setting stamped on cap." The cap has a 1000 on it. That setting is probably a safety overkill for yahoos who might tip over the machine. You can tip it over if the blade's not down to stabilize it, or if you try, you might tip it over even with the blade down by reaching way out and picking up a heavy log. I took out the relief valve, and seems to be running nice and cool, though I haven't yet run it down the road. My gauge just before the control bank reads 2200 when not working. (Gauge could be a little bit off.) Thanks for all the replies.

The only thing you need to do now is get the reliefs in the work lines so you don't overstress the loader. Most of the work port reliefs are in the down function of the boom and dipper stick so they don't destroy themselves and in the turn function if it has a motor instead of a cylinder. I have replaced a few valve banks in forwarders. CJ

 

[Tx Jim]

I agree with CJONE. As I previously stated CC systems don't really require a relief valve and if they have a RV it needs to be set higher than stand-by pressure