Crossover Relief Valve or Not?

[lostcause]

I'm going to set up a loader mounted snow plow for winter - got the donor parts from an older Fisher 6.5 foot that's been sitting around for a while now. I'm wondering about the hydraulics though...

I was going to set this up on my last tractor and make something similar to the Deere 366 front blade, and when I studied the parts diagrams it uses a crossover relief valve between two single-acting cylinders and quick couplers to the the tractor hydraulics.

Looking at the AF11 loader mounted snow plow, it is just showing two single acting cylinders with hoses straight to quick couplers to connect to the tractor.

The question is what do I need for mine? I'm running a 3039R with a 3rd function controlled from the joystick thumb button to run the blade angle. I'm assuming that the loader mounted style is assumed to be run off the 3rd function and does that already have a relief valve in the system so it doesn't need an additional one.? The 366 front blade came about when loader mounted attachments weren't as common and electric 3rd functions were not around. Is that why it is needed in that system?

 

[Fallon]

If it's a true 3rd function there shouldn't be any problems. If it's a diverter, there will be problems. Regen on the curl circuit makes a pair of single acting cylinders work in 1 direction normally but not in the other direction. Read up on regen if it's a diverter.

For similar reasons a crossover relief valve works well on 2 equal sized single acting cylinders. But it wont work on a double acting cylinder as the 2 ends of the cylinder are different volumes. A crossover relief needs equal volumes in the cylinders or sides of the cylinder.

 

[RickB]

If it is a regenerative circuit you will have problems regardless whether the plow uses 2 single acting cylinders or one double acting cylinder. Not all loader valve bucket circuits are regenerative. Also, a snowplow with two single acting angle cylinders should have a crossover relief valve regardless of the control valve style. A crossover relief on a double acting cylinder will allow the cylinder to extend, providing 1/2 the benefit of the same valve used to protect two single acting cylinders.

 

[nybirdman]

I have a similar converted truck plow and third function(true) and added a cross-over relief after using with-out one for a couple years.
They do work;simple install,low cost.

 

[kennyd]

I'm going to set up a loader mounted snow plow for winter - got the donor parts from an older Fisher 6.5 foot that's been sitting around for a while now. I'm wondering about the hydraulics though...

I was going to set this up on my last tractor and make something similar to the Deere 366 front blade, and when I studied the parts diagrams it uses a crossover relief valve between two single-acting cylinders and quick couplers to the the tractor hydraulics.

Looking at the AF11 loader mounted snow plow, it is just showing two single acting cylinders with hoses straight to quick couplers to connect to the tractor.

The question is what do I need for mine? I'm running a 3039R with a 3rd function controlled from the joystick thumb button to run the blade angle. I'm assuming that the loader mounted style is assumed to be run off the 3rd function and does that already have a relief valve in the system so it doesn't need an additional one.? The 366 front blade came about when loader mounted attachments weren't as common and electric 3rd functions were not around. Is that why it is needed in that system?

That is a true 3rd function-actually it's a rear remote extended to the front, regen is a non-issue here.

I would definitely recommend a CRV for any loader mounted plow setup. We sell one, as does a few other suppliers.

 

[LD1]

The simple answer is yes you "SHOULD" have a CRV.

IF not you risk blowing a hose at best....or bending a cylinder/breaking the plow at worst if you catch a curb or hit something un-movable.

AS to 3rd vs diverter.....as a new layer in this thread.....either can work. IF it is a diverter and IF you have a regen only valve (two big IF's)....you can simply re-plumb the diverer to the lift/lower functions of the loader valve

 

[Dave M7040]

Remember with a FEL, the relief valve built into the loader valve is only able to provide any protection when a control valve is directing flow.

When the loader valve is in its neutral position the relief valve is no longer part of the circuit.

This lack of protection is why owners using forks on their loaders often damage cylinders when they use the forks tilted forward for pushing or back dragging objects.

Dave M7040

 

[PILOON]

Crossover valves in reality only protect the extended blade corner.
They work by dumping the extended cylinder contents over to the collapsed cylinder.

So if plowing snow away from a curb and U hit that curb the blade will then flip and dump your blade full onto the curb.

Personably I prefer the type of blade that flips if hitting a protrusion, like a rock or stump with the full flip blade winning over the cutting edge flip.
(I have just seen all too many cutting edge types very badly worn beyond repair.)
All 'flip' types depend on spring tension with some more easily adjustable than others.

The full flip style generally use eye bolts anchored at top of blade that are easy to adjust.

 

[RickB]

Crossover valves in reality only protect the extended blade corner.
They work by dumping the extended cylinder contents over to the collapsed cylinder.

So if plowing snow away from a curb and U hit that curb the blade will then flip and dump your blade full onto the curb.

Personably I prefer the type of blade that flips if hitting a protrusion, like a rock or stump with the full flip blade winning over the cutting edge flip.
(I have just seen all too many cutting edge types very badly worn beyond repair.)
All 'flip' types depend on spring tension with some more easily adjustable than others.

The full flip style generally use eye bolts anchored at top of blade that are easy to adjust.

Crossover relief valves protect the cutting edge, moldboard and any cylinder that is not fully extended or retracted.

 

[Industrial Toys]

I have used several much larger machines with snow blades, without any such relief and never had a problem. Did I just get lucky? Most blades have some trip means for obstructions anyway. I'm thinking that is way more important.

For what it's worth. My last blade has the bottom edge trip arrangement and I have had nothing but grief from it. Changed all the torsion springs, and that edge still trips without reason, often sending the loader sideways like an ice skate!