hydraulic bypass question

lwalsh · Jan 25, 2011

I think I know the answer but I want to verify. Am I correct in saying that a loader valve will not bypass from excessive load applied to the cylinder? I hit an immovable object with my 2720 front plow. Outside corner of the plow caught the frozen ground while going slow. The plow was in the straight position and instead of stopping the tractor it swung the plow about 15 degrees and blasted the underside of the tractor with hydraulic fluid from the banjo fitting on the output side of the valve. No apparent damage and the bolts are at 40 ft/lb per spec. I should mention it is a home built plow setup and the swing cylinder doesn't have much of a mechanical advantage. It's a single cylinder only about 6" offset from the pivot pin. Did I just get lucky?

beenthere · Jan 25, 2011

Pics will help follow along.

countrybumpkin · Jan 25, 2011

NO and that is why you really should run a CRV.

kennyd · Jan 25, 2011

lwalsh said:
I think I know the answer but I want to verify. Am I correct in saying that a loader valve will not bypass from excessive load applied to the cylinder? I hit an immovable object with my 2720 front plow. Outside corner of the plow caught the frozen ground while going slow. The plow was in the straight position and instead of stopping the tractor it swung the plow about 15 degrees and blasted the underside of the tractor with hydraulic fluid from the banjo fitting on the output side of the valve. No apparent damage and the bolts are at 40 ft/lb per spec. I should mention it is a home built plow setup and the swing cylinder doesn't have much of a mechanical advantage. It's a single cylinder only about 6" offset from the pivot pin. Did I just get lucky?

No, the regular PRV (pressure relief valve) is not "in the circuit" when the valve is in nuetral. Both work ports are blocked so the fluid (and pressure) have no place to go but will find the weakest link-in your case the banjo. Lucky? Yes you sure are! Usually it's a blown hose, bent frame or a bent cylinder.

Snowplows have CRV's (crossover relief valves), AKA "cushion valves" for this very reason. They let the fluid "crossover" to the other cylinder (if used in a two SA cylinder setup typically found on plows) or to the other side of the cylinder for single DA cylinder setups like yours. They are also good to have on thumbs circuits on backhoes.

Here is a good one to get: Surplus Center - 1/2 NPT 30 GPM 1500-3000 PSI HYD CUSHION VALVE