I have built a grapple for my New Holland L555 and the cylinder is way to strong for the grapple. Breaking welds when full of sticks. So, I have heard of this pressure relief valve but know nothing about them. Which one do I need if at all? How and where do I mount it etc? Or is there one somewhere already on the L555 to adjust? The grapple is running off of factory aux hydraulics.
Pressure relief valve
- Thread starter cole0324
- Start date
PILOON
Super Star Member
Think that a relief valve will need a bypass back to tank.
On the other hand a flow restricter could solve the problem.
A restricter slows things down for more precise control, basically, as name suggests, a restriction in the line.
If your handy, a fitting welded shut with a tiny hole drilled thru the weld will restrict flow.
You could start with 3/32" and drill larger as required.
On the other hand a flow restricter could solve the problem.
A restricter slows things down for more precise control, basically, as name suggests, a restriction in the line.
If your handy, a fitting welded shut with a tiny hole drilled thru the weld will restrict flow.
You could start with 3/32" and drill larger as required.
Stonehaller
Platinum Member
A relief valve will reduce hydraulic pressure and thus, the cylinder force by dumping some of the oil back to tank. Since you are using a factory auxiliary port you may want to look in to a cross port relief. A cross port relief will dump oil from one side of the cylinder to the other side if it exceeds the relief pressure setting. These are often used as torque limiters for hydraulic motors. You could install this valve in the lines that go to the cylinder and not have to run a separate return line back to the transmission.
AKKAMAAN
Veteran Member
A flow restrictor will NOT releif excessive pressure and prevent from mechanical damages!
In my animation here you can see how that relief valve (2500psi), RV, should be plumbed....between control valve and cylinder....it is preferable to have a separate return to tank from the RV...but if you use it for shock protection (external force on the cylinder), it should be Tee'd into the other cylinder line together with a check valve (anti cavitation valve). This to refill oil on the low pressure side.
actionaj
Gold Member
Cool animation AKKAMAAN.
How you do that. I agree a pressure relief valve is what is needed. A restrictor will only slow your actuator speed down. You still will have system pressure.
How you do that. I agree a pressure relief valve is what is needed. A restrictor will only slow your actuator speed down. You still will have system pressure.
glastron23
Silver Member
AKKAMAAN .. your system will work but what if you install a reducing valve then you will not need to replumb to the tank. just install it in the line and let the RV on the tractor handle the relief. this will also prevent the cylinder from drifting down if there is more load placed on the cylinder after the control valve released. this will act as a load lock, with your style if there is more load after then the cylinder will drift. Jim Sun Hydraulics
AKKAMAAN
Veteran Member
Good thinking Jim...but how do we get the retract return oil back to tank if it at the same time prevents from drifting???
glastron23
Silver Member
cross over relief???
AKKAMAAN
Veteran Member
cross over relief valves is basically for shock relief to provide anti cavitation refill to low pressure side and they still need contact with tank on the low pressure side if bi directional actuator is other than 1:1 ratio (motor, double rod cylinder or double cross connected cylinders see pic)
Stonehaller
Platinum Member
A port relief with a make up check or a cross port relief on cross connect cylinders will provide shock protection in that they allow the cylinder to move when the control valve is closed, if the relief pressure is exceeded. On a single cylinder, a cross port relief will limit the force only when the control valve is open. When the control valve is open, high pressure is supplied to one side of the cylinder and the other side of the cylinder is connected to tank through the control valve. A cross port relief would dump oil from the high pressure side to the low pressure side, which is connected to tank through the control valve, if the relief pressure is exceeded. This will limit the force of the cylinder. When the control valve is closed you will have no shock protection but I do not think that is what cole0324 needs. He only wants to limit his grapple force when he is closing it. A cross port relief would also limit the grapples opening force but you should not need much to open it anyway. I figured a cross port relief would be the simplest for cole0324 to install since he would only need the valve and a couple short hoses so he could insert it in the lines to his cylinder and he would not have to figure out how to connect a separate tank line.
Cross-Over Relief Valve - 1/2" Port - Buyers HCR050
Cross-Over Relief Valve - 1/2" Port - Buyers HCR050