To Make it Run Better, Turn the Hydraulic Pressure Up, Right?

I was recently asked to consult with a sawmill that was experiencing leakage, shock and damage to the frame on their lumber stacker. This caused extensive downtime resulting in lost production. The stacker used a 10” diameter cylinder to raise and lower the stack. The hydraulic schematic recommended that the pump compensator be set to 1200 PSI; however someone had turned the valve up to 1800 PSI. When the cylinder fully bottomed out, the pressure rapidly went up to 1800 PSI. A loud bang was then heard, all lines in the system vibrated and the entire stacker frame shook violently. Thinking that the excessive pressure was causing the issue I did a quick calculation of the force developed at 1800 PSI. The number of square inches on the 10" cylinder was found to be 78.54 square inches.

     Force = Pressure X Number of Square Inches on the Full Piston Side of the Cylinder

     Force = 1800 PSI X 78.54 sq. inches

     Force = 141,372 lbs.

I reduced the setting of the compensator to the recommended setting of 1200 PSI. This nearly eliminated the noise and shock when the cylinder bottomed out. With the pressure at 1200 PSI, we can see the amount of force that was reduced on the cylinder:

        Force = 1200 PSI X 78.54 sq. inches

        Force = 94,248 lbs.

The difference in force between 1800 PSI and 1200 PSI is 47,124 lbs. or almost 24 tons! In my 40 years of the hydraulic field, I've never seen anyone turn the pressure down. It's like the knob turner's wrist only works in a clockwise direction! All plant personnel need to be made aware of the negative effects caused by pressures being out of adjustment. In addition to reducing shock and leakage, turning pressures down reduces electrical energy consumption of the electric motor and heat generation in the system.