Safe De-Energization. Solving Dangerous Hydraulic Energy Misconceptions.
Misconception: There Is No Energy in the System When the Pump is Shut Off.
A hydraulic system can inherently store energy, even with the pump shut off. A hydraulic system can store energy in up to three zones depending on the design.
Misconception: Stored Energy Immediately Dissapates When the Pump is Shut Off.
Many systems lack components, system designs or configurations to allow pressure to immediately dissipate when the pump is shut off. Without the proper design it is impossible to visually detect stored energy.
Misconception: The System Will Bleed Off When You Activate a Manual Directional Control Valve with the Pump Shut Off.
Certain types of valves, e.g., counterbalance or pilot-operated check valves, will not function unless the pump is operating. Additionally, many manual directional control valves are pilot-operated, meaning they do not operate without pilot pressure, which is only present when the pump is operating.
Misconception: Activating the Override Pushpin on a Solenoid-Operated Directional Control Valve with the Hydraulic Pump Shut Off will De-Energize a System.
While override pushpins are provided to mechanically override a solenoid-operated directional control valve, they present the same problems as manual, pilot-operated valves if the system is equipped with counterbalance valves or pilot-operated check vales. Larger solenoid-operated valves are pilot-operated, consequently, the spools do not shift when the pump is shut off because pilot pressure is generally only present when the pump is running.
Misconception: Hydraulic Systems Equipped with Accumulators Autmatically De-Energize When the Pump is Shut Off.
Many hydraulic systems are equipped with accumulators for the specific purpose of providing energy in the event of an unexpected power failure. These systems generally have to manually de-energized. There are some hydraulic systems equipped with automatic accumulator de-energiztion devices, however, there is generally no way to verify the energy is depleted.
Misconception: Sound is a Reliable Means of Verifying When an Accumulator is De-Energized.
Oil discharging from an accumulator makes a distinct sound, which ceases when the accumulator is discharged. However, an accident can easily happen when someone hears an accumulator de-energize and then leaves the area. Another technician has no way to verify the system is de-energized.
Misconception: "Cracking" a Connector and Cycling the Cylinder is a Safe and Reliable Method to Air-Bleed a Hydraulic Cylinder.
Air-bleeding to the atmosphere creates a variety of hazardous situations. For eample, exhausting high-pressure oil can cause severe injury or death if oil penetrates the skin. Discharged oil creates an extreme fire-hazard, especially if the oil is near an ignition source. Many connector designers are not conducive to careful cracking. Spilled hydraulic oil has severe environmental implications, with tens of thousands of gallons of oil air-bled out of hydraulic systems annually.