|An increasing number of today's liftgates are equipped with power-down pump systems instead of gravity-down pumps. Power-down pump units have grown in popularity because they provide more consistent lowering speeds, regardless of the weight of the liftgate platform or weather conditions.
Power-down pumps use hydraulic force to both raise and lower the liftgate. By contrast, gravity-down pumps use hydraulic force only to raise the liftgate platform, relying on the weight of the liftgate and an electronically activated valve to lower the platform. This may result in less consistent speeds, when compared with the use of hydraulic force.
A power-down hydraulic system works in a closed-loop fashion. The piston inside the cylinder forces the exchange of hydraulic fluid from one side of the piston to the other, through the pump reservoir. With power to the pump, fluid is forced from one side of the piston into the reservoir then is pumped out of the reservoir to the other side of the piston with no overflow. If power to the pump is interrupted and the operator activates the lowering function, then fluid is forced from one side of the piston back into the reservoir.
However, due to lack of power, the fluid is not able to be pumped back to the other side of the cylinder, causing excess fluid to collect in the reservoir. Once the reservoir capacity is reached, excess fluid overflows through the reservoir breather cap. The following questions and answers may help you understand when and why this occurs.
Q: Why does my power-down pump occasionally experience fluid overflow during the lowering phase?
A: You may be experiencing a power loss to the pump motor. During a power loss, the pump unit cannot pump the fluid from
Q: Why not just make a larger pump reservoir?
A: There are two reasons. One, space constraints do not allow for a larger pump reservoir. Two, we have found that most customers fill their reservoir to the top. If we made the reservoir larger, and then people filled it to the top, it would overflow when the pump is operated because there would be nowhere for excess fluid to go.
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