Engineering Essentials: Types of Speed-Control Circuits

Meter-out circuit

Regulating flow from the cylinder is another way to control speed. This circuit maintains a constant backpressure during rod extension and prevents lunging if the load drops quickly or reverses.

Bleed-off circuit

Flow to the cylinder is regulated by metering part of the pump flow to tank. This circuit is more efficient than meter-in or meter-out, as pump output is only high enough to overcome resistance. However, it does not compensate for pump slip.

Variable-volume pump

Pump flow can be controlled by various means such as manual, electric motor, hydraulic, or mechanical. How closely flow output actually matches command depends, in part, on slip, which increases with load. With a pressure-compensated, variable-volume pump, output flow decreases with the increasing pressure. This type of pump can be used for traverse and clamp operations. An external relief valve is usually unnecessary when a pressure-compensated pump is used. For details on the different types of pumps, their operation, and how they vary flow, refer to the pumps section of this Handbook.