Hydraulic Graetz Circuit

In hydraulics, the Graetz circuit is a type of bridge circuit. It is a combination of various control and regulating elements. The Graetz circuit is used with double-acting linear or radial motors.

Properties of the Graetz Circuit

The movement speed of hydraulic radial or linear motors depends on the applied volume flow in the hydraulic lines. As long as the movement speed is irrelevant, simple directional valves are sufficient to trigger the desired movement. However, if the speed needs to be controllable in both directions and remain identical in each direction after adjustment, the Graetz circuit is a cost-effective, simple, and reliable solution.

The Specific Advantages of a Graetz Circuit

The Graetz circuit makes it possible to precisely synchronize both travel paths of a double-acting cylinder. It can achieve the same for the rotational speed of hydraulic radial motors. It is a simple and self-monitoring circuit used to establish a constant speed in double-acting hydraulic motors.

This is particularly advantageous when the rotational or travel speeds need to be varied by means of a throttle valve.

Design of the Graetz Circuit

The Graetz circuit consists of the following components:

• 4x check valves
• 1x throttle valve
• Shut-off valve
• Directional valve
• Additional back-pressure valve

The check valves ensure that the volume flow only moves in one direction. The hydraulic medium is guided through the check valves and then through the centrally located throttle valve. From there, it flows onward to the motor. The pressurized side pushes the piston in the desired direction. The opposite side is depressurized, forcing the hydraulic medium located there back into the tank.

When the directional valve is actuated, the flow direction is reversed. Readjustment of the throttle valve is not necessary. The speed of the extending cylinder remains exactly the same and corresponds to the speed during retraction.

The Advantages of the Graetz Circuit

The Graetz circuit offers the following advantages:

• Change of working direction without switching the hydraulic pump
• Cost-effective arrangement
• Self-regulating properties

In simple hydraulic systems, reversing a volume flow requires switching the hydraulic pump. To do this, the pump must be connected to a switching gearbox or the electric motor must run in reverse. The directional valve in the Graetz circuit avoids this. The volume flow is switched while the pump direction remains the same.

Since both flow directions are controlled with the same throttle valve, the arrangement is very cost-effective, simple in design, and space-saving. Additional control or regulating components are not required.

Areas of Application for the Graetz Circuit

The Graetz circuit is useful where high precision is required alongside hydraulic power. Typical examples include the operation of hydraulic gate and lifting systems, heavy construction equipment, or precision presses.

Furthermore, mechanical converters can be attached to the hydraulic motors on both sides. This makes it possible to operate a machine with double the performance using a single central power source. This reduces costs and saves space.