Cat^® Backhoe Loader: Hydraulic Flow Switch

Before we get into one-way and two-way hydraulic flow and how it connects with your Cat backhoe loader’s hydraulics, let’s take a quick look at history.

Hydraulics as a concept has been around for thousands of years, beginning with moving water around to irrigate crops to building aqueducts and powering mills. It wasn’t until the 19th century that it was put to use in the very first steam-powered excavator—though it used chains, ropes and a team of operators to actuate the bucket instead of pure hydraulics. At the end of the century, the first all-hydraulic excavator from Kilgore Machine Company of America was built. This advanced version needed only one operator. In 1951, the first mass-produced hydraulic excavator patent was given to Mario and Carlo Bruneri of Italy.

When you think about it, thousands of years of research and development are contained in the precise, power-dense hydraulic system of your Cat backhoe loader—from crop irrigation in Mesopotamia to apartment building in a bustling city. The tools you use now might’ve been unimaginable a century ago, but they’re keeping the lineage of building a better world alive.

The basic idea behind hydraulics is when you apply force to a fluid at one point, that force is transmitted through the fluid to another point. Nowadays, hydraulics are found everywhere—from raising or lowering the seat of an office chair to airplanes and elevators.

In the case of your backhoe loader, an incompressible fluid is pumped through various hoses, valves and cylinders to move pistons that transmit the force through rods to actuate the boom, stick, loader and your chosen attachments. Because an incompressible fluid like oil is used, very little force is lost.

Your backhoe loader’s hydraulics also capitalize on a concept called hydraulic multiplication. When a one-inch-diameter piston presses on hydraulic fluid that moves a three-inch-diameter piston, that force is multiplied by a factor of nine. This is because the area of the second piston is nine times that of the first. The trade-off is that the first piston must move nine inches for the second to move just one inch.

Let’s say your Cat backhoe loader’s hydraulic pump runs at 3,300 pounds per square inch (PSI), and the pistons in its arm have a diameter of five inches. That means each cylinder can produce close to 65,000 pounds of force.

Your Cat backhoe loader harnesses its hydraulics to power different attachments. If it comes equipped with auxiliary hydraulics lines (also called combo lines), the flow direction can be selected for one-way or two-way flow.

Adjustable flow direction allows you to unleash your backhoe loader’s greatest strength: versatility. With a single machine and multiple attachments, you can go from breaking concrete with a hydraulic hammer (one-way flow) to picking up those broken pieces using your hydraulic thumb attachment and bucket (two-way flow).

A handle located in the rear of your backhoe loader allows you to switch between flow directions. When the handle is rotated to point towards the ground, you’re ready to run work tools that require two-way flow. If you rotate the handle clockwise so it’s parallel with the ground, you can now operate work tools that require one-way flow.

The flow direction you choose depends entirely on your attachment.

One-way flow work tools generally deliver high-pressure impacts. This includes attachments like the Cat B9 Hammer and Cat CVP16 Vibrator Plate Compactor.

Two-way flow work tools need to be able to actuate precisely in multiple directions. This is necessary for attachments like the Cat A68 Pin Lock Auger or a Cat Pro Series Hydraulic Thumb.

Beyond adjusting the hydraulic flow direction for attachments, you can also adjust the flow rate to match specifications or jobsite needs. Depending on your model, this can be done using the operator screen located inside the cab.

It’s important to point out that safety is paramount when dealing with hydraulics. Using the wrong flow direction for the attachment, or incorrect flow rate and pressure, can damage your Cat backhoe loader’s hydraulic system and attachment. Damaged equipment can lead to bodily injury.

Along with proper operation, regular maintenance of your backhoe loader’s complex hydraulic system helps reduce downtime and overall ownership costs. Compared to repair costs, maintenance costs are a drop in the hydraulic fluid reservoir. 

Your Operation and Maintenance Manual (OMM) lists filter schedules, oil specs, fluid intervals and average temps. You should also visually inspect your backhoe loader’s rods, seals and lines for signs of damage daily. Look for scratches or hydraulic fluid on the rods, ballooning of the hydraulic lines and leaking or corrosion of couplers and fittings.

So, be sure you consult your OMM to determine the optimal settings for your machine and attachments and your machine’s recommended maintenance routine. If you have additional questions, your Cat dealer will be happy to assist.