What You Need to Know About Truck Hydraulic Systems

How Do Truck Hydraulic Systems Work?

At their core, hydraulic systems operate on Pascal’s Law, which states that when pressure is applied to a confined fluid, the pressure is distributed evenly throughout the system. In simpler terms, small amounts of force can be multiplied to lift or move heavy loads.

In semi-trucks and heavy-duty vehicles, hydraulic systems are typically used for:

• Hydraulic Brakes – Air-assisted hydraulics apply brake pressure.
• Power Steering – Uses hydraulic fluid to ease steering effort.
• Liftgates & Dump Beds – Hydraulic cylinders raise and lower heavy equipment.
• Towing & Recovery Equipment – Hydraulic winches and booms assist in lifting vehicles.

Key Components of a Truck Hydraulic System

A well-functioning hydraulic system consists of several crucial components:

1. Hydraulic Pump

The pump is the heart of the system, converting mechanical energy into hydraulic pressure. Common types include:

• Gear Pumps – Simple, durable, and cost-effective.
• Piston Pumps – High efficiency and pressure capacity.
• Vane Pumps – Smooth operation but more sensitive to contamination.

2. Hydraulic Fluid

Hydraulic oil is the medium that transfers power throughout the system. It must have:

• High viscosity index for consistent performance.
• Anti-wear properties to protect components.
• Thermal stability to resist overheating.

3. Hydraulic Cylinders

Cylinders convert fluid pressure into linear force. They are essential for dump trailers, tow trucks, and heavy lifting applications. Hydraulic cylinders come in various types, including single-acting and double-acting cylinders, each designed for specific applications and load capacities.

4. Control Valves

Valves regulate the direction, pressure, and flow of hydraulic fluid. These include:

• Directional Control Valves – Direct fluid flow to different actuators.
• Pressure Relief Valves – Prevent system overpressure.
• Flow Control Valves – Adjust hydraulic fluid speed.

5. Reservoir (Hydraulic Tank)

The hydraulic reservoir stores fluid, allows for heat dissipation, and prevents contamination. Proper venting and filtration keep the system running efficiently.

6. Hoses & Fittings

High-pressure hoses transport hydraulic fluid between components. They must be rated for pressure and resistant to leaks or abrasions. Properly routed and securely fastened hoses prevent excessive wear, kinking, and potential failure under high-pressure conditions.

Common Hydraulic System Issues & Troubleshooting

Hydraulic systems can be highly efficient, but malfunctions can cause severe downtime. Here are common problems and their causes:

1. Slow or Weak Operation

• Low hydraulic fluid levels – Check for leaks and refill as needed.
• Air contamination – Air bubbles reduce efficiency. Bleed the system.
• Pump failure – Worn-out pumps reduce pressure output.

2. Overheating

• Clogged hydraulic filters – Restricted flow causes excessive heat.
• Low-quality hydraulic oil – Ensure proper viscosity and additives.
• Excessive system pressure – Adjust relief valves to recommended levels.

3. Leaking Hydraulic Fluid

• Worn-out seals and gaskets – Replace aging components.
• Cracked hoses or fittings – Inspect for wear and replace immediately.
• Over-pressurization – Keep pressure within manufacturer specifications.

4. Noisy System (Whining or Chattering Sounds)

• Cavitation (air pockets in the fluid) – Check fluid levels and remove restrictions.
• Pump or motor wear – Replace damaged components.
• Loose fittings – Tighten or replace leaking connectors.

Proper Maintenance for Truck Hydraulic Systems

Regular preventive maintenance extends the life of your hydraulic system and prevents costly breakdowns. Here’s what you should do:

• Check Hydraulic Fluid Levels Daily: Low fluid levels cause cavitation and reduce system efficiency. Top off with the recommended hydraulic oil.
• Inspect Hoses & Fittings for Leaks: Leaks reduce pressure, leading to poor performance. Look for cracks, swelling, or loose connections.
• Change Hydraulic Filters Regularly: Clogged filters reduce flow and increase system pressure, leading to overheating and wear.
• Monitor System Pressure & Temperature: Keep the system within manufacturer-specified limits to prevent overloading components.
• Flush & Replace Hydraulic Fluid: Over time, hydraulic oil degrades and becomes contaminated with moisture, dirt, and metal particles. Follow the manufacturer’s recommended service intervals.

Choosing the Right Hydraulic Fluid for Your Truck

Not all hydraulic fluids are the same. Selecting the right one for your application is crucial. Consider:

• Operating Temperature – Cold climates need low-temperature hydraulic oil.
• Load Capacity – High-pressure systems require high-viscosity fluids.
• OEM Recommendations – Always follow manufacturer guidelines.

Popular Hydraulic Fluids Used in Heavy-Duty Trucks

• AW (Anti-Wear) Hydraulic Oil – Best for most general applications.
• Synthetic Hydraulic Fluid – Higher performance and longevity.
• Biodegradable Hydraulic Oil – Eco-friendly alternative.

Keep Your Hydraulic System Strong

Truck hydraulic systems are critical for powerful, precise, and efficient operation. Keeping fluid levels in check, performing routine inspections, and addressing issues promptly will help avoid expensive repairs and downtime.

If you're in Joplin, MO, and need hydraulic system service or repairs, Ol' Truck Repair has got you covered!