Complete Guide to Construction Equipment Hydraulic Systems

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Your earthmoving equipment relies on high-performing, reliable hydraulics technology to give you the power you need to maximize productivity on the job. As an equipment owner, you know that whether it’s an excavator, wheel loader or telehandler, all heavy equipment needs to have a properly functioning and well-maintained hydraulics system.

But how do hydraulics systems work and what is the leading cause of systems failures? How can you prevent hydraulic failures and guarantee maximum, long-term performance? Our guide to construction equipment hydraulics systems covers everything you need to know about operating and maintaining your earthmoving equipment’s hydraulic components. 

How Do Hydraulic Systems Work? 

Hydraulic systems are a type of mechanical design used in equipment manufacturing to provide lift, reach, tilt and other functions the equipment needs. Construction equipment uses hydraulic systems that not only power these essential functions but do so in a way that’s precise, smooth and controlled, increasing efficiency and safety compared to manual, non-hydraulic alternatives.

Hydraulic systems operate based on the principle of fluid pressure flowing through a closed-loop circuit. The machine contains a reservoir of hydraulic oil that gets pumped through a valve and into the cylinder of the hydraulic component it powers. The pressure of the fluid being pumped toward the cylinder forces the component to move, which initiates the lifting or tilting function, in conjunction with other mechanisms, such as hydraulic actuators and electric motors. 

Essentially, hydraulics systems work by using a transfer of force from one point to another through the movement of fluid.

Hydraulics are just one way of delivering power to moving components and many may wonder why heavy equipment relies on hydraulics rather than electricity or pneumatics. The answer is that a hydraulic system is capable of lifting heavier loads at greater force, which is key to understanding hydraulic systems. 

Other power systems use various mechanical components, such as pulleys, gears or electrical circuits to achieve the same amount of power for a particular function. Hydraulics uses fewer moving components, meaning less likelihood of errors, wear and failure. Fluid pressure can power heavier loads at a constant rate of force and torque, which is not possible with other mechanical systems that experience a diminishing rate of power as speed increases.

Why Water Is Not Used in Hydraulic Systems

Heavy equipment owners may wonder why water isn’t a suitable fluid to use in hydraulic systems. There are several reasons why water is not the right type of fluid for hydraulics systems, including:

  • Water is incapable of providing the heat transfer, power generation and lubrication properties that hydraulic oil provides.
  • Water has both low freezing and boiling points, making it risky to operate in extreme temperatures.
  • Water molecules contacting oxygen will lead to rust on metal components.

It’s important for equipment owners to know that even the presence of water in hydraulic oil can damage the hydraulic system components. That’s why you should routinely inspect hydraulic oil to ensure there’s no water accumulating inside the reservoir.

5 Basic Components of a Hydraulic System

Hydraulic systems operate using a few key components, each playing a vital role in supplying and converting power to achieve load handling functions. Below is an overview of the five main hydraulic system components your equipment contains.

1. Reservoir

The reservoir is what holds the hydraulic oil. It’s a protective container that keeps the hydraulic fluid readily available for use by the hydraulic system components. The reservoir itself is sealed and designed to prevent hydraulic fluid from becoming contaminated with foreign materials, dirt and condensation through its filters. 

The reservoir also plays a role in helping to power the hydraulic system by providing a capacity for heat transfer. It allows air to escape through a breather valve before the fluid gets drawn into the pump. Reservoir filters are designed to be replaced regularly, typically when the dirt-holding capacity reaches 80%.

2. Pump

The pump is the component of the hydraulic system that converts mechanical energy into hydraulic energy. It generates power based on its ability to overcome the pressure of the fluid induced by the weight load.

A hydraulic pump contains both an inlet and an outlet. By mechanical or electrical motor, the pump creates a vacuum when its inlet forces the hydraulic liquid from the reservoir into the inlet line, then through the pump and finally out the outlet into the hydraulic system. 

In earthmoving equipment, such as excavator hydraulic systems, the type of pump used is a variable displacement pump. This allows for the rate of fluid pumped at any given revolution of the pump’s shaft to be varied. Variable displacement provides more control over the amount of power needed for load handling.

Depending on the manufacturer’s maintenance intervals, equipment hydraulic pumps can last between 10 and 15 thousand operating hours before replacement or the need for a hydraulic pump rebuild.

3. Valves

Valves play the role of controlling the direction of hydraulic oil flow. They help in starting, stopping or directing the hydraulic fluid based on the amount of power required for handling the load. Valves are categorized based on their function and can be directional control, pressure control or flow control valves. Complex hydraulic systems employ a series of valves to ensure optimal pressure regulating efficiency.

The ability of valves to control the flow of hydraulic fluid is essential in regulating the amount of pressure through the hydraulic lines. Improper valve function can lead to leaking or bursting lines. That’s why you need to ensure that your valves are routinely adjusted whenever your equipment undergoes a fluid change. Doing so can help your valves last the entire life span of the equipment.

4. Actuator

Hydraulic actuators are the moving component of the hydraulic system that activates the lifting. Once it reaches a certain level of pressure, the actuator uses the fluid pressure to convert it into mechanical energy, firing the cylinder that performs the lifting or load handling function. The actuator of a hydraulic system in earthmoving equipment moves linearly, though other actuators can provide rotary or oscillatory motions.

Actuators consist of a cylinder, piston, rod and seal. The seal may need to be replaced eventually, but the main components of the actuator should last if properly maintained. The biggest risk with this component is a hydraulic cylinder leak, which occurs when the seal wears out or the cylinder or rod develops cracks. Depending on the source of the damage, you may need to invest in hydraulic cylinder rod repair or a complete hydraulic cylinder rebuild.

5. Pressure Regulator

A pressure regulator is a control mechanism that regulates how hydraulic fluid pressure is maintained throughout the system. The pressure regulator helps to ensure that the appropriate amount of fluid is released from the reservoir to achieve the desired pressure level. If fluid pressure reaches a certain threshold, the pressure regulator ensures that the excess fluid returns back to the reservoir until the pressure level drops again.

Pressure regulators maintain output pressure values at a certain level to minimize the amount of fluctuation in pressure levels throughout the system. Also known as a relief valve, a pressure regulator in a hydraulic system can be repaired or replaced, depending on the issue. A properly maintained pressure regulator can last the life span of the equipment.

Common Causes of Hydraulic Systems Failures

Hydraulic system failures can range from a repairable degradation failure to a sudden catastrophic failure, depending on the cause. Some of the common causes of hydraulic system failures include:

  • Fluid contamination caused by ingressed dirt and dust particles or air and water molecules.
  • Temperature extremes in the hydraulic fluid causing changes to the viscosity of the fluid that strains the system.
  • Abrasions and tears that cause hydraulic hose leaks.
  • Incorrect amount and quality of hydraulic fluids.
  • Improper maintenance and repairs, such as not using and installing the correct components or failing to replace faulty and worn components in a timely manner.

Of the above causes of hydraulic system failures, fluid contamination is the leading cause. Contaminants, including air and water, enter the system and wear down the pump and other hydraulic system components over time. If not properly filtered out, the contaminants build up and lead to a system failure. Changing the hydraulic fluid filter regularly is a key practice in how to maintain a hydraulic system.

What Are the Main Maintenance Needs of a Hydraulic System? 

Hydraulic systems in earthmoving equipment have specific and regular maintenance needs that all owners should be aware of. From routine cleanings and inspections to fluid testing and changes to parts repairs and replacements, hydraulic system maintenance can be complex and require technical expertise.

Below are the basics of how you maintain a hydraulic system that you can use as a hydraulic system maintenance checklist.

1. Cleaning

Keeping hydraulic system components clean is critical in maintaining high-functioning parts and reducing wear. Clean components are less prone to rust and wear, meaning they’ll be less susceptible to developing cracks and abrasions that lead to premature failure. It’s essential to maintain a consistent cleaning schedule for these components to prevent contamination. 

Hydraulic systems in earthmoving equipment face significant exposure to rugged environments and can accumulate dirt, debris and dust easily throughout the hoses and valves and within the reservoir. Ensure your equipment undergoes a hydraulic hose service to prevent hoses from wearing out due to built-up contaminants. You can also routinely flush and clean your hydraulic fluid reservoir to remove water.

2. Fluid Testing and Changing

Hydraulic fluid is the lifeblood of your equipment, so it’s vital to regularly test your fluid quality and levels as part of ongoing preventive maintenance habits. When maintaining your hydraulic fluid, keep in mind some of the following checklist items:

  • Fluid color: When hydraulic fluid changes from golden to dark brown or black, it could be an indicator of oxidation or thermal stress.
  • Visible signs of contamination: Look for contamination, including dirt and water, and have a technician perform fluid analysis.
  • Odor changes: While operating your equipment, sniff out any potential issues with your hydraulic fluid. Hydraulic fluid fumes have a strong, unpleasant smell.
  • Sufficient fluid levels: Check hydraulic fluid levels daily to ensure they’re regularly topped up. When topping up hydraulic oil, always add the same brand and viscosity grade.
  • Proper fluid storage: Keep your hydraulic fluid stored in clean and sealed containers. Keep containers in an enclosed area with adequate ventilation away from the elements.
  • Fluid handling hygiene: Always clean the fluid cap before adding hydraulic fluid to the reservoir to prevent transferring contaminants.
  • Oil filtration: When adding hydraulic oil to the system, you can filter it through a portable filter to maximize equipment productivity and performance.
  • Filter changes: To get the most out of your hydraulic fluid, you should change and check your fluid filters regularly.

3. Temperature Regulation

One of the biggest risks in hydraulic systems is the development of hot spots that can cause the system to overheat. Hydraulic fluid being pushed through pumps and lines causes it to heat up, which is why it’s important to routinely check the system’s temperature.

Equipment has a built-in thermometer that operators can watch to ensure it doesn’t rise beyond a certain threshold recommended by the manufacturer. However, a total system temperature may not identify particular hot spots. To get a good idea of the risk of temperature fluctuations, use a handheld infrared thermometer to check for localized areas of temperature extremes. Valves and electric drive motors are two main sources of hot spots that can be scanned manually.

4. Systems Inspections

Visual inspections should be part of your daily hydraulic system maintenance checklist. Pre- and post-operation inspections ensure that you catch any issues immediately before they become a catastrophic problem. When conducting your inspections, be sure to review these three key component categories of your hydraulic system:

  1. Rods and cylinders: The rods and cylinders are load-activating components and must be routinely inspected for safety reasons. Ensure that the seals are intact and that there are no signs of wear, corrosion or pitting. Have your equipment undergo a hydraulic cylinder service to repair any issues before they lead to a system failure. 
  2. Hoses and couplings: Hoses and couplings carry the hydraulic fluid and must be reliable. Routinely inspect hydraulic hoses, tubes and fittings for leaks and damage. If you do spot a hydraulic leak, you can use a hydraulic hose repair clamp as a temporary solution to patch up your hose until you’re able to get it repaired or replaced by a professional technician. Observe also whether there are any fluctuations in line pressure and thickness, such as ballooning.
  3. Pumps and motors: Pumps and motors are what keep the hydraulic system operating reliably and consistently. Inspect your pumps and motors by listening for unusual noises that can indicate air bubbles. Air bubbles mean low-pressure flow and may also cause a vibration. If you notice the signs, then be sure to take your equipment to a technician for a hydraulic pump service to fix the issue.

5. Parts Replacements

Follow your manufacturer’s maintenance schedule to ensure that you are replacing parts before they fail. Some of the most common parts that need to be replaced in the hydraulic system in earth moving equipment include:

  • Replace breather caps regularly, as often as once per year, depending on the type.
  • Replace filters as frequently as hydraulic fluid is changed.
  • Another filtration component that needs to be replaced at the same time as filters are filter screens.
  • Replace seals whenever they’re visually worn or if there is a leak.

When replacing parts on your equipment, always ensure you are using your manufacturer’s genuine parts to guarantee the validity of your warranty and ensure you’re protecting your equipment’s longevity. For Cat® earthmoving equipment, always consult a Cat certified technician to ensure that you’re getting genuine Cat hydraulic parts replacements.

Gregory Poole for Cat® Hydraulic Systems Maintenance, Repairs and Parts

Get the best maintenance and repair service for your Cat equipment at Gregory Poole. Our certified technicians have the expertise necessary to properly inspect, diagnose, maintain and repair your Cat hydraulic systems. We also guarantee high-quality parts replacement jobs by providing customers with genuine parts, including Cat hydraulic fittings, hoses and couplings, as well as rods, cylinders, pumps and motors.

Learn more about our hydraulic shop services, including full-service hydraulic repairs on all Cat equipment, as well as pump, cylinder and motor repairs on non-Cat brands. Find one of our 13 Gregory Poole locations across eastern North Carolina.

Contact us today for hydraulic servicing inquiries by filling out a quick online form.