Excavator Loses Hydraulic Power When Hot - What's Wrong?

Hydraulic power is the backbone of all excavator operations. It provides the power that is needed to perform most of the primary functions such as moving the boom, lifting loads, dipping, moving bucket cylinders, or moving the excavator back and forth. Excavators are not limited to earth excavation works only but are also useful in lifting/loading works such as laying pipes, building materials, and off-loading trucks.

However, at times, the excavator may lose hydraulic power due to various faults in the complex hydraulic system. This article will explain why the excavator loses power when the hydraulics becomes hot.

Hydraulic Power

Hydraulic power in excavators (and indeed all other machines that use it) is also referred to as fluid power. It uses pressurized fluid which is controlled and circulated through the excavator's hydraulic systems to perform the various operations. The fluid used in most hydraulic systems is water-soluble oil or a mixture of water and glycol. The fluid must not be susceptible to the effects of heat within the hydraulic systems.

The hydraulic power is generated in the excavator by a hydraulic pump. The pump is a group of various components that work together to enable a smooth flow of energy and power using hydraulic fluid. The excavator hydraulic pump consists of:

• Motor
• Pump
• Sump
• Actuators
• Valves
• Hydraulic fluid

The pump uses these components to configure hundreds of power applications and transfers them to specific units in a simplified and exceptionally reliable manner that reduces mechanical complexities involved in excavator load applications.

This pump converts the fluid pressure into mechanical power that is capable of driving the excavator output and load units. The pump acts as the source unit and pumps the energy to the output devices of the excavator that perform different functions.

As such, the pump directs the mechanical power to specific units such as lifts, motors, and buckets where it is required. The hydraulic system works like an electric power grid system that transmits power from the station (hydraulic pump) to the consumers (lifts, buckets, and motors).

The hydraulic power from the hydraulic pump performs power transmissions, fluid, and mechanical operations, and also controls some electrical systems. In other words, the hydraulic system of the excavator is the power behind the exceptional reliability of this monster.

Hydraulics Power Loss

If the hydraulic system is properly maintained, it is reliable and durable. However, the system can develop problems that lead to loss of power or complete failure in various operations of the excavator. One of the major issues affecting hydraulic systems is overheating.

Heating or overheating in the hydraulic system is brought about by inefficiencies in the entire hydraulics system. When inefficiencies occur in the system, it leads to the generation of heat and loss of power.

If you discover that your hydraulic system is running very slowly or has a total failure, then it means it has an overheating problem. Overheating occurs when the power input is not utilized efficiently by the hydraulic system to provide mechanical output functions. Thus, the unused power is lost as heat. If this heat lingers within the system, it leads to loss of mechanical power and the excavator is unable to discharge its functions as expected.

Heat generation is normal in the pressurized fluid within the hydraulic system. However, the system is designed in a way that effectively deals with the heat load produced. The heat load in the hydraulic system is always equal to the total power loss through various causes. To deal with the heat, the hydraulic system dissipates the heat load throughout its system.

If the power lost due to heat is more than the amount of heat dissipated by the system, overheating occurs. In other words, the system's efficiency in dissipating heat determines the amount of heating and power loss.

Most hydraulic systems, including the ones in the excavators, dissipate heat through hydraulic oil reservoirs. The excavator has a large hydraulic oil reservoir and a long flow path to increase the fluid surface area for natural heat dissipation.

Hydraulic Fluid Temperature and Stability

The hydraulic system must maintain a stable fluid temperature for effective hydraulic functionality. The system must therefore continually dissipate heat beyond the system's heat load. Optimally, the hydraulic fluid temperature should never rise above 820C (1800F) while the heat load dissipation should not rise beyond the fluid's installed cooling capacity. Any pressure or heat load that exceeds these parameters will lead to hydraulic system overheating.

Normally, the installed cooling capacity within the hydraulic system is between 25%-50% of the input power of the hydraulic system.

If the hydraulic system runs slowly after the fluid warms up, it is a clear indicator that there is a serious flaw in the fluid flow process that is leading to a loss of input power. Overheating can be a result of various issues within the entire hydraulic system. The most common causes of hydraulic fluid overheating include:

1) High Fluid Temperature

High fluid temperatures are caused by issues that compromise the capacity to dissipate heat or those that lead to an increase in heat. When fluid temperature rises, various components within the hydraulic system become hot making the whole system to overheat. The fluid as well as the pump becomes too hot to run normally.

• Hot Hydraulic Pump- when the pump becomes too hot it may fail, leading to serious damage to the entire hydraulic system. A failed pump may send debris and other contaminants into the system leading to its total failure.
• Hot Fluid- when the fluid becomes too hot, it becomes thin and loses its viscosity. This prevents the fluid from lubricating the system properly, leading to the generation of more heat. At the same time, some fluids may oxidize and become too thick, a situation that restricts their flow, leading to more heat.
• High fluid temperatures lead to damage to seals and other critical components in the system. When the seals become damaged, they lead to fluid leakage and aeration which reduce the power output of the system. Moreover, these leakages increase the heat within the system and cause more failures.

2) Air Contamination/Cavitation

Leakages in the hydraulic system valves lead to some air entering into the fluid system. This leads to the formation of air bubbles which contaminate the hydraulic fluid. The aeration results in a process of compression and decompression of the air bubbles which produce a series of knocking noises in the system.

At the same time, the air in the hydraulic fluid causes wearing as the air bubbles implode due to the massive pressure. The air implosion of the air bubbles increases temperature leading to wear and damage to various components which then contaminate the fluid with debris. Moreover, the air causes erratic movements of the actuator lever in the system. These issues lead to a loss of hydraulic power in the excavator.

3) Reduced Pressure in the System

Internal leakages (in valves, cylinders, or pistons) in the hydraulic system reduce the fluid pressure in the system. When the fluid is compressed to release mechanical power, the compression is lost through the leakages. As such, heat is generated as the fluid passes through the system and loses pressure without doing any work. This raises the heat load in the system, leading to further loss of the excavator's operating power.

4) Contaminated Fluid

When the hydraulic fluid becomes contaminated with dirt, particles, and debris from worn components the filters become clogged. The hydraulic pump is forced to work overtime to force the fluid through blocked pathways, leading to overheating.

5) Faulty Heat Exchanger

The heat exchanger acts as the medium for heat dissipation. When it becomes faulty, blocked, or damaged, it reduces the cooling capacity of the entire system, leading to overheating.

6) Water Contamination

If water contaminates the hydraulic fluid, it causes corrosion on different components within the system. Water corrosion comes from condensation build-up within the walls of various fluid pipes and the reservoir. Contaminated fluid has a milky appearance and leads to corrosion in different components, thus compromising the hydraulic system.

7) Low Reservoir Fluid

The fluid reservoir acts as the heat absorber and is part of the hydraulic cooling system. The hydraulic reservoir has a large capacity to allow the heat to dissipate naturally and cool the system. If the fluid volume is very low, it can only dissipate very little heat, leading to an overheating in the system.

Preventing and Reducing Overheating

Overheating in the hydraulic system can be addressed by simply decreasing the system heat load or increasing the heat dissipation capacity.

To decrease the heat load and avoid overheating in your hydraulic system:

• Inspect and ascertain all components (pumps, actuators, pistons, valves, filters, seals, and others) are in good working condition.
• Identify any leaks and have them sealed or the faulty parts replaced.
• Check for all worn-out or aged parts and have them repaired or replaced.
• Ensure regular and thorough maintenance routine.

To increase heat dissipation:

• Check reservoir fluid and have it topped up to the required level at all times.
• Clean the system to clear any obstructing matter that may be in the system pipes.
• If the fluid is very thin or contaminated, remove the contaminants or replace the fluid altogether.

Moreover, ensure that all the critical components of the system are in optimum working condition to avoid overheating and loss of hydraulic power:

• Power unit,
• Filler breather,
• Relief valves,
• Suction strainer,
• Hydraulic fluid reservoir,
• Hydraulic cylinder, and,
• Control valves

Always remember to diagnose and repair any overheating problem as soon as it appears to avoid damaging your excavator's hydraulic system beyond repair.