Hydraulic Efficiency

01 Jul 2014 CW Staff

Hydraulic Efficiency: Theory
Hydraulic systems convert mechanical energy input from an electric motor or internal combustion engine into a fluid flow and pressure that can accomplish a specified amount of work. Hydraulic pumps convert the mechanical energy of the prime mover into fluid flow. The pressure is generated by the restriction of this flow in the system. Unfortunately, the hydraulic pump cannot be 100 per cent efficient in this energy conversion. A typical hydraulic pump is only 80-90 per cent efficient in this process. The energy is lost in two main forms.

Mechanical losses energy lost to fluid friction
Volumetric losses energy lost as the result of internal fluid leakage (slippage) within the pump.
The amount of mechanical and volumetric loss in a pump is primarily a function of the fluid´s viscosity and lubricity properties. Mechanical losses are the highest when fluid viscosity is high and volumetric losses are the highest when fluid viscosity is low. Hydraulic fluid viscosity is high at low temperatures and decreases as the fluid temperature rises, staying within this optimal operating range is not simple. Specially formulated hydraulic fluids can reduce the magnitude of these losses by utilising a high viscosity index to maintain fluid viscosity in the optimum range across a wide operating temperature range.

Increasing system pressure also reduces hydraulic pump efficiency. Higher pressures generally lead to both increased mechanical losses (there are higher loads on the pump) and increased volumetric losses (higher pressure increase the amount of internal leakage). In addition to the hydraulic efficiency benefits from maintaining hydraulic fluid viscosity in the optimum range, additional efficiency gains can be achieved through selection of optimal base fluids and additive technology to reduce traction û the inherent resistance of the fluid to shear under Elasto Hydrodynamic Lubrication (EHL) conditions.

Theory into Practice
Differences in hydraulic efficiency can be quantified by comparing two fluids in a simple hydraulic circuit.

The circuit contains a hydraulic pump and the system pressure is controlled over a specified range. The mechanical energy input to the system and the flow rate from the pump can then be measured and used to calculate the mechanical and volumetric efficiency of two different fluids.

Hydraulic Efficiency = Productivity Improvements
A prime candidate for demonstrating the impact of hydraulic efficiency on energy consumption and cycle time is an excavator. An excavator employs high pressure hydraulics, driven by a diesel engine, to operate the boom as well as to turn the machine and drive the tracks. Hydraulic system pressures can reach 4,000 psig (275 bar) and temperatures often approach 100¦C.

A demonstration was arranged with a medium sized excavator to compare a typical SAE 10W fluid, commonly used in mobile equipment applications, with a hydraulic fluid specifically designed to optimise hydraulic efficiency. For the purpose of this demonstration, a single operator and batch of fuel was used to operate the excavator through a prescribed set of motions. In this demonstration, application of efficient hydraulic fluid resulted in up to 6 per cent reduction in fuel per cycle and a decrease of up to 5 per cent in time to complete each work cycle. The machine operator also noted that the responsiveness of the system improved immediately upon addition of the test fluid.

The results of this demonstration clearly show the impact of increasing hydraulic efficiency: reduced fuel consumption or increased productivity! Use of this specifically designed hydraulic fluid for a full year in a medium sized excavator would reduce fuel usage by as much as 900 gallons and reduce CO2 emissions by as much as 9 metric tonne. Similar energy savings opportunities exist in industrial hydraulic applications.

Conclusion
Applying knowledge of how hydraulic efficiency can be improved through proper hydraulic fluid selection can help increase the bottom line. Utilising a well-formulated hydraulic fluid can help reduce efficiency losses in hydraulic systems, leading to energy savings and increased productivity.

(Communication by the management of the company)

Hydraulic fluid can help reduce efficiency losses in hydraulic systems, leading to energy savings and increased productivity. Today´s globally competitive business world drives manufacturers to get the most out of their equipment. Even a small increase in machine productivity can lead to a huge difference between profit and loss. Additionally, there is an increasing concern about sustainable business practices and energy efficient systems. In response to this, industrial and mobile equipment hydraulic systems have become smaller and lighter, and utilise higher pressures to achieve maximum system efficiency. Now, advanced hydraulic fluids are available to meet the demands of these systems, as well as to contribute to the overall hydraulic system and energy efficiency. Hydraulic Efficiency: Theory Hydraulic systems convert mechanical energy input from an electric motor or internal combustion engine into a fluid flow and pressure that can accomplish a specified amount of work. Hydraulic pumps convert the mechanical energy of the prime mover into fluid flow. The pressure is generated by the restriction of this flow in the system. Unfortunately, the hydraulic pump cannot be 100 per cent efficient in this energy conversion. A typical hydraulic pump is only 80-90 per cent efficient in this process. The energy is lost in two main forms. Mechanical losses energy lost to fluid friction Volumetric losses energy lost as the result of internal fluid leakage (slippage) within the pump. The amount of mechanical and volumetric loss in a pump is primarily a function of the fluid´s viscosity and lubricity properties. Mechanical losses are the highest when fluid viscosity is high and volumetric losses are the highest when fluid viscosity is low. Hydraulic fluid viscosity is high at low temperatures and decreases as the fluid temperature rises, staying within this optimal operating range is not simple. Specially formulated hydraulic fluids can reduce the magnitude of these losses by utilising a high viscosity index to maintain fluid viscosity in the optimum range across a wide operating temperature range. Increasing system pressure also reduces hydraulic pump efficiency. Higher pressures generally lead to both increased mechanical losses (there are higher loads on the pump) and increased volumetric losses (higher pressure increase the amount of internal leakage). In addition to the hydraulic efficiency benefits from maintaining hydraulic fluid viscosity in the optimum range, additional efficiency gains can be achieved through selection of optimal base fluids and additive technology to reduce traction û the inherent resistance of the fluid to shear under Elasto Hydrodynamic Lubrication (EHL) conditions. Theory into Practice Differences in hydraulic efficiency can be quantified by comparing two fluids in a simple hydraulic circuit. The circuit contains a hydraulic pump and the system pressure is controlled over a specified range. The mechanical energy input to the system and the flow rate from the pump can then be measured and used to calculate the mechanical and volumetric efficiency of two different fluids. Hydraulic Efficiency = Productivity Improvements A prime candidate for demonstrating the impact of hydraulic efficiency on energy consumption and cycle time is an excavator. An excavator employs high pressure hydraulics, driven by a diesel engine, to operate the boom as well as to turn the machine and drive the tracks. Hydraulic system pressures can reach 4,000 psig (275 bar) and temperatures often approach 100¦C. A demonstration was arranged with a medium sized excavator to compare a typical SAE 10W fluid, commonly used in mobile equipment applications, with a hydraulic fluid specifically designed to optimise hydraulic efficiency. For the purpose of this demonstration, a single operator and batch of fuel was used to operate the excavator through a prescribed set of motions. In this demonstration, application of efficient hydraulic fluid resulted in up to 6 per cent reduction in fuel per cycle and a decrease of up to 5 per cent in time to complete each work cycle. The machine operator also noted that the responsiveness of the system improved immediately upon addition of the test fluid. The results of this demonstration clearly show the impact of increasing hydraulic efficiency: reduced fuel consumption or increased productivity! Use of this specifically designed hydraulic fluid for a full year in a medium sized excavator would reduce fuel usage by as much as 900 gallons and reduce CO2 emissions by as much as 9 metric tonne. Similar energy savings opportunities exist in industrial hydraulic applications. Conclusion Applying knowledge of how hydraulic efficiency can be improved through proper hydraulic fluid selection can help increase the bottom line. Utilising a well-formulated hydraulic fluid can help reduce efficiency losses in hydraulic systems, leading to energy savings and increased productivity. (Communication by the management of the company)