Hydraulic Power Pack Considerations

Hydraulic Power Packs are the very heart of your Hydraulic Circuit, they need to be designed correctly.

What is the function of a hydraulic power pack?

The function of Hydraulic power pack is to convert a primary drive source (typically an electric motor or diesel engine) into a hydraulic flow which in turns moves a hydraulic cylinder, motor or actuator

Who was the original genius behind hydraulic power packs?

Laissez Pascal.  During the mid-seventeenth century, Laissez Pascal’s observed that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container

What are the main components required for a Power Pack?

From a very basic power pack through to the more complex units, they all require a primary mover (motor or engine), Hydraulic Pump, Oil reservoir, A pump inlet filter (Strainer) & Pump outlet Filter (Pressure line)

Hydraulic power packs come in many different shapes and sizes; from very large (and generally stationary) industrial units through too much smaller and compact packs designed for mobile applications.  To ensure your power pack provides consistent and reliable performance, we first need to understand the application in which it will be used.

The following elements will all have an influence on the final power pack design: Operating Environment (ambient temperature) The number of cycles performed by the actuator/motor, pressure and flow requirements and finally, availability of a suitable power source for the primary driver (Electrical Motor or Engine)

The key elements for the Hydraulic Power Pack are described below.

Oil Reservoir

The hydraulic fluid reservoir holds excess hydraulic fluid to accommodate volume changes from: cylinder extension and contraction, temperature driven expansion and contraction, and leaks. The reservoir is also designed to aid in separation of air from the fluid and also work as a heat accumulator to cover losses in the system when peak power is used.

Design engineers are always pressured to reduce the size of hydraulic reservoirs, while equipment operators always appreciate larger reservoirs. Reservoirs can also help separate dirt and other particulate from the oil, as the particulate will generally settle to the bottom of the tank. Some designs include dynamic flow channels on the fluids return path that allow for a smaller reservoir.

Primary Driver

The primary driver is the component that will drive the hydraulic pump and in turn, develop a flow of hydraulic oil.  Choice of primary driver will be dictated by the application in which the Hydraulic Power Pack is to be used.   For mobile applications typically we utilise the combustion engine output due to a lack of available electrical power.  Industrial power pack applications generally utilise electrical motors as their primary drivers.  Electric motors provide instant torque, smooth running and quiet operation.

All primary drivers have to be sized specifically for the particular power pack application; it will be their job to provide sufficient horsepower to drive a hydraulic pump capable of delivering the required flow and pressure for the hydraulic circuit.

To calculate the size of the primary mover (typically an electric motor or engine), we must first establish the size of the hydraulic pump to give the required flow for the system.  Once we have sized the pump, we then know the power required to drive the pump and specify the correct size motor or engine.

Hydraulic Pump

The choice of Hydraulic Pump will depend on various factors including, pressure, flow and duration of cycle.  A simple fixed displacement gear pump can be utilised for applications that require a constant flow and pressure (driving a hydraulic motor at a fixed speed for example)

Pressure compensated pumps provide a greater level of efficiency by providing pressure only when required.  These pumps are generally more expensive but will give improved performance.  Using a variable-displacement, pressure-compensated pump rather than a fixed-displacement pump reduces circuit horsepower requirements dramatically.

When calculating the power input to the pump, the total pump efficiency must be included. This efficiency is the product of volumetric efficiency. The average for axial piston pumps = 0.87. The formula shown on our fluid power formula page allows for an efficiency of 80%

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Filtration Requirements

Filter efficiency is the most important but not the only factor involved when evaluating the filter design. A filter can be ineffective if it is installed in the wrong place and if it is given the wrong job.

When creating a filtration concept, some fundamental rules play a crucial role. For example, the hydraulic filter is always to reduce wear which means it should filter to a finer level than the critical tolerances. Filters should be used with the highest possible flow rate.

Suitable seals on cylinders and on breather filters should prevent contamination from entering the system etc. Therefore we can distinguish between protective filters and working filters.