Whether your products move, turn, shape, mould, lift, dig, or haul, you can depend on Eaton’s hydraulics products to deliver the performance you need to stay competitive. Eaton’s unwavering dedication to leadership in mobile and industrial applications has made Eaton one of the world’s preferred suppliers of hydraulic solutions. Eaton pumps, motors, transmissions, valves, cylinders, controls, hose and fittings offer a unique combination of proven technology and innovative design that translates directly into reliable performance and enhanced uptime. Whether you need a single component, a custom-engineered solution, or anything in between, Eaton is the partner of choice for mobile and industrial applications that simply have to work.
Vickers®, one of the most experienced and respected names in hydraulics, became part of Eaton in 1999. A comprehensive supplier of power and motion control components and systems, Vickers vane and piston pumps, valves, electro-hydraulic controls, cylinders and filtration products are found in industrial, mobile, aerospace, marine and defense applications worldwide. Vickers also pioneered the industry’s first fluid analysis service, a tradition proudly continued by the Eaton Fluid Analysis Laboratory.
At Eaton, we know how important it is to listen. And listening to our customers has shown us that quality; reliability and performance are the standards by which a company's products should be judged. Since 1921, Vickers has gained vast experience in the design and manufacture of hydraulic pumps. This is the heritage passed on to our pumps. Refinement of the basic pumps concept has brought the industry a truly superior series of high performance pumps.
Understanding Transient Response – a hydraulics 101 from Eaton
When a sudden load change causes system pressure to exceed the lowest value of the pump's pressure regulation range, or when a sudden load change occurs while system pressure is in the regulation range,the pump must rapidly adjust the output flow to meet the new load condition. This requires that the yoke be repositioned rapidly. The time elapsed during the pressure change is a measure of the dynamic response of the pump and its associated circuit and load, and depends upon the following factors:
1) The Speed at Which the Yoke Angle is Changed
This is a characteristic of the pump. For example, small yoke cylinder area and high control value gain contribute toward rapid yoke motion for both increasing and decreasing displacements.
2) Pump Driving Speed
Pump speed affects time response because the rate of flow is proportional not only to yoke angle, but also to pump driving speed. When pump speed is high, the output flow will be high and pressure build-up time will be short.
3) The Compliance of the Circuit
Circuit compliance is determined by the volume of oil under compression, the bulk modulus of the oil (varies with temperature and kind of fluid), elasticity of the lines and whether an accumulator is used. Small oil volume, high-bulk modulus, low-expansion lines and absence of an accumulator contribute to fast pump response. A given flow change will result in a rapid pressure change, causing the pump to regulate rapidly.
4) The Nature of the Load
The nature of the load influences how rapidly a change in load resistance or flow-control is reflected in a change in system pressure. Since changes in system pressure cause the pump to regulate, the nature of the load is a factor in the speed of pump response. In general, if the load has a high resonant frequency (low inertia, high spring rate, low damping), response of the pump to changes in load resistance or flow control valve settings will be faster than in the case of a
low-frequency load system.
5) The Use of an Accumulator
Although the use of an accumulator decreases the speed of pump yoke response, the speed of load response is the important factor. With an accumulator in the system, flow will be supplied rapidly to the load when needed, thereby contributing to fast load response. Although the pump yoke repositions more slowly because of the accumulator, the load does not sense the reduced yoke response since the pump's function is temporarily taken over by the accumulator.
Minimum Accumulator
In order to keep the accumulator size at a minimum, the pump response should be as fast as possible. The size of the accumulator determines the time during which it can supply a given flow at a steady pressure. If a pump requires a relatively short time to adjust flow to a new rate, a small accumulator may be used or the accumulator may be eliminated.