Often times hydraulic components can begin to act differently or unpredictably when the conditions of the hydraulic system change from the expected. In some cases, when hydraulic flow is either lower or higher than anticipated, the valves will not perform as they were designed. Cartridge valves are no exception and can sometimes be even more sensitive to altered flow rates when compared to many other hydraulic components, specifically when it comes to high flow rates due to the nature their compact design.
Applying the science
The reason why high flows can affect valves can be attributed to simple physics. The higher the flow rate, the greater the forces the hydraulic oil has on the internal components of the valve. This phenomenon is simply known as flow forces. When you think of a firefighter's hose or garden hose without water flowing through it, it is very flexible and easy to move, however, when water is flowing through at the full rate, the hose naturally begins to straighten out and becomes more difficult to maneuver. This is due to the flow forces from the water acting upon the internal sidewalls of the hose. Similarly, the hydraulic oil inside the valve will act upon all the different surfaces of the spool, sleeves, poppets, and other components with forces that are proportional to the surface area of those components that encounter the hydraulic oil flow.
What begins to happen in these circumstances is because of the high flow rates, or flow rates that the valve is not designed or tested for, the valve can either become stuck in its current position unable to be shifted, or the opposite will occur where the valve unexpectedly shifts without the intention to. For this reason, it is imperative that hydraulic system designers and operators follow the manufacturer's recommendation for valve flow ratings. The combination of hydraulic oil flow and pressure strikes a critical balance for valve performance and must be adhered to achieve proper functionality.
Image 1: Casoli, P., Vacca, A., Franzoni, G., 2003, A numerical model for simulation of “load sensing” spool valves, The 18th International Conference on Hydraulics and Pneumatics, Prague, Czech Republic, September 30 – October 1, 2003
Parker Hydraulic Cartridge System Division’s valve collection is ideal for consumers due to the wide selection of cartridge style valves with a wide range of flow and pressure capabilities. Additionally, HCS’s cartridge technology features low-pressure drops, which correlates with lower internal flow forces, making Parker’s cartridge technology easier to work with, perform more predictably and reliably, and able to use in a wider variety of hydraulic system applications.
For more information on Parker's cartridge valves, contact us.
Article contributed by Stephen Brunton, product manager, Hydraulic Cartridge Systems Division.