A common place integrated hydraulic circuits can be found are on mobile applications in the construction, forestry and material handling markets. To meet the essential feature of load controls in these applications, a counterbalance valve is often used.
The basic function of a counterbalance valve is to control a load, by providing a restriction through a differential area. They also help prevent cavitation when controlling an overrunning load. Load control is achieved when enough pressure is present at the work port of the valve to overcome the spring setting. Specifically, when an actuator is pressurized, pressure is developed at the work port. This pressure builds and acts on the differential area until it overcomes the spring setting, shifting the poppet and allowing fluid to pass through to tank.
In addition, there is also a pilot signal (usually the opposite side of the actuator) that connects to the counterbalance valve. This signal enables the valve to shift with much less load pressure. If the load attempts to “run away” (when it moves faster than the pumps can supply flow), the pilot signal is diminished, resulting in the piston to restrict flow to tank thus controlling the load.
An added feature of a counterbalance valve is a built-in thermal relief. Because oil expands as its temperature rises, actuators can have unintended movement in load holding applications. The built-in thermal relief will allow drops of oil to pass when work port pressures reach the spring setting eliminating unintended movement in load holding applications.
There are many factors to consider in selecting the right counterbalance valve for a specific application. From flow selection, vented or non-vented, to adjustment types and setting selections, there is a lot to consider. However, the pilot ratio is one of the most important features when selecting a counterbalance valve.
Defined, a pilot ratio is the ratio of pilot area to differential area. This means the higher the ratio, the less amount of pressure needed to assist the valve and unseat the poppet. However, a caveat for selecting a higher pilot ratio is less restriction, less control, and less horsepower required.
The decision of pilot ratio is highly dependent on application. For example, the most popular counterbalance valve ratio is 3:1, often used in position-critical applications such as pick and place applications, where control is essential. On the flipside, a 10:1 ratio is common amongst high speed and motor control applications where positioning is not critical, and required horsepower is reduced. At the end of the day, it is important to remember the following:
Other functions a counterbalance valve performs include holding a load, protecting against hose failures, and offering control in critical metering applications. However, it is important to note that counterbalance valves are only needed if the application has varying loads or speeds. If they are fixed, Parker Hydraulic Cartridge System Division’s flow control valves and pilot operated check valves should be used.For example, using a counterbalance valve on outriggers may result in tipping mobile equipment over. When this happens, back pressure developed assisting the counterbalance valve through the pilot signal, causing the cylinders on the equipment to give out.
As one might realize, picking the right features for a counterbalance valve might seem harder than expected. With Parker’s Hydraulic Cartridge Systems Division’s Application Engineers, finding the right products for a specific application is easy. For more information on Parker’s cartridge valves, and how to select the right counter balance valve, contact us.
Article contributed by Nate Borries, technical sales associate, Parker Hannifin's Hydraulic Cartridge Systems Division