Waste management vehicles perform many different functions. An easy way to understand how such functions operate can be represented by the concept of a hydraulic valve that actuates a cylinder by changing the direction a fluid is traveling. The industry demands each of these functions operate both safely and efficiently. A refuse front loader application has functions that can be grouped into high and low usage. The high usage functions are the arms, forks and packer while the low usage functions are the tailgate, tailgate lock and top door.
In a perfect world, it is desirable to have all these functions consolidated into one valve assembly. However, this can cause a problem where parallel path pressure from the high-usage functions find its way into the work ports of the low-usage functions. When this parallel path pressure from the high-usage functions follow the path of least resistance into the low-usage function work ports the potential result can manifest itself as function drift or pressure intensification.
Both function drift and pressure intensification are undesirable in hydraulic systems, with adverse effects on safety as well as efficiency. The solution for this is the application of tandem circuitry. When applied correctly tandem circuitry can isolate pressures and prevent function drift.
One way to prevent this unwanted function drift for the low usage functions is by placing the high usage, parallel sections first in the assembly and making the first low-usage section with tandem circuitry. By doing this, parallel path pressure cannot be conveyed to downstream work sections, and the low usage sections do not see high pressure in the power core when the high usage sections are operating.
Parker’s VA35 valve model line features this type of tandem circuitry. This product coupled with Parker’s specialists in refuse market provide the customer with a solution responsive to their needs. In addition to the refuse market, tandem circuitry solutions with the same type of arrangement could be applicable in other pieces of mobile equipment where function drift and pressure intensification are challenges to applications such as those found in material handling and construction markets.
Tandem circuitry offers a solution by which unnecessary complexity can be removed from the application. In the case of tandem circuitry, this reduction in additional system complexity results in a corresponding reduction in system cost. The installation of the VA35 valve assembly with tandem circuitry eliminated the need for in-line pilot-operated checks offering significant cost savings. This is based upon three low-usage functions per valve assembly. While the refuse market is the primary example of where substantial cost savings can be realized other mobile equipment system cost savings can be of value as well.
This article was contributed by Galen Methvin, product sales manager, Hydraulic Valve Division