With a deviation of just 1.5%, new flow dividers from Bucher Hydraulics, Klettgau, Germany, offer higher precision compared to their more-conventional counterparts. The new versions complement an extensive product family of the company’s MT series of flow dividers. These automatically operating units split a volume flow into two part-flows that can vary within certain limits. The standard division ratio is 1:1, but other ratios are readily available.
Basic MTDA flow dividers come in different sizes and designs for volume flow rates of 2 to 250 l/min. The products feature a division accuracy of ± 3% of nominal flow rate. In principle, any division ratio is possible with these valves. The practical application rather than technical feasibility sets the limits, according to company officials.
More than five years ago, the product family was expanded by a high-pressure version, called the HD. Like standard flow-divider valves, the HD is available in two nominal sizes for volume flow rates of 2 to 250 l/min. Operating pressure is to 420 bars.
Differential lock valves are the third group within the MT product family. The maximum volume flows and maximum sustained pressure correspond to those of the high-pressure flow divider valves. These differential lock valves have become indispensable in mobile hydraulic applications. Despite a simple operating principle, the units perform important functions that affect driving comfort, traction and operational readiness.
The differential lock valves are based on double-action flow dividers, which either divide the volume flow of a hydraulic system or combine two volume flows. Depending on the on-board hydraulic supply of a mobile machine, the differential lock valve can also be directly combined with a separate pilot unit. Design permitting, the existing pilot unit of the work hydraulics may also be used instead—as is common practice with larger machines. While the number of drive motors determines which valve to use, all are based on the same standard versions. Like the flow dividers, differential lock valves are available in different sizes and designs for volume flows of 2 to 250 l/min. Both nominal sizes have designs for driving two, three or four motors.
The valves offer several options to suit unusual technical requirements. Such variations could, for instance, provide additional connections for sensors, should the need arise to measure pressure while driving. It could also involve specific division ratios or adaptation to differing wheel dimensions. Division ratios can be freely selected to suit the application. The valves’ functions can be expanded by adding make-up valves, anti-shock valves and anti-shock make-up valves.
To supplement systems with differential lock valves, Bucher Hydraulics offers changeover valves for hydraulic motors. These valves let the driver switch from a quick-motion circuit such as “travel gear” to a parallel circuit with the differential lock valve. For the user, such systems provide reliable results and fast working speeds. In addition, the hydraulic design is simple with high operational safety.
Twice as precise
In addition to these products, Bucher now offers new flow dividers offering much higher division accuracy. They are identified as HG (from the German abbreviation for “high precision”) and can divide volume flow with an accuracy of ± 1.5 %. The new HG units share a unified plunger axis design with Bucher Hydraulics high-pressure flow dividing valves (HD) and differential lock valves (DV).
While the company’s standard flow dividers offer a division accuracy of ± 3%, this is based on the nominal flow rate. For high precision flow dividers, the tolerance applies to the pumped oil volume. It is not only more precise across the entire range, it also reach this accuracy class at a much lower pumping capacity, said Bucher officials. This allows for designs requiring a reduced mechanical expenditure to ensure synchronous operation.
Because volume flow has a significant influence on precision, the HG flow dividers are available in four different control flow ranges between 16 and 50 l/min, all for a maximum operating pressure of 250 bars. The products have a zinc-nickel coating that fulfills the minimum requirements for corrosion resistance during the 720-hour salt spray fog test.
The first high-precision units were built several years ago for a client project, which subsequently evolved into the new product family. One application that requires precision flow dividers is a car carrier trailer with two loading decks. The upper deck must be lowered evenly, and the cargo must not shift due to cylinders working asynchronously. Other applications are found in agricultural and construction equipment.
The QXT range of internal gear flow dividers completes the product portfolio. These units are available with division volumes of 5 to 250 cm³/rev for 2, 3 or 4-part flows and pressures to 320 bars. These internal gear flow dividers feature high division accuracy, exceptionally smooth operation and reduced pressure pulses as well as a long service life.