Slack & Parr launches high-accuracy flow divider using innovative gear design

01 December, 2022

The company’s FDRX and FDLX flow dividers are built around an innovative ‘floating gear’ design to offer divisional accuracy greater than 1% at working pressures of up to 350 bar (5075 psi) – a level that would ordinarily only be associated with transducer and feedback systems.

Slack & Parr’s Neil Anderton explains how the technology works and the engineering challenges the company overcame to develop the solution. “Flow divider technologies are designed to split a flow of hydraulic oil from a single source to fill a series of vessels or cylinders to predetermined ratios. The technology is most commonly used to lift and lower loads, with applications in transport and logistics, marine and agriculture, including heavy-duty handling systems, forklifts and loading ramps.”

In developing any flow divider solution, the principal engineering challenge is how to split the flow as accurately as possible. “The reason this is so critical is that it determines how smoothly and evenly the load is lifted or lowered,” says Anderton. “In many industries and applications – particularly those handling fragile or valuable loads – this is vital to a successful operation. In this case, accuracy refers to the difference in rate between the first and last cylinder filling with the right amount of hydraulic fluid to reach its final position. Achieving optimum accuracy means each cylinder fills and empties at the same rate or ratio and the load is lifted or lowered evenly, regardless of pressure differential or unequal load distribution.”

Anderton adds that even small differences in flow rate can mean the cylinders quickly fall out of sync with each other, which can in turn significantly impact operational performance and, in some cases, safety. “We know that to achieve accurate flow we need to build accuracy into each component, therefore reducing the potential for contact between components and ‘slip’, which happens when the fluid forces its way backwards through the flow divider under pressure,” he explains.

When, almost two decades ago, Slack & Parr developed its now well-established FDR and FDL model flow dividers, the company’s challenge was to make the clearances between the internal gears, plates, dowels and casings as small as possible. This meant engineering clearances of just a few microns – significantly less than a human hair – to reduce the opportunity for slip while still providing enough space and alignment for the gears to rotate correctly.

‘Floating gear’ design

More recently, in Slack & Parr’s work to develop the FDRX and FDLX models and increase this level of accuracy even further, the company engineered an innovative ‘floating gear’ design. This allowed the gear to centralise itself accurately within its housing during operation. According to Slack & Parr, the result is that tooth-to-tooth contact between gears becomes extremely precise, gaps are eliminated, and clearances between the gear plate and the housing are also reduced.