Efficiency is key in hydraulic control

Edited by the Engineeringtalk editorial team Aug 25, 2005

When Kelvin Engineering redesigned its PF range of pedestrian-controlled forklift trucks, it turned to Hydraulic Projects to develop a compact high-efficiency hydraulic lift system control system.

When Kelvin Engineering set about redesigning its popular PF range of pedestrian-controlled forklift trucks, it turned to valve specialist Hydraulic Projects (Hy-Pro) to develop a compact high-efficiency hydraulic lift system control system.

The PF series is a workhorse of industry whose comparatively simple robust design ensures long term reliability and simple servicing, yet it offers many features and options so is the first choice for many materials handing operations.

It is available in 13 sises with capacities from 300 to 1500kg, with single and duplex lifting mast, fixed and tilting masts.

One of its key features is that it does not have support legs protruding forward beneath the lifting mast which would compromise manoeuvrability; instead the load is safely counterbalanced by the main body of the truck.

"With counterbalance trucks detailed design is critical", explains Director Simon Tubbs.

"Weight distribution is important, but so is an efficient special layout so that we keep the unit compact".

The hydraulics system is the core of any lift truck, so Tubbs and his colleagues put special emphasis on this during the redesign projects.

The key requirements were simplicity, reliability, cost and energy efficiency.

"Being electrically driven, you don't want to waste power with inefficient hydraulics or you'll not get adequate run time between recharging".

Tubbs put considerable efforts into researching possibilities for the hydraulic control valves and identified Hy-Pro as the best supplier.

The two companies worked together to develop a single valve bank that could address all functions and every option for the entire PF range.

The design brief for the main lifting valve specified a high flow rate to give relatively rapid lifting, but also fine control for gentle movements at initial pick up and final positioning.

To achieve this Kelvin shipped an older PF down to Hy-Pro in Dawlish where the hydraulic performance was mapped and new criteria agreed.

The required lifting speed could be met with Hy-Pro's V-140 G3/8 40 litre/min valve, but to get the extra fine control required for inching, positioning and gentle offloading a new spool was designed.

This is machined to have bespoke metering cutouts designed to guarantee the inching performance.

Hy-Pro often develops bespoke designs for particular duties - in fact most customers source at least one bespoke valve from them.

To support this function Hy-Pro has a well resourced design department which increasing runs its projects using advanced three-dimensional modelling software rather than conventional CAD.

A tilt valve was also required so that the mast could be reclined by up to 6 degrees to secure the load during transit and also tilted forward by 2 degrees to assist with unloading.

Both valves are manual levered controlled, with the lift valve providing infinite speed variation between inching and full speed.