Finn Corp.’s Express Blower, right, has a rear gate that is raised by a pair of hydraulic cylinders, shown above. A mechanical rod lock automatically holds the massive lift gate in position unless pressurized hydraulic fluid is routed to the lock to release it.
Finn Corp., Fairfield, Ohio, is a leading supplier of hydro seeding and blower trucks for the pneumatic application of seed, straw, mulch, pea gravel and other landscaping media. Typically, the media are dispersed through a pneumatic applicator and fed by hydraulically powered augers and conveyors in the truck bed. Marketed under the Express Blower name, these trucks generate substantial blowthru force to channel the media up to an applicator nozzle, usually handheld by an operator on the ground. A master control, program display, and operational indicators are mounted on the truck body for easy ground access.
Naturally, people sometimes need access to the truck bed for maintenance, inspection, or other tasks. Access to the bed occurs through a rear hydraulic lift gate. Until recently, this gate was operated by two people — one operating the hydraulic power unit and another climbing under the open gate to set a steel prop rod into place. The door would then be lowered until it contacted a mechanical stop to hold the door open at various heights for the particular task at hand.
The lift gate is powered by a pair of double-acting hydraulic cylinders, which swing the gate up and down in a 65° arc. Hydraulic motors, augers, beater bars, and a transfer conveyor for the media are all enclosed in the truck bed, so this gate operates with considerable frequency in the field.
In search of a solution
At the request of Finn, engineers from Hydrotech, Cincinnati, a fluid power distributor, began exploring the possibilities available for mechanically locking the cylinder rods in place automatically without having to use the prop rod. They also wanted to ensure that the gate would not move in the event of hydraulic pressure loss. Their search ended with Advanced Machine & Engineering (AME), Rockford Ill., which manufactures the Amlok mechanical rod lock.
AME’s Ken Davis explains, “We had previously encountered many similar applications, though none in this exact area. By combining our Amlok rod lock, rod, and rod eye, plus cartridge valves and bodies supplied by Hydrotech’s engineering staff, we worked with Finn to devise a system to mechanically hold the lift gate securely at any angle, with rod release occurring only on operator command.”
The Amlok rod lock is a mechanically applied, hydraulically released rod lock. If the directional valve feeding the lock is de-energized, the hydraulic hose breaks, or other loss of hydraulic pressure occurs, the rod lock mechanically holds the rod in place, securing the lift gate position so it cannot move up or down.
In normal operation, when the valve is energized, the lock allows the rod to move freely. Because doubleacting cylinders are used, a shuttle valve feeds the pressure side to the directional valve. Because only one operator is now required to raise and lower the lift gate, greater efficiencies are being realized in the operation of Finn Express Blower trucks and the company’s other vehicles.
Doug Wysong, chief engineer at Finn Corp., adds, “At our annual summit meeting of Express Blower customers, they emphasized the need for an automatic door prop system. Hydrotech introduced us to Amlok from AME, and we quickly had a system installed on our prototype truck — and an answer to our customers needs. In my estimation, this is a prime example of how a corporate partnership works to solve the needs of the enduser,” commented Wysong.