Greenhouse Scissors Lift Truck
Hydrodiagnostics worked with a Canadian based greenhouse construction company on a specialized machine. The machine is used by the greenhouse construction crew to install glass panels in the roofs of greenhouses. It is based on a Yanmar rubber tracked dump truck that has had the cab and the dump bed removed and replaced by a scissors lift platform. It is a fairly large machine; the engine horsepower is estimated at around 150 HP. The machine has Eaton Series 1 hydrostatic pumps that operate the tracks for travel, with a medium size gear pump as the hydrostatic system charge pump and to operate the auxiliary functions. It uses the solenoid operated valve that originally operated the dump bed cylinder to control the lift platform cylinders. Other solenoid operated valves control cylinders and motors on the platform that help the construction crew handle the glass panels while they are being installed in the greenhouse roof. The machine was located at a large greenhouse construction site in Northwest Ohio.
The problem with the machine was that the propel system would not function at all, the cylinders and motors to assist with handling the glass panels were inoperative, and the only thing that did work was that the platform would go up while the engine was running. It would only go down if an emergency lowering valve was opened.
Hydrodiagnostics began diagnosing the problems. The valve manifold block that controls the lift platform was found to have a stuck raise valve. The manifold block was removed, and disassembled and the valves cleaned. The manifold block was reassembled and tested, and was found to be working properly. The manifold was reinstalled on the machine, and the platform raise and lower system worked as it should, but none of the other hydraulic functions worked, including the propel system. After more diagnosis, it was found that one of the directional control valves for the cylinders and motors that assist the construction crew with the handling of the glass panels was stuck. An attempt was made to clean and free the valve spool, but it was unsuccessful. There was an unused directional control valve on the manifold, so it was swapped with the inoperative directional control valve, and the glass panel handling cylinders and motors began to work as they should. The propel system also began to work. All of the machine functions were checked, and the machine was fully operational again.