Garnett Cross Training in the Maintenance of Oil Hydraulics

Cleanliness of hydraulic oil is one of the most important aspects of maintaining a hydraulic system to ensure many years of trouble free operation.

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This lecture goes over the need for filters in a hydraulic system and how they are integrated.

This lecture inspects a couple of filters.

This lecture provides an overview of a hydraulic system. Basic components and symbols are presented. The topic of oil flow rates is introduced.

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This lecture starts with presenting how hydraulics is similar to mechanical leverage, where small amounts of oil pumped per rotation of a pump is used to exert a force amplified by the area of a cylinder. The lecture goes in to detail operations of relief valves and directional control valves. The lecture ends with a hydrostatic drive.

This lecture covers the construction of cylinders to enable you to perform maintenance on cylinders like replacing seals.

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This lecture covers the challenge of operating multiple cylinders in parallel.

This lecture covers using the correct pipe sizes for a hydraulic system. On the suction line under sized pipes will cause cavitation. On the pressure line under sized pipes will cause a high pressure differential which will result in the system overheating and unnecessary power consumption.

This lecture covers a checklist of items to ensure the components of a hydraulic system are the correct size.

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This lecture covers the calculations to correctly size the components for a 90 litre per minute system.

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The lecture covers pipe sizing to avoid turbulence and the calculations to determine turbulence.

This lecture covers the challenge of operating cylinders in series. They must always be operated on at a time.

This lecture covers how an open circuit hydrostatic drive operates where the return line returns the oil back to tank. A check-list is provided to ensure the components and pipes are the correct size.

This lecture introduces the internal operation of a piston pump. Covers the following terminology, rotating group, swash plate, balanced pressure and shoe plate.

This lecture covers the design of piston pumps, showing how the internals operate.

This lecture covers piston pump usage in Closed Circuit Hydrostatic Drive.

This lecture covers the closed circuit hydrostatic drive where the pump flow is reversible and the oil can flow in either direction through the pipes. Special bi-directional filters are required so oil always flows in one direction through the filter element.

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This lecture presents the space and vector diagrams for variable hydraulic piston pumps and motors.

A variable piston pump controls the speed and direction of rotation of the connected hydraulic motor.

A variable hydraulic piston motor with a constant flow rate from the pump results in a variable speed and variable torque of the  motor. With a maximum angle on the motor swash plate results in maximum torque and slow rpm, while the minimum angle on the motor swash plate results in high rpm and minimum torque.

This lecture covers inline pumps - piston and gear pumps. Closed loop hydrostatic drives and bi-directional filters are covered in further detail.

This lecture covers the design of gear pumps.

In this lecture a gear pump is opened up to observe the the operation of the pump and highlight the drain port.

This lecture covers the tight tolerances on gear pumps and to how to bed a new pump in and wether it is best to repair or replace a gear pump.

This lecture covers the dangers of over pressurizing gear pumps.

This lecture is review of a circuit with preset pressure relieve valve and the dangers of adjusting the relief valve to address higher loads.

This lecture covers the viscosity of oil (how thick it is) and temperature affects the viscosity.

The lecture covers the use of high quality couplings to be used to couple the prime mover(electric motor or engine) to the pump to avoid damage to the prime mover and pump. The suggested design of reservoirs is covered.

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This lecture coves the identifying marks on hydraulic hoses and shows you how to interpret them. A resource is provided giving details for the safe handling of hydraulic hoses.

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This lecture covers check valves and cartridge valves. Details are provided how the valves operate and are used in a hydraulic circuit.

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This lecture covers the operation of pilot operated check valves and how pilot operated check valves may be used for load holding and require positive pilot pressure to move a cylinder.

This lecture covers the operation of flow control valves and how they are used in hydraulic systems for speed control in bleed-off, meter-in and meter-out configurations.

This lecture covers the operation of a prefill valve, how a prefill valve can be used in complex systems to handle high flow rates and high working pressures.

This lecture introduces directional control valves and how they are used to control the flow of oil in a hydraulic system, to control cylinders and hydraulic motors.

This lectures goes over the internals of solenoid valves, operation and installation.

This lectures continues with the internals, operation and installation of solenoid valves.

The lecture starts with the NG10 valve again and continues to discuss flow rates, mounting of the valves and the NG6 valve.

This lecture covers directional control valves for high flow rates which use a smaller solenoid controlled directional control valve to control the larger directional control valve via pilot lines.

This lecture covers directional control valves for high flow rates with a throttling plate between the smaller and larger control valves to adjust the flow of the pilot lines and the speed at which the spool of the larger valve moves. The lecture provides details on how the valves are integrated in circuits.

This lecture goes over a physical NG25 valve which has been cut open to see the internals of the valve.

This lecture goes over a physical NG16 valve and reviews it's operation.

This lecture covers the composite gasket mounted relief valves operate, how to maintain them and how they are used in hydraulic systems.

This lecture covers unloading valves, how they operate and are used in a double pump system for fast approach and slow pressing speed. (High - Low System)

This lecture covers a double pump system with unloading valves for fast approach and slow pressing operations.

This lecture covers both displacement or ram cylinders and regenerating systems.

In a regenerating system design, the pump flow rate is assisted by the oil leaving the cylinder rod end and entering the pump pressure line to increase the cylinder approach speed. In general, an unloading valve is installed in the circuit so as to stop the regenerating process, once the cylinder has contacted the load allowing the cylinder to continue at slow speed and high pressure. 

This lecture proves a valuable step by step approach to fault finding in a hydraulic system.

This lecture introduces sequence valves covering both sequence valves with and without check valves. Sequence valves maintain a minimum working pressure on the primary circuit.

This lecture covers the use of sequence valves, to sequence the operation of cylinders.

This lecture covers the use of sequence valves to make a system operate the heaviest load first.

This lecture covers pressure reducing valves how they can be used in a hydraulic system to lower the working pressure.

This lecture covers how over center valves can be used to avoid runaway conditions with cylinders - requiring positive pressure to operate the cylinder.

This lecture covers how an over center valve is used with in a hydraulic system with a hydraulic motor to avoid a runaway condition.

This lecture provides valuable information on how vane pumps operate and how to maintain them. How they must be assembled, the typical minimum rpm required.

Bent axis piston pumps are covered, going over a cross section breakdown of a pump and how they operate.

This lecture presents vane pumps how they operate.

In this lecture a vane pump is opened to see how it operates. Terminology covered: cam ring, cavitation due to restriction on the inlet, rotating group, score marks from contamination, direction of rotor rotation, vanes are directional, vanes are hydraulically balanced.

This lecture covers the internal operation of a vane pump using detailed diagrams.

This lecture presents a double vane and gear pump, provides tips on installing a double vane pump and how double pumps are used on equipment.