Industrial Hydraulic Technician (IHT)

The job performance assessment consists of the following six stations:

• Hydraulic Symbols
  • Identifies pressure source graphic symbols
  • Identifies hydraulic graphic symbols that describe flow lines and connections
  • Identifies directional control valve symbols
  • Associates directional valve center position with actuator control
  • Identifies hydraulic pressure control valves from detailed symbols
  • Associates simplified flow control valve symbols with component function
  • Identifies flow control valves from both simplified and detailed symbols
  • Associates detailed flow control symbols with component function
  • Identifies symbols for hydraulic pumps and motors
• Statics
  • Understands the relationship between height of a liquid and the gauge pressure reading in psi
  • Understands the relationship between height of a liquid and gauge pressure reading in inches of mercury (in-Hg)
  • Understands that hydraulic pressure results from load resistance
  • Uses cylinder bores and rod diameters to figure static pressures
  • Relates resistive and overrunning loads to static pressures in cylinders
  • Understands that cylinder movement is caused by sufficent ressure against a movable area
• Components
  • Determines hydraulic flow capacity from conductor sizes
  • Calculates speeds and forces associated with single rod cylinders
  • Understands how hdraulic flow rate and cylinder rod velocity are used to determine volumetric effciency
  • Distringuishes between operation of a pressure relief, pressure reducing, unloading, sequence, counterbalance, and brake valves
  • Understands that load holding valves are required on truck mounted aerial lift cylinders
  • Understands the characteristics of hydraulic pressure relief valve and unloading relief valve circuits
  • Understands that hydraulic pressure compensated flow control valves maintain constant actuator speed regardless of load
  • Understands that hydraulic pressure compensated flow control valves maintain constant pressure across a variable orifice
  • Understands that flow through a sharp edged orifice is less affected by change in fluid temperature than other types of restrictons
  • Understands functions, porting, and purpose of differential areas in pilot operated hydraulic check valves
  • Understands that load holding, pilot operated to-open, check valves require an open center or float center directonal control valve
  • Understands that thermal expansion of fluid can cause high pressure and thermal lock in cylinders equipped with pilot operated check valves
  • Distinguishes between the operation of a counterbalance valve and pilot operated to-open check valve
  • Determines the pressure required to shift a pilot operated check valve
  • Interprets hydraulic pump specifications from performance curves
  • Understands the relationship given by Ohm’s law
  • Predicts directional control valve operation from performance curves
  • Understands that pilot drains on directional control valves should have separate lines where the system experiences high return line pressure
  • Understands the purpose and operation of priority flow divider valves, bypass flow regulators, and proportional flow divider valves
  • Calculates fill times, oil capacities, and charge pressures for hydro-pneumatic accumulators
• Controls
  • Identifies limit switch positions
  • Identifies single-phase two-speed, and three-phase AC motor symbols
  • Understands forward and reverse rotation wiring diagrams for singlephase and three-phase AC electric motors
  • Identifies basic electrical symbols from ladder diagrams
  • Understands the basics of hydraulic system electrical controls
  • Distinguishes between ladder diagram elements: Electrical contacts (push button switches, sensors, and relay contacts), and output elements (resistance loads, such as relays, solenoids, lamps, and motors)
  • Understands that electrical contacts have negligible resistance, whereas output elements have appreciable electrical resistance
  • Understands that in a ladder diagram, the voltage drops across the switch if it is open or across the load if it is closed
  • Understands the interaction between a ladder diagram and directional control valves
  • Identifies the function of electrical components in a circuit
  • Understands that solenoid coil hum is caused by alternating current and the bias spring
  • Understands that a solenoid shading ring helps hold the armature in place as the main magnetic coil attraction draops to zero
  • Understands that the shading ring in AC directional control valve solenoids minimizes hum by providing an induced current that lags the applied current
  • Associates AC solenoid failures with failure of the armature, or failure of the plunger to seat
• Basic Circuits
  • Understands the function of a Graetz rectifier.
  • Understands that system pressure in a series hydraulic circuit results from the combined load on all actuators
  • Understands that pressure in a parallel hydraulic circuit results from the load on the actuator with least resistance
  • Understands that the pressure relief valve diverts unneeded flow to the reservoir when a fixed displacement pump is used
  • Recognizes basic hydraulic circuits from circuit schematics
  • Identifies purposes for hydraulic meter-in, meter-out, bleed-off, brake, sequence, and counterbalance circuits
  • Recognizes the characteristics of meter-in, meter-out, and bleed-off circuits
  • Recognizes the limitations of meter-in, meter-out, and bleed-off circuits
  • Identifies circuits that match applications
  • Understands that hydraulic regenerative cylinder circuits increase cylinder rod velocity
  • Understands how components interact in a hydraulic regenerative circuit
  • Calculates the cylinder rod force, cylinder rod velocity, and flow rate in various lines in a hydraulic regenerative cylinder circuit
  • Distinguishes hydraulic accumulator circuit purposes from circuit schematics
  • Understands that hydraulic system heat generation in aerial trucks is caused by boom actuation and portable hydraulic tool usage
  • Understands that a variable displacement, pressure compensated pump reduces energy loss by avoiding relief valve operation at full pump pressure during holding or clamping
  • Understands that load sensing circuits with variable displacement, pressure compensated, pumps maintain pressure approximately at load pressure
  • Understands that hydraulic circuit synchronization can be achieved by mechanical tieing, metering, flow dividers, two equal displacement pumps, or replenishing circuits