ROC-M Exam flashcards
ROC-M Exam · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Torque and power relation
- Torque equals force times radius. Rotational power equals torque times angular velocity, so power in watts is torque in newton-metres multiplied by 2π times revolutions per second.
- Gear ratio
- The ratio of driven gear teeth to driver gear teeth. Output speed decreases by this ratio while output torque increases by the same ratio, ignoring friction losses.
- Bearing L10 life
- The rating life in millions of revolutions that ninety percent of a group of identical bearings will achieve or exceed under a given load and speed.
- Mechanical efficiency
- The ratio of useful output work to input work, equal to mechanical advantage divided by velocity ratio, always less than one for real machines.
- Hoop stress formula
- For a thin-walled cylinder, circumferential stress equals internal pressure times radius divided by wall thickness. It is twice the longitudinal stress and governs design.
- Boiler horsepower
- A measure of boiler capacity equal to 33,475 Btu per hour, roughly 9.81 kilowatts, corresponding to evaporating about 34.5 pounds of water hourly at 212 degrees Fahrenheit.
- Low-water cutoff
- A required protective control that senses low boiler water level and shuts off the burner to prevent overheating and catastrophic failure of the pressure vessel.
- Safety valve capacity
- The rated relieving capacity of the safety valve must equal or exceed the maximum steam-generating capacity of the boiler it protects at the set pressure.
- NPSH available
- The absolute pressure head at the pump suction above the liquid vapor pressure. It must exceed the pump's required NPSH to prevent cavitation and loss of performance.
- Affinity laws
- For a centrifugal pump, flow varies with speed, head with speed squared, and power with speed cubed. Impeller diameter changes follow the same pattern.
- Cavitation
- Formation and collapse of vapor bubbles in a pump when local pressure falls below vapor pressure, causing noise, vibration, erosion, and loss of head.
- Positive displacement pump
- A pump that traps a fixed volume of fluid per cycle and delivers essentially constant flow regardless of discharge pressure, requiring relief protection against blockage.
- Reynolds number
- A dimensionless ratio of inertial to viscous forces, calculated as density times velocity times diameter divided by viscosity, used to classify laminar and turbulent flow.
- Water hammer
- A pressure surge caused by rapid velocity change in a pipe, approximated by density times wave speed times velocity change, capable of damaging piping and supports.
- Check valve function
- A valve that permits flow in one direction only and closes automatically on reversal, protecting pumps and preventing backflow in piping systems.
- Valve flow coefficient
- The Cv value is the flow of water in US gallons per minute that passes through a valve with a pressure drop of one pound per square inch.
- Sensible heat equation
- For air, sensible heat in Btu per hour equals 1.08 times cubic feet per minute times the dry-bulb temperature difference in degrees Fahrenheit.
- Coefficient of performance
- The ratio of useful heating or cooling delivered to work input. Higher values indicate more efficient refrigeration or heat pump operation.
- Superheat
- The temperature of refrigerant vapor above its saturation temperature at the same pressure, measured at the evaporator outlet to confirm complete evaporation.
- Cooling tower approach
- The difference between the leaving water temperature and the entering air wet-bulb temperature, indicating how closely the tower reaches the theoretical limit.
- Motor synchronous speed
- The rotational speed of the magnetic field in an induction motor, equal to 120 times supply frequency divided by the number of poles.
- Motor slip
- The difference between synchronous speed and actual rotor speed, expressed as a fraction of synchronous speed, which produces the torque in an induction motor.
- Variable frequency drive
- An electronic controller that varies motor speed by adjusting supply voltage and frequency proportionally, maintaining magnetic flux and reducing starting current.
- Proportional control
- A control mode where output changes in proportion to the error signal. It reduces but usually cannot eliminate offset without integral action.
- Magnetic particle testing
- A non-destructive method that magnetizes ferromagnetic parts and applies iron particles to reveal surface and near-surface discontinuities such as cracks and laps.
- Liquid penetrant testing
- A non-destructive method applying a visible or fluorescent dye to a clean nonporous surface, then developing it to reveal surface-breaking discontinuities in any material.
- Predictive maintenance
- Maintenance scheduled from measured equipment condition, such as vibration, oil analysis, or thermography, rather than fixed time intervals.
- Ultrasonic thickness testing
- A non-destructive technique measuring remaining wall thickness by timing sound echoes, used to track corrosion and erosion against minimum allowable thickness.
- Lockout tagout
- A procedure isolating hazardous energy sources, applying locks and tags, releasing stored energy, and verifying zero energy before maintenance work begins.
- Confined space entry
- Entry into a space with limited access and poor ventilation requires atmospheric testing, an attendant, a permit, and rescue provisions before and during entry.
- Hierarchy of controls
- A ranked approach to hazard reduction: elimination, substitution, engineering controls, administrative controls, and finally personal protective equipment as the last defense.
- ASME Section VIII
- The section of the ASME Boiler and Pressure Vessel Code covering design, fabrication, inspection, and testing of unfired pressure vessels.