Dictionary
Engineering Glossary
A comprehensive dictionary of engineering terms used in maintenance, reliability, and industrial operations. From cavitation to OEE, understand the language of your trade.
10 min readUpdated July 2026
Steam and Fluid Terms
Terms related to steam systems, fluid mechanics, and thermodynamics:
| Term | Definition |
|---|---|
| Cavitation | The formation and collapse of vapour bubbles in a liquid when local pressure drops below the fluid's vapour pressure. Causes noise, vibration, and erosion of pump impellers. |
| Flash steam | Steam formed when high-pressure condensate is discharged to a lower pressure. The pressure drop causes a portion of the hot condensate to 'flash' back into steam. |
| Saturated steam | Steam at the saturation temperature for its pressure — it contains no moisture (dry saturated) or some moisture (wet saturated). The most common type of process steam. |
| Superheated steam | Steam heated above its saturation temperature at the given pressure. Contains no moisture and is used for turbines where dry steam is essential to prevent blade erosion. |
| NPSH (Net Positive Suction Head) | The absolute pressure at the pump suction above the fluid's vapour pressure. NPSH available must exceed NPSH required by the pump or cavitation will occur. |
| Blowdown | The controlled discharge of concentrated boiler water to control dissolved solids (TDS). Bottom blowdown removes sludge; surface blowdown removes dissolved solids. |
| Dead heading | Operating a pump with the discharge valve closed or blocked. The pump recirculates fluid internally, causing rapid temperature rise and potential damage. |
| Specific volume | The volume occupied by a unit mass of a substance (m³/kg). For steam, it varies dramatically with pressure — from 1.694 m³/kg at atmospheric to 0.194 m³/kg at 10 bar. |
| Enthalpy | The total heat content of a substance (kJ/kg). For steam, it includes sensible heat (energy in the liquid) and latent heat (energy of vaporisation). |
| Latent heat | The energy required to convert a liquid to a gas at constant temperature and pressure. For water at 100°C, latent heat is 2257 kJ/kg. |
Control and Automation Terms
| Term | Definition |
|---|---|
| PID (Proportional-Integral-Derivative) | A control algorithm that adjusts an output based on the error (proportional), the integral of the error (past accumulation), and the derivative of the error (rate of change). The most common industrial controller. |
| SCADA (Supervisory Control and Data Acquisition) | A system that monitors and controls industrial processes from a central computer. SCADA provides real-time data, alarms, and historical trends. |
| PLC (Programmable Logic Controller) | An industrial computer that executes control logic for machines and processes. Operates on a scan cycle — reads inputs, executes logic, updates outputs. |
| DCS (Distributed Control System) | A control system where multiple controllers share the process across a network, each handling a section. Used for large continuous process plants. |
| VSD / VFD (Variable Speed Drive / Drive) | An electronic device that controls motor speed by varying the frequency and voltage of the power supplied. Saves energy on centrifugal pumps and fans. |
| Setpoint | The desired value of a process variable that a controller tries to maintain. |
| Process variable (PV) | The actual measured value of the parameter being controlled (e.g., temperature, pressure, flow). |
| Manipulated variable (MV) | The output that the controller adjusts to maintain the process variable at the setpoint (e.g., valve position, motor speed). |
Reliability and Maintenance Terms
| Term | Definition |
|---|---|
| OEE (Overall Equipment Effectiveness) | A measure of manufacturing productivity: OEE = Availability × Performance × Quality. World-class OEE is 85%+. |
| MTBF (Mean Time Between Failures) | The average operating time between failures of a repairable asset. Higher MTBF = more reliable equipment. MTBF = Total operating time / Number of failures. |
| MTTR (Mean Time To Repair) | The average time to repair a failed asset and return it to service. Lower MTTR = faster recovery. MTTR = Total repair time / Number of failures. |
| Availability | The percentage of time an asset is available for operation: Availability = MTBF / (MTBF + MTTR). A common reliability KPI. |
| Reliability | The probability that an asset will perform its function for a specified period under specified conditions. R(t) = e^(-λt) where λ = failure rate. |
| RCM (Reliability Centred Maintenance) | A structured method to determine the optimal maintenance strategy for each asset based on its failure modes, failure effects, and consequences. |
| FMEA (Failure Mode and Effects Analysis) | A systematic method to identify potential failure modes, their causes, and their effects. Used to prioritise preventive actions. |
| RCA (Root Cause Analysis) | A systematic investigation to identify the fundamental cause of a failure, not just the symptoms. Techniques include 5 Whys, Fishbone, and FTA. |
| BEP (Best Efficiency Point) | The flow rate at which a centrifugal pump operates at maximum efficiency. The target is to operate within 70–120% of BEP. |
| L10 life | The bearing life at which 10% of a population of bearings will have failed. The standard rating for bearing life — typically 50,000–100,000 hours for pump bearings. |
Process and Quality Terms
| Term | Definition |
|---|---|
| TDS (Total Dissolved Solids) | The total concentration of dissolved substances in water (mg/L or ppm). In boiler water, high TDS causes foaming and carryover. Controlled by blowdown. |
| pH | A measure of acidity or alkalinity (0–14). pH 7 is neutral, below 7 is acidic, above 7 is alkaline. Boiler water should be pH 10.5–12.0. |
| Conductivity | A measure of water's ability to conduct electricity, proportional to dissolved solids. Used as a proxy for TDS in online monitoring. |
| KPI (Key Performance Indicator) | A measurable value that indicates how well an organisation is achieving its objectives. Maintenance KPIs include availability, MTBF, and maintenance cost as % of asset value. |
| CAPEX / OPEX | Capital expenditure (one-time investment in assets) / Operating expenditure (ongoing operational costs like maintenance, energy, labour). |
Safety Terms
| Term | Definition |
|---|---|
| LOTO (Lockout/Tagout) | A safety procedure to ensure that dangerous equipment is properly shut off and not started up again before maintenance is complete. Involves physically locking isolation devices. |
| JSA (Job Safety Analysis) | A step-by-step analysis of a task to identify hazards and implement controls before the work begins. Also called SWMS (Safe Work Method Statement). |
| Permit to Work | A formal authorisation system for high-risk work (hot work, confined space, working at height). Ensures hazards are assessed and controls are in place before work starts. |
| Hierarchy of Controls | The preferred order of risk control: Elimination → Substitution → Engineering → Administrative → PPE. |
| PPE (Personal Protective Equipment) | Equipment worn to protect against hazards — the last line of defence in the hierarchy of controls. |
How CHI can help
Ask CHI about engineering terminology and to explain any concept you encounter in your work. The CHI assistant can explain any engineering term, provide examples, and relate the concept to your specific equipment and processes.