3.1.1 — Valve Identification & Purpose
A technician should be able to identify valves by construction (hand valve, solenoid, pilot-operated, balanced-port), by function (isolation, control, relief), and by location (liquid line, suction line, discharge line, oil line). Correct identification matters because the same symptom — such as low suction pressure — can be caused by a stuck metering device, a closed liquid line solenoid, a failed regulator, or a restricted filter-drier.
Every valve or accessory exists to achieve one of five system goals:
Control Mass Flow
Start, stop, or modulate the flow of refrigerant through lines and components to match system load and protect against flooding or starvation.
Maintain Safe Pressures
Keep high-side and low-side pressures within design limits for efficient heat transfer and to protect compressors, vessels, and piping from overpressure.
Protect Components
Shield compressors, heat exchangers, and controls from contamination, moisture, non-condensables, liquid slugging, and reverse refrigerant migration.
Improve Efficiency
Enhance part-load performance, enable capacity staging, reduce condenser water waste, and minimize energy consumption across changing load conditions.
Enable Servicing
Allow isolation of components, gauge connection, refrigerant recovery, and controlled access so that the system can be commissioned, maintained, and repaired safely.
Drawings tell you what the designer intended; the installed piping tells you what was actually built. Learn to read symbols for isolation valves, check valves, solenoids, regulators, strainers, receivers, and relief devices, then cross-check against the equipment schedule and control sequence.
Common Drawing / Spec Details You Must Extract
Look for: line sizes (for example, 22 mm or 7/8 in OD), materials, design pressures, valve tags, flow direction arrows, and control interlocks. Also note service clearances and access requirements — a device that cannot be serviced safely often becomes a chronic reliability problem.
Operational Thinking: What Changes Across the Device
When you analyze a device, ask what changes across it: pressure (kPa and psig), temperature (°C and °F), state (liquid/vapour), mass flow (kg/s and lb/min), and contaminant concentration. For example, a metering device intentionally causes a pressure drop; a filter-drier intentionally causes a small pressure drop while removing moisture and particles; a receiver intentionally changes where refrigerant mass is stored.
Before replacing any valve, confirm that it is actually the source of the symptom. Many valves respond correctly to a fault elsewhere in the system. Replacing a correctly-operating device wastes time and money — and leaves the real fault in place.