{
  "object_id": "c03-packing-compression",
  "title": "Packing preparation, reference heights and verification",
  "application": "Selected hand-operated-valve fallback only where adopted and no specific manufacturer compression instruction is available. Not an automatic-control-valve procedure.",
  "precedence": "Actual manufacturer packing dimensions,arrangement,compression or gland-torque instructions and approved work procedure take precedence.",
  "preparation": [
    "Established isolation,depressurization and opening-work state",
    "All old packing removed without damaging stem/box",
    "Actual stem,box,gland/follower condition inspected and defects dispositioned",
    "Eligible material/service/fire/temperature and exact ring arrangement identified",
    "Specified preparation/cutting/splits or unsplit disassembly route preserved"
  ],
  "routes": [
    {
      "name": "Die-formed ring precompression",
      "fraction": [
        0.02,
        0.03
      ],
      "denominator": "Original reference height of each individual ring as installed",
      "operation": "Packing gland and spacer precompress each ring."
    },
    {
      "name": "Completed die-formed stack compression",
      "fraction": [
        0.2,
        0.25
      ],
      "denominator": "Original reference height of the completed set,defined for this stage",
      "operation": "After the entire set is installed,compress the full stack."
    },
    {
      "name": "Separate braided graphite set route",
      "fraction": 0.3,
      "denominator": "Completed five-ring set reference height",
      "operation": "Install firstfour rings,tighten until resistance is felt,install fifth,then compress completed set."
    },
    {
      "name": "Manufacturer gland-bolt torque",
      "torque": null,
      "operation": "Use actual specified torque with selected bolt/gland/packing basis; no torque invented or borrowed from flange-stud example."
    }
  ],
  "fractional_height_model": {
    "ring": "h_1=(1-q_r)h_0",
    "set": "H_1=(1-q_s)H_0",
    "definitions": {
      "h_0": "Declared reference height of one ring",
      "q_r": "Dimensionless fractional reduction of that ring",
      "h_1": "Compressed height of that ring",
      "H_0": "Separately declared reference height of complete set",
      "q_s": "Dimensionless fractional reduction of that set",
      "H_1": "Compressed set height"
    },
    "units": "One consistent length unit; teaching examples use mm.",
    "limits": "Independent reference examples,not dimensions of one valve; no automaticaddition/multiplication of reductions,force,torque,leakage or adequacy inference."
  },
  "teaching_examples": [
    {
      "id": "individual-ring",
      "reference_mm": 10,
      "reduction_fractions": [
        0.02,
        0.03
      ],
      "compressed_heights_mm": [
        9.8,
        9.7
      ]
    },
    {
      "id": "complete-die-formed-stack",
      "reference_mm": 40,
      "reduction_fractions": [
        0.2,
        0.25
      ],
      "compressed_heights_mm": [
        32,
        30
      ]
    },
    {
      "id": "separate-braided-set",
      "reference_mm": 40,
      "reduction_fraction": 0.3,
      "compressed_height_mm": 28
    }
  ],
  "verification_sequence": [
    "Stroke valve in prepared state under selected procedure",
    "Reset prescribed compression/load if required",
    "Establish prescribed pressurized condition and observe actual leakage",
    "Any permitted adjustment followed by another observation",
    "Record actual set,reference or torque basis,movement and leak result"
  ],
  "variant_limits": [
    "Graphitic end-ring configuration not transferred to PTFE/combination packing",
    "Deep box uses specified spacer/bushing/lantern arrangement,not automatic additionalrings",
    "Split-field eligibility differs shop-installed solid rings",
    "Product-specific per-ring/set instructions may differ from fallback",
    "Control-valve friction/actuator requirements remain separate",
    "No prescribed online adjustment,opening or repacking authorization",
    "No invented gland torque,leak criterion or acceptance from calculated height"
  ]
}