SOP: HPU Energy & Nitrogen Systems

⚡ HPU ENERGY & NITROGEN SYSTEMS

"Hydraulic Lungs" of the Turbine

Ensuring stored energy for Emergency Shutdown (ESD) even during total blackout

⚠️ HIGH PRESSURE WARNING (160 Bar)

DANGER OF LETHAL FORCE:

  • Hydraulic oil at 125-160 Bar can penetrate skin (injection injury), leading to amputation or death.
  • Nitrogen accumulators are pressure vessels. NEVER attempt to disassemble bladder/piston without first bleeding gas pressure.
  • Always use "Bleed-Down Valve" before servicing any HPU component.
Nitrogen (N₂) Accumulator Logic - "Stored Breath"

Why N₂ Pre-Charge Matters

Accumulator bottles are not just oil tanks; they contain a bladder with Nitrogen gas. This compressed gas provides the "spring" force that pushes oil out when pumps stop.

Safety Function: During total blackout (no pump power), Nitrogen expansion pushes stored oil into cylinder to close Wicket Gates and MIV.

Quarterly Pre-Charge Check Protocol:

  1. Isolate: Close oil isolation valve to accumulator bank.
  2. Bleed Oil: Slowly bleed oil system side pressure to 0 Bar.
  3. Connect Kit: Attach N₂ charging kit to gas valve on top of bottle.
  4. Measure: Read gas pressure.
    • Target: ~60-70% of System Operating Pressure (e.g. if System = 125 Bar, N₂ Pre-charge should be ~80-90 Bar). *Consult OEM manual.*
  5. Action: If < 10% below target, top up from N₂ bottle. If < 50% target, suspect bladder rupture.

Warning Sign: If HPU pumps cycle on/off rapidly (every few seconds), Accumulator has lost its "gas spring". Check pre-charge immediately!

Emergency Shutdown (ESD) by Weights

Gravity - The Last Line of Defense

Even if HPU fails and Nitrogen leaks, gravity MUST close the unit. This is achieved via "Weights" or mechanical counterweight on MIV.

Inspection Points:

  1. Release Mechanism: Hydraulic lock holding weight up must move freely. Lubricate pivot points monthly.
  2. Drop Path: Ensure area under weight arm is clear of tools, debris, or personnel.
  3. Cushioning: Weight should drop fast initially (80% stroke), then slow down (cushioning) at end to prevent water hammer.

"Blackout Test" (Annual):

Simulate total power loss. Verify weights drop and fully close MIV without any electrical or hydraulic assistance.

Flexible Hose Lifespan Management

The 6-Year Rule

Flexible hydraulic hoses are rubber components that degrade over time due to pressure cycles and heat. Hose burst = instant loss of control.

Component Max Life Replacement Trigger
Main Pressure Lines (125 Bar) 5 Years Burst outer rubber; "Weeping" at crimp
Pilot Control Lines 6 Years Stiff/brittle rubber; Abrasion marks
Return/Drain Lines 8 Years Any visible kinking or oil saturation

Inspection (Monthly): Look for "sweating" (oil sheen on hose surface) or fraying of steel braid. Sweating = Imminent Burst. Replace immediately.

Oil Hygiene & Pilot Valve Health

Pilot Valve Sensitivity

ESD logic relies on tiny electro-mechanical "Pilot Valves" to direct main oil flow. These valves have clearances < 5 microns.

Risk of "Stiction":

  • Varnish: Oxidized oil leaves sticky brown residue on valve spools.
  • Result: Solenoid activates, but valve spool does not move. ESD fails.
  • Prevention:
    • Maintain oil cleanliness ISO 16/14/11.
    • Install "Electrostatic Oil Cleaners" if varnish is detected.
    • Cycle (exercise) all ESD valves monthly to prevent seizing.
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