Wednesday, May 13, 2020

Crankcase relief door

  • The spring loaded valve is of aluminium alloy for low inertia. A non stick heat resisting rubber O ring ensures positive sealing. The valve is designed to be fully open at a crankcase pressure of 0.2bar. 
  • A dome shaped flame trap of oil soaked wire gauze inside the crankcase with a free area equal or above that of the valve opening area is designed to dissipate the heat from the explosion.
  • A deflector shield secures the valve spring and directs any gas emitted in a downward arc of 120° where the damage caused will be minimal.
  • Fitted to engines with bore of 200mm and above with a crankcase volume of 0.6m3 and above (one door at either end of crankcase). Engines with bore of 300mm and above must have a door fitted to each crank throw compartment.
  • Free area of valve a min of 45cm2 and 115cm2 per m3 of crankcase volume.
  • When a crankcase explosion occurs, flame speeds may reach 300m/s with a substantial rise in crankcase pressure. If this pressure is not relieved it can reach several bar and result in the blowing off of the crankcase doors. This then allows a large amount of air to be drawn in to the crankcase to fill the vacuum caused by the so called primary explosion. The result is  a high risk of a devastating secondary explosion which can cause extensive damage, fire and fatalities.
  • To prevent this sequence of events, the explosion relief door prevents an excessive pressure rise, and because it is a non-return valve, stops air being drawn back into the crankcase after the pressure has been relieved.

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