According to the manufacturer's recommendations for a main propulsion diesel engine on an oil rig supply vessel where the fuel oil day tank is above the engine, the maximum allowable pressure drop across the primary suction fuel filter element is 1.5 psig. What would be the equivalent pressure drop in inches of mercury, when the fuel oil day tank is below the engine?
⢠Pressure unit conversions between psig and inches of mercury (" Hg) ⢠Relationship between pressure and suction/vacuum on the fuel system when the tank is above vs. below the engine ⢠How static head (height difference between tank and engine) affects suction-side pressure readings
⢠First, if 1.5 psig is the allowable drop when the tank is ABOVE the engine (positive pressure at the inlet), what is that same pressure expressed in inches of mercury? ⢠Next, when the tank is BELOW the engine, does the same absolute pressure loss across the filter correspond to the same number of inches of mercury, a larger number, or a smaller one? Think about how vacuum is measured. ⢠Consider whether the manufacturerâs limit is really about the numeric reading on the gauge or about the actual pressure difference across the filter element itself.
⢠Convert 1 psi to inches of mercury using the standard conversion factor, then scale to 1.5 psi. ⢠Be clear whether youâre dealing with psig (gauge pressure) or inches of mercury vacuum, and how they relate. ⢠Ensure that your final choice reflects the same pressure difference in another unit, not a different operating condition.
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