Quote:
Originally Posted by funola
Problems that will arise may include ... overheating of injector nozzles and injection pump elements, damaged lift pump, from insufficient cooling due to lack of fuel flow.
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I referenced this possibility in an earlier post, which is why I stated at that time that I'll be adding a temperature probe at the float bowl to monitor this in real time. And if it is a problem I'll add a fuel cooler to the return line very similar to the power steering fluid cooler.
Actually there is one concern that I have with the system and that is the capacity of the flow sensor and the potential pressure drop across it which could allow the engine to drain the float bowl and draw air at the very limits of the operating envelope...I'll share my calcs on that later.
Quote:
Originally Posted by dieselbenz1
If the eccentric gear flow meter is a volumetric meter it should work well. The issue with measuring flow especially using a different type of meter is that when flow is interrupted it takes a while once flow is established to stabilize a flow meter therefore accuracy is compromised. If you can setup the float to generally be cracked open at idle that would be ideal, (proportional acting). If the float operated more as an open closed valve that may result in more flow than is actually being measured as the meter would see no flow then flow.
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Your theory is exactly correct - the problem here is not with the design of the positive displacement eccentric gear meters but the manufacture of this particular cheap Chinese one with tolerances and precision so poor it takes a huge flow just to start the gears turning and then sometimes they stick. The aircraft flow meters are almost all the vane type, which actually reduces the possibility of jamming due to contaminants. The floats are extremely sensitive so are "generally cracked open" at idle anyway. The k-factor in flow meters is surprisingly linear except at very low flow rates. The trick is to get one where the idle flow is in the linear range without exceeding the capacity on the top end. I'll share the calcs later.