Deaerated fuel
Join Date: Jul 2004
Location: Sydney NSW
Posts: 513
Likes: 0
Received 0 Likes
on
0 Posts
entrained gases and dust removed?
I may be wrong but deaeration is a process to remove entrained gases and dust.
When a liquid is pumped at pressures near its saturated vapour pressure the presence of dust, entrained gases and even cracks in the pump impeller cause voids in the liquid, and bubbles of gas known as cavitation. This reduces the flow, pressure head and pump life.
“Upstream” and “downstream” in a pump refer to pressure head with “up” being the highest and “down” the lowest and does not refer to direction of liquid flow. Use the terms inlet and outlet instead.
One technique where problems are likely is to apply an inducer to the inlet. An ideal inducer is reversible and its purpose is to help develop the necessary pressure head without shocks that can of themselves produce cavitation.
Regenerative pumps are least likely to experience cavitation problems because the liquid enters and exits the pump over several revolutions of the impeller. They can therefore produce a large pressure difference for comparatively small flows but are capable of producing very high pressure heads and need a quick response pressure relief valve. This liquid reflief outflow is likely to "cavitate" and some ingenuity is resorted to in recirculation. Regenerative pumps are ideally reversible and have the inestimable boon of having the pump cavity remain filled when the pump stops.
I hope this helps to explain what the terms mean and place them in the context of aircraft fuel pumps in particular.
When a liquid is pumped at pressures near its saturated vapour pressure the presence of dust, entrained gases and even cracks in the pump impeller cause voids in the liquid, and bubbles of gas known as cavitation. This reduces the flow, pressure head and pump life.
“Upstream” and “downstream” in a pump refer to pressure head with “up” being the highest and “down” the lowest and does not refer to direction of liquid flow. Use the terms inlet and outlet instead.
One technique where problems are likely is to apply an inducer to the inlet. An ideal inducer is reversible and its purpose is to help develop the necessary pressure head without shocks that can of themselves produce cavitation.
Regenerative pumps are least likely to experience cavitation problems because the liquid enters and exits the pump over several revolutions of the impeller. They can therefore produce a large pressure difference for comparatively small flows but are capable of producing very high pressure heads and need a quick response pressure relief valve. This liquid reflief outflow is likely to "cavitate" and some ingenuity is resorted to in recirculation. Regenerative pumps are ideally reversible and have the inestimable boon of having the pump cavity remain filled when the pump stops.
I hope this helps to explain what the terms mean and place them in the context of aircraft fuel pumps in particular.
Last edited by enicalyth; 23rd May 2007 at 07:58. Reason: ambiguity
Join Date: Jun 2003
Location: Madrid
Posts: 156
Likes: 0
Received 0 Likes
on
0 Posts
TO MEMO the previous answer is right but I guess that your are looking for a more operational info regarding GRAVITY FUEL FEEDING when engine fuel pumps are inop. (FCOM 3.02.28 p10).
If flight time above FL 300 is greater than 30 min, it is time enough for all the air bubbles to be gone cause of the decreased pressure in the fuel tank (like a coke bottle when opened), so the fuel can be considered as deaerated (with no air diluted) and engines can be feeded by suction.
If flight time above FL 300 is greater than 30 min, it is time enough for all the air bubbles to be gone cause of the decreased pressure in the fuel tank (like a coke bottle when opened), so the fuel can be considered as deaerated (with no air diluted) and engines can be feeded by suction.
Join Date: May 2004
Location: INDIA
Posts: 28
Likes: 0
Received 0 Likes
on
0 Posts
Airbus FCOM procedure...gravity fuel feeding
Hi there , just wanted to confirm that what u mean is that if we fly above fl300 and wait for 30 min as advised in the fuel feeding table the file is assumed to be deaerated , ie all of it's air molecules have been taken away or got rid off, but if we see the FCOM gravitynfeeding pro it also says tht this 30 min time is for type jet a/a1 fuel and that type b fuel grvity feeding ALT or level is fl 100 , can u please explain the procedure in a little easier manner, and how does this affect the fuel feeding procedure. I am currently studying for my command upgrade and I was asked this by a trainin cap tin and I did gave him an answer on the similar terms of what u have mentioned but he wasn't too satisfied with it , so is there an easier and more meaning full answer to it ? Just wondering and also please clarify the diff in gravity fuel feeding levels ie fl300 for type A n A1 and why fl 100 for type b fuel,
Looking forward for an easier answer... Thanks guys
Looking forward for an easier answer... Thanks guys
