View Full Version : Engine start without pumps
AnthonyGA
28th Oct 2007, 04:24
Is it possible to start engines without any external (non-engine) fuel pumps running? I'm thinking of the 737-800 but perhaps all airliners are similar (?) in this respect. If you can start them without any fuel pumps running, what are the consequences, apart from warnings or alarms? I'm guessing that they might run at idle on the ground but that any other circumstances might cause problems (?).
hoggsnortrupert
28th Oct 2007, 04:53
On most types there are Engine driven pumps, these are mechanical, driven by a quil shaft from a reduction, and start working upon engine/gearbox rotation as on a start initiation, although it may not be SOP!
I would on occassion start engines with Electric pumps off, as it is a sure way of testing if the associated engines Mechanical pump is working before getting into the air.
Be sure to check your type manual or ask your engineer what is fitted to the type you operate.
N/Snort.:ok:
On the 737 a DC electric start using an external air source has no electrical pumps running and works fine, with the EDP providing the 'pressure'. Gravity feed from the wings will run the engines up to high level too.
Golden Rivet
28th Oct 2007, 11:38
ran a 737-300 at full power last week on the ground with the pumps off. Not a jot of difference.
You may find the engine pumps cavitate at altitude without boost pumps running.
smudgethecat
28th Oct 2007, 16:38
The boost pumps and the mechanical pumps used in the FFG/ MEC/HMU are totally different and serve completly different purposes, the boost pumps sole purpose is to ensure fuel arrives at the engine under all conditions , the pumps in the fuel control system are there to raise the fuel pressure to the high levels required on the H.P side of things, why would not use the boost pumps when starting? there there to be used.
AnthonyGA
28th Oct 2007, 20:09
I asked because someone told me that you couldn't start the engines without running the pumps. That didn't seem likely since the engines have their own pumps, and (at least in aircraft like a 737 or 747) the fuel tanks are presumably above the engine pumps and thus would drain by gravity into the pumps as long as the aircraft is straight and level. I believed that you could start and run the engines but that they might not perform ideally in all situations without the additional pressure from the other pumps in and around the tanks. From what everyone has said here, it looks I was right and he was wrong.
Intruder
29th Oct 2007, 00:07
I've done it on a 744 with GE engines. The engine-driven pumps are perfectly adequate in normal conditions...
smudgethecat
29th Oct 2007, 04:53
I would read this, http://www.rolls-royce.com/history/publications/jet_engine/default.htm
AnthonyGA
29th Oct 2007, 08:45
The book looks very interesting, although it is expensive—and since it is published by Rolls-Royce, I rather doubt that it contains a lot of information about GE's or P&W's contributions to the technology. I note in the previews available on the site that everything is described in terms of Rolls-Royce engines, a bit like a promotional brochure, but it still looks fascinating.
Truck2005
31st Oct 2007, 05:48
Tony,
Take it from me, that book is almost a bible and has been a must over the many editions for sooties like me.
Wile I'm sure AnthonyGA will benefit from reading that publication, I detedt that we are getting way away from the original question, the answer to which, for the 737 are:-
Yes, it is
Booster pump low pressure lights on overhead panel only
You would probably get full power on the engines at sea level.
Unless AGA has any more questions I intend to close this thread as it has answered the query and is wandering off-track.
allthatglitters
31st Oct 2007, 11:04
I'm think you will find that there are requirments for the engines to run up to full power with fuel booster pumps off. As a flight crew the last thing you would wish for is you have a total electriacal failure and to make matters worse the engines stop.
Most aircraft in the past I ran would operate perfectly at take off power with all pumps off, normally carried out after tank entry and fuel system breakdown... this included the B737 Jurassic and classic.:)
barit1
1st Nov 2007, 11:23
hoggsnortrupert posits:I would on occassion start engines with Electric pumps off, as it is a sure way of testing if the associated engines Mechanical pump is working before getting into the air.
Well, I can guarantee that if the engine mechanical pump is NOT working, you won't get the engine started, much less airborne.
Think about it: How much pressure does the electric pump(s) produce? And what is compressor discharge (or burner) pressure at idle, and at takeoff? The mechanical pump must overcome that air pressure, otherwise compressed air would backflow into the fuel system! :ugh:
The engines I know have mechanical pumps that produce upwards of 1000 psi; this not only runs the engine, but drives internal servos in the fuel control unit, variable stator servos, etc. The electric pumps won't come close to handling this job.
Sorry guys and girls, warning not taken!:ugh: This thread is about booster pumps. Now closed.