Why do you need to turn on fuel pump when switching tanks ?

[DaV8or]

We are supposed to switch the boost pump on to switch tanks?? Huh... never knew. No point in starting now. If I were ever to run a tank dry, I'd likely do it then I suppose...

[OR75]

I don't use the fuel boost pump when switching tank. 

I switch tank preferably when level off and within gliding distance from an airport and monitor the fuel pressure. It usually goes down a few psi then goes back to where it was. 

[EDNR-Cruiser]

I switch it on because the POH says so... - it may not be necessary but it won't hurt either. Why would I care? I am just happy if the engine keeps running... I once had a problem with a PA28 switching tanks and despite the aux pump running and the other tank half full the engine quit. Switching back to the initial tank helped and the engine started after some coughs...
Minutes later I switched back to the right tank and - surprise - the engine kept running. Never found out what the problem was but since then I always hold my breath when switching tanks...

[Shadrach]

I don't believe my POH says anything about it, but inconsistency is more the norm than the exception when it comes to the factory.  I use my pump to start the engine, and that's about it. I don't need the pump for winter time starts.  If I miss the pressure drop before running a tank dry, I will turn it on to hasten the restart. 

Those of you referring to air bubbles have me confused. Where does the air come from?  The only way that I know of to get air into the system is to run a tank dry.

[RobertGary1]

I really don't think I'd risk a take off or landing without the boost pump. You're one diaphragm failure from a dangerous accident if the mechanical pump fails. If my boost pump died no question id ground the plane. 

 

-Robert

Edited September 6, 2015 by RobertGary1

[gsxrpilot]

I can not think of a single valid reason to use the boost pump at cruise altitude. Even running a tank dry and having to restart the engine is just an annoyance and certainly not an emergency. Of course if my engine coughed every time I switched tanks, I'd use the boost pump to eliminate that annoying cough, but it never has. And I just don't see using the boost pump "just in case". I agree to using the boost pump during take off. Losing the mechanical pump at that time would be an emergency at best and catastrophic at worst. I don't use it on landing as I'm more of a pattern altitude until the runway is made and then chop the power rather than a stabilized approach kinda pilot. Of course when I'm on the ILS or other Instrument approach, it's stabilized and the boost pump is on.

So why not use it just because? I'm sure like most things, it's only got so many cycles in it before it's an expensive replacement. Therefore I'll use it when it makes sense and not "just because".

[Andy95W]

I always did just 'cause that's what I was taught.  I'm going to stop using the boost pump for tank changes and engine starts.  I will always use it for takeoff, and I'll have to decide about landing.

hmm... old dog, new tricks? 

[Shadrach]

I really don't think I'd risk a take off or landing without the boost pump. You're one diaphragm failure from a dangerous accident if the mechanical pump fails. If my boost pump died no question id ground the plane. 

 

-Robert

Actually, I believe the mechanical pumps have 2 diaphragms.

[Guest]

Actually, I believe the mechanical pumps have 2 diaphragms.

They are probably one of the most reliable items on our engines.  In more than 30 years of maintenance I've never changed one due to outright failure.

Clarence 

Edited September 6, 2015 by M20Doc

[bonal]

It might be more critical on an injected engine than a carburetor since the carb has a bowl full of fuel to run on 

[carusoam]

 

Bonal,

wait it till you run the carb's bowl out...

My first Mooney flight, I switched to the both position while taxiing.

bought the plane anyway.

learned the value verbal mediation at that moment as well.

 

best regards,

-a-

Edited September 7, 2015 by carusoam

[Hank]

Reading the posts by the Injected guys, it's apparently more important. Or at least noticeable if you don't. My C typically flies at ~3 psi fuel pressure; top of the green is 6 psi. She does occasionally dip down to 1 psi, with no change in tone, feel, speed or altitude. Flipping the lever 180° takes less than a second. I've never noticed a hitch in the giddyup when doing so.

[Ned Gravel]

I always did just 'cause that's what I was taught.  I'm going to stop using the boost pump for tank changes and engine starts.  I will always use it for takeoff, and I'll have to decide about landing.

hmm... old dog, new tricks? 

 

 

One of the first pre-start items on my checklist. If it is not working, I cannot fly. Why? Because if the engine-driven fuel pump also fails in flight, I will be headed to the edges of the flight envelope without the help of the big cooling fan up front. Clarence taught me that.

Lost mine in Wichita this past March. Thank God I was in Wichita.....

Consequently, for me it is also important in all TOGA and landing situations.

 

Ned Gravel, 
Lucky steward of C-FSWR, a '65 E model at Rockcliffe, Ontario, (CYRO)
Sent from my iPad using Tapatalk

Edited September 7, 2015 by Ned Gravel

[RobertGary1]

They are probably one of the most reliable items on our engines.  In more than 30 years of maintenance I've never changed one due to outright failure.

Clarence 

I've heard that about fuel servos and piston rod end cap bolts. But I've had both go TU in flight. I'll hedge my bets by turning on the boost for take off and landing. Not much solace in people standing around at your funeral going "I've never hear of that".  

 

-Robert

Edited September 7, 2015 by RobertGary1

[Guest]

My post speaks to reliability.  Nowhere did I suggest how one should operate their boost pump.  In fact if you read Ned's post above yours, you'll see my position.

Clarence

[Raptor05121]

I've only got 0.8 hrs in my Mooney, but I have already learned that engaging the boost pump before switching tanks is a good idea!

My plane was stored for the past few months by the previous owner without fuel in the tanks due to a fuel seepage. I added 10 gallons to each side for the short 40 mile ferry flight back home. First start-up was right tank, boost pump on. Engine fired and 10 minutes later, we were off. After leveling off, I enabled the boost pump and immediately switched to the left tank. Watching the fuel pressure gauge, it dropped down to about 3psi and I felt the RPMs lower. My hand was still on the fuel selector and right as I was about to switch back, the pressure shot up and we got full power again. I realized I didn't prime it on the ground to purge the air out of the left tank lines. Lesson learned. Boost pump ALWAYS when switching tank for me.

[Shadrach]

Alex, that only happens with dry tanks. While turning on the boost pump likely hastened the restart, the engine driven pump is self priming and baring a problem, would have been more than sufficient to get the fan running again.  Leaving your pump off would have been a good test of the integrity of the fuel system. However, as these pumps rarely go soft and have a redundant second diaphram, they are about as bullit proof as can anything on the airplane.

[mike_elliott]

Alex, that only happens with dry tanks. While turning on the boost pump likely hastened the restart, the engine driven pump is self priming and baring a problem, would have been more than sufficient to get the fan running again.  Leaving your pump off would have been a good test of the integrity of the fuel system. However, as these pumps rarely go soft and have a redundant second diaphram, they are about as bullit proof as can anything on the airplane.

A tell tale sign of a diaphragm going on the mechanical pump is you will notice your fuel pressure decreasing with an increase of Density altitude.

1) Turn on boost pump

2) Land immediately

3) replace mechanical pump (a B&tch on an IO360, but doable without yanking an engine)

[Shadrach]

A tell tale sign of a diaphragm going on the mechanical pump is you will notice your fuel pressure decreasing with an increase of Density altitude.

1) Turn on boost pump

2) Land immediately

3) replace mechanical pump (a B&tch on an IO360, but doable without yanking an engine)

yup, another sign is blue staining around the fuel pump drain outlet underneith the cowl.

[RobertGary1]

Also just decreases pressure overall. I was used to seeing my mechanical pump around the middle of the green and then a rise when I turned on my boost. Than I installed my new engine from Lycomjng and the mechanical pump always runs right at the top of the green. So the new pump is stronger. The one pump was fine. 

 

-Robert

[bonal]

Always check boost pump for operation as part of run up and switch on when I take the runway if it did not function then I would not fly I leave it on in climb until I know I have enough AGL to get down safe. Don't use on landing as I have the field made but always ready to hit the switch if I ever sense a power problem. When ever I am doing something related to fuel delivery my attention is on my pressure gauge but I don't engage the boost for tank changes I have never seen any change in pressure or performance form the engine.

[romair]

My boost pump quit working...I'm about 1 hour from my home field...other than the implicit risk of having no back up pump in case the engine fuel pump fails, are there any other problems with flying with an inop boost pump that I'm not aware of? I plan on taking it out once I get home and sending it for overhaul.

[Guest]

My boost pump quit working...I'm about 1 hour from my home field...other than the implicit risk of having no back up pump in case the engine fuel pump fails, are there any other problems with flying with an inop boost pump that I'm not aware of? I plan on taking it out once I get home and sending it for overhaul.

If you're in the air when it quits I guess you keep going until next landing.

If you're on the ground how do you operate the plane in accordance with the PoH if the pump does not work?

Clarence

[gsxrpilot]

My boost pump quit working...I'm about 1 hour from my home field...other than the implicit risk of having no back up pump in case the engine fuel pump fails, are there any other problems with flying with an inop boost pump that I'm not aware of? I plan on taking it out once I get home and sending it for overhaul.

Nope.

[Shadrach]

I can't think of anything that would prevent you from flying home sans boost pump. However, I do not believe it is legal. Is it risky? Certainly more risky than flying with an operable boost pump.  

Summer time starting might be a bit tricky without a method of priming. One would have to be mindful of heating up the starter.

Is there MX available off the field? Would your Mechanic consider submittting a ferry permit to the FAA?

I understand how you feel. I'd not want my plane living outside until a suitable replace,net could be obtained and installed.

Edited September 7, 2015 by Shadrach