Boost Pumps?

[Northern Mooniac]

I'm picking my mooney in a few weeks, and just curious about the boost pumps.

I has a prime pump button, low boost and high boost.

I get the prime for engine starting, what do you use the low and high boost for?

[DonMuncy]

It is to provide fuel in the event of a failure of the mechanical fuel pump. It is actually only one pump for both low, high and prime.

I use high boost and primer for starting, but have never used it in flight.

[Northern Mooniac]

Why do you use both high boost and the primer?

I would have thought it would be recommended to use the low boost on approach similar to a cirrus?

[DonMuncy]

The K does not recommend the use of a boost pump except in the event of a failure. (I think).

It is my understanding that the boost pump puts fuel into one area of the induction system and the primer into another (not sure where, or which is which). Someone told me about the use of both, and I have good luck starting with that method.

[kortopates]

Be sure to read the POH, especially the systems section. And any good transition training CFI will/should clarify this as well as cover emergency procedures and ensure you have a good checklist tailored for the equipment in your plane. 

[Guest]

The main fuel boost pump delivers fuel through the the engine fuel system and ultimately to the fuel injection nozzles in either the high or low settings.  In airframes without the priming system the high boost setting is used to prime the engine through the fuel injection nozzles. Low boost is normally used to increase fuel delivery pressure to the engine driven fuel pump with heat soaked engines.

In those airframes with a priming system fuel is delivered through two priming jets located at the front of the left and right induction elbows.

Clarence

[BradB]

In the TN, low boost is on for climbing when above 12k and all the time above 18k.

 

 

[kortopates]

3 hours ago, BradB said:

In the TN, low boost is on for climbing when above 12k and all the time above 18k.

Perhaps even more importantly, whenever you see TIT climb above 1450F in climb, the low boost should come on. All of these are too suppress vapor formation in the lines (vapor lock) as the fuel is being sucked up from the engine driven pump at high FF into hot heat soaked engine compartment. Usually this use is recommended only as needed as stated by Continental in their Operators manual, but Mooney seems a bit unique in suggesting this a normal procedure. The truth it is should only be necessary for a heat soaked engine and once cooled down in cruise (assuming not running it real hard) the low boost should be able to safely turned off.

There is one more usage of the TN low boost for in-flight non-emergency conditions that also applies all the big bore Continental installations: changing tanks, just like most lycomings.

[jlunseth]

Don is correct when it comes to the K.  The boost pump is not used for any flight regime except emergencies, and if you are smart, for starting.  I am probably the guy who told him to use the boost and then the prime to start a K.  Clarences description of where the fuel goes is correct, but with one addition.  Supposedly, if you use the boost pump with the fuel flow knob full off, there is a return line and you can run the boost pump all day and the fuel will go back in the tank, not into the cylinder.  I say "supposedly" because that is not what I have found in my K (231).  Running the boost pump too long is the one way I can create a backfire, so I don't recommend that - running it too long.

The K engines are very easy starters, the only issue is that the fuel lines may be empty even if the plane has only sat a short time, so if you use the primer only, the engine will catch but then die for lack of fuel.  The simple solution is to fill the fuel line first, and you do that by pulling all the knobs full out and running the high boost until the fuel pressure becomes stable.  It doesn't matter what number it becomes stable at, just that it becomes stable.  That tells you that the line is full.  If you don't have a fuel pressure gauge, run the high boost for ten seconds.  Then put all the knobs full in and run the primer for whatever length of time the POH recommends for the particular OAT.  That puts fuel in the induction system.   Then start the engine.  

Sometimes, even though you have filled the lines with the high boost, there is still some air.  I leave the safety cover in place over the boost switch and push the top of it.  That makes the switch an "instant off" switch, in other words, it does not go into the detent position and all you have to do to stop the pump is let go.  So when the engine catches and if it starts to die, just touch the top of that switch, which will keep the engine running until the mechanical fuel pump has a chance to clear the lines out and get a consistent flow to the cylinders.  Works every time and under all conditions.   I even started at Leadville that way once, after the POH recommmended "high altitude start" failed.  

But again, you do not use the boost pump for any regime of flight in the K except emergencies and start up.