Boost Pump, Fuel Pressure issue

[Sue Bon]

I decided to go for an end-of-the-year VFR flight and had the following problems: The boost pump tried to work, had no success, and then gave up and died. I managed to get the engine started without it and then noticed that the fuel pressure was too high. I taxied into the sun and let the engine run for about 10-15 minutes and the fuel pressure gauge went down a bit, but was still in the red line. I decided not to risk it and put my plane back in the hangar.

Are these issues connected? A CFI friend said the fuel pressure issue could just be moisture in the instrument and not actually a problem with the pressure itself. A guy on the ground that helped me push my plane into the hangar said he once had fuel pressure in the red that suddenly went to zero and he found himself looking for a field to land in.

I'm nervous that the electric fuel pump will have to be ordered from the US and will take forever. I hope not.

 

[Shadrach]

2 hours ago, Sue Bon said:

I decided to go for an end-of-the-year VFR flight and had the following problems: The boost pump tried to work, had no success, and then gave up and died. I managed to get the engine started without it and then noticed that the fuel pressure was too high. I taxied into the sun and let the engine run for about 10-15 minutes and the fuel pressure gauge went down a bit, but was still in the red line. I decided not to risk it and put my plane back in the hangar.

Are these issues connected? A CFI friend said the fuel pressure issue could just be moisture in the instrument and not actually a problem with the pressure itself. A guy on the ground that helped me push my plane into the hangar said he once had fuel pressure in the red that suddenly went to zero and he found himself looking for a field to land in.

I'm nervous that the electric fuel pump will have to be ordered from the US and will take forever. I hope not.

 

https://aeromotors.azurewebsites.net/

Send an email (or call) Aeromotors.  They may have a unit on the shelf that they can send out right away. The trouble is, you may need to wire funds as I don't think they take credit cards. 

Fuel pressure right at redline is not a concern for operations as Mooney's redline specification is much lower than the RSA fuel system redline (45psi IIRC).  The question is what changed?  Do you know where it usually runs with the mechanical pump alone?  Mine is about 28psi using the engine driven pump alone; the boost pump pushes the needle to redline.

You were smart not to fly. The boost pump is your only way of delivering fuel to the engine in the event of a mechanical pump failure.  While mechanical pump failures are rare, a boost pump failure can on occasion induce other problems. There have been cases (rare) where internal pieces of boost pump parts have departed the pump housing and fouled the system up stream. 

If there is anything I can do stateside to help facilitate a pump for you, don't hesitate to PM me. 

[Sue Bon]

23 minutes ago, Shadrach said:

Do you know where it usually runs with the mechanical pump alone? 

It's usually at about 27.

It goes up to 28 with the boost pump.

[EricJ]

Was it cold?   Esp.  below freezing?   There could have been some water or moisture frozen somewhere, especially in the boost pump since that's low in the system.   As mentioned, it could even have been in the instrument, but who knows.    Checking the electrical connections to the boost pump make sure it's getting sufficient power is a good idea before concluding it's the pump.

Bummer that you didn't get to fly, but I think you made the right call.   The boost pump is the only backup to the mechanical pump, and if they were both acting fussy that's not a good thing.

I hope you get it sorted without too much trouble.

[N201MKTurbo]

The fuel always flows through the boost pump. If the vanes broke apart and left the pump, it could reduce the restriction of the pump and cause the fuel pressure to increase. The screen down stream of the boost pump was added to catch the vanes when they fail.

[Shadrach]

23 hours ago, N201MKTurbo said:

The fuel always flows through the boost pump. If the vanes broke apart and left the pump, it could reduce the restriction of the pump and cause the fuel pressure to increase. The screen down stream of the boost pump was added to catch the vanes when they fail.

I was think similar. It’s conceivable that even if the pump merely seized that the restriction would be less than with the impeller “windmilling” in the line.

[AndreiC]

Since I dealt with Aeromotors recently (my boost pump is with them as we speak), I can tell you that they have on-the-shelf refurbished Dukes pumps. If yours is made by the other common manufacturer (forget now the name), they have to have yours to refurbish. Takes them 4-5 days in that case. 

[Sue Bon]

4 hours ago, AndreiC said:

Since I dealt with Aeromotors recently (my boost pump is with them as we speak), I can tell you that they have on-the-shelf refurbished Dukes pumps. If yours is made by the other common manufacturer (forget now the name), they have to have yours to refurbish. Takes them 4-5 days in that case. 

Thanks. I actually did call them. They said just that. I'll have to have it taken out when the shop opens up after the Christmas/New Year's holiday and see what's up.

Thanks all!

[ArtVandelay]

The fuel always flows through the boost pump. If the vanes broke apart and left the pump, it could reduce the restriction of the pump and cause the fuel pressure to increase. The screen down stream of the boost pump was added to catch the vanes when they fail.

On my J the fuel pressure sensor is downstream of the boost pump, on the engine after the engine pump, so I think a restriction in the boost pump would lower the fuel pressure?
I would do a full power runup and check fuel flow to see if it’s at spec.

[Sue Bon]

1 minute ago, ArtVandelay said:

so I think a restriction in the boost pump would lower the fuel pressure?

Yeah, as I understand it, that's exactly what he was saying. If the vanes broke apart, the flow would be less restricted, thus increasing the fuel pressure. I might be wrong.

[ArtVandelay]

Yeah, as I understand it, that's exactly what he was saying. If the vanes broke apart, the flow would be less restricted, thus increasing the fuel pressure. I might be wrong.

Ahh, I mis read it and thought he was saying the debris would restrict the flow. And did you try switching tanks?

[N201MKTurbo]

Just now, ArtVandelay said:

On my J the fuel pressure sensor is downstream of the boost pump, on the engine after the engine pump, so I think a restriction in the boost pump would lower the fuel pressure?
I would do a full power runup and check fuel flow to see if it’s at spec.

The engine driven pump draws fuel into the pump by mechanical force from the engine, then the spring in the pump pushes it out. A lower restriction in the feed line to the engine driven pump, could allow more fuel to be drawn into the mechanical pump on each stroke, but the spring in the pump determines the output pressure, not the volume of fuel in the pump. But with more volume in the pump, the spring would be more compressed and it would have more force.

I was thinking the broken boost pump would have less restriction than the functioning pump. That’s why Sue’s fuel pressure increased.

[Sue Bon]

16 minutes ago, ArtVandelay said:

And did you try switching tanks?

No. Nor did I think to do a runup. Once the weather improves, maybe I'll go do both. But the boost pump really sounded like it died on the spot. I have a feeling it will need to be overhauled or replaced.

[Shadrach]

15 minutes ago, N201MKTurbo said:

The engine driven pump draws fuel into the pump by mechanical force from the engine, then the spring in the pump pushes it out. A lower restriction in the feed line to the engine driven pump, could allow more fuel to be drawn into the mechanical pump on each stroke, but the spring in the pump determines the output pressure, not the volume of fuel in the pump. But with more volume in the pump, the spring would be more compressed and it would have more force.

I was thinking the broken boost pump would have less restriction than the functioning pump. That’s why Sue’s fuel pressure increased.

So the question is under normal circumstances, does the mechanical pump drive the boost pump’s impeller when the boost pump is off? 

[N201MKTurbo]

43 minutes ago, Shadrach said:

So the question is under normal circumstances, does the mechanical pump drive the boost pump’s impeller when the boost pump is off? 

That is a good question. It has been years since I dissected a boost pump. I have 3 cores in the hanger in a dusty old box, I will have to look one over when I'm out there today.

[N201MKTurbo]

47 minutes ago, Sue Bon said:

No. Nor did I think to do a runup. Once the weather improves, maybe I'll go do both. But the boost pump really sounded like it died on the spot. I have a feeling it will need to be overhauled or replaced.

They are kind of a consumable. I have replaced 5 or 6 in 6000 hours of Mooney flying.

[Shadrach]

7 minutes ago, N201MKTurbo said:

That is a good question. It has been years since I dissected a boost pump. I have 3 cores in the hanger in a dusty old box, I will have to look one over when I'm out there today.

My guess is that the mechanical pump does drive the boost pump unless the sleeve bearing on the impeller shaft fails. 
The elimination of the fuel lubricated, sleeve bearing, is just one of many improvements that Aeromotors makes to the dukes pumps during overhaul. 

[Shadrach]

4 minutes ago, N201MKTurbo said:

They are kind of a consumable. I have replaced 5 or 6 in 6000 hours of Mooney flying.

They used to be. I think the upgraded Aeromotors pumps will prove much more durable. 
 

 

[N201MKTurbo]

1 minute ago, Shadrach said:

My guess is that the mechanical pump does drive the boost pump unless the sleeve bearing on the impeller shaft fails. 
The elimination of the fuel lubricated, sleeve bearing, is just one of many improvements that Aeromotors make to the dukes pumps during overhaul. 

I don't recall a sleeve bearing per se, it just had a hole bored into the pump housing that the pump shaft passed through. It had a small carbon seal at the bottom end and the shaft was held in place by the pin that drove the impeller wheel.

[N201MKTurbo]

1 minute ago, Shadrach said:

They used to be. I think the upgraded Aeromotors pumps will prove much more durable. 
 

 

I have a Weldon pump. It has about 15 years and 1500 hours on it. It is still going strong.

[Shadrach]

5 minutes ago, N201MKTurbo said:

I have a Weldon pump. It has about 15 years and 1500 hours on it. It is still going strong.

Yes they are superior to the original Dukes design. I asked Ole (owner of Aeromotors) about upgrading. He said he would happily sell me one bu that his overhauled Dukes unit would be just as reliable. I’m only about 5 years post overhaul, but I have to say the new pump performs noticeably better. It’s not quieter but it sounds better, builds pressure faster an is unaffected by temperature. I believe the “continuous use” restriction is eliminated.

[Ragsf15e]

1 hour ago, Sue Bon said:

No. Nor did I think to do a runup. Once the weather improves, maybe I'll go do both. But the boost pump really sounded like it died on the spot. I have a feeling it will need to be overhauled or replaced.

While it sounds like your pump died, a little digging could be in order.  These other guys know more, but the electric pumps usually start leaking pretty good before totally giving up.  There's a little drain below it.  Any chance there’s a blue fuel streak behind it or on the ground below it where you shut down or where you start the engine?

[Sue Bon]

2 minutes ago, Ragsf15e said:

While it sounds like your pump died, a little digging could be in order.  These other guys know more, but the electric pumps usually start leaking pretty good before totally giving up.  There's a little drain below it.  Any chance there’s a blue fuel streak behind it or on the ground below it where you shut down or where you start the engine?

Ohh, interesting! I didn't notice anything. Maybe I'll go look in the hangar tomorrow. It's been raining all day, so any evidence left on the apron will be gone.

[PT20J]

An engine-driven diaphragm pump has an output pressure that varies inversely with fuel flow: pressure will be highest at idle and lowest at full power.

The amount of fuel pumped at idle per pump stroke is so low that a restriction at the input should not have an effect on the pressure. I'm reasonably certain that the design of the boost pump precludes a failure from restricting fuel flow. That would be an unacceptable failure mode.

It's not clear from the description exactly what happened to the boost pump. If it is jammed, I would expect the motor to draw excessive current and flip the breaker/switch. So, how did you know the pump was bad? Did it stop making a sound, or did you just not see fuel pressure? If the latter, maybe something is up with the gauge.

 

[Shadrach]

3 minutes ago, Ragsf15e said:

While it sounds like your pump died, a little digging could be in order.  These other guys know more, but the electric pumps usually start leaking pretty good before totally giving up.  There's a little drain below it.  Any chance there’s a blue fuel streak behind it or on the ground below it where you shut down or where you start the engine?

Leak was the failure mode for mine both times I sent out for reseal/IRAN by DG Supply twice (they don’t service dukes any longer) and then Aeromotors. The Dukes pump was never a robust device. It sounded like it was laboring, especially on cold days. Some times on cold days it would not turn on the first flick of the switch.  
I only used it for priming for fear of wearing it out. Upgraded dukes pump spins like a top. I leave it on for pattern work.