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Electric Fuel Pump

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RVadmirer

Well Known Member
Does anyone know if the typical fuel system with in-line fuel pumps, (mech and elec) can be compromised by a failure or plugging of the electrical pump? I have read of this happening but can't find the article. A buddy has a plumbing system designed by an Engineer that provides a solution to the failure of either and I'm wondering if this would be a very good idea or just more complexity and weight with 1 in a million need..... :confused:
 
Some fuel pump systems have a bypass valve for this purpose. If the electrical pump fails, the mechanical pump on the engine will continue to draw fuel through the bypass valve.

Vern
 
RVadmirer said:
Does anyone know if the typical fuel system with in-line fuel pumps, (mech and elec) can be compromised by a failure or plugging of the electrical pump? I have read of this happening but can't find the article. A buddy has a plumbing system designed by an Engineer that provides a solution to the failure of either and I'm wondering if this would be a very good idea or just more complexity and weight with 1 in a million need..... :confused:
Click to expand...

This post reminded me of a conversation several years ago where a fellow Mid-Atlantic RV owner told me that his stock Van's electric boost pump malfunctioned, stopped fuel from flowing, leading to loss of the aircraft. As I recall, he was able to duplicate the fuel flow stoppage from the defective pump. As I recall, he contacted the pump manufacturer and confirmed that the pump does have the potential for this failure mode.

I searched my Mid-Atlantic RV archives and found this email from Rich Zeidman, May 2005:

Here is my statement to the FAA, including revisions from last night. I
bought the salvage back from the insurance, so I'll be rebuilding for quite
awhile.

Statement of Richard Zeidman, Pilot of RV6A N42RZ on May 11, 2005

On May 10, I flew with a passenger to Sussex County Airport (GED) and on the return flight, I stopped for fuel at Ridgely Airpark (RJD) for about 5-10
minutes. Upon engine restart no fuel pressure was noted. I suspected a vapor
lock and after 15 minutes the fuel pressure returned and an uneventful
flight home to New Garden followed. The next day, I returned to check the
problem. No discrepancies were visible on the fuel pump externally, but I
added a blast tube to help keep the engine fuel pump cool. A short solo test
flight was performed to check problem. The electric aux pump was on
throughout most of the flight. After takeoff, I climbed to 3000 ft and
headed west about 10 miles.

I then turned east and did slow flight for several minutes and a full power
off stall. I was over New Garden airport when I finished and decided to head
east toward my home. I was descending at 2000ft at 160 kts about 2-3 minutes later , I think I tested the aux pump switch and then when I noticed a power loss. I immediately tuned 180 toward New Garden and switched tanks from r to l and went full rich and checked my aux pump was on. Power loss continued and I noted RPM was now 900. I realized I was not going to be able to reach New Garden so I switched to 121.5 and called mayday and headed for a nearby field. After touching down normally with full flaps, the plane rolled several hundred feet and bounced. After the bounce the nose gear dug in and the plane flipped on it?s back. Upon releasing my harness I realized I was trapped and as soon as help arrived, I asked them to remove some of the broken plexiglass and I was able to slide out.

I confirmed now that the electric boost pump was malfunctioning, causing the
both night?s problem.

I disconnected the fuel line to the carb and the electric pump worked fine.
I reconnected it and initially it worked ok, 5psi, for about 5 minutes. It
changed tempo slightly after that. I then turned it off and back on and it
started buzzing and would not pump at all. I cracked the line to the carb
and the pressure dropped to zero. It is not allowing fuel to pass, so the
engine pump cannot work. I repeated the test again later.
Click to expand...

My recollection is that this incident was brought to the attention of Van's aircraft at the time.

Based on this incident, I added a check valve in parallel to the Van's electric boost pump on my RV-6A. That way a failure of the electric boost pump won't block all fuel from flowing to the engine.

Note that the high pressure fuel pump supplied with the RV-10 kit has a parallel check valve built right in to the fuel pump assembly.

Tim Lewis
RV-6A N47TD 1060 hrs
RV-10 N31TD (reserved) - Painting
 
AFP pump bypass

RVadmirer said:
Does anyone know if the typical fuel system with in-line fuel pumps, (mech and elec) can be compromised by a failure or plugging of the electrical pump? I have read of this happening but can't find the article. A buddy has a plumbing system designed by an Engineer that provides a solution to the failure of either and I'm wondering if this would be a very good idea or just more complexity and weight with 1 in a million need..... :confused:
Click to expand...

The Airflow Performance electric fuel pumps sold by Vans (and Airflow Performance) do not draw fuel through the pump, when the pump is off. There is a gold colored check valve mounted in the manifold on the pump's outlet end. During mechanical only operation, this valve is open. The open valve allows the mechanical (engine driven) pump to draw fuel directly from the selected fuel tank. In this mode, the electric pump is not part of the circuit.

afpfuelpressurecheckval.jpg


If you have a CAD viewing program I can send you a couple of drawings I made, to show how the fuel flows through the system, with the electric pump on and off.
If you want to see them, send me an email (you can find my email address in my user profile) requesting a copy.
Charlie Kuss
 
Charlie is absolutely correct regarding the AFP pump, which is in fact an Airtex pump. That check valve keeps fuel from flowing back to the tank when the electric pump is on. When it is off, the engine pump sucks fuel through it so if the electric pump fails, it is ops normal.

The low pressure Facett pump used with a carb has a flow through feature when it is off, no check valve and by pass needed.
 
David-aviator said:
The low pressure Facett pump used with a carb has a flow through feature when it is off, no check valve and by pass needed.
Click to expand...

While it does not appear to be common failure, the evidence indicates the flow through feature of the Facet low pressure pump can fail, and that it has failed in flight -- resulting in a forced landing and significant damage to the aircraft.
 
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Facet pump failure.

My thoughts 4 years after my facet pump failure.
1. If I had been paying closer attention, I would have noticed that the pump didn't sound quite right for a about month prior to the accident. If you notice this, get rid of your pump.
2. I am much more particular now in my pre start, electric pump check.
3. In my current plane, an RV7, I switched to the cylindrical pump, No 478360, used by many certified GA planes (also made by Facet). I'm not sure it's better, but it makes me feel better!!
Rich Zeidman
RV7 N42PZ
TSN 380 hrs
 
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THANK YOU!

I never saw any of these posts in "New Posts" so didn't think anyone was interested. Just checked the Safety sub-forum and found all this great input.
Thanks again. Must now rethink my plumbing.

I would assume the addition of a check valve would only work if the plumbing is a parallel system such as my buddy's and not applicable to my setup where all run in series?
Thanks again, very important issue to me!
 
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Another Point

With the Fuel Injection Pump from AFP that Van's sells you typically mount the fuel filter before the pump. In theory any debris that would cause problem with the fuel system is caught in the filter.

Maybe in the carb versions with the Facet pump a filter before the pump would be prudent.

Ted
 
Facet does recommend a pre-filter, there was at least one reported case of inlet debris causing a problem/blockage. If you look at the inlet side of the pump or fuel flow sensor you will see that the opening in not very large and some stringy or fuzzy debris could block fuel flow. I installed a 74 micron filter after the selector to protect down stream components.
 
RVadmirer said:
I would assume the addition of a check valve would only work if the plumbing is a parallel system such as my buddy's and not applicable to my setup where all run in series?
Click to expand...

The stock Van's fuel system design puts the electric boost pump in series with the engine driven boost pump. It sounds like this is the approach you are taking. The check valve installation I described is for this very setup (fuel pumps in series). The check valve provides an alternate fuel flow path around the electric boost pump if that pump fails in a "no flow" mode like Rich's did.

The installation is pretty simple. I put a "T" fitting (AN-824) upstream of the Facet pump and another "T" fitting downstream of the Facet pump, and a check valve between the two "T" fittings. Fuel can flow though either the Facet pump or the check valve to reach the engine driven pump, and then on to the carb.
 
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