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  #11  
Old 04-15-2021, 04:40 AM
fixnflyguy fixnflyguy is offline
 
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 1,373
Default I have 2 electrics in series

I am running an O320H2AD Carbureted and eliminated the engine driven pump because of the mounting location. I utilize 2 of the Facet low pressure cubes in series, one mounted in the tunnel per plans (boost pump) and the other mounted on the firewall downstream of the gascolator that I run full time in lieu of a mechanical. Either pump will operate as the primary or boost with the other one "free flowing". I pondered the parallel set-up, but scrapped that idea for several reasons, mainly because of complexity and seemingly more failure points than in series.
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  #12  
Old 04-15-2021, 06:36 AM
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DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
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Quote:
Originally Posted by Av8torTom View Post
Is there ever a time when you have a engine driven pump failure that results in restricted fuel flow through the pump?
Specific to the question, I'd say "Not possible". A standard pump operates with two simple disk check valves. One or both might leak for a variety of reasons, with a loss of pumping efficiency due to backflow, but I can't imagine how they could block flow.

Photo is looking up from the bottom. Diaphragm chamber is on the other side of this plate.
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  #13  
Old 04-15-2021, 08:59 AM
KayS KayS is offline
 
Join Date: Jul 2009
Location: lake constance
Posts: 355
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Quote:
Originally Posted by Av8torTom View Post
So are you suggesting a parallel arrangement?
Nope, i don't. had to replace a mechanical fuel pump recently and found the concept to be very clever. just make sure you install an overflow fitting with transparent tube. check it on a regular basis and you're good to go.
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  #14  
Old 04-15-2021, 02:25 PM
Freemasm Freemasm is offline
 
Join Date: Nov 2017
Location: Orlando
Posts: 343
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Quote:
Originally Posted by fixnflyguy View Post
I am running an O320H2AD Carbureted and eliminated the engine driven pump because of the mounting location. I utilize 2 of the Facet low pressure cubes in series, one mounted in the tunnel per plans (boost pump) and the other mounted on the firewall downstream of the gascolator that I run full time in lieu of a mechanical. Either pump will operate as the primary or boost with the other one "free flowing". I pondered the parallel set-up, but scrapped that idea for several reasons, mainly because of complexity and seemingly more failure points than in series.
I tried to not comment but, please tell us you have sufficient electrical architecture for this configuration. Part of the elegance of the vintage configuration is the independent power sources for both ignition and fuel supply. I'll say again, those old system and component designers were good.
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  #15  
Old 04-16-2021, 08:12 AM
fixnflyguy fixnflyguy is offline
 
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Location: Winston-Salem, N.C.
Posts: 1,373
Default I do

I do have a back-up battery separate power source. I'm not the only electrically dependent system out there, and I had at once been tempted to install the Romec pad mounted pump (with reduced pressure) , but didnt do it. The H2AD in a -4 requires a "cowl bump" of fairly good size to clear a standard diaphragm pump as well as a long set of lines run to the carb...I did not want to do that. The reliability of the little cube pumps is very high in my opinion, and I had an actual alternator failure (spade terminal cracked in half) but the battery will carry that pump a loooong way. My real concern would be a battery/master failure and complete electrical loss, hence the additional battery. Still looking at lighter battery options, but I like the idea of 2 for more than just the fuel pumps.
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  #16  
Old 04-17-2021, 10:36 AM
SoupSandwich SoupSandwich is offline
 
Join Date: Apr 2021
Location: Sioux Falls, SD
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Quote:
Originally Posted by Av8torTom View Post
Question. Vans calls for the electric fuel pump and the engine driven fuel pump to be in series (carbureted engine). That is, fuel flows from the tanks, to the fuel selector to the electric fuel pump thru the gascolator to the engine driven pump to the carburetor.

Does anyone utilize parallel pump systems where both electric and engine driven pumps can deliver fuel to the carb independently of each other?

Is there ever a time when you have a engine driven pump failure that results in restricted fuel flow through the pump?

Thanks,

Tom
Not Vans, but I did have an issue a couple months ago where my fuel supply was cut off in my Piper Archer because the electric pump had an issue, it was intermittent and would resolve when we turned the electric pump on leaving us to look at everything except the electric pump. We ended up doing a lot of troubleshooting and replaced a lot of parts, always thinking we had the issue fixed and then we would lose fuel pressure again, meaning it would drop to zero, in flight. Thankfully turning on the electric pump always resolved the problem, and in most cases we could turn the pump off after a minute and things would be fine again.

Still don't fully understand WHY, but when we finally replaced the electric pump after replacing literally the entire fuel system firewall forward (pump, hoses, and gascolator) it has not come back.
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  #17  
Old 04-18-2021, 07:51 AM
Scott Hersha Scott Hersha is offline
 
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Location: Cincinnati, OH
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Quote:
Originally Posted by SoupSandwich View Post
Not Vans, but I did have an issue a couple months ago where my fuel supply was cut off in my Piper Archer because the electric pump had an issue, it was intermittent and would resolve when we turned the electric pump on leaving us to look at everything except the electric pump. We ended up doing a lot of troubleshooting and replaced a lot of parts, always thinking we had the issue fixed and then we would lose fuel pressure again, meaning it would drop to zero, in flight. Thankfully turning on the electric pump always resolved the problem, and in most cases we could turn the pump off after a minute and things would be fine again.

Still don't fully understand WHY, but when we finally replaced the electric pump after replacing literally the entire fuel system firewall forward (pump, hoses, and gascolator) it has not come back.
This same issue has been reported on this forum many times over the last several years, and I think itís mostly, if not always, on a low pressure carbureted engine. I had these same issue on my RV6 20 years ago, and couldnít find the problem. I also experience the fuel pressure drop under certain conditions on my RV4. I spoke with a Tempest rep at Sun N Fun a couple days ago, and they were baffled at the symptoms. In my case, when I take off - full power, steep climb angle, high fuel flow - my fuel pressure will slowly drop to zero after I turn off my boost pump. Nothing changes with engine operation. Power is unchanged, as is all engine indications. When I level off, the fuel pressure slowly builds, but may take 15 minutes to do so. Iíve changed the VDO style pressure transducer, but that didnít help, and I didnít think it would because when I turn on my boost pump in this situation, the pressure quickly rises to normal. I just got back from SNF, 4.5 hours each way, and all fuel pressure indications were normal both ways, because I left the boost pump on until level off. The Tempest rep wanted me to collect data and give their experts a call when Iíve done that, even though itís not their pump - itís a Lycoming part - but very similar apparently. If I do an enroute step climb, the same thing happens - fuel pressure to zero, all other engine indications and operation normal - unless I use my boost pump, which will keep the low fuel pressure warning quiet. Iím reluctant to install a new engine driven fuel pump, because that has been done by several people here, and by me on my RV6, and it didnít change anything. According to the Tempest website the engine driven fuel pump should last until TBO...... OR 10 years, whichever comes first. I mentioned this to the Tempest rep at the show, and he wasnít convinced I needed to change the pump, as long as there is nothing leaking out of the witness line. I check that on every post flight.
Iím corn-fused, how about you?
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RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
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RV8/2018 built/Sold(sadly)
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JAN2021
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  #18  
Old 04-18-2021, 08:21 AM
SoupSandwich SoupSandwich is offline
 
Join Date: Apr 2021
Location: Sioux Falls, SD
Posts: 5
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Quote:
Originally Posted by Scott Hersha View Post
This same issue has been reported on this forum many times over the last several years, and I think itís mostly, if not always, on a low pressure carbureted engine. I had these same issue on my RV6 20 years ago, and couldnít find the problem. I also experience the fuel pressure drop under certain conditions on my RV4. I spoke with a Tempest rep at Sun N Fun a couple days ago, and they were baffled at the symptoms. In my case, when I take off - full power, steep climb angle, high fuel flow - my fuel pressure will slowly drop to zero after I turn off my boost pump. Nothing changes with engine operation. Power is unchanged, as is all engine indications. When I level off, the fuel pressure slowly builds, but may take 15 minutes to do so. Iíve changed the VDO style pressure transducer, but that didnít help, and I didnít think it would because when I turn on my boost pump in this situation, the pressure quickly rises to normal. I just got back from SNF, 4.5 hours each way, and all fuel pressure indications were normal both ways, because I left the boost pump on until level off. The Tempest rep wanted me to collect data and give their experts a call when Iíve done that, even though itís not their pump - itís a Lycoming part - but very similar apparently. If I do an enroute step climb, the same thing happens - fuel pressure to zero, all other engine indications and operation normal - unless I use my boost pump, which will keep the low fuel pressure warning quiet. Iím reluctant to install a new engine driven fuel pump, because that has been done by several people here, and by me on my RV6, and it didnít change anything. According to the Tempest website the engine driven fuel pump should last until TBO...... OR 10 years, whichever comes first. I mentioned this to the Tempest rep at the show, and he wasnít convinced I needed to change the pump, as long as there is nothing leaking out of the witness line. I check that on every post flight.
Iím corn-fused, how about you?
I see the drop in pressure during steep climbs, but not to zero... My zero pressure conditions would happen at straight and level flight as well, and it was typically a very sharp drop. We replaced the electric pump a few weeks ago and have not seen the symptom return.

In this whole process, we did discover that the POH for the Archer, unlike many other pipers (again, not Vans, but applicable), does specify that the electric fuel pump is to remain on during climb out... I'm not sure if this is a Lycoming O-360 180hp thing (not sure what you have)? At any rate, I now turn on the pump when doing steep climbs to keep pressures up during climb.
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  #19  
Old 04-18-2021, 05:56 PM
Scott Hersha Scott Hersha is offline
 
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Location: Cincinnati, OH
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I do have a Lyc O-360-A1A on my RV4, and also had this on my RV6 years ago. If leaving my boost pump running until level off, and during step climbs makes everything happy, then Iím happy to do that.
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RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019 Flying
Cincinnati, OH/KHAO
JAN2021
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  #20  
Old 04-18-2021, 08:44 PM
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newt newt is offline
 
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Location: Sydney, Australia
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I'd been led to believe that pressure drops during steep climbs were a sensor artifact caused by the way the fuel pressure sender works.

https://vansairforce.net/community/s...6&postcount=10 (thread includes a link to a Dynon technical advisory describing the issue)

I've sometimes noticed that a rapid climb causes a fuel pressure indication reduction on my O-320 carburetor engine. I usually turn on the electric pump. If I run an experiment and don't turn on the electric pump, the needle can slowly reduce to zero during an extended climb but the engine doesn't seem to notice; It's clearly still getting plenty of fuel, it's never given me so much as a burp, let alone a stumble.

- mark
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