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Fuel pumps in series can get blocked

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gcrowder2

Joined: 09 Jan 2006
Posts: 136
Location: Golden, Colorado USA

Posted: Wed Feb 22, 2006 7:07 am Post subject: Fuel pumps in series can get blocked

I switched the pumps on my setup from series to parallel as the Ellison 

throttle body

on my Subaru setup only requires 3 psi.  One big negative on two pumps in 

series is that if

there is a blockage, both pumps are taken out.  In the parallel arrangement, 

if  one pump

gets blocked, the other pump can still deliver fuel.



                                                Glenn



[quote]From: "Craig Ellison" <craig.ellison2(at)verizon.net>

Reply-To: europa-list(at)matronics.com

To: <europa-list(at)matronics.com>

Subject: Re: RE: 914 Fuel System

Date: Tue, 21 Feb 2006 17:43:31 -0800




<craig.ellison2(at)verizon.net>



All,



I too had my system set up in parellel and changed to series after talking

to John H.  One reason I remember of the conversation was about allowing

proper readings on the fuel pressure/MP differential gauge.



craig ellison

A205/N205CN

Almost ready to fly



---

Ivor Phillips

Joined: 16 Jan 2006
Posts: 253
Location: London UK

Posted: Wed Feb 22, 2006 7:56 am Post subject: Fuel pumps in series can get blocked

Glen that is not actually the case,  If one Pump became blocked,     ( There 

are small mesh filters on the inlet)      the second pump would draw its 

fuel around the Bi-pass pipe and Non-return valve,

But i agree i would also prefer the Parallel system,

On the Pierburg website there no mention of running these pumps in series , 

schematics only show parallel,        Makes you wonder!!!



 	  Quote: 	
		    I switched the pumps on my setup from series to parallel as the Ellison

 throttle body

 on my Subaru setup only requires 3 psi.  One big negative on two pumps in

 series is that if

 there is a blockage, both pumps are taken out.  In the parallel 

 arrangement,

 if  one pump

 gets blocked, the other pump can still deliver fuel.




	


Ivor Phillips

tonyk(at)kaon.co.nz
Guest

Posted: Wed Feb 22, 2006 12:06 pm Post subject: Fuel pumps in series can get blocked

The reason for the change to series based pumps is to bring the fuel pressure down to that specified by Rotax. If you measure the differential fuel pressure to airbox pressure as recommended then you'll find that the pressure delivered by parallel pumps is too high.



Having said that. There are many 914's flying with parallel pumps as this is what Rotax used to show in the installation manual.



Unless you intend retrofitting  the UMA pressure sensor there is no need to change.



For new installations the Rotax manual now shows pumps in series with bypass valves



Tony

daseitz(at)cfl.rr.com
Guest

Posted: Wed Feb 22, 2006 12:56 pm Post subject: Fuel pumps in series can get blocked

--

europa flugzeug fabrik

Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA

Posted: Thu Feb 23, 2006 8:00 pm Post subject: Re: Fuel pumps in series can get blocked

 	  tonyk(at)kaon.co.nz wrote: 	
		  The reason for the change to series based pumps is to bring the fuel pressure down to that specified by Rotax. If you measure the differential fuel pressure to airbox pressure as recommended then you'll find that the pressure delivered by parallel pumps is too high. 	


I have them in parallel, and it would be a rather "Rube Goldberg" arrangement to make them series.  That's because I have (all in the trigear console tunnel) a sump I made.  It's attached to the front of the floor-mounted fuel valve and has 2 outlets.



In a parallel setup, do you think cutting back the volts on the boost/emergency pump will relieve the pressure?  I was thinking a 3.9V 10W Zener diode (if I can find 'em), parallel pair (reasonably matched in Vz) for redundancy.  I know I can test it for flow rate etc., but do you see a reason not to do this?



 	  Quote: 	
		  Unless you intend retrofitting  the UMA pressure sensor there is no need to change. 	


I think that don't come out quite right.    The 914 carbs may indeed tolerate excess pressure, but to restate what a famous football coach here once said, "On any given Sunday....a carb may flood!"



Reg,

Fred F.

BEBERRY(at)aol.com
Guest

Posted: Fri Feb 24, 2006 1:12 am Post subject: Fuel pumps in series can get blocked

I am really learning about fuel pumps and pressures etc (I think) and  wonder 

if anyone can comment on the problem I have with getting a smooth  running 

engine at RPM below about 3600 on my 914.  Could it be  overmuch fuel pressure 

and carb flooding with both pumps on in my parallel  system?  On the other hand 

when doing test engine ground runs I have  the pumps, filters etc in view and 

there is always only one pump fully  working as witness the amount of fuel 

flowing through the transparent  filter barrels..

 

Going back to some recent discussions on filters and accumulation of  grot.  

A good while ago I removed a huge amount of stuff from my  carbs and jets, 

none of which had been trapped by the filters which were  as clean as a whistle.  

With my briefish experience of the Rotax I  find this curious.

 

Patrick

paul.mcallister

Joined: 09 Jan 2006
Posts: 177
Location: Waukesha, WI USA

Posted: Fri Feb 24, 2006 6:45 am Post subject: Fuel pumps in series can get blocked

Fred,



The standard Europa design has the fuel return coming in at the bottom of

the tank.  I made my system return the fuel into the top of the tank via a

1/4" aluminum line.  I found in my setup with parallel pumps that I did not

did not exceed the maximum return fuel pressure as specified by Rotax.



Paul

n100rh(at)sbcglobal.net
Guest

Posted: Fri Feb 24, 2006 7:29 am Post subject: Fuel pumps in series can get blocked

Paul,

Makes perfect sense. This way you aren't returning back against the 

hydrostatic pressure of all the fuel in the tank.



Ralph

RK Hallett III

Reno,NV



Paul McAllister wrote:

 	  Quote: 	
		   



 Fred,



 The standard Europa design has the fuel return coming in at the bottom of

 the tank.  I made my system return the fuel into the top of the tank via a

 1/4" aluminum line.  I found in my setup with parallel pumps that I did not

 did not exceed the maximum return fuel pressure as specified by Rotax.



 Paul

europa flugzeug fabrik

Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA

Posted: Fri Feb 24, 2006 8:27 am Post subject: Re: Fuel pumps in series can get blocked

 	  n100rh(at)sbcglobal.net wrote: 	
		  Makes perfect sense. This way you aren't returning back against the hydrostatic pressure of all the fuel in the tank. 	


If the return line still runs along the floor, I was assuming that the head pressure would be identical -- full tank vs. upward push in the return line.  Partial tank; we're in the hole. However, I can just about remember what my Physics 101 prof looked like!  Whatever works, though, I always say.



Best would be the routing return line back along the fuselage side, thence to tank top.  That one I'm pretty sure of...    



Reg, 

Fred F..

paul.mcallister

Joined: 09 Jan 2006
Posts: 177
Location: Waukesha, WI USA

Posted: Fri Feb 24, 2006 9:15 am Post subject: Fuel pumps in series can get blocked

Fred,



Mine runs through the firewall along the side of the fuselage under the

window still and into the tank. It never gets to run uphill.



Paul

rparigor(at)suffolk.lib.n
Guest

Posted: Fri Feb 24, 2006 9:36 am Post subject: Fuel pumps in series can get blocked

Quick note on parallel vs series.



In parallel, if 1 pump destroys itself, and some debris jams the 1 way

valve in the pump opened, the other pump, although may be perfectly

functional may not create enough pressure to prevent the playing of silent

night.



Has anyone actual had a pump 1 way fail opened?



Like someone mentioned a Andair or similar 1 way in series with each pump

output could help with both pumps, or one 1 way not allowing back feed

from the aux pump back through main.



Not going to help the excess pressure though.



One thing I noticed on my build is that all fittings are not created

equal. Some have smaller internal holes than other. This for certain can

cause restriction on 914s where flow rates can be 40gph plus. I chose

fittings or bored so restriction held to minimum.



Paul it would be interesting to see if your lack of a too high

differential fuel pressure with both pumps on are in fact because of not

returning to bottom of tank, or because of lack of restriction in return

line??



The thicker the air, the greater the return pressure should be.



Ron Parigoris

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