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Jims Web Site
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Date: 10-1-2013
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Number of Hours: 10.00
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Manual Reference: (none)
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Brief Description: Worked fuel pump location
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Initially, although some fuel made it through to the fuel pumps, the fuel pressure seemed low. It would run about 3.5 psi, but the gauges I purchased indicated a gtreen arc at aroun 5-9. While the pressume would likely have been adequate for a float carburetor, it would meed remarking the gauge. It also left no reserve pressure.
The, it developed the [um[s would not always self-prime. I could get them pumping by applying pressure through the fuel tank vent, which showed the pumps were working. However, this is not a satisfactory long term approach.
I splint the fuel line at its entrance point to the fuselage, and tried installing aq pump there. While this worked, it had, IMHO, several negative implications:
1) Eiither both pumps had to run all the time, or be electrically switched whern moving the mechanical valve from one tank to another.
2) Although two pumps would be used, there was no redundancy. If a pump failed, there weas no backup.
3) Worse still, when a pump failed, it would be impossible to get the fuel from that wing tank. If a situation existed in which one tank had been exhausted, and the pump on the other tank failed, a forced landing was very likely to be necessary.
Both pumps really needed to serve either tank, and be located after the sediment bowl. Thus, the original location on the firewall seemed best.
I checked the manufacturer's data on the pumps Zenith sent. I learned several things:
1) The Zenith-supplied pumps were speced to produce only 3.5 psi or thereabouts.
2) These pumps were only intended to draw fuel upwartds about 24" - marginal or inadequate for an upper firewall location.
3) There was no check valve in this model pump, which I alredy knew. I'd installed an external check valve on each pump to remedy this.
However, I also discoveree the same manufacturer had a pump of the same form and fit which produced 7 psi, would drawe upwards much further, and had an internal check valve.
I purchased the new pumps, and placed them in the ld firewall location.
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temporary pump location
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New installation
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