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  #21  
Old 04-28-2018, 05:36 PM
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Sam Buchanan Sam Buchanan is offline
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I think you need a different pump......
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  #22  
Old 04-28-2018, 06:02 PM
Larco Larco is offline
 
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Maybe I am way off here with my understanding, but if the manufacture of the pump says not for continuous duty then why would they sell a block off plate for the engine driven pump when installing their system?
I would not want a pump that I could not leave on continuous if needed? But that is just me. :-)
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  #23  
Old 04-28-2018, 06:34 PM
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Quote:
Originally Posted by TS Flightlines View Post
'Probably' 2500+ continuous flight hour operation, based on the automotive installs and driving miles those pumps get before replacement is necessary.

Tom
This seems very low to me. I've had cars I've driven 200,000 miles and never never had to replace a pump.

Current vehicle is 4 years old...let's say approximately 2 hrs/day (more weekdays, less on weekends, but that's close) * 365 ~= 700/year * 4 years = 2800 hours so far . Watch, now it'll fail next week LOL!

The Andair pump says right on the spec sheet: Continuous duty. That's what I want in an electric boost pump, so I don't worry if I ever forget to turn it off, and I know it'll be good if the engine-driven pump fails for at least enough time to get me safely on the ground no matter where I am.

This is Experimental aviation, though, so everyone can choose their own solutions. YMMV.
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  #24  
Old 04-28-2018, 10:23 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by TS Flightlines View Post
'Probably' 2500+ continuous flight hour operation, based on the automotive installs and driving miles those pumps get before replacement is necessary.

Tom
Pumps installed in automobiles use dedicated fuel return lines or return directly into the tank. Not the same application here, as in this application excess fuel is returned back to the pump inlet, creating the "potential" for overheating the pump motor. You can't apply the track record of those auto pumps in this application, eventhough the pumps are the same. I would be like saying the Subaru engine has a great track record in automobiles and therefore will provide that same reliability in an airplane. Its all about the application intended by the design and these auto pumps aren't designed for re circulation. They transfer their heat to the fuel passing through them and their design presumes that fresh, relatively cool fuel will be flowing through them at all times to absorb this heat.

If you don't believe me and you have one of these style of pumps, put your mixture at ICO and turn the boost pump on. Let me know how long it takes to fail. I would guess 30 minutes tops. That is tongue and cheek of course, as this would create a potential fire risk.

I am not saying these are bad. I have one of these style pumps in my plane. Just pointing out that it is not idiot proof and has failure scenarios that may not be obvious the user.

Larry
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Last edited by lr172 : 04-28-2018 at 10:53 PM.
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  #25  
Old 04-28-2018, 10:27 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Larco View Post
Maybe I am way off here with my understanding, but if the manufacture of the pump says not for continuous duty then why would they sell a block off plate for the engine driven pump when installing their system?
I would not want a pump that I could not leave on continuous if needed? But that is just me. :-)
It is continuous duty in their fuel injection setup, where fuel is returned directly to the fuel tank and not back to the pump inlet, not necessarily in the case when that pump is used as a boost pump on a bendix FI setup.

Larry
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  #26  
Old 04-29-2018, 02:18 AM
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Quote:
Originally Posted by mfleming View Post
So I really did search high and low for this information but no joy.

I recently bought (but have not installed) a boost pump.
I've just learned that the pump cannot be run continuously. It seems the pump recycles fuel and eventually the fuel heats up.

I don’t have plans to run it all the time...just the normal takeoff/landing/fuel switching etc....
  • Are all boost pumps like this?
  • How long CAN I run the boost pump without worrying?
  • What happens its I run it too long due to distraction or perceived need?

I know there are experienced builders on this site who recommend this pump, so I'm pretty sure the pump is high quality and reliable.
I'm just confused on how to manage it and the consequences of running it to long.
Excellent question- most of the fuel pumps intended for 20-35psi fuel injection systems are adaptations or decendents of pumps designed for in-tank fuel-submerged applications. They are constant- displacement , meaning that they flow 25-50 gallons per hour(depending on model) through some sort of regulator or relief valve regardles of engine fuel flow, and consume 3.5-6 Amps continuous. This (and all)amperage flow can be expressed as BTU’s and these pumps are all designed to be fuel-cooled!

I personally regard adaptations of such pumps as “boost pumps” to be inherently dangerous as they accommodate this flow by recirculating fuel through a very short loop so they become fuel BOILERS if used continuously at low engine power settings. If you ever need to use one as emergency backup, be sure to fly at high-power/high fuel flow settings, and don’t be deceived into thinking that low power settings during this event are “babying” the pump. I’d suggest writting this into POH emergency proceedures.

These are well-designed pumps usually rated for continuous duty, but the ONLY way to safely operate them continuously is to have an adequately sized(i.e. 3/8” on RV’s), unobstructed, dedicated fuel-return line going back to the tank from the low pressure outlet of the regulator or relief valve.

These concerns do not apply to low-pressure, pulse-type pumps on engines with carbs- normal engine flows are completely adequate for keeping those cool, and anyway the carb float bowl vents any vapor that might be formed.- Otis
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Last edited by Hartstoc : 04-29-2018 at 02:30 AM.
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  #27  
Old 04-29-2018, 03:15 AM
rv8ch rv8ch is offline
 
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Default user a timer for flashing light or buzzer

Perhaps a timer on the "fuel pump on" warning light or buzzer would solve your problem of possibly forgetting to turn off the boost pump? I found this one on amazon - probably lots of other ways to do this.

https://www.amazon.com/Timer-Delay-R.../dp/B00PD65UGA

I thought of a red light on all the time, but I don't like red lights unless there is a problem, and during takeoff and landing it's probably not a good idea to train yourself to ignore red lights. Having the warning light come on after say 10 minutes might be enough.

Or maybe just a green light when the fuel pump is on? Would not bother you too much during times when you really want it on, like takeoff and landing, and you would probably notice it in cruise if you forgot to turn it off.
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  #28  
Old 04-29-2018, 03:46 AM
-goose -goose is offline
 
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Yes agree green light when on is what I went with.
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  #29  
Old 04-29-2018, 06:57 AM
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DanH DanH is online now
 
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Interesting. Lots of opinions, and not one little bit of temperature data.

A few points should be agreeable to all.

(1) To the OP's question, there cannot be a stated time limit for pump operation. If such an operating time limit exists, it depends entirely on outlet fuel flow. At low engine demand, the pump recirculates more, while high demand means less re-circulation.

(2) "Normal" operation of a typical Lycoming installation has the pump ON for departure and approach, OFF for the rest of the flight.

(3) Some run 'em at any low altitude ("low" meaning too low to get an engine restart if the engine driven pump goes TU), and for sure, it ain't worth having if it won't run continuously after engine pump failure.

Ok, let's get some facts. This is an easy-to-use temperature sensor:

https://www.digikey.com/product-deta...4AH-ND/5055993

Wiring is just 12V power, ground, and sense. Connect an ordinary digital multimeter to sense and a common ground. Output is analog voltage, 10 mV per degree F, so (for example) 1.85 VDC on your meter is 185F.

To mount, solder the sensor's metal can to a small metal strip or square. Add a dab of heat-conductive silicone paste to the underside, and clamp the square to the pump body. Wrap the sensor in some kind of insulation, enough to minimize the effect of local air temperature.

Next time you fly, turn on the pump, and leave it on. Note the temperature, and start a clock. Note temp at intervals. Report back please.
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Last edited by DanH : 04-29-2018 at 07:00 AM.
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  #30  
Old 04-29-2018, 06:59 AM
TS Flightlines TS Flightlines is offline
 
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Joe--I was citing an 'average', and yes many do operate for more than 200,000 miles. My point was the Walbro motors can run for that long. Yep, in a full return system, the pump does run continuously, as in an automotive system.
I thought that was the original question. And perhaps my estimate of a failure time was 'off'. The life expectancy of the pump is when it quits.
If you want to test it, set it up LIKE the fuel system you plan to use, and let it pump and see how long it takes before it fails. Eat lunch first---

Sam probably has the correct answer-
Tom
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