Fuel PSI in B206B

[ptwaugh]

Can anyone tell me:

a) What is normal fuel PSI?

b) If you lose ONE boost pump, what will it be?

c) If you lose BOTH boost pumps, what will it be?

I know that if either fails you get a caution annunciation, but I'm wondering if you can also see by the preasure if one or both have failed, and what those preasures are likely to be.

Thanks

[paco]

It should be in between 4-30 psi. I wouldn't expect the reading to change by much if the boost pumps fail while the engine is running. They are only there to supply a head of pressure to the engine-driven pumps's sucking action, which is pretty powerful, to prevent cavitation, although the time they were installed, this was more relevant for the JP4 fuel in use at the time.

Phil

[the beater]

If you lose one pump you'll lose some pressure, how much depends on the pump as they all seem to vary in pressure. If you lose both pumps, the pressure will be zero. From memory, I think there is a 6000' pa limitation (the engine driven pump will keep the engine going, if this fails you'll know about it!). You can use the pump switches/CBs to determine the failed pump and then switch it off.
When I first flew the Jetranger, I was taught to start on one pump only. I seem to recall a letter from Bell/Textron that informed operators to start with both pumps on. I now can't find this. Does anyone have a copy?

[Devil 49]

If both boost pumps fail, you'll determine the integrity of the supply tubing from the tank to the engine pump. A former employer required that the post engine rinse runup include a segment with the pumps disabled. If the tubing wasn't air-tight, the engine could flameout...
The engine fuel pump does the heavy lifting, but it's a suction pump. The boost pumps keep it supplied even if a little leak's present in the takeup line inside the tank. Boost pumps keep the leak positive, fuel out, not air in. However,with NO boost pumps, a little air leak means more air in the line until the big sudden silence. Good news, if you have a system of checking the supply lines, you find out which ones leak and can get'em fixxed before the boost pumps fail.

[helilad]

Alot of operators start 206 with one pump on to conserve battery power for start ie. give the start everything you got. Seems like common practice to switch both pumps off for the two min shutdown ,1.to conserve batt by swithing all consumables off. 2.to check if engine driven pump works.[flameout on ground not a problem]

I often wondered why the boost pumps were on cbs as opposed to switch/cbs like 407 ??

[RVDT]

A few myths flying around here!!

The inlet pressure on an A250 is required to be in a particular range.

The engine driven pump (gear pump) relies on the medium to be incompressible. Gear pumps are hopeless at pumping air. The inlet pressure on a 250 engine can be below 0 (MD500 has NO boost pump) yet as described, if you have any leaks your pump eventually fills with air and stops pumping fuel which of course is an issue.

Helilad - you comment regarding 2 pumps OFF to check if the engine pump is still running is a complete fallacy. It may test the integrity of the fuel line for air leaks (after a period of time) but it will not run the engine. The output from the gear type ED pump is ~ 600 PSI. This procedure is in fact a test procedure on the L after fuel system maintenance to prove the integrity of the fuel lines for air leaks.

Later designed aircraft/engines have a combination of jet pump, regenerative (side channel) and then gear pump to provide fuel to the engine without the need for boost pumps. These systems may require a system to PRIME for start but do not use boost pumps. Positive pressure in the fuel lines is a bit of an issue when you have a fire whether it is in flight or post crash.

As to the original question - what is normal? Green range.

If you lose ONE pump - Green Range

If you lose BOTH pumps - 0 at the pump and less at the engine.

The pressure will vary with altitude as the gauge is only an absolute pressure instrument and the column of atmosphere that is above the tank is less. (see previous post's)

[ptwaugh]

Well, in the B206, the manuals indicate that the engine driven pump is capable of sucking up fuel without a problem, but that you best descend below 6000 PA or you'll have 10 gals unusable if both boosts have failed.
I can't tell where the preasure measurement is being made, but based on this discussion it would appear that it is made near the engine, ie. above where the two feed lines meet, which makes sense.

Given this then I would assume that based on there being PSI in the GREEN with the FUEL PUMP illuminated that would indicate only one failed while a near zero reading would indicate both have failed.
Thanks.

[helilad]

Helilad - you comment regarding 2 pumps OFF to check if the engine pump is still running is a complete fallacy.

Totally agree ,I said it was common practice for those reasons people believe in. I didnt say it was the thing to do !

[paco]

With some inspectors in Canada, you will fail your PPC if you pull the fuel boost CBs whils running down, on the basis that the book says they shall be on when the engine is running.

If your battery is that low that one pump's power is significant, you need a new one!

You're quote right, whoever said the reading would be zero with both pumps off - with one off , the reading will dip a little. A CRAFT moment......

(Can't remember a f..ing thing)

Phil

[FH1100 Pilot]

Some of us remember when a 206 with both boost pumps running would indicate, like, zero pressure - then pull one pump and the pressure goes up! Never understood that. Do they still do it, or has Bell fixed that anomaly?

Paco, I'm not sure (long time since I've flown a 206) but doesn't the manual say that both boost pumps must be operating "if flight is intended" or something like that? Pulling them on shutdown should not be a problem and is not contrary to the RFM.

And yes, if your battery is so bad that one pump makes a difference you need a new battery. Or...maybe the realities of aviation kick in, and your battery is old but not quite to the point of needing replacement, and maybe the day is colder than usual for the way the fuel control is set up and the engine is starting slower. And maybe you're in a field somewhere...somewhere far from a mechanic (or lodging) and it's getting dark. The 206 battery up in the nose is a looooong way from the starter, and the voltage drop across those lines must be considerable. I hate to see 206 pilots sitting there for protracted periods with every possible electrical consumer running before finally attempting a battery start. I mean, I cringe.

Helilad, the reason Bell used circuit breakers for the fuel boost pumps is because they never intended for them to be pulled! A circuit breaker is *not* a switch, and continuous use of it as one can be detrimental. It was those early 206 pilots in the field that started the (erroneous) practice of pulling the boost pump and "caution" breakers on shutdown and leaving them out for the next start. (Me? Guilty, but I've seen the light.)

H-500, FH1100, same engine, same engine-driven fuel pump, different boost pump setups. H-500 has simply a start pump, then it goes off. FH1100 has just one electrical boost pump, no pressure gauge, just a caution light. Why the difference in designs? Who knows. When I was at the FH1100 factory, we changed our RFM to reflect Bell's policy of always having the boost pump on when flight is intended. It just seems logical to always keep the fuel system under positive pressure. (But then, we never shut our fuel valve off, and we wonder why 206 have to? Lawyers...)

This thread has sort of drifted off-topic, but it does point out how much misinformation is still out there on the 206. Even after all these years!

[Gomer Pylot]

PT, to answer your original question again, the fuel pressure should be somewhere in the green, and that's all one can say. Different pumps put out different amounts of pressure, and it's entirely possible to have one pump fail and see no decrease in pressure at all. If one pump is much stronger than the other, and the weak one fails, the pressure may not change at all. OTOH, it might drop considerably if the strong one fails. There is no way to know without checking the pump pressures individually, and even then you can't know for sure. All one can say is that the fuel pressure should be in the green, and if one pump fails the pressure will either remain the same or change.

[paco]

FH1100 - in the copy I have here (and it is a Canadian one) it says right in the Limitations section:

Fuel boost pumps SHALL BE ON at all times when the engine is being operated.

That's for a 206B. I just checked - it's in the A and B3 manuals as well.

I hear you about sitting there with everything on - I get antsy when I see someone dithering about on the prestart checklist!

Phil