Cherokee fuel pressure

J

JordanD

Here so I don’t get fined
When you turn the fuel pump on in the Cherokee, is there supposed to be a jump in fuel pressure? In the one I'm flying I don't see an apparent increase in fuel pressure when I turn the pump on, but the book doesn't really say if there's supposed to be one, it just says "monitor fuel pressure" which is a little ambiguous to say the least. Is this something I should bring to the owners attention?
 
In flight or during start? For engine start you should hear the pump come on and see a jump in pressure. In flight don't think there is a noticeable change. I never look for an increase when I turn it on, just a change when I turn it off!!
 
unclenobby said:
In flight or during start? For engine start you should hear the pump come on and see a jump in pressure. In flight don't think there is a noticeable change. I never look for an increase when I turn it on, just a change when I turn it off!!
Click to expand...
In flight and on the ground before takeoff. I haven't been using it for starting. When the engine's warm it's started up easily without it. I'll try it next time before start and see if I hear it. Is it pretty much the same sound as the aux pump in the 172?
 
There shouldn't be a jump if the engine is running already. You should hear it come on and see a jump before you start the engine. Min fuel pressure is .5 PSI, so you don't need much to be legal, but you should see it kick up to 3 or 4 PSI with just the electric pump. What I do is run the electric pump before I start just to make sure it works. Then I turn it off to start to make sure the engine driven pump works. Then I run the electric pump on takeoff and landing only as a backup to the engine driven pump. The electric pump is only a backup. It doesn't need to produce more pressure than the engine driven pump but is just there is the engine driven pump fails.
 
JordanD said:
In flight and on the ground before takeoff. I haven't been using it for starting. When the engine's warm it's started up easily without it. I'll try it next time before start and see if I hear it. Is it pretty much the same sound as the aux pump in the 172?
Click to expand...

The ONLY time you can be assured of the fuel pump functioning as designed is prior to engine start. So, whether you use the pump for start or not, you should toggle the system. Sit still and quiet to listen to the pump while you are looking at the fuel pressure. As noted above, 0.5 psi is normal min fuel pressure. BTW: 0.5 psi is about as high a force you can blow when trying to clean out a carb after a dip in the parts washer. :)


To encourage overhead discussion: Inappropriate use of checklists. Since the pilot does not check working condition of equipment reguired for flight, therefore the INOP condition of a system remains unknown to him, did he take off with a known deficiency since it is reasonable to expect he would have noticed the INOP if he had followed the POH?
 
DE727UPS said:
There shouldn't be a jump if the engine is running already. You should hear it come on and see a jump before you start the engine. Min fuel pressure is .5 PSI, so you don't need much to be legal, but you should see it kick up to 3 or 4 PSI with just the electric pump. What I do is run the electric pump before I start just to make sure it works. Then I turn it off to start to make sure the engine driven pump works. Then I run the electric pump on takeoff and landing only as a backup to the engine driven pump. The electric pump is only a backup. It doesn't need to produce more pressure than the engine driven pump but is just there is the engine driven pump fails.
Click to expand...
Gotcha. I vaguely remember there being a jump when at idle in the Cherokee 140 I flew a couple years ago.

One more thing that makes me wonder. If Piper uses it as a backup during takeoff and landing for the engine driven pump, why isn't the same thing recommended in the fuel injected Cessnas? Different kind of fuel pump doing a different job for a different type of fuel system?
 
JordanD said:
Gotcha. I vaguely remember there being a jump when at idle in the Cherokee 140 I flew a couple years ago.

One more thing that makes me wonder. If Piper uses it as a backup during takeoff and landing for the engine driven pump, why isn't the same thing recommended in the fuel injected Cessnas? Different kind of fuel pump doing a different job for a different type of fuel system?
Click to expand...

Piper has a low level wing, which means the fuel must be forced into the carb/cylinders. With a Cessna High wing system it's a gravity fed fuel system. There is no need for a backup pump because as long as the aircraft is right side up the fuel is going to flow to the engine. With a piper, if the engine driven pump quits you have the aux. pump to back it up. It has nothing to do with fuel injection in Cessnas, carb/fuel injection they still have the same fuel schematics.
 
Ayork62493 said:
Piper has a low level wing, which means the fuel must be forced into the carb/cylinders. With a Cessna High wing system it's a gravity fed fuel system. There is no need for a backup pump because as long as the aircraft is right side up the fuel is going to flow to the engine. With a piper, if the engine driven pump quits you have the aux. pump to back it up. It has nothing to do with fuel injection in Cessnas, carb/fuel injection they still have the same fuel schematics.
Click to expand...
Not quite, the carbureted cessnas have no engine driven pump or electric pump. They are gravity fed all the time. Only the injected cessnas have fuel pumps, because you need pressure to run the RSA fuel injection system.
 
Roger said:
Not quite, the carbureted cessnas have no engine driven pump or electric pump. They are gravity fed all the time. Only the injected cessnas have fuel pumps, because you need pressure to run the RSA fuel injection system.
Click to expand...

Well there ya go:D
I have yet to fly a fuel injected Cessna. Is the pump running at all times then? Or is just used to certain situations?
 
Why isn't it standard practice to turn it on for takeoff and landing as a backup on the Cessnas?
 
"I vaguely remember there being a jump when at idle in the Cherokee 140 I flew a couple years ago."

Could be. I've never seen it in the Cherokees I've had. The problem with the one I have now is the fuel pressure is very low with even with the pumps working. You can confirm both pumps work easy enough but I'm not showing much pressure. It comes up to maybe 2 after it runs for a while. Mechanic put a gage in the fuel system and we got good pressure, so it's just a bad fuel pressure gage. Problem is, that gage is part of several instruments that work fine, so I hate to mess with it. I'm thinking of just putting in a fuel flow meter.

One thing I've always wondered. If you lost both fuel pumps in a Cherokee, could you just fly upside down to get the engine to run?
 
Look for a increase in amps as you turn the pump on. If there is a complete circuit that is performing work it will load the electrical system. I fly an arrow that shows very little change in fuel pressure when the pump is activated.
 
Yeah, most of the Cherokees will not show an increase in fuel pressure when you turn the electric pump on while the engine is running. As to the reason for the non-use of the boost pump in the fuel injected cessnas during takeoff and landing, I don't know. Pretty sure gravity feed wouldn't be sufficient to run the fuel injection system at anything like takeoff power should the EDP fail.
 
In our 180D the needle erects to 90 degrees when engaged prior to engine start. Once the the engine is running, engaging or disengaging the manual pump will affect the gauge.
 
mojo6911 said:
Because if the force of gravity ceases, you have bigger problems to worry about.
Click to expand...

I'm surprised that the gravity pressure would be enough to keep the fuel injection system functioning at full capacity. I mean on many injected aircraft engines normal fuel pump output pressure is in the neighborhood of 35 PSI at takeoff power. I think that even with fully functional gravity you'd get a very substantial loss of power if the engine driven pump quit.
 
Roger said:
I'm surprised that the gravity pressure would be enough to keep the fuel injection system functioning at full capacity. I mean on many injected aircraft engines normal fuel pump output pressure is in the neighborhood of 35 PSI at takeoff power. I think that even with fully functional gravity you'd get a very substantial loss of power if the engine driven pump quit.
Click to expand...

It isn't, if the engine driven fuel pump were to fail in a fuel-injected Cessna, you wouldn't have sufficient fuel pressure, that's why they have the aux fuel pump
 
7700 said:
It isn't, if the engine driven fuel pump were to fail in a fuel-injected Cessna, you wouldn't have sufficient fuel pressure, that's why they have the aux fuel pump
Click to expand...
But then why does it not get turned on for takeoff and landing like on, say, a Cherokee?
 
You must log in or register to reply here.
Back
Top