Kavlico, Fuel Pressure Sensor, PN 103755-000

[skippydiesel]

Hi All,

 

Rotax 912 ULS

 

My fuel pressure readings have become a bit weird, while in Cruise (all good on the ground). Random (increasing in frequency) drops to below 2 psi - instant recovery  to 5 .5 psi when Boost turned on.

 

Note: Engine continues to purr away without any hesitation.

 

Done the usual "fixes" :

• Draining fuel pipe to sensor.
• Relocated sensor to highest available location in engine compartment.
• Cleaning Gascolator filter screen (which looked nice and clean anyhow).
• Ensuring sensor has access to ambient air pressure.

 

Thinking sensor on the way out. Looking for replacement :

 

                                       OM is Kavlico PN 103755-000 V2, 1/8-27 NPT, 15 psi. Part Marking P255-15G-E4A. Pressure Range 0.6 -15 psi. About $300 AU delivered.

 

Looking for :

 

• Most Cost Effective Supplier (only found two in AU)
• Alternative part, same specifications, /compatible with Dynon system, that you can recomend.

 

My thanks for any constructive assistance.😈

[IBob]

Skippy, any chance of getting your hands (temporarily) on a steam gauge?
You could then identify whether you have a fuel pressure problem or a fuel pressure sensing problem.
 

[IBob]

I had a lot to do with pressure transducers over the years.....in industrial refrigeration and hot water systems, also in hydraulics etc.
I note from the P255 data sheet: 

https://www.mouser.com/datasheet/2/657/sensata_p255_stainless_steel_pressure_transducer_d-1769810.pdf

that it's principally for dry media, with Note 1 saying "For wet conductive media please contact us."
It also notes that the internal seal needs to be compatible with the media.
In short, I would be checking with the manufacturer that what you are looking at is compatible with petrol.
 

[IBob]

FWIW, I would say $300 is about the going rate for an economically priced transducer (sender).

They come in:
2-wire, (loop powered),
3-wire, as this one is, 5v/0v/signal (output)
4 wire, power/0v power/Signal+/signal- (less used nowadays)

This one has a 5V power in, and gives an output signal of 0.5v to 4.5V which is presumably 0 to 15PSI (though I note elsewhere that Dynon say you won't see anything below 0.5PSI.)
So any sensor, suitable for use with petrol, with those operating parameters should be a direct swap-in.

Depending on how far you want to dig, and on what adjustable parameters your Dynon offers, you could also swap in something with different parameters. For instance, the oil pressure transducer on the Rotax has an output signal of 4 to 20mA, (which is an industry standard) and it's quite possible the Dynon can be configured to accept that. All depends what Dynon setup you have.

0 to 15PSI is a good range for 912 fuel pressure unit. These senders are inclined to fail if the pressure exceeds their max rating. Typically we used to specify them as max pressure x 2, so for instance in a refrig setup where we might see 12 or 13 bar, we would fit 25bar transducers: that gave as a good degree of accuracy, with plenty of pressure safety margin and excellent reliability.

One other note: some refrig enginerooms might have 20 to 30 pressure transducers over multiple compressors and the various vessels. Things may have improved now, but a few years back, of those 20 to 30 we would often get 1 or 2 that failed almost immediately. Of the rest, if they lasted a week, they gave no trouble after that.

 

 

[Blueadventures]

I have a UMA fuel pressure sensor, works good.  They don't like heat so mounted away from engine in the compartment in an air flow area to keep it as cool as possible.

[facthunter]

 Engine vibration is destructive also. All these senders are quite Unreliable. It's a harsh environment for them Nev

[Underwood]

10 minutes ago, Blueadventures said:

I have a UMA fuel pressure sensor, works good.  They don't like heat so mounted away from engine in the compartment in an air flow area to keep it as cool as possible.

Have a UMA fuels pressure sender also, it is working fine after 10 years service mounted on the cabin side of firewall but with the threaded portion going penetrating into the engine bay.

but they arent cheap (£295 in UK)

[IBob]

49 minutes ago, facthunter said:

 Engine vibration is destructive also. All these senders are quite Unreliable. It's a harsh environment for them Nev

These are certainly considerations, Nev, but I don't entirely agree: our refrigeration ones were mounted into pipework on very big ammonia compressors, most of which run 24/7 until overhaul.
Having said that, the 0 to 15PSI sender for the fuel is far more delicate than the oil pressure sender, by a factor of about 10. Personally, I would not be mounting it in the engine bay, for reasons not only of heat and vibration, but also because these are gauge pressure units that rely on also sensing a steady and accurate ambient pressure.

[skippydiesel]

18 hours ago, IBob said:

Skippy, any chance of getting your hands (temporarily) on a steam gauge?
You could then identify whether you have a fuel pressure problem or a fuel pressure sensing problem.
 

Good thinking IBob - I am a tad deterred by the randomness of the sudden fuel pressure drop (last  1 hr flight no problemo) and the difficulty of plumbing such a system in to my very tight airframe.😈

[skippydiesel]

13 hours ago, Blueadventures said:

I have a UMA fuel pressure sensor, works good.  They don't like heat so mounted away from engine in the compartment in an air flow area to keep it as cool as possible.

I wish I had done what you suggest when the aircraft was in my workshop - not much chance of a modification parked out in the open. Thanks anyhow.😈

[skippydiesel]

A further uncomfortable thought - could  this be an early symptom of my engine driven fuel pump  starting to fail (only done 140 hrs)?😈

[IBob]

6 minutes ago, skippydiesel said:

A further uncomfortable thought - could  this be an early symptom of my engine driven fuel pump  starting to fail (only done 140 hrs)?😈

Yes, that occurred to me too, Skippy. That's why I suggested borrowing a steam gauge if you can: identifies whether the problem is the fuel pressure or the sensing.

And if it's any consolation regarding location, I see the Kavlico unit boasts 'Outstanding Shock & Vibration Performance' and an operating temperature range from -40 to 125'C (depending on seal material).
 

Edited February 22 by IBob

[Thruster88]

1 hour ago, skippydiesel said:

A further uncomfortable thought - could  this be an early symptom of my engine driven fuel pump  starting to fail (only done 140 hrs)?😈

If the fuel pressure is normal with boost pump on and low with engine pump only then yes the mechanical engine pump is faulty. This happened to my RV6, the engine still ran fine with just the engine pump but the pressure was very low, new pump pressure normal.

[IBob]

14 minutes ago, Thruster88 said:

If the fuel pressure is normal with boost pump on and low with engine pump only then yes the mechanical engine pump is faulty. This happened to my RV6, the engine still ran fine with just the engine pump but the pressure was very low, new pump pressure normal.

Thruster, I take your point, but I don't think it's that clear cut: what Skippy is reporting is intermittent apparent pressure drops. It seems to me that could be either pump or pressure sensing: if the sender is failing, it is possible that it does not respond reliably to the (lower) pressure of the mechanical pump, but does respond to the (higher) pressure of the booster. That's why I think it would help, if possible, to determine whether it is pump or sender/circuitry before shopping for a replacement.

[Red]

Check grounding and all connections of sender, if you haven't already 

 

[skippydiesel]

Just returned from a short flight - pressure dropped to below 2 psi on long fast descent, engine at relativly low power/rpm???

 

Once again no hesitation from engine, Boost pump on, restored good pressure reading - as entering circuit, left Boost on until landed.😈

[Blueadventures]

19 minutes ago, skippydiesel said:

Just returned from a short flight - pressure dropped to below 2 psi on long fast descent, engine at relativly low power/rpm???

 

Once again no hesitation from engine, Boost pump on, restored good pressure reading - as entering circuit, left Boost on until landed.😈

May be worth opening up the mechanical fuel pump and inspect the condition of the diaphragm and the two valves.  Not a serviceable unit but may show a failed area.  (Not sure how old it is I purchase a replacement item every 5 years.)  Might also pay to buy a new one and keep on the shelf until required, they have a year warranty not used.)

[onetrack]

Blueadventures, I have never found a product yet where the manufacturers warranty applies from installation date. It always applies from purchase date. It's false economy to keep perishable components on a shelf, on the basis they "might be required one day". Murphys Law says the day you pull that part down from the shelf to use it, after having stored it for some time, you find the item is U/S because of aging. 6 mths is the maximum you should store parts/components that contain perishable constituents.

[Thruster88]

1 hour ago, skippydiesel said:

Just returned from a short flight - pressure dropped to below 2 psi on long fast descent, engine at relativly low power/rpm???

 

Once again no hesitation from engine, Boost pump on, restored good pressure reading - as entering circuit, left Boost on until landed.😈

Check that the fuel pump vent/drain hose is not blocked with a wasp nest.

[Blueadventures]

17 minutes ago, onetrack said:

Blueadventures, I have never found a product yet where the manufacturers warranty applies from installation date. It always applies from purchase date. It's false economy to keep perishable components on a shelf, on the basis they "might be required one day". Murphys Law says the day you pull that part down from the shelf to use it, after having stored it for some time, you find the item is U/S because of aging. 6 mths is the maximum you should store parts/components that contain perishable constituents.

Maybe my poor wording;  If he was to buy a fuel pump would need to be installed whenever and replaced at 5 years from the purchase date.  If it was installed many months after purchase and then found it was faulty; for warranty would need to be less that 12 months since purchase.  As pressure reading is in green with electric pump on then good chance the gauge is good.  So good chance fuel pump needs replacing.  (Skippy could try and borrow a fuel pump off someone; even a recently replaced 5 yearly one that was working fine; if you do that stay within glide of airfield.)

[Red]

2 hours ago, skippydiesel said:

Just returned from a short flight - pressure dropped to below 2 psi on long fast descent, engine at relativly low power/rpm???

 

Once again no hesitation from engine, Boost pump on, restored good pressure reading - as entering circuit, left Boost on until landed.😈

Not sure what Instrument you are reading pressure on, but have you noticed voltage when it happens?, I always find it handy to fit a video camera pointed at my panel when flight testing such things

[Red]

P.S. IME, as you already suggested in your first post, I'd agree that this sort of symptom is more likely an indication problem rather than the pump itself

[skippydiesel]

12 hours ago, Red said:

Not sure what Instrument you are reading pressure on, but have you noticed voltage when it happens?, I always find it handy to fit a video camera pointed at my panel when flight testing such things

I have Dynon EFB. It has both fuel pressure and flow readouts. Fuel pressure also has  a "low fuel pressure"  auditory warning (tends to focus the brain).

 

No I have not checked voltage - will take note next time.

I have just realised , nor have looked at the fuel flow reading - will also check that out.😈

Edited February 23 by skippydiesel

[Underwood]

Your EFIS may have a logging function where you could look up the numbers of certain parameters on your last flight

[skippydiesel]

53 minutes ago, Underwood said:

Your EFIS may have a logging function where you could look up the numbers of certain parameters on your last flight

Yes it does - pain the proverbial to access. Will do, if needed,  after checking the above mentioned indicators.😈

Edited February 24 by skippydiesel