High Fuel Pressure Alarm setting - FI pumps

AlexPeterson · #1 10-15-2018, 05:52 PM

Greetings,

What are opinions on setting a high pressure alarm for fuel pressure? I'd always had 30 psi set to trigger an alarm, simply because I'd not ever seen more than about 27 psi or so with the previous pump. However, I just replaced the engine driven fuel pump and frequently saw just over 30 on the first flight. I changed the engine monitor to only alarm for high pressure over 35 now, but am curious what others see for high pressures.

AlexPeterson · #2 10-15-2018, 06:26 PM

Quote:

Originally Posted by airguy

What type of injection system do you use?

I have Bendix, and run 40-42 normally with a high pressure alarm at 45, but I'm not really a good example of "normal" because I've got a very modified fuel system.

I happen to have an Airflow Performance. But, I understand that there are only two fuel pumps for the Lycomings - high for FI and low for carbs. Maybe there are others.

RV7A Flyer · #3 10-15-2018, 07:41 PM

Quote:

Originally Posted by AlexPeterson

I happen to have an Airflow Performance. But, I understand that there are only two fuel pumps for the Lycomings - high for FI and low for carbs. Maybe there are others.

I'd set the high and low red alarm limits at whatever the manufacturer says are the limits, and set yellow caution limits something like 10% lower (higher) than that, respectively.

I'd use long-term trending, such as via Savvy Analysis, to watch for any impending issues.

dlloyd3 · #4 10-15-2018, 07:53 PM

Several complaints on the MooneySpace forum about the new pumps and higher pressures. Might not make any real difference for our fuel injection systems, we are not constrained by certification and can reset our alarm limits.

Raymo · #5 10-15-2018, 08:31 PM

My new mechanical pump did the same when new (Tempest). Just increase your max PSI alarm to 32 or 33 and, as you put hours on the pump, it will settle down to 27-28. Normal pressure is 25-30 PSI. Keep in mind that your pressure sensor is not 100% correct either.

I have around 175 hrs on my pump and it now runs 27.

AlexPeterson · #6 10-15-2018, 08:46 PM

Quote:

Originally Posted by dlloyd3

Several complaints on the MooneySpace forum about the new pumps and higher pressures. Might not make any real difference for our fuel injection systems, we are not constrained by certification and can reset our alarm limits.

Interesting - thanks. The max pressure into the AP FI system is 80 psi, so no worries there. The high alarm would be simply to alert to something amiss.

DanH · #7 10-15-2018, 09:40 PM

Quote:

Originally Posted by AlexPeterson

I'd always had 30 psi set to trigger an alarm, simply because I'd not ever seen more than about 27 psi or so with the previous pump. However, I just replaced the engine driven fuel pump and frequently saw just over 30 on the first flight. I changed the engine monitor to only alarm for high pressure over 35 now, but am curious what others see for high pressures.

My recent experience is identical.