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IO540 with PX375 fuel pump

J

jwilbur

Well Known Member
I know many of you are using the Andair PX375-TC fuel pump in your RV10s. I'm looking for some help understanding the spec of this pump. Assuming the full power fuel flow requirement of the IO-540 is ~26 GPH, will the PX375 do the job? The spec says this: "16 GPH @ 27-30PSI / Open Flow 55-60 GPH @ 5 PSI". I've sent email to Andair but true to their email reputation, I've heard mostly crickets.

Link to PX375 spec sheet: http://www.andair.co.uk/wp-content/plugins/wizbit-ecommerce/assets/media/PX375-TC.pdf

Would someone mind explaining these numbers to me in the context of the IO-540 takeoff flow requirements?

Thank you,
 
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jwilbur said:
Assuming the full power fuel flow requirement of the IO-540 is ~26 GPH, will the PX375 do the job? The spec says this: "16 GPH @ 27-30PSI
Click to expand...

Apparently not.

Try one of these. And hey, they answer emails ;)

 
I think there's more to it than that. The 24 volt version of the pump has a graph of GPH vs. pressure in the spec sheet. At 26 GPH, the pressure is ~29 PSI. I think this means at that flow rate the pump can maintain that pressure. So assuming I'm interpreting correctly and assuming the 12 volt and 24 volt pumps are the same I think I need to know what the fuel pressure is/needs to be at takeoff power in an IO-540.

Can anybody tell me what that is?

24 volt PX375 spec: http://www.andair.co.uk/wp-content/plugins/wizbit-ecommerce/assets/media/PX375-TC-28V.pdf
 
jwilbur said:
I think there's more to it than that. The 24 volt version of the pump has a graph of GPH vs. pressure in the spec sheet.
Click to expand...

There is more to it. And I'm not being entirely fair. However, the first spec sheet you linked was for the 12V model, and that sheet says right at the bottom "The PC375-TC has been developed as a fuel boost pump for the Lycoming IO-360 range of engines."

So assuming I'm interpreting correctly and assuming the 12 volt and 24 volt pumps are the same I think I need to know what the fuel pressure is/needs to be at takeoff power in an IO-540. Can anybody tell me what that is?
Click to expand...

That would be the "more to it". If I recall correctly, the general answer is anything more than about 20 psi, assuming standard nozzle restrictors...meaning the 12V Andair would probably work fine. The fuel servo (Bendix, Precision, or AFP) is relatively insensitive to supply pressure. Small restrictors (good for idle) may require higher pressure for a high flow rate.

FWIW, calling AFP will get you precise answers to the above as fast as you can ask the questions. Their pump costs less.
 
DanH said:
"The PC375-TC has been developed as a fuel boost pump for the Lycoming IO-360 range of engines."
Click to expand...

That line in their spec sheet is what prompted my line of questioning. I'm assuming I'm not the first to investigate this carefully before installing. The only answers I've found, however, are people saying the pump "works fine" in their RV10. Now I want to be sure it will continue to work fine if the engine driven pump fails.

DanH said:
FWIW, calling AFP will get you precise answers to the above as fast as you can ask the questions. Their pump costs less.
Click to expand...

I have no doubt this is true. But I very much prefer the simplicity of the Andair plumbing.
 
Good Catch!

jwilbur said:
That line in their spec sheet is what prompted my line of questioning. I'm assuming I'm not the first to investigate this carefully before installing. The only answers I've found, however, are people saying the pump "works fine" in their RV10. Now I want to be sure it will continue to work fine if the engine driven pump fails..
Click to expand...

Joe, I think you have answered your own question. This pumps' specifications and recommended application, fall short of providing your full fuel flow at a pressure sufficient to operate your IO540 at take off conditions without the benefit of the engine driven mechanical fuel pump.

Clearly, 16GPM at 30psi is only sufficient to fuel an IO360 at TO. It is good that you are checking this, considering your comments about other RV10 flyers using it. Good catch!! These things do happen in our experimental world, but not too often on VAF.
 
If that pump fails and you need to send it to the UK to have it fixed you're going to hate the weeks you'll spend sitting on the ground waiting for it... You don't even want to think about having it fail away from home.
AFP is awesome and quick with support and their fuel pump has the bypass plumbing built-in.

Lenny
 
As simple as it gets

AFP is as simple as it gets:
Like Dan said, one line in, one line out.
Make a phone call, someone picks up and answers your question.
Need service, send it in and have it back in a week.
Decades of track records and thousands of pumps installed in RVs and other experimentals.
Why are you bothering with a foreign company who does not reply to your emails.:confused:
 
N427EF said:
... Why are you bothering with a foreign company who does not reply to your emails.:confused:
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Because I foolishly ordered the pump based on what "everyone else is using."

I had the same question on the flow rates a couple weeks ago. I even had one successful email exchange with Andair about which pump was right. They told me if I wanted they could upgrade the PX375 pump (3/8 ports) with the guts of the PX500 pump (1/2 inch ports). The PX500 is designed for the 540 but the typical RV10 uses 3/8 fuel lines.

I asked around some more and again saw so many were using the PX375 - even one case where someone had a PX500 and exchanged it for the PX375. So I got a quote for the PX375 through Aircraft Spruce (who are excellent to deal with, by the way). I was going to ask them about the modification and forgot. A few hours after I placed the order I remembered the flow rate question. I posted here hoping for a solid answer that what I ordered was good. Eventually I contacted ACS who are contacting Andair to see about the modification. I hope to get a new price on that soon.

Depending on what I hear I may change course and go with AFP. I never gave AFP much thought, honestly. I assumed it was the same crazy plumbing mess as the stock system.

Note to self: Don't be a lemming.
 
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The Andair 375 is the correct one - you're good. There are plenty of previous threads about the flow rate and its the correct capacity for our engines. It works great, has less moving (breakable) parts and is a lot less convoluted than the AFP pump. Admittedly the new AFP one is a little LESS complex, but it still has several more parts, joints and is considerably heavier.
 
CharlieWaffles said:
There are plenty of previous threads about the flow rate and its the correct capacity for our engines.
Click to expand...

I'm not doubting you personally, but I'd like to see for myself some numbers from something to support this and can't find any. I've searched for said threads and can't find them. All I've seen so far is people saying, "I've got it and it works." I want to use this part for the reasons you give but I need to know for myself that it's right and so far I'm not really convinced.

For example, on your IO-540 what is the required pressure and flow rate at full takeoff power? You must have a manual with your engine.
 
Joe,

Not sure if this data point is any help but here it is. At full power (sea level), ~26gph my fuel pressure is around 27psi with the AFP pump on. With lower fuel flows it goes to 29psi.

Lenny
 
FAR 23.955, 23.991

23.955

"(c) Pump systems. The fuel flow rate for each pump system (main and reserve supply) for each reciprocating engine must be 125 percent of the fuel flow required by the engine at the maximum takeoff power approved under this part.

(1) This flow rate is required for each main pump and each emergency pump, and must be available when the pump is operating as it would during takeoff;"

23.991

"(d) Operation of any fuel pump may not affect engine operation so as to create a hazard, regardless of the engine power or thrust setting or the functional status of any other fuel pump."



http://www.ecfr.gov/cgi-bin/text-idx?rgn=div5&node=14:1.0.1.3.10#se14.1.23_1991
 
I have the Andair fuel pump. Mine is an early version for the IO-540. It's basically a pumped up version of the IO-360 model they had at the time. Off hand I do not recall the model but it has 3/8" ports. I did a fuel flow test because I thought the DAR would want that but he did not ask. I do not recall the GPH it put out but it was more than adequate in both level, and with the tail down in a climb out attitude. Its a nice compact, light weight and quiet pump. That said, if it ever does go south, I will probably replace it with an AFP unit because it is cheaper, is a USA based company, and they provide good customer support.
 
Lenny Iszak said:
At full power (sea level), ~26gph my fuel pressure is around 27psi with the AFP pump on. With lower fuel flows it goes to 29psi.
Click to expand...

According to the plot in the 24 volt spec, this is right on the line. See page three in spec sheet.
The link to the 24 volt PX375 spec: http://www.andair.co.uk/wp-content/plugins/wizbit-ecommerce/assets/media/PX375-TC-28V.pdf

BillL said:
23.955 "The fuel flow rate for each pump system ... for each reciprocating engine must be 125 percent of the fuel flow required by the engine at the maximum takeoff power ... "
Click to expand...

And this seems to settle it in my mind. The stock Andair 375 pump is a little too close for comfort. I'm going to wait and hear what the difference in price is on having the PX375 pump modified. I'll post the answer when it comes. In the mean time I'm going to contact AFP and get a price on a pump and filter from them.
 
On take off my 540 shows initially shows 22 - 25 psi at 25 - 26 gph without the boost pump. Then the VP200 kicks in the boost pump and the psi jumps up. Engine does not falter which leads me to believe it will run fine at takeoff power with 22 psi. YMMV.
 
AFP

IO-540 26GPH at 25psi on take off.

Testing the output on my installation, the pump delivers 51 GPH to an elevated position 4 feet above the fuel pick up.
This would simulate a "vertical " take off.
The pump delivers 200% of the fuel required to run an IO 540.
 
N427EF said:
IO-540 26GPH at 25psi on take off.

Testing the output on my installation, the pump delivers 51 GPH to an elevated position 4 feet above the fuel pick up.
This would simulate a "vertical " take off.
The pump delivers 200% of the fuel required to run an IO 540.
Click to expand...

Sooo, Ernst, I think I missed something here. It appears you say it delivers 51 gph at 48" of fuel, 35" h2o or 1.26 PSI? Doesn't it need to be at 25 psi so the engine will run when the mechanical pump fails?

This argument would be sound if you assume the mechanical pump is in series and the only function of the boost pump is to feed it. But does not seem to be the total function of the boost pump. If it was a carburetor system, then, all might be ok.

Can you help clarify?
 
Best advice I can give you:
Ask Don Rivera, at airflow performance.

Bill, I'll try to keep it real simple.
A fuel flow test is recommended as part of your test procedure before first flight.
Some people tie down the tail of the airplane and disconnect the fuel hose at the fuel controller to simulate a climbing attitude and measure the output of the electric fuel pump and basically test the the fuel system for flow and quantity.
Tying down the tail is not a realistic climb attitude in an Rv and elevating the fuel measuring container 4 feet above the fuel controller for this test would be more realistic or the most extreme situation I could imagine.
Using the above described test set up produced the following results for my RV-10 and almost the same numbers for my RV-8.
51 GPH pumping with the AFP fuel pump. It has been a flawless fuel system in 2 airplanes.
Here is a diagram for my fuel system.

IMG_2462.JPG
 
Thanks, Ernst. I believe we are addressing two different things.

1. The tilt flow testing will address suction and usable fuel elements. In that test it is best to have a high flow rate. The highest flow rate will be at low resistance to the boost pump output (pressure). If there were a high suction resistance then the delivered fuel would contain bubbles, of not be able to deliver the fuel because of cavitation (vaporization) of the fuel prior to the boost pump. This test is definitive. In the usable fuel range, 200% of rated flow is excellent for evaluation of the system to the pump.

2. The OP is addressing the delivery, at a specified pressure. Having passed test #1, then the boost pump must deliver 125% of maximum fuel flow, at pressure, necessary to keep the engine running. That might be 5 psi for a carb or 22, 25 psi for the fuel injected engine (I don't know the exact numbers). The exact numbers can come from testing the engine or the specifications sheet for the users specific engine.

Thanks for your response.

Comment: The list of what we might call "installation tests" is not totally clear regarding what is being validated and why. The fuel system presents some mysteries for people and could relate to fuel system related loss of power or reduced power. Some of these tests have have pressure/flow margins built in to allow for elevated temperatures that might occur a few times each year or less. Tests are necessary since all of these factors are different in our individual planes as components, routing and configuration are changed from a baseline (factory) configuration or are left to the builder to decide. Someday, maybe a full list of validation procedures will be made for experimental that will address the whats and whys, and how to. For now we just follow instructions and muddle through.
 
resolved

As advertised, Don at Airflow performance was easy to get in touch with and over the course of several days answered many questions. I thing the PX375 from Andair will probably do fine supplying fuel to an IO-540 if the mechanical pump quits and it is a very light pump. No question about that.

In the end I feel more comfortable with the flow rate margin on the AFP pump which also has a much lower pressure drop when the pump is switched off (perhaps making the job of the mechanical pump easier). I hate gaining the extra pound of weight but I think overall it's worth it. If Andair made the PX500 with 3/8 fittings I would probably have gone with that.

Andair said they could modify the PX375 with the PX500 guts, but after waiting a couple days for a confirmation and/or price that they would do the modification, I gave up and cancelled the order. This was all through Aircraft Spruce who are just excellent to deal with. I was a very high maintenance customer and Josh with ACS just rolled with it. It was a pleasure dealing with them. I figured if ACS has trouble communicating with Andair, it was going to be next to impossible for an individual customer like me to get any reliable communication with them if there were any issues. And given I was requesting a modified pump, there would probably be issues.

Can't speak for anyone else, but for me, I'm happy with the decision.

I think maybe some of the guys here should get a commission from AFP.

Thanks to all who helped out,
 
At 2700 ft airport, how many gal At take off? My rv10 fuel flow At take off os 25 gallons At 2700 ft.
 
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