What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Cooling shroud for fuel pump

S

SuperCubDriver

Well Known Member
I?d like to install a cooling shroud on the mechanic fuel pump on an IO-375. It looks like the shroud goes on with the pump mounting bolts. I know it can be difficult to install a pump when removed so I thought I ask for any advice. Good thing is the engine is still off the airplane, so I have good access.


 
I've been thinking of doing this, too. If you only remove one bolt at a time, the pump will stay in place and there are no worries. Or, if you have a helper handy, have someone hold the pump in place while you remove both bolts, so it doesn't fall out. Then put it back together with the shroud in place, and you should be good. Mind you, I haven't done this so I don't have any experience with this method. Just sharing some thoughts. I did switch to a different fuel pump a while back, though. With the engine in place. So it can be done.
 
BSwayze said:
I've been thinking of doing this, too. If you only remove one bolt at a time, the pump will stay in place and there are no worries.
Click to expand...

I don't believe that method will work. If you remove one bolt, install the cover with that bolt, you won't be able to remove the other bolt with the cover in place.
 
I tried and tried to no avail. You'll have to cut the shroud or remove the pump.
 
That is correct. Both bolts have to go off at the same time so may be some kind of a strap will work while removing the bollts.

I just thought of cutting the upper flange. This way the shroud could be bend open and one bolt could stay in place while fastening the other.
 
Last edited:
The only other possibility I can think of is slotting the bracket holes inboard. You might be able to flex the bracket enough to slide them under the bolts from the sides.
This could possibly allow installation without complete removal of the pump.
 
Do you really need it? I bought one but have yet to install it because in 4 years (hot years here in Texas) I have had no problems.
 
SuperCubDriver said:
That is correct. Both bolts have to go off at the same time so may be some kind of a strap will work while removing the bollts.

I just thought of cutting the upper flange. This way the shroud could be bend open and one bolt could stay in place while fastening the other.
Click to expand...

On every fuel pump I have removed, the bolts can't come all the way off without removing the pump as you go. They hit the side of the housing, so you have to work the bolts off and you remove the pump.

In other words, you can't get the bolts off and hold the pump in place.
 
Thanks to all the replies and hints.
So the bolts won?t come off with the pump still in place with the other bolt.
I think the solution is what Mel said to slot the bracket holes inboard and bend the shroud for installation. Slotting of the upper flange could help bending enough or splitting the whole thing and reconnect with a hinge. I believe bending will work and I will report back within the next two days.

The reason I want the cooling shroud is because I intend to burn autofuel and I will use any tricks I know to keep the fuel system cool and unrestrictive. On my -7 I?m having the ECI fuel injection system with a constant return flow and it works very well and never experienced vapor issues. Tested it with fuel temp of 110F and up to 15000ft (fuel cooled during the ascent however) with an already hot engine parked for 20 min on the hot apron.
Now this injection system is not available anymore and I went with the AFP system for my -8. I will also use the Andair Duplex boost pump and so will have even more redundancy.
Here in Germany we pay around $12 for AVGAS. Autofuel is around $6. So your AVGAS is even cheaper than our autofuel !!
 
SuperCubDriver said:
Thanks to all the replies and hints.
So the bolts won?t come off with the pump still in place with the other bolt.
I think the solution is what Mel said to slot the bracket holes inboard and bend the shroud for installation. Slotting of the upper flange could help bending enough or splitting the whole thing and reconnect with a hinge. I believe bending will work and I will report back within the next two days.

The reason I want the cooling shroud is because I intend to burn autofuel and I will use any tricks I know to keep the fuel system cool and unrestrictive. On my -7 I?m having the ECI fuel injection system with a constant return flow and it works very well and never experienced vapor issues. Tested it with fuel temp of 110F and up to 15000ft (fuel cooled during the ascent however) with an already hot engine parked for 20 min on the hot apron.
Now this injection system is not available anymore and I went with the AFP system for my -8. I will also use the Andair Duplex boost pump and so will have even more redundancy.
Here in Germany we pay around $12 for AVGAS. Autofuel is around $6. So your AVGAS is even cheaper than our autofuel !!
Click to expand...

I would not recommend a slot under that bolt head. Just asking for something to come loose. Why not just remove the pump and fittings to install the shield?
 
Some ideas

First of all, it is kind of questionable whether you need it, but what the heck, now is the best time for you to install it, while the engine is off the airplane.

I fly from some hot-and-high airfields, and I do have a cooling blast tube on my pump, but the shroud would be a nice 'belt and suspenders' addition, and if I ever have the engine off the airplane again, I will do it.

The typical problem in installing the fuel pump correctly is that the "plunger" or "lifter" or what ever you want to call it that actuates the pump from a cam lobe is above the pump, and when you are trying to install the pump, the lifter keeps falling down.

So here is the trick for you -- turn the engine upside down on your stand. Now gravity will hold the lifter in place for you. It also will help if you can turn the engine over to the point where the lifter is at the bottom of its stroke (meaning relaxed, not pushing on the pump lever arm).
This way, you should be able to put the pump on being sure that the pump lever arm is properly aligned on the lifter.
 
Herman FWIW, if the electric pump is aft of firewall and run 100% or until climbing to cooler air, the shroud would not be necessary. The critical time will be after landing and heat soaked engine and another take off. The shroud will not be effective in that environment.

The shroud is no guarantee vapor lock will not occur. Fuel under pressure is a good guarantee it won't happen. Thats how the problem was cured with automobiles, fuel leaves tank under pressure problem over.
 
I put the shroud on my pump during the build because I planned on burning auto fuel,,,which I now do. Whether or not it helps, I do not know, but I have no intentions of removing it.
 
I tried to modified the shroud by slotting the mounting holes and cutting a slot in the upper cover to be able to bend it open for installation. Trying to install it I run into other interferences so I decided to leave the pump alone. I?m also thinking on future maintenance and no shroud will make things easier. May be one day I design "my own" shroud.
I know the plunger thing from another thread, somewhat similar to the fuel pump pushrod on a Chevy 454. Here the pushrod can be removed, put into the freezer and installed cold with some grease on it so it won?t move for the pump installation.
 
Sectioned Cooling Shroud

I know it's an older thread, but I only saw it today. Just as an idea, I will show what I did. It has not flown yet, so I don't know if it's effective or not.

I wanted to have a removable shroud, once the engine is mounted. Therefore I did some modifcations on the shroud. See yourself...

24636145021_779cff91a1_z.jpg

cut the brackets off and fabricated new onces

24636151791_5a4f4f1704_z.jpg

mounting brackets installed on the engine

24434126850_391dd3d4f4_z.jpg

shroud installed, note that the shroud has been shortened on the lower end
 
Nice mod. Wish I had thought of that before installing mine. Looks like you also modified the holes surrounding the hose fittings.

Living in the desert southwest, I thought having one might be a good idea. I installed one before hanging the engine. I never did hook up a cooling tube.

Recently, at 550 hours, I noticed the left attachment tab had cracked. I thought I could remove it, one bolt at a time, without removing the pump. As stated earlier, that doesn't work. What a poor fuel pump design.

In addition to removing the pump, I had to remove all the fuel pump fittings to get the shroud off. That meant finding and installing new o-rings and a new gasket for the fuel pump.

All in all, I was down for about a week. I'm not installing a new shroud.
 
I have and recommend a fuel pump shroud.

What experience and engineering data do you have that supports this theory that it is not needed? Lycoming and the OEM manufacturers do everything possible to cut down on weight. If they did not feel it had to be there it would likely not be there.

Those that feel it should be let off because of difficulty of installation or "Later years removed the shroud" (likely did not want to reinstall) are just lazy. The installation is not that hard and this is a poor excuse for not installing. Buy a gasket, get or build a long allen socket, have a couple of spare fitting O-rings and get to work.

I called Don at Air Flow performance to see what his experience has taught him and he strongly agrees it should be there. Maybe he will post his thoughts.

I have always preached to not change anything in the fuel system design without careful thought. Just removing a part for convenience is not careful thought.

George Meketa
RV8
 
444TX said:
What experience and engineering data do you have that supports this theory that it is not needed?
Click to expand...

Meaningful data would be a measurement of fuel temperature at the pump inlet and pump exit, with and without a pump shroud. If such measurement demonstrated significantly less increase in fuel temperature with the shroud, then installation is justified. If anyone has those numbers, they've not shared them.

I can only offer my own experience. By measurement, I run much higher lower cowl air temperatures than the RV fleet average. I do not have a pump shroud. There has been no evidence of need in over 500 hours flying the Deep South. If I had detected the slightest symptom of vapor lock, I would have already made the above fuel temperature measurements.

Lycoming and the OEM manufacturers do everything possible to cut down on weight. If they did not feel it had to be there it would likely not be there.
Click to expand...

Lycoming doesn't supply or require pump shrouds with their engines. Some airframers use them, and some don't. It's a pointless point.
 
Last edited:
Dan. I am disappointed in your reply.

I have always considered a fuel pump shroud on a high horse power RV to be standard attire. Maybe I am wrong. Call Don at Air Flow Performance and see what he thinks and let us know. That would be experienced advice.

The Air Force had larger engines installed on their T67 trainers without upgrading the fuel system to match. They had several engine outs that ended in fatal stall spins blamed on vapor lock. No engine problems in the hot Hondo Texas environment, all in high altitude Colorado. Just because you are OK hot and low does not make it OK hot and high.

Like I have stated in the past, now and will in the future. Any changes in fuel system design should be done with careful thought. There have been more than a few Experimental accidents caused by seemingly small changes.

Many years ago while visiting the Dallas area, some friends and I were looking at a upcoming first flight RV. I felt the electric fuel pump that was installed was not correct and told my friends but not Jay Pratt. I received a call from Jay soon after asking about my concerns. The plane had fuel pump related problems on the first flight that could have easily caused a crash. I vowed to not let things slide after that. So, if there is a fuel issue discussion and I feel there may be a safety issue, however small, I will post on it.

George Meketa
RV8, PA12, Cessna 180, Bonanza (all at the same time)
A&P, ASE certified master mechanic, shop owner
 
Last edited:
I put the shroud on my pump during the build because I planned on burning auto fuel,,,which I now do. Whether or not it helps, I do not know, but I have no intentions of removing it.
Click to expand...

If your intent is to burn low octane gas with or without ethanol, it is highly desirable to do whatever you can think of to keep your fuel cool.
Keeping the mechanical fuel pump supplied with cool air will contribute to the overall fuel system cooling. Can't quantify the cooling efficiency but real life experience is worth something. Running on 91 Octane mogas E10 for over 3 years in all kinds of temperatures and altitudes, I have not had any vapor lock issues or any other fuel related problems.
My engine compartment temps run anywhere from 140F to 160F depending on OAT (measured on the firewall above the right exhaust pipe).
 
DanH said:
Meaningful data would be a measurement of fuel temperature at the pump inlet and pump exit, with and without a pump shroud. If such measurement demonstrated significantly less increase in fuel temperature with the shroud, then installation is justified. If anyone has those numbers, they've not shared them.

I can only offer my own experience. By measurement, I run much higher lower cowl air temperatures than the RV fleet average. I do not have a pump shroud. There has been no evidence of need in over 500 hours flying the Deep South. If I had detected the slightest symptom of vapor lock, I would have already made the above fuel temperature measurements.
Click to expand...

Just a minor word of caution about temperature measurement of liquids; If the fuel is already at saturation temperature at the pump inlet (i.e. the boiling point), then the cooling shroud will not necessarily result in a temperature reduction of the fuel vs the non-cooled configuration, but may result in better liquid "quality" at the pump outlet. This is due to the latent heat of vaporization of liquids where heat energy absorbed by a saturated liquid results in phase change instead of temperature rise.

It may be better to measure and quantify temperature reduction of the fuel pump housing itself, vs the non shrouded configuration.

Skylor
RV-8

P.S. I have a very cool running IO-360 Angle Valve WITH a fuel pump shroud in my -8 and I have not tried to quantify the effectiveness of the shroud.
 
My day to be picky . . .

So - fuel - Pressure AND Temperature are important for keeping fuel a liquid. You can look up the boiling point of water on Everest for an example.

If you are going to run a test, be sure to measure both at the inlet to the fuel pump. Then (or simultaneously), like DanH mentioned, measure the temperature after the pump as well. This will determine how much a cooling shroud will help, and with the pressure, determine if it is enough. Lets be careful up there.
 
Last edited:
Impressive, an engineer and an english major.

Sorry for wasting everyones time.

George Meketa
Rv8, Flying
 
444TX said:
Impressive, an engineer and an english major.

Sorry for wasting everyones time.

George Meketa
Rv8, Flying
Click to expand...

You did not waste anyones time George, you made many very valid points. I looked up the noun/verb thing as, like many things, it did not look right and I wanted to improve my knowledge. I think half the time it is the self-correct feature that does it. Back to fuel - - You have a quite valid argument that any change could take a fuel system in the wrong direction. I just wanted to provide a little more complete picture, to augment your comments not replace. The collective "we" like to make "improvements" to Vans design, and I am a believer in validating changes. Lots of teeth mark scars on my posterior from product development as a reminder. I will hold stories for later.
 
Just a minor word of caution about temperature measurement of liquids; If the fuel is already at saturation temperature at the pump inlet
Click to expand...
Skyler, a very good explanation of temperature dynamics in a very complex chemical environment.
There should however be no reason that fuel is anywhere near saturation temperature at the inlet side of the mechanical fuel pump. Properly constructed, the fuel hose should come directly from the firewall and at approximately 12" of length and fire sleeved, it would hardly be possible to bring the fuel to "saturation temperature" before reaching the fuel pump inlet.
After all, it is the mechanical pump or as we call it, the "fuel heater" that is the
largest contributor to vaporizing fuel and the resulting vapor lock issues.
A number of measures can be employed to keep the temperature of the fuel under control. Among these are, a pump shroud and in my case a constant flow return line as well as most fuel system components installed on the cool side of the firewall. 100LL provides an extra measure of margin as opposed to lower octane fuels and Lycoming never intended for anyone to use mogas, hence no provision for cooling any part of the fuel system.

I can only offer my own experience. By measurement, I run much higher lower cowl air temperatures than the RV fleet average.
Click to expand...

Can you quantify the lower cowl temperature of the average RV fleet?
What temps do you measure in your lower cowl and where is it measured?

My engine compartment temps run anywhere from 140F to 160F depending on OAT (measured on the firewall above the right exhaust pipe).
Click to expand...
 
N427EF said:
There should however be no reason that fuel is anywhere near saturation temperature at the inlet side of the mechanical fuel pump. Properly constructed, the fuel hose should come directly from the firewall and at approximately 12" of length and fire sleeved, it would hardly be possible to bring the fuel to "saturation temperature" before reaching the fuel pump inlet.
Click to expand...

Dead on.

After all, it is the mechanical pump or as we call it, the "fuel heater" that is the largest contributor to vaporizing fuel and the resulting vapor lock issues.
Click to expand...

Agree, but I submit (an opinion, to be clear) that most aircraft suffering fuel vapor issues do in fact heat their fuel to some significant degree prior to arrival at the engine driven pump. The hot pump body surely adds some heat to the fuel. The unquantified issue is "how much?", and does a pump shroud actually reduce the heat added in any significant way.

George brought up a good example, the USAF's T-3A IO-540 powered version of the Slingsby T-67. The fuel system was a mess, and the STC to fix it was a lot more than just adding a pump shroud. You can review the list on pages 59 through 62 here:

http://fas.org/man/dod-101/sys/ac/docs/t3bar.pdf

Can you quantify the lower cowl temperature of the average RV fleet? What temps do you measure in your lower cowl and where is it measured?
Click to expand...

Values reported here and in private measurements suggest stock cowls have exit temperatures in the 120F to 160F range, while efforts to reduce mass flow and increase heat transfer can push air exit temperature as high as 210F. For any given airplane, exit temperature rises inversely with aircraft velocity...i.e. when you fly slow, exit temp goes up due to less mass flow.

My own measurements (and a few others) were done using a probe located in the cowl air outlet, shielded from radiant exhaust pipe heating. You can see the wire running to the probe, and the insulated radiant shield, just to the right of the tailpipe. The empty bracket on the left mounted a pitot-static probe.

 
Last edited:
You must log in or register to reply here.
Back
Top