Need engineering help understanding my check valve flow direction - Please!

[gmbusguy1]

Phil,
Are you using the same pickup for both the engine and generator?  Generally not a good practice, should be separate pickup tubes and the gen tube should not extend as far into the tank as the engine tube so that the genny cannot run you out of fuel.

Len just curious as to why this is not a good idea?

with the proper check valve it works fine and you have one less hose and potential leak to worry about

just my view

Thanks

chris

[plyonsMC9]

Hi Len,

No.  They are completely separate assemblies, feeds, etc.. 

I'm still not sure why prime is being broken - I had a very large previous thread on this  - but I do know it made a big difference to move the pump much closer to the tank.  I now only have about 6 inches between the fuel pump and the fuel tank.     1 flare fitting, and I don't know what the other fitting is.  My flare fitting wasn't extremely tight.  but it wasn't flopping around either.     Copper tube (3/8 " ) goes into the fuel tank about 24 inches.  Looks to be about 4-5 inches off the bottom of the tank.

I'll try to post more pictures of the assembly when I can get back home near the bus.  We'll be travellling again in a couple of days, so hopefully more photo opps.

Thank you!
Phil

[Sojourner]

Phil....your problem is that you have too large pick-up tube. Why...the bigger tube inside dimension the more liquid/weight to lift and once the air entered while fuel's level is below pick-point during braking with the flow is too slow to fill up the inter displacement  of extra large pick-up tube. You posted ½" in the earlier post.

Remedy to fix this problem is to install 5 or less psi (or whatever is less than generator's pumping) relief valve after the first electric pump. The relief pressure goes to fuel tank to dump air and/or fuel. This way you will always have fuel only going to the generator's pump.

If you can find a relief valve...you can use a small needle valve instead. Adjust the relief flow so that it can maintain at least above .5 (point-5) psi to generator's pump

I suggest replacing pick-up for smaller one that the generator spec calls for....that alone will reduce most of your problem.

Sojourn for Christ, Gerald

[JackConrad]

Phil,
  I had a similar problem on a 102A3 that I installed a Powertech generator in.  It would run fine and after a while it would die. I determined it was definately a fuel issue.  What I finally found was a cracked brass fitting on the suction side of the pump. It would work OK until the fuel warmed up the fitting causing it to expand slightly and allow the crack to open.  Jack

PS: I have used 3/8" tubing for tank pick-up tube in several tanks with no problems yet.

[Len Silva]

Phil,
I feel pretty positive that your problem is a leak in the suction line somewhere between the pump and the fuel. At this point I would just replace the whole thing, suction leaks can be very hard to find.  Something is happening in the tank when you hit the brakes. A tiny split in the pickup tube is being uncovered, or the tube itself is shifting in a fitting.

Chris,
Most every generator or fuel heater installation manual I have read calls for a separate pickup, primarily because the larger user can starve the other for fuel.  Even if that doesn't happen, the most practical reason is so that the generator pickup can be installed a few inches above the main engine pickup so that the generator cannot run you out of fuel and leave you stranded in the desert to die a miserable death like a poor forsaken animal .

[kyle4501]

Sounds like fuel is sloshing away from the fuel pickup OR the pickip is moving in the tank & air is getting in the system. This would explain why the opportunity is sensitive to braking & fuel level.

Copper is not the best material to use for the pickup as it fatigue cracks easily. Install a new steel tube to replace your old copper one. This won't cost too much - will it?   

[John316]

Kyle,

I wish that you wouldn't have said that!!! We JUST installed a nice copper line into our tank (while it was out on the ground), for our Oasis heating system. I thought that copper would have been the best...Oh joy. Now I guess that we will see how long it lasts...Bummer. The pipe is installed from the top, so no way of replacing it, unless we pull the tank...

Oh, well. Thanks for the heads up.

God bless.

John

[kyle4501]

"They" used to use a double walled soft annealed copper for these things, but that was then . . . . I don't know if you can even get the stuff now, what with plastics taking over the flexable tubing market . . .

[Sojourner]

About leaking air into fuel line after the pick-up above the submerged fuel level....that would mean you have problem all the time...it is not problem because Phil said whenever low fuel level & hard braking only.

Phil...do what I suggested in previous post and problem is solved.

Sojourn for Christ, Gerald

[kyle4501]

Well Phil, you have some choices to choose from. . . .

Try what is easiest/ cheapest first, then progress up the scale of difficulty & expense as you are best able.


BTW, concerning having an air leak all the time & the problem manifesting during hard stops & low fuel in the tank . . . .
That is a typical symptom of a small leak. If the leak is small enough, it only renders the system marginal for normal running. But when you put the additional loads of hard braking & low fuel, the system can't keep up.

I've had the problem several times in the past. Amazing what a tiny air leak can do.

I can't imagine the 3/8" line is too big . . . . You are lifting the same volume of fuel regardless of the line size - the fuel moves faster in a smaller tube which leads to a higher pressure drop which can lead to problems on the suction side - especially if there is a small leak. 


If you're going to add a relief valve & return line, I'd locate the relief valve as close to the generator as possible - just like the factory did on the main engine.

[plyonsMC9]

Phil....your problem is that you have too large pick-up tube. Why...the bigger tube inside dimension the more liquid/weight to lift and once the air entered while fuel's level is below pick-point during braking with the flow is too slow to fill up the inter displacement  of extra large pick-up tube. You posted ½" in the earlier post.

Sojourn for Christ, Gerald

Gerald - MY MISTAKE!!  Original post was wrong- for that I do apologize.  My copper line is actually 3/8"  Wrico said 5/16 was ideal, but usually 3/8 was OK - 1/2" would be BAD.  Good to hear from you - I will also begin looking around for a reliefe valve -   is there a line then from the relief valve back to the fuel tank?

We are going to review the flare fittings on the fuel line this weekend. 

And - look at steel for the pickup.   Didn't know the copper was bad!  Wow!  I'm learning lots of stuff here.  And SOOOOOOOOO thankful for the heads up before I installed the WRONG check valve.  What a hassle to go through just to find out that the generator would no longer function.  Ouch!!   I'm guessing steel can be purchased easily from an auto/truck parts store? 

What is "cracking pressure" ?  I've not heard that before .  Thanks again!

Phil Lyons

[Dallas]

Hey Phil,

Since that nasty ol' generator is causing you so much trouble, I'll be glad to take it off your hands if you want to drop in down here in Texas for a visit. Heck, I'd even be nice enough to loan you some tools to remove it. I might even serve you a nice cold adult beverage at no charge, just because I'm that kinda guy.

[kyle4501]

Cracking pressure is the pressure required to 'crack' the valve off the seat & allow flow (but not full flow).

All the check valve will do is prevent the fuel from flowing back to the tank. Like when turned off for extended periods.

My understanding is the engine starts fine & is shutting down due to lack of fuel.

If fuel flow to the engine stops, the engine stops- unless you have some sort of reserve at the engine.

Just my opinion, but if you're having fuel delivery problems, adding another restriction (check valve) isn't likely to help.


A relief valve will require a return line to the tank. The original 2 stroke setup required the fuel return because the fuel was used to cool the injectors. Cars use a fuel return to help minimize vapor lock.
Again, I don't see this as a good solution to the current problem either - although it may the system may tolerate air better, it doesn't prevent it from entering in the first place.


If you want to use 5/16", Summit Racing has this:

http://www.summitracing.com/search/Part-Type/Tubing/Tubing-Outside-Diameter-in/5-16-in/?keyword=steel%20brake%20line

Good luck & keep us posted. . .

[luvrbus]

Kyle, he does have a return line to the tank on a Kubota, I for one still think it a shut solenoid problem you don't start one of these easy if air is in the system or it ran out of fuel,leads me to  think it is shutting down at the pump.
The way mine works is 12 volts opens it to start 110V keeps it open for running.
I had this same problem with mine a while back replaced all the lines to the tank and it still would shut down so I did the old bungee cord repair to hold the solenoid open and it never shut down mine has the shut off on the side of the pump his may be in the pump. Or he could have a bad shutdown sensor telling the engine to shut down 

  good luck

[kyle4501]

Good point, I was assuming that possibility had been ruled out since he was looking for another solution (check valve).

Maybe a volt meter could be wired in to see what the solenoid is doing/ being told to do?

If that shows normal, maybe something can be rigged up to see if the solenoid is activating the shutdown without being told to . . . .