GPM flow for 3/8 pipe...

[jkern]

... i think you can see where this is going! the PE4200 claims to move 270 gallon per hour of fuel at 20 PSI nominally. so at 20 PSI how many gallons per minute or hour will the stock 3/8 pipe/hose flow? and am i creating a major restriction by using the stock piping in these terms. ok you engineers, get those fluid dynamics books out

 

[Partyat33]

Well, there are a # of factors to consider not the least of which is the length of tube and any elevation changes. With that info you could calculated the flow at a given pressure.



Hope that helps a little.



Dennis

 

[15w40]

I agree with what Partyat33 says. Also when I measured the internal ports of a PE4200 with a micrometer they were smaller than 3/8”. They measured 0. 365”. I plan on using 3/8” lines even when PE says to use ½”.

 

[The patriot]

Originally posted by Partyat33

Well, there are a # of factors to consider not the least of which is the length of tube and any elevation changes. With that info you could calculated the flow at a given pressure.



Hope that helps a little.



Dennis

Yes, along with how many bends, and how sharp of a bend.

The amount of fuel in your tank will even change it somewhat.

Eric

 

[jkern]

while i agree that elevation and elbows will have some effect on the answer that i am looking for, i don't think that it would be appriciable. i just want to make sure that i am not harming the pump by having to much downstream resistance related to pipe sizing. this is my forth lift pump in 40k miles i hope to have this one last a while longer and just wnat to do everything i can to ensure that.



jkern

 

[Oil Burner]

There are losses associated with 90's and elevation changes, but:



3/8 ID at 20psi yields approximately 54. 44 ft/s



3/8 ID tubing has a usable area of . 11045 sq. in. Flowrate is Velocity multiplied by Area. After calculations and conversions, the flowrate at 20psi, with NO restrictions and a 3/8" id, is about 1126 GPH.



If the pump is the restriction at . 365" i. d. , then the same calcs say the max flow is 1067 GPH. I am not talking about the pump, just the 3/8 line itself!!!! The pump is a whole different story and may only flow 270 GPH, I'm just pointing out that a 3/8 line should be capable of flowing at least triple that.



If the pump is designed for a 1/2" line, but 3/8" is used, then the pump will be slightly off on its efficiency curve. Is it enough to make a difference? Gotta see the pump curve. Should be o. k. Sorry for the long post.



just my . 02

-Jason

 

[Ncostello]

I havent done any hydraulic calculations or fluid dynamics studies on this yet... but the last time I tried to fill up a 1000 gallon fire truck tank with a 3/4" garden hose it took much longer than an hour. Our 2. 5" fill pipe in the bay had a bad valve and I couldn't use it. The static pressure on the system is usually around 40-50 and I dont know what the residual was while flowing.



So 1126 GPH sounds kinda high for 3/8". Not saying your wrong cause I havent done the math or research. I'm too busy here calculating the centroids of some strange shapes we have to lift in place with a crane. Dont forget that the fluid in contact with the walls of the tubing remains somewhat static and the real flow diameter is less than 3/8". Just a thought.

 

[illflem]

1126gph is too high. My pipe flow calculator only goes down to 1/2''. At 18 gpm (1126gph) the friction loss in ten feet of straight pipe is almost 18psi. If you had 20 psi at the head you would only have 2 psi at the end of 10 feet.

At 270 gph (4. 5gpm) it takes 800 ft though 1/2'' pipe to get a 20 psi drop (0. 0279 psi drop per foot). If you figured a 3/8 would only do half of this it would be still plenty, I think it's probably more than half though.



10 gpm (600gph) is about the most you can get though a 3/4'' garden hose 25 feet long at 40 psi.



I fill my 400 gallon sprayer in 45 seconds off a 120 psi, 10 feet of 2'' pipe connected to a 12'' main. Fill pipe is heavily braced or it would take off.

 

[Ncostello]

No fair Illflem!! Your using a flow calculator!! But it sounds right because it took me nearly two hours for 1000 gallons!

 

[illflem]

You can download the calculator I use here, takes about 15 seconds for the download http://www.irrigationtutorials.com/sprinkler09.htm

I used a specific gravity of 1. 0 (water) because I didn't know the SG of diesel, now I do, it's less than water . 82 - . 95 at 60°, it will flow more with less friction.



Found some cool flow charts for fuel here http://www.simplexdirect.com/FuelSupply/mainten04.html

I've looked around on the net for a calculator that will do sizes less than 1/2'' with no luck.



on edit found one, now you can do it yourself for any size tubing- http://www.freecalc.com/fricdia.htm



3/8'' (. 375) drawn tubing at the flow rate of a 24 valve pump (4. 5 gpm) will lose . 75 psi per foot at 70° with a viscosity and SG of 0. 9

When you consider there is about 10 feet of 3/8'' line feeding the lift pump I find 7. 5 psi too much extra work for the lift pump. This doesn't concider fittings. 1/2'' may be the way to go.

 

[jkern]

ok...

those are the kind of numbers and calulations i was looking for... i guess then the general consensus is that the 3/8 pipe is really more than adquate. but i pose this question then... if my pump is rated at 22psi output, then thru 10 feet of pipe a couple of elbows and banjo bolt or two, why do i read 22 psi at the test port on the fuel filter? shouldn't this number be about 15-17psi or so???



jkern

 

[illflem]

I take it you have a add on pusher pump.

The reason your pressure remains the same could be that even though the stock pump is rated at 4. 5 gpm it really isn't pumping that much. It could even be caused by restrictions downstream from your gauge in the return line and relief valve setting.

 

[Ncostello]

Lets say your Fuel injection pump wasn't rotating. And also assume that while not rotating... nothing was allowed to pass thru. A total restriction.



If your lift pump was set to bypass at 20psi, it would reach that pressure and begin to recirculate fuel within itself. You would read 20psi anywhere in the system no matter how much fuel line or how many fittings there are. Its static at that point.



In reality, if that particular injector pump only allowed 4gpm to pass at full speed, you would still read close to 20psi anywhere in the system since its not much beyond the static state. Assuming the lift pump was designed to flow much higher than whats needed.



If the injection pump really started to pass high flows, then line length and restriction would cause a pressure decrease in the system as the flow would be impeded... volume cant keep up and the pressure is relieved.

 

[Oil Burner]

Great info on this thread. There are some smart people in the TDR. I agree with the above, my calcs did not take into account any losses associated with the roughness of tubing, elbows, fittings, etc. Sorry, i didn't mean to give false info, just a quick calculation on friday afternoon. I agree with illflem that it should still be well over 270 gph. But the only thing that still runs through my mind is that the pump manufacturer calls for 1/2" line. I would figure that the pump was designed to push against less head pressure than would be associated with a 3/8" line. might affect the life of the pump but maybe not enough to even worry about. just a thought.

-Jason

 

[illflem]

I agree Jason. I don't have a 24 valve so don't have a need to worry but feel the 3/8'' line is marginal especially with the pump in the stock position. It's just getting worked harder than it needs to and may be the cause of the frequent failures. At the rated flow 7. 5 psi of friction loss is almost 50% of it's regulated output. I'm not an engineer but do know that friction loss on the suction side of a pump is something to be avoided because it works the pump harder than the same friction loss on the output side. Even though a person isn't seeing a pressure loss on the output side with his gauge the pump is working harder to produce it than it needs to.



Another thing to be considered that I didn't enter into the friction flow formula is that as diesel fuel gets colder it's viscosity goes up = more friction loss, harder to pump. The viscosity of diesel at 32F is about 30% more than it is at 70°. The friction loss at 32° jumps to 11. 17 psi in ten feet.



If I had a 24 valve one of the first things I'd do even if it wasn't hp modified is relocate the pump to the tank area and feed it with a 1/2'' line. The 3/8'' output line from the pump would probably be ok.

 

[Big White Beast]

Illflem.........

I agree about the temps. I can cleary see a 2 psi gain as the fuel warms up. Usually about a 1/2 hour into a drive.



I'm sure everyone agrees the stock location of the pump is not good but if you mount a pusher or relocate the pump you have the noise problem. Mounted to the rail it transmits the noise all through the cab. That is one reason I'm sure that DC wont relocate it.



A reliable pump in the tank would be the way to go to help mask that noise, it would just be a service nightmare.



As far as flow people keep forgetting the stock filter is only rated at 45 GPH. Bigger lines wont overcome that bottle neck.



Garrett

 

[jkern]

Garrett, you are right about the noise in the cab... i posted awhile back about what i can do to eliminate some of it, cause the PE4200 mounted on the frame rail is quite a bit loud in the cab.



so i guess the general thought of this post is that the 3/8 line is ok, and the actual restriction is the filter.



i appriciate all the input, this has been a very informative thread.



jeremy

 

[illflem]

Garrett, you sure about the 45 gph on the filter, it seems a little low.

Another thing to consider- not sure on the 24s but on the 12s the return from the injectors goes to the filter inlet. Don't know how much volume it is but it doesn't have to come all the way from the tank.

 

[Ncostello]

Illflem... I'm pretty sure the return from the VP44 and the injectors "T" into each other on the back side of the cyl head and return to the tank. None of it returns to the filter.



That does sound low... thats only 3/4 gallon per minute. However seems like I read somewhere the ISB only needs . 70 GPM at full tilt.



If all this is true. . a lift pump only need maintain adequate pressure to the small volume needing delivered. 270 GPH (PE Pumps) isn't going to do a bit of good.

 

[Big White Beast]

OK here's the scoop...........

You all got me to thinking about the GPH so I called Fleetgaurd. The product I inquired about was the FS19579 filter for the 24V applications. (At least my years) This filter supercedes all others.



Rated flow per Fleetgaurd is 59. 97 GPH. Just shy of 60 so it will flow 1 GPM. I would assume that it is tested in our type housing as that's what it is made for.



So it looks like the 3/8" lines are still more than adequate to handle that flow. I added my pusher to help the stock lift pump out. Even with the pre-filter I added for the pusher 20-21 psi is average idling. 17-18 cruising. If I remember right the pre-filter from Napa has a rated flow of 45 GPM unfortunately it doesn't have the Micron rating of the stock filter, 30 I think.



Neil is correct that all the fuel is returned to the tank via a "T".



On another note, I was looking at the service manual for the fuel system and noted that the gassers have the FP in the tank. Seems they could do something to that effect if they put their minds to it for the Diesels.



Garrett