Problems with dead pedal between 25mph and 45 mph

[digidoggie18]

On 8/18/2018 at 11:20 AM, dripley said:

I looked on line and it seems the 100 might come with the kit. Seems to me the 150 might be purchased that way also. I would be good to call Vulcan or DAP and talk with them and see what the pump comes with. It should be a complete kit. It is a bit vague on their sites as to what is included but a phone call would clear it up.

 As far as the quick diconnects, mine are still working fine. If i ever do have a problem or change fuel lines i would get rid of them. 

 Also on the intank pump kit, mine has a 3/8" pick up, just the way it came. I did not know a lot about this back then and never gave it a thought. I do see a 3 to 3.5 psi drop in pressure on mine. My ADII 165 has an an adjustable presuure regulator where the 100 and 150 are preset at the factory with a spring. Mine is easy to adjust while the others will require a different spring or stretching the existing one. Others here know more about that than i do. Not a deal breaker just a differnce in design. But the 165 or whatever they make now is more expensive. No matter what of the above you get the kit should be complete to the VP.

 What would be a good sized pickup to get then? 5/8?

 

[Mopar1973Man]

Typically they all supply 1/2 draw straw with the kit. I happen to have a 1/2" AirDog replacement straw that is steel. 

Edited August 20, 2018 by Mopar1973Man

[trreed]

Not to throw a wrench in everything here, but those "150 GPH" and "165 GPH" ratings are flow on an unrestricted pump at 0 psi....  When the pump starts to make the 15-16 psi pressures they're set at, the flow drops to around 50 GPH... and less as the demand increases.  Both FASS and AriDog are overrated, and their advertising gimmicks are just that. Just my opinion.

 

So my recommendation is to get a mechanical pump.  My pump was benched and flows 55 gph at 2000 RPM and 110 GPH at 4000 RPM.  It's similar to a GDP FuelBoss

Edited August 20, 2018 by trreed

[Mopar1973Man]

54 minutes ago, trreed said:

Not to throw a wrench in everything here, but those "150 GPH" and "165 GPH" ratings are flow on an unrestricted pump at 0 psi....  When the pump starts to make the 15-16 psi pressures they're set at, the flow drops to around 50 GPH... and less as the demand increases.  Both FASS and AriDog are overrated, and their advertising gimmicks are just that.

 

You correct about flow rates. There are a few things you missed. The total flow rate between the return and the supply is still fairly close to the total it is reduced volumes minus the captured pressure and filter flow loss. The pump is not under deadhead load like Raptor and non-returning pumps. The Non-returning pumps tend to redirect the output flow to the inlet again which makes them cavitate and create air bubbles in the pump if the pressure is turned up too high. 

 

[dripley]

I dont disagree with what you are saying on the flow ratings. I have heard it enough here to believe it. I dont know any other way to describe them other than the numerical designations the manufacturer puts on them. The main reason I bought the 165 was not the flow rating but that it came with the kit to mod the fuel basket and get rid the intank pump. The cost difference between the 100, 150, and the 165 was only $30-$40 as I remember. Just made good financial sense at the time. Plus it came with the filter head for better filtration. There are pros and cons to both for one to choose from.

[trreed]

With more demanded pressure, flow will decrease as load on the motor will increase. Again, the advertised flow rates are at zero restriction.  Pump efficiency curves are always advertised in pressure head (usually feet or meters) vs flow rate (GPM, GPH, etc), and then have the efficiency ellipses overlayed.  I doubt we can get ahold of Pure Flow's pump curves for the AirDog, but every pump curve has a negative relationship between pressure head and flow, while power demand increases.

 

So you're telling me you have 100 GPH going through the restriction in the return without overloading motor or excessive fuel heat and 50 gph actually going to the VP? I doubt that very much.  @AH64ID has posted repeatedly about how the filters for the AirDog are 90 GPH filters. Makes one wonder why the under sized filters unless Pure Flow knows their pump is only a true 150 GPH pump without restriction.

 

The only way to actually tell would be to put flow meters on the inlet and both outlets of the pump to compare inlet flow to outlet flow. However, that poses additional issues based on the type of meter you use.  If you use the turbine type, you need to have laminar flow into the turbine for an accurate reading, which is challenging with the amount of 90* elbows in most systems.

Edited August 20, 2018 by trreed

[Mopar1973Man]

True. I look at thing a bit different. I'm not WOT racing. Just daily driving with 2.0 to 2.5 GPH flow rates injected. Way different when you talking racing and high volume requirements when flow rates even on my truck can reach as high as 30 GPH injected. Way different story but since that style of driving for me is less than 1% of the time I really don't sweat that side of the coin. When 99% of the time I'm cruising with 15% to 20% engine load. 

Edited August 20, 2018 by Mopar1973Man

[Dieselfuture]

 

[trreed]

24 minutes ago, Mopar1973Man said:

True. I look at thing a bit different. I'm not WOT racing. Just daily driving with 2.0 to 2.5 GPH flow rates injected. Way different when you talking racing and high volume requirements when flow rates even on my truck can reach as high as 30 GPH injected. Way different story but since that style of driving for me is less than 1% of the time I really don't sweat that side of the coin. When 99% of the time I'm cruising with 15% to 20% engine load. 

WOT vs daily driver is a small piece of this.  The core is still when a pump is loaded, the flow rate falls.  Just taking one of these pumps up to the 15-20 psi pressures we need cuts that advertised flow down.  And then we get into the driving habits pulling the flow down even more.  2.5 GPH demand is still 2.5 GPH demand.  And having a pump advertised at 150 GPH that really puts out 1/3 of that flow at operational pressures is just bad practice.  Good marketing, but bad practice.

Edited August 20, 2018 by trreed

[notlimah]

So your pump varies the amount of gph it flows based on the usage Mike? 

[Mopar1973Man]

17 minutes ago, notlimah said:

So your pump varies the amount of gph it flows based on the usage Mike? 

 

Yes and no. 

 

Yes, the flow to the injection pump is only going to flow what the overflow valve and the injected flow will be. The return flow will rise and fall so technically no the pump output is the same all the time it just balanced back and forth between VP44 supply or the return line back to the filler neck.

 

[Haggar]

Here is a typical pump flow/head curve....  (flow is flow, head is the pressure working against the pump (whether on the inlet or outlet side...)  (these are not the numbers we work with but  1psi is 2.3 ft of head )

 

Notice how for the pump to flow over 50gpm,  it needs to see less than 50 ft of head resistance.  But if we have 75 feet of head resistance, it will only flow about 40gpm.   As we get closer to 112 ft of head (your filters are getting dirty....) and flow goes nearly to zero....  yes zero gpm  it has stalled....

 

for sales sake we get a cherry picked number.  If i was selling you this pump (and an advertising guy  not an engineer)  I would say it flows 50 gpm.   I would say it can operate at 110ft head.    I didn't lie, but I didn't tell you the complete truth. 

 

The gear rotor and vane type pumps we use fall under the "positive displacement" types, but they are far from positive displacement.  So there is a flow/head curve associated with it.  

 

 

Here is the "curve" for positive displacement pumps.....    It is unitless, but you get the idea.  It will hold a flow rate for a set of conditions, but then migrates away from ideal, as the restriction to flow increases.    This "slippage" can be internal recirculation of fluid, or speed of prime mover slowing, etc etc.

 

HTH

 

Hag

[Mopar1973Man]

Ummm... Pump head is the vertical lift if feet of the liquid column.  We aren't pumping vertically much more than more than 12 to 18 inches. Horizontally pumping maybe 15 feet. Then lifting maybe 12  to 18 inches out of the fuel tank. 

 

I work with fire pumps that lift 200 to 400 feet on 2.5 fire hose. What the AirDog has to lift is mere few feet vertically.

 

[AH64ID]

55 minutes ago, Mopar1973Man said:

 

Yes and no. 

 

Yes, the flow to the injection pump is only going to flow what the overflow valve and the injected flow will be. The return flow will rise and fall so technically no the pump output is the same all the time it just balanced back and forth between VP44 supply or the return line back to the filler neck.

 

 

It really doesn't matter if you're burning 2 GPH or 20 GPH as the supply flow will be the same (assuming the pump is keeping up with the set pressure). The return to the filler neck is excess fuel that is bleed off from the pressure regulator to keep it set where it should be. As demand increases filler neck return may decrease as needed, so under very high demand you could be pumping more fuel than at lower demand. Then you still have the VP and head returns. 

 

In a perfect world the injection pump is supplied with the same fuel flow regardless of the burn rate. This is why is doesn't matter if your burning 2 or 20 GPH for filter selection as you're pumping at filtering at 60+ GPH regardless. 

 

Then you look at how the AD regulates pressure and the return to the filler neck and you'll realize that the f/w sep is getting the full AD flow potential thru it ALL the time. The fuel needed to make "X" psi continues onto the 2nd filter and then to the VP. The excess fuel is then routed back to the tank. So if you run a 20 GPH filter with 100+ GPH of flow you can imagine how little it's actually going to do. 

 

Long story short... burn rate is 99.999% immaterial to filter selection on a diesel. 

 

 

 

[Mopar1973Man]

After all that still in all after 13 years 250k miles the first pump head lasted that long. Keep a solid 15 to 17 PSI its entire life. Filters haven't bothered the flow or pressure much being they are very stable. Now some with wild swings I can see this being a problem. I can see this with someone with debris issue and change filter very short intervals. As for my system, I'm still running 60k miles filter changes and barely getting the filter dirt by then. Again pressure is very stable only a 2 PSI drop from Idle (17) to WOT (15) typically. 

 

Donaldson, Fleetguard and AirDog filters have been used and no difference in pressures. 

[AH64ID]

It's not that the filters cannot let the required flow thru, it's that they are not as efficient at filtering and separating water, and they will put undue pressure on the pump. The pump will do everything it can to ensure the proper output pressure is maintained, regardless of what filter is on there. Basically, you shouldn't see a pressure drop even with the low flow filters. 

 

IIRC your 1st pump lasted a long time, but nowhere near what the expected service life was (IIRC best guess was around 1/2 to 2/3 of the expected service life). That being said it's nearly impossible to know why it failed earlier than expected. 

[Mopar1973Man]

1 hour ago, AH64ID said:

That being said it's nearly impossible to know why it failed earlier than expected.

 

I know why the bearings rusted out. Salt water from the road got up into the bleed hole and the bearing rusted and failed.

[Haggar]

Mike,

 

Don't think of "total head" as a change in elevation.  It is the sum of all of the restrictions that impede flow.  It is said and implied like that because that is the actual impact on the system, but the actual elevations don't need to look like that.

 

There is elevation, (and what is fun is the fact that you "lift" the fuel to the pump, suction side restrictions can have a higher impact on system performance than discharge restrictions...)  which is the elevation of the supply,  elevation of the pump and elevation of the discharge.  

 

Now you add the restrictions (pressure drops) of fuel flow in the hose, what the surface roughness of the hose is, the fittings.  The elbows in the system,  then the biggies, like pressure regulators and filters.  (and valves.... valves can be real resource hogs)

 

Here is a representative of pressure loss in hoses. (-6 is 3/8 and -8 is 1/2)

That is for straight lines, not bent. 

Elbows (depending on internal design and radius) can add about 30 times the restriction of 1 foot of pipe/hose.  (banjos are usually worse)

 

Here is a generic pressure drop vs flow rate for filters.  Viscosity makes a huge difference, but this gives you an idea, the more you try to flow through the filter, the more pressure drop (head) it adds to the system.   These charts are for clean filters.  Start to imagine what happens as they get dirty.

 

 

 

Here is a great graph (sorry it is for Fuel injected gas vehicles,) but look how fast head and flow change positions.... even with a good pump....   Notice flow rate is in litres per hour   Which is about .26 gph   so the top of the flow is 100 gph.

 

Hope the background gives you some visual of what is going on.

 

HTH

 

Hag

[015point9]

My return line is 5/16 I think.  Would I cycle more fuel if I used 1/2 for return line also? 

[trreed]

Return from where? Your airdog should already have a 1/2" return.  The return from the injectors/head won't return enough fuel to warrant a need for a 1/2" line.

Edited August 21, 2018 by trreed