Diesel Place banner

1 - 20 of 60 Posts

·
Registered
Joined
·
3,799 Posts
Hey, Frank. I thought the pump was a recipricating pump. (runs back and fourth, not rotary)
 

·
Registered
Joined
·
704 Posts
Nice pic, but a little small. Do you have a larger version? I can host it if Yahoo has a size limit.


Also, it looks like you took a really good look at the filter head. What are your thoughts on the inlet check valve from the tank? Do you think it is restrictive or unneccessary. I am not talking about the white ball.
 

·
Registered
Joined
·
1,309 Posts
Discussion Starter #4
Amric, I had a 4.2 MB photo to start with but I couldn't get it in my album. How can I get it to you? The area under the check valves is a lot smaller than 1/2". I am sure it is big enough for the majority of us. The guys running the big numbers might have a flow problem. Every restriction in the system adds a little to the total suction head. I am sure GM knew exactly how much the filter adds to the system. We do know that we can add too much because some have had to add lift/prime pumps to prevent cavitation/aeration. The check valves are needed to prime the filters and probably to keep the line from the filter to the pump full of fuel to insure a fast start. That is what the white ball does when the filter is removed. Later! Frank
 

·
Registered
Joined
·
1,309 Posts
Discussion Starter #5
Max, the pistons are reciprocating. The cam in the center is pushing the plunger in and the springs are returning them. Radial piston pumps or engines usually have a connecting rod attached to a crank shaft. A lot of hoist air motors work this way also. Later! Frank
 

·
Registered
Joined
·
218 Posts
What is the purpose of the gear pump in the upper picture, or is this a picture of a totally different pump?
 

·
Registered
Joined
·
4,755 Posts
The gear pump is attached to the rear of the High pressure section through a common shaft. The gear pump is not a positive displacement pump. As a matter of fact you can pour fuel in the inlet and watch it run out of the exit. This is the reason you must prime the fuel system with the pump on the fuel filter! If the gear pump section was a positive displacement type pump the motor could self prime but it would take cranking the engine for awhile. The purpose of the gear pump (low pressure) is to draw the fuel from the tank through the filter and deliver the fuel under pressure to the high pressure section of the pump. It uses the pressure from this pump to control the high pressure output of the high pressure pump. I have the entire pump apart on my work bench and can answer all questions of how it works as I've traced the entire circut out. For High Hp applications the addition of a lift pump to help supply the gear pump is a must.
 

·
Banned
Joined
·
6,539 Posts
Now this is good stuff and it applies to my new truck as well. Thanks guys!!!!!
 

·
Banned
Joined
·
2,067 Posts
Diesel tech,


I know this is a strecth but could you visulize any method for air to escape? We all know that air builds where there is a higher pressure like on the incoming side of a fuel filter. We also understand air rises to the top of a system. With those two concepts in mind, could air be returned to the tank?


I wish I could be there to see the pump. Are you going to the DHRA race May 1rst? If you brought the pump and other componets , that would be my final straw. I would have no chioce but to drive down to Kentucky!
 

·
Registered
Joined
·
716 Posts
So how high of psi can the lift pump supply? If they are identical, the cummins guys are pushing over 15-18psi with lift pumps. Is this ok on the gear pump? Seems to be.

Has the Cp3 pump actually not been able to supply enough fuel to the rail yet?(with a lift pump). Any cooling issues when using high amounts of fuel?

Thanks
 

·
Banned
Joined
·
2,067 Posts
I remeber reading a MOTOR AGE article ( courtesy of HOOT) that stated the low pressure pump would sufffer physical damage with any input pressure greater than 20 PSI.
 

·
Banned
Joined
·
6,539 Posts
From the Cummins Cutaway pics in the Cummins section

 

·
Registered
Joined
·
1,309 Posts
Discussion Starter #13
All gears pumps are positive displacement. The fuel is simply runing around the outside of the gears just like when it is turning. Diesel Tech, there a good training course on the GM site that shows a cut away of the pump running that you might find interesting. Later! Frank


Maybe I should elaborate on the above statement before someone gets their shorts in a bunce. A positive displacement pump delivers a fixed volume of fluid for every revolution of the pump. To do this it must have a constant supply of fuel to the pump inlet to prevent cavitation. This pump was not designed to pull fuel from and empty line all the way to the tank. You can change the total output of the pump by varying the speed . The output volume of our pump is constantly changing with the engine speed. Thus it is a positive displacement varible speed pump. I was lucky enough to see the animation run. I am sure there is a good reason why Bosch chose to mount the pumps together but I am not going to speculate on that. I hope the spelling is good in this post. I am without my spell checked today. Later! Frank Edited by: Frank Blum
 

·
Registered
Joined
·
1,146 Posts
hoot,


D Tech said high horsepower applications, not sure that would apply. No doubt about the engine, but anything south...........
j/k
 

·
Registered
Joined
·
139 Posts
Warning on use of lift pumps.......If supply pressure is too high you will blow past the fuel filter o ring.O ring was designed for suction not pressure...
 

·
Registered
Joined
·
161 Posts
Welcome GMworldclassmaster. Glad to have yet another tech. on board!



Steve
 

·
Registered
Joined
·
1,309 Posts
Discussion Starter #18
I don't have a clue what the positive and negative pressure ratings of the OEM filter are. For a list price of $600+ it should be good! I do know that the Racor 645/660/690 Models may be located on the suction or pressure side of the fuel transfer pump. They are rated 40 PSI max under the hood and 60 PSI for a chassis mount. I would be real surprised if the rest of the popular brands weren't the same. Same here on having another Tech on the forum. Later! Frank Edited by: Frank Blum
 

·
Registered
Joined
·
4,755 Posts
The low pressure side of the pump will allow fuel to go through it with the gears in a stationary position! A positive displacement pump doesn't do this( at least all the one's I've worked with). The pump will move a fixed volume of fuel when properly supplied but by changing what is supplied you change what will come out. Since it will allow fuel through to the control solonoid everything works out fine. The control solonoid let's the necessary fuel to the high pressure side and the rest is sent to the center section to lubracate the interworking and then be returned to the tank. So adding a lift pump to supply the low pressure side just allows the pump to supply more fuel to the high pressure side when needed. This solves the pressure drops we have seen when running high Hp engines. I see no area designed to remove air from the fuel. The fuel travels from the front Aluim. plate through the center casting to the rear mounted low pressure pump on the bottom. The outlet is on the top of the gears where the fuel travels back into the center casting and goes to the front aluim. plate and up to the control soloniod. This passage also feeds into the center of the high pressure pump to lubracate the shaft, bearings and high pressure pistions. Excess fuel goes from here to the return line. The fuel that is let through the control valve feeds to the top of each high pressure pistion where there are two valves and a high pressure bleed/check valve on each pistion. When the pistion travels down the cylinder is filled by sucking the intake valve open and the low pressure fuel fills the cylinder. Once the pistion starts up the bore the valve closes and pressure begins to build. Once the pressure rises above the outlet check valve opening pressure fuel travels out to the common rail. To control the high pressure Bosch uses a bucking regulator valve that's part of the intake valve assemble. The low pressure holds this assemble in place as the pistion travels up the bore. If the pressure becomes to high the intake assemble moves up and allows the fuel to be returned into the intake area instead of going out the port to the common rail. A very simple but effective way to control high pressure with low pressure.


Two things need to be address when adding a lift pump. How much power are you going to add and how much pressure will the fuel system take. Right now we are OK with 5 - 7 psi on the system. The Dodge boys run 15 - 19 but they donot have the fuel going through the EDU like the D-max does. We tested the EDU at 5 psi for 30 days non stop with no leaks. We have raised the pressure to 10 psi and are rerunning the test to see if any leaks start. Once the test completes we will run a High Hp truck at 5 psi then rerun at 10 psi to see if there are any changes. That will let us know what we need to do. If your not going over 400 RwHp you really donot need the lift pump unless you have added a post OEM fuel filter
 

·
Registered
Joined
·
1,309 Posts
Discussion Starter #20
I have only rebuilt/disassembled a couple hundred pumps in my short 40 year career so I will bow out to superior knowledge. Later! Frank Edited by: Frank Blum
 
1 - 20 of 60 Posts
Top