Obviously you don't even know what "positive displacement" means or how the lift pump works.

>>The spring in the Fuel Supply Pump is there to return the Pump Piston (which creates the negative pressure and brings in the fuel).


>>A cam lobe on the IP Camshaft by way of a Roller Tappet and a Thrust Rod Pushes the Piston the piston ejecting the Fuel from the Fuel Supply Pump.

Effectively, both of these above statements are wrong and mixed up.

Here's what's really happening;

The spring pushes the piston towards the IP and delivers the fuel.

The cam lobe and push rod return the piston, drawing in fuel.

That is more proof you don't know what you're talking about.

>>That is more proof you don't know what you're talking about.

I wouldn't be so sure if I were you.

The lift pump, with its piston, rod and spring looks like it could be a positive displacement pump, but, it isn't.

As I mention above, look at the pipe layout.

Also, if you think about it, why would MB use a positive displacement pump in this application?, where a near constant pressure pump would be much more suitable?

Please go and have a proper look and a proper think about this. In the interim, I'll see if I can scan in the section diagram I have in my Bosch book where this is described.

Actually, I am 100% sure.

I strongly suggest you look up what "positive displacement pump" means before making a fool of yourself again.

1: Pressure as soon as the engine starts turning.
2: Constant and known maximum volume of fuel pumped.

Incorrect. What controls the system pressure is the relief valve on the side of the injection pump.

I suggest you do.

Down boy.

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
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Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

At the risk of being the 3rd man in.......an engine oil pump is an example of a positive displacement pump....lift pumps, fuel pumps, etc. are not exactly a postive displacement pump, they are spring driven.

>>Actually, I am 100% sure.

You're just digging a bigger hole for yourself - it's not pleasant to watch - nor are your arrogance and bad manners pleasant to read.

twcaldwell gets it right.

I have an excerpt from the FSM that shows the pipe layout, which hopefully should be attached. Note, the fuel flows out of the lift pump at the fitting closest to the IP, as the piston pumps on its return stroke, while being pushed by the spring.

I have re-checked the definition of fixed displacement pumps, and the fuel lift pump is definitely not in this category. The volume pumped per cycle is not fixed, as it is spring driven, not driven by the push rod.

Attached Thumbnails

 

Great, another that doesn't know what "positive displacement" means.

Back to shop class 101.

The method of drive makes zero difference. By definition, positive-displacement (PD) pumps displace a known quantity of liquid with each revolution of the pumping elements. This is done by trapping liquid between the pumping elements and a stationary casing. Pumping element designs include gears, lobes, rotary pistons, reciprocating pistons, vanes, and screws. The volume is constant given each cycle of operation.

Piston pumps comprise of a cylinder with a reciprocating plunger in it. The suction and discharge valves are mounted in the head of the cylinder. In the suction stroke the plunger retracts and the suction valves opens causing suction of fluid into the cylinder. In the forward stroke the plunger push the liquid out the discharge valve.

THAT is your problem. You are not even thinking of the vehicle being discussed. We are discussing the OM61x lift pump, NOT the OM60x lift pump!

You completely fail to understand what that means!

"Positive-displacement (PD) pumps displace a known quantity of liquid with each revolution of the pumping elements"

The stroke and method of pumping make no difference. A PD pump moves a fixed quantity of fluid. If if did not it would not be positive-displacement. The engine itself is a positive-displacement pump but due to volumetric losses it does not move the same amount of air on each stroke. Despite that it is still a positive-displacement pump because it forces a trapped volume of fluid from point A to point B.

Nonpositive-displacement pump pumps on the engine are the turbo, water pump, heater pump and radiator fan.

>>We are discussing the OM61x lift pump, NOT the OM60x lift pump!

It works on exactly the same principles, it's just that I happen to have the OM60x pump picture available.

No, they don't. They are not the same pumps. You might as well be talking about a CDI or Mack engine.

Is the pipe layout fundamentally the same on a OM60x and a OM61x engine regarding lift pump input and output?

From a recent thread about IP check valves, discussing lift pumps on these engines with Barry124, and Yellit, I asked the question there, and was told it is the same input / output layout. The general Bosch book I have also shows that layout.

For a lift pump, there's no need to define a fixed volume being pumped each rev - as long as the pump pumps more than is needed, then it's OK. Having a near fixed pressure on the other hand does give an advantage in calibrating and setting up the IP with a known fuel pressure.

Working from that information, given by Yellit IIRC, which I have no reason to doubt, I can be quite sure, that the pump isn't positive displacement.

It isn't positive displacement because the stroke isn't fixed, it's determined solely by the volume of fuel that goes either down the relief valve or to the injectors.

Another way of looking at it is that these pumps can't produce more than about 18 psi - even pumping into a clamped pipe. This 18 psi corresponds to the pressure which can be created by the spring - the spring that does the pumping.

Now, I've posted quite a bit of evidence to support my view. Please could you post some evidence to support your views. Please also drop the arrogance - it's going to make the fall that much harder.

NO. Get with what I've been saying for the last 7 posts.

Then, I can be quite sure, you have no idea what you are talking about.

That makes NO, zero, zip, nada, none, nil difference! Please, please, please go reread what positive displacement means!

More proof you don't know what you are talking about. These pumps are capable of well over 30psi.

Evidence that proves yourself completely wrong.

I already have. You simply can't get it through your skull that you don't even know the basic definition of "positive displacement"!

I suggest you open your mind and actually learn something.

>>NO.

Show me. Post something written by MB or Bosch that demonstrates that you're right.