diaphragm fuel pump, the spring is on the wrong side of the diaphragm, how does this work?

[[486]]

kubota v2203

the pumping chamber is above the diaphragm
the spring is retracting the diaphragm away from the pumping chamber (holding the follower on the camshaft)

now, it'd never work with the spring going the other direction (the follower would not touch the camshaft) but I just don't see how it maintains pressure
one would think that it'd have a pressure pulse only at the top of the cam and zero fuel pressure (hell, 100% vacuum as it is sucking from the tank in that section of travel) when the pump is off the lobe

Maybe you can assume there's an air bubble caught in the filter housing or something that provides some accumulator effect beyond the pump's outlet check valve?
But then there's an air bleeder on the fuel filter housing that would eliminate this accumulator effect...

 

[M92PV4U]

 

[M92PV4U]

Do you have it taken apart?

 

[[486]]

was expecting that quote when I made the thread lol

Do you have it taken apart?

yeah there ain't shit to see

you know how most of them like you'd see on a car with the springy arm, they all got the return spring squeezing the diaphragm against the valve plate and the cam lobe lifting the diaphragm against the spring to suck more fuel in, not the other way around

 

[M92PV4U]

I am not going at invisioning things in my head. Does it have inlet and outlet check valves? Or are you saying that there is no way to open the diaphragm to the open position?

 

[[486]]

One on top is what came on the thing, I bought the one on the bottom figuring I'd put a beefier spring in it to up the fuel pressure

On both of them the spring biases the cam follower and the diaphragm away from the check valves in the top cap. Obviously it works, but I can't picture it having an upper limit to the fuel pressure it produces.

It also wouldn't have constant fuel pressure across all cylinders. It runs off a lobe on the injection pump cam, so you'd have lower/zero fuel pressure for the same cylinder or two that are drawing fuel in to their injection pump element at the same time the lift pump is in the suck stage of its operation...

Unless there's some kind of fuel pressure accumulator type thing going on in there, but there's nowhere for an air pocket for such a function.

 

[1oddtech]

The spring is all that pushes the fuel to the pump, the cam just resets the plunger to allow the spring to press the fuel out. It's how it regulates the inlet fuel pressure.

 

[[486]]

The spring is all that pushes the fuel to the pump, the cam just resets the plunger to allow the spring to press the fuel out. It's how it regulates the inlet fuel pressure.

look at pictures
pumping chamber is on "vacuum" side of spring tension
pressure is only when cam lobe is rising