Piston type lift pump question LP vs HP

[BobS]

I have gathered the following information from over on DTR so correct me where I am wrong:

The maximum pressure to a Bosch VE pump should not exceed 20 psi for any extended duration or the VE pump will encounter seal related leaks.

The lower pressure piston lift pumps are regulated to 15 psi maximum output.

The only physical difference between the lower pressure and second generation higher pressure lift pumps is the ones for the second generation are set at 30 psi by incorporating a longer length pressure relief spring.

So the question is why can't we take a high pressure lift pump that is sold through most auto parts stores and trim the pressure relief spring to get the lower pressure that we can use with the VE pump?

[dpuckett]

Because it would probably cost about the same in the long run, plus you KNOW the LP VE pump is set to 15psi or so. No experimentation required.

Daniel

[sdstriper]

The part number for the Low Flow Lift Pump is over there too, in the Tech section, along with the rest of the parts that it would take to convert. There is a spacer, couple gaskets, fuel line and the pump, No spring trim necessary.

[Bob Beauchaine]

If you already have a HP pump you could always get a LP rebuild kit. As I understand it they are the same except for the spring. The piston pump is made by Carter and Cummins might be able to supply a rebuild kit otherwise I've got to agree with everyone elce.

Bob

[Greenleaf]

When the fuel pressure reaches the injection pump, it is fed into the vane supply pressure pump. This pump increases the internall pressure to a varying degree. Much above and well over 15/20 psi.

It's been stated that 30 psi supply will have an effect on the timing of the injection pump. Will tend to advance a bit. I'm not sure if it's due to additional pressure above what it normally would be at, or not......

On another note, the shaft seal is a lip seal. A lip seal is good to say, 14 psi. Yet the lip seal on the shaft of our pump is subjected to internal pump pressure. I blow lip seals all the time on my farm tractor transfer pump. They don't hold much in the way of pressure as they are not intended for that application.

[gman07]

As for that seal, I heard KTA is running a seal retainer of sorts to run higher inlet pressures...

KTA, want to enlighten us some, or is it one of those super-secret black topics?

[Greenleaf]

It's still a lip seal of sorts I imagine. I have heard tell of a retainer but that won't assist the "lip" portion of said seal. A retainer would, IMHO, simply keep the seal body from blowing out of the pump housing bore.

I simply run with 16 psi supply and don't fret the small stuff. No problems thus far.