"JD I can not see where the 14.2 minimum pressure at 600RPM comes from. It seems from your manual shot that is the bypass valve opening pressure not minimum gallery pressure."
It was from another page in the general specs.

"I could be talking crap but it seems to me you don't have an absolute disaster on your hands. Maybe the extra gear pump will up all the figures." and

"Me ? Well, why it has reasonable pressure I would keep on driving until a problem arose and then I would be in for a major rebuild, this doesnt mean my way of thinking is correct, rather I'm probably a bit rougher than most"

I tend to agree, (re - disaster). However, adding some more context, the bus is a motor home and breaking down in the middle of 'no where' is something I want to avoid. It's heading to Eucla in Sept with the family to watch whales etc. Hence a little preventative maintenance. We took it to Uluru a few years ago and after driving past the wrecks and emptiness, the penny dropped for the missus (and kids). "what are we going to do if we break down?" My reply was we won't because that why I have been doing all the work on it.

"Maybe the extra gear pump will up all the figures." I'm hoping so. The pump is a standard listing in the parts book. So, it should be within the engines operating range.


I understand the difference (and relationship) between flow and pressure. Hence, the original question which is trying to understand how this 3 gears pump is different to the 2 gear pump. It's not a traditional 2 stage high low pressure (and flow) pump with the impellers in line and separate volutes.

Might seem obvious but have you considered a different oil?
My old KZ Prado read a bit low after I cooked it. Nothing serious, 70psi cold start, 30-40 when hot, clearly didn’t like getting cooked.
I gave it a change to Penrite super flash full synthetic diesel oil and hot pressure would hardly even register. Oil clearly meant for a nice new engine.
Dumped that asap and went back to straight 40 Castrol diesel oil and all good again.
She had over 560,000 on the stock bottom end too.

Hi Jeffo,

I already use Phillips 66 ECT.

phillips66lubricants.com/product/guardol...d-diesel-engine-oil/

We all know this basic stuff below but I can't figure out what the extra gear does on the new pump. In an air compressor gradually increasing pressure cylinders build on the incoming pressure but liquid is incompressible so no matter how many gears there are there can be no pressure increase - positive displacement - oil in = oil out. Has it just got something to do with sharing the load over an extra gear to reduce stress and wear on the shafts etc? That is it does nothing but make the pump stronger and longer life??



Oil pumps
Most oil pumps are driven directly by the crankshaft or camshaft.

All oil pumps are called positive displacement pumps - the amount of oil that leaves is the same as that enters. In other words, the pump moves oil from one side, to the other. This can be contrasted with a coolant pump, for example, which tries to move water but will not do so if the pressure is too great on one side.

As engine RPM increases, the pump turns faster and more oil is pumped. This is convenient because at higher engine speeds lubcrication and cooling requires a greater flow of oil.

A note on oil pressure
It is important to note that oil pressure is not produced by the oil pump. The oil pressure is caused by restrictions to the flow of oil - through narrow passageways, jet nozzles, and tight bearing clearances. If we simply connected a pipe to the outlet side of the oil pump and allowed it to discharge back into the sump, then there would be no oil pressure - the oil could flow unrestricted.

Knowing this, it’s now clear why worn bearings (particularly main bearings) would lead to a loss of oil pressure: the clearance in these bearings is now larger, and the oil’s flow is less restricted.

Just been looking at the 3 gear pump. The middle gear appears to do nothing pressure-wise, it is just an idler. What it does is reverse the direction of the output gear. Perhaps the only reason for such a set-up is to have the oil departing the pump in a different place to suit a special project or engine construction design?

What it does appear to achieve is to have one pair of gears completely dedicated to suction and the second pair (using the idler on both sides) dedicated to flow/pressure. Maybe it is just an efficiency thing with no stunning improvements?

Are the actual pump gears the same?
It looks to me the designers thought to eliminate end plate wear at the pump gears due to the helical drive thrust.

No, different part numbers.

"We all know this basic stuff below but I can't figure out what the extra gear does on the new pump.... " Me too, hence the question. The oil travels around the outside. There are only two outsides; same with the 2 gear pump....

I guess time will tell. Maybe the diagram is different to actual some how?

Just had another thought. Do Cummins make "handed" engines ie left and right rotation for boats etc. If they do maybe that 3 gear pump is required to pump the oil with the drive going in the opposite direction?

I am starting to think JD's 3 gear pump (which gives opposite direction gears) is for a Cummins with left-hand rotation. Instead of having a multi use pump you just change to left or right pump as required.

I may be barking up the wrong tree but if this is so putting a 3 gear pump on the bus would be a disaster as it would be sucking and not blowing.

Lang

Are the 2 Diagrams Drawn in the same scale..?

Look to me as If the two different Pumps are for Different Shape/Depth Sumps..
Possibly One is for Automotive Applications & the other is for Industrial Use.....(maybe)..??

In the diagrams one has the relief valve built into the body of the pump and the other doesn't. That could create a problem as the one without must have a relief valve somewhere else in the system.
Just thinking.