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Are 2 stage hydraulic pumps good

1K views 4 replies 3 participants last post by  TUDOR 
#1 ·
I'm working on a homemade tractor with a Sauer Sundstrand series 42 hydraulic pump (42R41D). I need that pump to work the four hydraulic wheel motors, the two steering pistons, and the bucket controls. It has the capability to install a gear pump the the front. A Williams 050405 (can't seem to find any info online).
Would it be worth it to install the second pump?
Would the two pumps be connected in series or in parallel?
How would I connect them?
I'm a novice at hydraulics so any help will be appreciated!
 
#3 ·
As applied to log splitter pumps, two stage is a misnomer that is in common use. The pumps are properly called double or tandem pumps with one being larger for more flow and that is unloaded at a specific pressure while the second, smaller pump continues to work at increased pressures so that a smaller primary mover (engine) can be used with little loss of total speed.

For an actual two stage pump, the first stage pump feeds the second stage pump so that output pressure can be increased with less heat generation.and limited loss of flow. The flow rate is nominally the same as with only the first stage, but the pressure (and horsepower needed) is increased to match the requirement for the final relief pressure and flow rate.

Welcome to MTF, SethJohn.

To your questions, the Series 42 pump is for your drive motors only. Hydrostatic drives work as a closed loop system with a charge pump that replenishes any fluid lost through normal clearances. Additional hydraulics (steering, bucket lift, etc) will be better served with an auxiliary pump for open center hydraulic systems. The only common ground for the two systems is the reservoir..

As far as the Williams pump is concerned, the (very) limited info that I could find was that they are quite pricey, and very specific if it is to mount on the front of the Series 42, and that's why I suggest an auxiliary pump in another location.

Just how large is this home made tractor going to be? That is a pretty potent hydro pump.
 
#5 ·
The series 42 incorporates a charge pump at the front (input shaft end) of the housing. The Williams pump is for the auxiliary hydraulics The Series 42 is for the wheel motors only. The only common point between the Series 42 and the Williams is the reservoir. The balance of the two circuits are isolated from each other.

I see a utility pump already installed on the Series 42 where the Williams pump would normally be located. As long as it flows the correct volume of fluid, it will run your auxiliary circuits when configured properly. Pressure tells how hard a system can work, flow rate dictates how fast it will work. If the flow rate is too high, some systems can be problematic for controlling. If too slow, you could read a book while waiting for the full response of the circuit being used.

Here is the PDF for the Series 42 hydrostatic pump service manual,.


The best way to hook everything up is to first determine what needs to be included and what each particular item's needs are for flow and pressure. Keep in mind that I'm not a hydraulics engineer, but merely a guy who has been playing with hydro GTs for about 40 years and who took a couple of work related basic hydraulics courses over 30 years ago. I've been retired for 19 years.
 
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