Need and education

[gilbertson]

I have a set up coming that I would like to fit on my mini backhoe, it is a .91 cubic inch variable dispalcement pump, with 2 motors that are 16.4 cubic inch displaement. being the novice that I am I was wondering if some would enlighten me on what this means and what size motor I would need to run the setup. Back how weighs less than 600 lbs and I dont need it to move fast but a little *** would be nice.

Thanks

Vern

 

[AKKAMAAN]

I have a set up coming that I would like to fit on my mini backhoe, it is a .91 cubic inch variable dispalcement pump, with 2 motors that are 16.4 cubic inch displaement. being the novice that I am I was wondering if some would enlighten me on what this means and what size motor I would need to run the setup. Back how weighs less than 600 lbs and I dont need it to move fast but a little *** would be nice.

Thanks

Vern

So you are setting up a hydrostatic drive.....
Looks like you got the pmp and the motors set up for high torque output...
I asuume the motors are 16.4 CUI each...so that will make 32.8CUI combined...

Your full speed, hydrostatic gear ratio (volumetric) will be 32.8/0.91=36.0 then depending on actuyaql working pressure there will be losses in both pump and motors (slippage)....I count 90% efficiancy in pump and motors at max pressure (highest travel resistance)and 95% at normal tarvel....

0.90x0.90=0.81% >> 36.0/0.81=44.4
0.95x0.95=0.90% >> 36.0/0.90=40.0

So you can count your full speed, hydrostatic gear ratio between 1:40 to 1:44

So at 4000rpm your motors will turn 90-100rpm at the most.
or 22.5-25 rpm on motors per 1000rpm on pump shaft

 

[gilbertson]

A couple questions.

1. What does a variable displacement pump do? The one I am getting has a lever on the side of the pump.

2. what can I relate cubic inches to in layman terms?

Thank you

 

[mmurphy]

To make things simple, lets say your variable pump is 10 cubic inches (big!!). With that varable pump you have the option of when you rotate that lever of using 10 c.i. per revolution when wide open down to 0 c.i. when in idle position. The pistons in side are either using very short strokes in idle, and long strokes in wide open position.
Cubic inches, take your galon of milk out of fridge. That represents 231 cubic inches. So wide open on pump it would only need to make 23.1 revolutions to consume 1 Galon.
I hope that helps.

 

[gilbertson]

Let me see if I get this;
231 cubic inches with a .91 cubic inch pump would have to make 254 revolutions to pump a gallon or 4.72 gallons per minute at 1200 rpm?

 

[mmurphy]

Gilbertson, math looks right although I did'nt check it through. I can't seem to do math anymore with out calculator!!!!!!

 

[AKKAMAAN]

A couple questions.

1. What does a variable displacement pump do? The one I am getting has a lever on the side of the pump.

With that lever you can vary the displacement (travel speed), from zero to max, both forward and hopefully also reverse

2. what can I relate cubic inches to in layman terms?

1 fl Oz=1.805 cui
1 usg =231 cui

How are you going to steer this thing??

 

[gilbertson]

I am going to install spool valves to operate the motors forward and reverse.

 

[AKKAMAAN]

I am going to install spool valves to operate the motors forward and reverse.

Are you sure that pump you is not BI-directional???
...if it is bi-directional, you wont need valves for forward reverse...but then you would need a closed loop setup...
Bi-directional pump can reverse the flow and that way reverse the motor..
Bi-directinal pumps are used on riding lawn mowers....

 

[gilbertson]

Pump says CCW so do not think it is reversable.