Help with hydraulic Motor Selection

[coal160]

I am in the process of re-plumbing a REALLY old terremite that has been hacked, cut on, and generally hill-billy ized for the last 25 - 30 years. What it has now is a single pump (unknown, with no nameplate, except that it is a vickers) being driven by a wisconsin thd 18 HP twin. This runs everything, including the drive motor. This makes it pretty much impossible to run the front end loader properly, due to every time I use the bucket, the drive is affected. Also, the drive motor is of unknown origin. What I want to do is change the pump out with SURPLUS CENTER's Item #9-7885, which is an EATON tandem pump with 8.9 GPM on the front (to drive the axle), and 7.8 GPM on the rear (to power the loader and backhoe) My problem is drive motor selection. I am thinking that I need something around 300 RPM to get 6-7 MPH, but that is only my guess. I have attached pictures of my pile, and a professionally drawn schematic of what I want to do... Any help would be greatly appreciated. Thank you very much.

 

[J_J]

You don't have enough HP to operate that pump
using both sections at the same time. You would need 34 HP/16.7GPM at 3000 psi to run that pump.

Some of out Power-Tracs use 4 hyd motors, one hyd motor for each wheel. You could use two wheel motors on the rear wheels, and connect them in series. A 3000 psi pump will drop 1500 psiacross each motor.

I have 45 HP engine turning a variable speed pump, pushing fluid through 4 hyd motors.

A 45 HP engine can turn a pump putting out 22 GPM's at 3000 psi.

Your 18 HP engine can only power a hyd pump, putting out about 9 GPM at 3000 psi. So you are limited to say a pump that can pump 9 GPM. They say the efficiency from the engine to pump is 85%, and the hyd motor efficiency is also 85%, so, the effective HP at the rear end will be something like 13 HP.

Here is an idea and you can use what you have now, and not affect the drive system.

The loader on my Power-Trac, uses a small 3 GPM Haldex hyd pump at 3000 psi, to turn the steering and operate the loader, with the ability to lift 1200 lbs. It runs off the fan belt. It works quite well, and no special belts necessary, just plain standard fan belt.

 

[coal160]

Your 18 HP engine can only power a hyd pump, putting out about 9 GPM at 3000 psi. So you are limited to say a pump that can pump 9 GPM. They say the efficiency from the engine to pump is 85%, and the hyd motor efficiency is also 85%, so, the effective HP at the rear end will be something like 13 HP.

I realise that the motor is a little underpowered by the pump specifications, but there will never a time that I am using the full flow/pressure of both the pumps. I.E. I cannot run the backhoe, loader, and drive the tractor at the same time. I admittidly know very little about hydraulics, am I missing something? Won't the power be kinda automatically go to whichever pump has a load on it? I think I basically want to get a motor that will spin at ~300 Rpm and use ~9gpm, and If I need to run the loader while I am driving, it will be a little power limited... I think... But on the other hand, thinking has gotten me in a lot of trouble before...

 

[J_J]

Sure you could use the one section of the pumps GPM's to move the machine, and when stopped, use the other section for the BH, or loader. You still have to find a hyd motor that will produce adequate torque, and the rpm you need.

Look in this section for a hyd motor that will run at the rpm and torque you want.

Surplus Center

 

[coal160]

Thanks for all the help. I may go with this: Surplus Center - 0.40/0.31 cu in EATON HYD DOUBLE PUMP. It has a front end of 6.4GPM, and a rear end of 4.8 GPM. It seems that it might be more of a match for my motor. This will really limit me on drive motor selection. Is there a calculator somewhere (I couldn't find one -at least one that my brain was smart enough to understand -using a google search) that gives me torque and RPM of a motor based on pressure and flow? Thanks.

 

[oldnslo]

Thanks for all the help. I may go with this: Surplus Center - 0.40/0.31 cu in EATON HYD DOUBLE PUMP. It has a front end of 6.4GPM, and a rear end of 4.8 GPM. It seems that it might be more of a match for my motor. This will really limit me on drive motor selection. Is there a calculator somewhere (I couldn't find one -at least one that my brain was smart enough to understand -using a google search) that gives me torque and RPM of a motor based on pressure and flow? Thanks.

Fluid motor torque

Torque in lbs = (PSI x FM CIR) / 2 pie

FM CIR is Fluid motor displacement in cubic inches per revolution


Fluid motor RPM = (231 x input GPM) / FM CIR

This does NOT take into account any inefficency in the motor.

Roy

 

[J_J]

Surplus Center - Hydraulic Cylinders Pumps Motors

Select tech help, look on left for calculators, select motor speed and torque.

 

[coal160]

That is exactally what I am looking for. Thanks!

 

[coal160]

Okay, one more quick question which may, or may not prove my complete ignorance about hydraulic systems. Can I use a hydrostatic pump to power cylinders? I would still use all the valving, etc, and would have to probably fix the swash plate in a fixed position to have repeatable control over the hydraulics, but is it detremental to the pump? Basically, I would use Surplus Center - 0.43 cu in HYDROSTATIC KANZAKI DUP-7A TANDEM PUMP, and use one side for my drive, and one side for my hydraulics... Thanks.

 

[oldnslo]

Okay, one more quick question which may, or may not prove my complete ignorance about hydraulic systems. Can I use a hydrostatic pump to power cylinders? I would still use all the valving, etc, and would have to probably fix the swash plate in a fixed position to have repeatable control over the hydraulics, but is it detremental to the pump? Basically, I would use Surplus Center - 0.43 cu in HYDROSTATIC KANZAKI DUP-7A TANDEM PUMP, and use one side for my drive, and one side for my hydraulics... Thanks.

Normally hydrostatic pumps do not have good suction capabilities on the inlet so they will not work well in "open loop" circuits.

Roy