I have aquired a 1972ish Jacobsen out-front 72" mower. the machine runs great except for some issues with the deck. the deck is pto driven to a 90* gearbox that turns the 3 blades via belts. due to the design of the gearbox and the 1970's seal materials, the gearbox leaks oil onto the belts and destroys them($50 a belt). i want to remove the gearbox and install 3 hydro motors on the deck and a pump running off the front of the machine. i was looking through northern tool and found a barnes gear pump that can also be used as a motor, but there are 7 differnet cubic inch sizes. the sizes are .065/1gpm, .097/1.5gpm, .129/2gpm, .194.3gpm, .258/4gpm, .388/6gpm, .517/8gpm
so if i want three deck motors then i need three .129ci/2gpm motors and a .517/8gpm pump?
barnes hydro pumps @ northern tool
anything also besides a tank, strainer, filter, and hoses?

 

That setup would drive the blades at approx engine speed. If one pump stalls out or slows down the other two will speed up and if two stall out the third one will REALLY speed up. It would be best to drive all three blades with ONE motor. You could also use a flow divider to keep all of the motors turning at the same speed.

You will also need an oil cooler on the return line. But you are basically heading in the right direction if you want to go hydraulics. You could put a valve on to stop the blades that would bypass the pump flow thru the cooler back to the tank.

It would be cheaper to just replace the bearings and seals in the PTO drive.

 

i was thinking of putting the motors in series so they would all be the same speed. to stop the blades i would just shut off the pto which stops the pump and motors.

 

Putting them in series with that pump would triple the speed. It would also blow the seals in the pumps since the return line for the motor would see very high pressure. Hydraulics are simple but yet they aren't.

It is still better to fix the PTO bearings that cause the seals to leak.

 

how about just one pump and one motor, would it work then?

 

You can do that but you will want a pump and motor sized to use no more than 1/3 of the HP available from your engine. How many HP does your engine produce? What is the RPM your PTO operates at?

You will also need a relief valve set at about 1500 PSI.

 

Is it REALLY worth redesigning a machine that worked well in its day? just replace the seals on the gearcase, and be done with it.

 

the current engine is 23hp but im planning on upgrading to a 27hp within a few years. the pto runs at 3600rpms.

 

That is a very high speed for a PTO, you might want to check that.

Plan on using 5-7HP for the pump at 1500PSI to keep it safer and allow for movement of the tractor. There are some formulas to use in the catalog that will help you size the pump when you know the RPM. Flow is proportional to RPM so check to see what the actual RPM you are turning and at what RPM the pump flow is rated. If the pumps are rated at 1800 RPM you would double the GPM output at 3600RPM.

There are PTO pumps available but they are not rated for those high RPMs. They would burn up.

1HP = 1GPM at 1500PSI
So 5HP = 5GPM at 1500PSI
and 7HP = 7GPM at 1500PSI