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Need some help with hydraulics


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#1 El Exorcisto OFFLINE  

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Posted November 08, 2011 - 11:20 PM

Ok, I'm tossing around an idea of putting together a hydraulically powered rider deck on the front of my recently acquired David Bradley Super 3. What would I need to look for in a pump and motor to spin three blades powered by a 212cc Honda clone? What do I need for a reservoir? Do I need any type of controller to adjust flow, or can I rely on a fixed speed set by pulley sizes?

I was figuring I would drive the pump by a pulley from the engine. That would be piped to the motor mounted on the deck. From the motor a belt would turn the main drive pulley of the deck.

Did I say I'm trying to do this as absolutely cheap as possible?

#2 Alc ONLINE  

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Posted November 09, 2011 - 06:34 AM

Sounds like a neat project , do you have any of the parts yet ( deck , pump ect ) ? I think it takes a lot of HP to run a deck but having hydraulics would be nice if you wanted to use it to drive say a log splitter , if you had a big enough motor /pump , hope you have good source of cheap parts because it would cost a pretty penny to do what your trying to do with new stuff , Al

#3 MH81 ONLINE  

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Posted November 09, 2011 - 07:48 AM

Sounds like a fun project, do you have the deck yet?

As for speed, you should be able to get in the ballpark with ratios, but you definitely want a pressure relief in case you get caught up in something.

Edited by MH81, November 09, 2011 - 12:11 PM.


#4 skyrydr2 OFFLINE  

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Posted November 09, 2011 - 07:54 AM

This will take some HP to run the pump needed to run the hydraulic motor. You will need at least a 3600 rpm end result at the spindle or spindles. And it takes more engine HP than it can produce hydraulicly.

#5 ducky ONLINE  

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Posted November 09, 2011 - 08:36 AM

I agree it will take more ponys than the Honda 212 to drive a deck

#6 El Exorcisto OFFLINE  

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Posted November 09, 2011 - 07:21 PM

I've seen a DB with a three blade deck driven by what looks like a 3HP Briggs. Would it be a lot easier if I just wanted to spin one 30" blade and made the deck?

#7 ducky ONLINE  

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Posted November 09, 2011 - 07:31 PM

Yes, if you take the hydraulics out of the equation it would take less HP to drive a deck. What size deck are we talking about?

#8 Gtractor ONLINE  

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Posted November 09, 2011 - 07:38 PM

David Bradley had a three bladed deck that was called a Tri-Cut. it was not designed to be operated on the Super 3 model. The DB tractor needed to run the Tri-Cut had either a 5 horse Briggs or 6 horse Briggs engine. DB also had a two wheeled tractor with a 6 horse Lauson/Tecumseh engine that would opweate the Tri-Cut. Horsepower was rated differently back then. I wish you luck but I don't think you will have enough umph.

#9 JDBrian OFFLINE  

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Posted November 09, 2011 - 07:52 PM

The posts above are talking about the loss in the hydraulic drive you are thinking of using. Lets put some numbers on it. The 212cc clone is probably rated at 7hp. The loss in a gear pump and motor would be up to 40%. That would leave you a net peak power of about 4.2hp. With all the expense necessary to go that route you may need to go to a larger engine to make sure you have the HP to make it a strong mower. Otherwise the money spent on the hydraulics would be wasted.

#10 El Exorcisto OFFLINE  

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Posted November 09, 2011 - 08:40 PM

I was thinking a 36-42" secondhand rider deck. Do you think I would have the juice to spin a single 30" blade? I'm not opposed to building a deck to use a single blade similar to the layout of a DR field mower, but is doesn't seem worth it to cut less than 30" in a swipe.

#11 johnhawk OFFLINE  

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Posted November 24, 2011 - 02:36 AM

Thanks for nice post . But is my project machnical engnearging ..............!

#12 Tennblue59 OFFLINE  

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Posted December 06, 2011 - 01:32 AM

There is an awful lot of wiggle room in the questions you asked, but let me see if I can help confuse you some!

Some hydraulic systems (such as lift cylinders, power steering systems) use relatively high pressure but low flow. These can have fairly small resevours and usually small pumps. You can often "cheat" these systems by using lower horsepower drives for the pump - just increases cycle time.

However hydraulic motors tend to be the exact opposite. Most motors have high flow requirments - think of a water turbine. The "work" happens because of a large volume of liquide flowing through the motor. The high flow requirements generate heat (efficiency loss) through friction, both with the flow volume, and within the motor. This heat buildup, and the high volume of flow require much larger resevours.

In hydraulic motors, think of flow supplying rotational speed, and pressure generating torque - this is not exactly true, but close enough. For a mower blade, you need both - the worst scenario - high flow (gpm) and high pressure (psi) = high horsepower, large pipe lines, large resevour, radiators to dissipate heat. Most hydraulic blade systems tend to use a large flywheel (stump jumper) to retain rotational energy. You can trade off torque (blade takes more time to "spin up to speed"), for speed and lower system overhead. You can use pulleys to multiply your speed, but you also lessen your torque that way.

A single blade often works better on a hydraulic system than 2 or three blades because the single blade is longer (higher cutting tip speed for the same shaft rotational speed) and the assembly is more massive (rotational inertia) than several smaller blade assemblies.

As has been stated, I think you are WAYYYY down on horsepower for this operation, and it would be a large system for a 2 wheel tractor. But work from the end back.
First you need to know the hydraulic motor requirements. Once you know what size motor you need, then you can spec the flow and pressure required to run it. That determines the line size. Flow and pressure requirments lets you spec the hydraulic pump - need one big enough to supply your motor's demand with frictional losses build in. Then pretty straightforward to determine the horsepower required to drive the pump. And finally that gives you minimum size for your resevour. A bit of math, but most hydraulic shops should be able to spec the parts if you give them the starting point - what you want to do!

And finally, you also need a pressure relief system in the line - that flywheel full of energy tends to keep spinning even after the pump shuts off - and would do nasty things to your pump and motor if not planned for.

This aint gonna be cheap..............




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