Hello, I'm looking to put together an attachment to mount on the front of my Bobcat S250. The purpose of the attachment is to imitate the 540rpm PTO shaft on the back of a standard tractor (1000rpm won't be needed) so that I can drive PTO-driven machinery through the bobcat's hydraulic circuit. To do this I'm going to need a hydraulic motor... and this is what's causing the problem! I can't seem to find a suitable motor. The bobcat's rated at 3300psi, however all the promising motors I've found are rated for a max. pressure somewhere below 2000psi. I was wondering if anyone has ideas on how to overcome this? Any help would be great thanks! Dan
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thetool
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You can install an adjustable port relief into the aux circuit on your main control valve(or two, one for each side, depending on what your'e going to run). This can be a pain, tho, if you're going to run other attachments where you need higher pressures.
Or you can build in a relief valve into your 3-pt. frame attachment, which I think would be best. You can probably get an entire valve to install upstream of your motor from some outfit like northern hydraulics.
Or you can build in a relief valve into your 3-pt. frame attachment, which I think would be best. You can probably get an entire valve to install upstream of your motor from some outfit like northern hydraulics.
skidsteer.ca
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A $70 cross over relief will solve the over pressure problem. But you really need to find a motor that will handle most if not all of your pressure otherwise you will have vary little hp to the pto and you will stall it a lot. Look through www.surpluscenter.com selection they have several motor that will run higher pressures.
I use a 6 ci version of this motor on my brusher to give 550 rpm with 17 gpm.
http://www.surpluscenter.com/item.asp?UID=2008122613081916&item=9-072-1039&catname=hydraulic its rated 3000 psi continuous and 4000 psi intermittent.
Ken
Thanks! thetool: I'm going to need all the hp I can get, so a relief valve probably isn't the best option, because that's a lot of psi to lose. skidsteer.ca: that looks like the perfect motor! But I forgot to mention one of my other problems.. I live in the UK! Hydraulic motors seem to be very limited over here (especially ones for high pressures), so I'm finding it difficult to find one similar to the one you linked to, I'm going o keep looking, there's got to be one somewhere! Dan
skidsteer.ca
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Suppose their is some pretty healthy duties/taxes for getting one shipped across the pond from Canada or USA?
Can't imagine the UK does not have any hydraulc systems running in that pressure range.
Maybe if you can find the web site for Char Lynn you can get their UK distributers?
skidsteer.ca
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Will that hydro motor work ok on my cat 226 ? I need to make a PTO drive unit for my machine ?
skidsteer.ca
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What is your sytem relief pressure and the hydraulic pumps flow?
You must chose a motor that is rated higher then your max pressure and has the right volume (epressed in cubic inches) to give the desired rpm when running with the volume of the pump you have. That all said the one in the link is likely vary close, but they offer several ci volumes to chose from to dial in to 540 rpm.
Ken
Sorry Ken I dont know the flow all i know is the machine is not a high flow and is a 2000 or 2001 model
skidsteer.ca
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Cat.com or your dealer can get you the gpm for your machine. You need that to size the motor properly or you have no idea what rpm the hyd motor would run.
Ken
bobcatbrian
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H&H fabrication makes one. I dont know anything about it. Check it out. www.hhfab.com
I would like to convert a Bush Hog type mower over myself to put on the S185 I just purchased. What kind of HP can I get out of a Hyd motor with my Hi-Flow machine? I think it's 27 gpm @ 2600 lbs of pressure. dennis
thetool
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There is a formula for calculating hydraulic hp from flow and pressure. Problem is, the pressure is changing all the time, depending on the load, so it's nothing more than an acedemic exercise. If you do the numbers based on rated flow and relief pressure, you may find that the hydraulic hp is more than the rated hp of the machine.
You are never going to have more hp than what your engine is putting out. And on the most efficient hydraulic systems, about 20% less, somebody check me on that.
This is very important to keep in mind if you're going to mount an attachment that is designed to be pulled by a tractor, and turned by a 540 rpm pto, to the front of a skid-steer, and operated by a hydraulic motor that emulates a pto.
With a skid-steer, capable of putting a lot of down-pressure on the attachment, this changes a lot of things relative to how to set stuff up on skid-steer or tractor attachments.
Especially with high-flow machines, the rated flow and relief pressure can mislead a guy into thinking he has all this hydraulic hp available, and he does not.
skidsteer.ca
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Dennis
It really depends on actual motor and pump efficency. These guys only assume 65% so you would have 30.7 hp acconding to this. But I think thats a bit low.
http://www.baumhydraulics.com/calculators/motor_calc.htm
I believe you have 3000 psi available.
I think you would be impressed with how well this works. You won't have the brute hp of a pto unit, but you will make up fo it in agility. And all the brute hp does on a rotary cutter is smash you equipment up. The hydralic drive is kinda like driving it with a rubber band, that won't snap when its stretched too far. No broken shear pins or smoking slip clutches or worse.
More hyd calcs here http://www.baumhydraulics.com/pages.php?pageid=4
Ken
Thanks Ken you correct on the psi, I think my 853 is rated at 2600 psi. I would like to get a 6 ft mower rigged up for my S185. would the 3rd hyd hookup (case drain) on my S185 be of any benefit? I know I'm going to need some kind of bypass so the blades will be able so spin to a stop when the hyd are shut off. Guess I need to finish my grapple bucket before my next project. anyway thanks for the info dennis
skidsteer.ca
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The bypass is a simple check valve, about $25 Some hyd motors require a case drain, usually higher flow one, and some don't. It does not add power , but if the design calls for it your loader is already equiped. I widened my 5' cutter out to 6' and cut the front back to expose the blade tips.
Have yet to try it out, waiting for the snow to drop, hope it does not go so fast it floods. That the best brush mowing time here when the frost is still in the ground but the snow is gone.
Ken
Danfoss makes a Hydraulic Motor that will run a PTO Drive. They are a European Based manufacturer of hydraulic components so you can buy using the Euro. There are also many off the shelf products that will do what you need. Conterra Industries in Alberta makes a regular and high flow PTO Attachment. Regards, Thomas
dozer
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I used the dang near the same one SkidsteerCA used on his brushhog. I used it for a snowblower conversion. My Bobcat 873 runs it no problem. The blower was previously on a 30hp tractor and the blower seems to work very similar. Make sure you have your GPM and PSI figured out first. Then Figure your RPM and HP. I used every calculator that Burden Sales had about 3 times to make sure the motor I purchased would work and it does.
So now I am changing the bracket on the blower to allow it to quickly attach and detach. I plan on converting a tiller, mower, and chipper with it as well and continue to use the same motor. Why spend $600 of motor and hoses when you can just move power from one attachment to the next?
The reason I didn't go with a straight PTO adapter attachment was the extra length. I couldn't find one adapter that didn't put that tractor attachment at least 2-3 more feet in front of you.
Good luck its worth the time and effort if you do it right.
Dozer
