Hydraulic Motor Sizing

[Hilbilly]

I want to convert my 3PTH snow blower to hydraulic and run it off my Skid Steer and have some questions for the hydraulic gurus.

First is the drive info. My skidsteer (SS) is a 1999 Bobcat 763 and the rated hydraulic flow is 15gpm at 3050psi. I'm guessing the 20 year old hydraulics are not providing that now but I could be wrong. Next is the blower; it is a 72" single stage Meteor blower. It has been used for the last 8 years on the back of my Massey 1547 Tractor with a rated PTO output of 38 hp. The setup works fine but like most old people with a rear mounted blower, my neck gets very sore after looking backwards for more than an hour.

I'm thinking of using this motor http://https://www.princessauto.com/en/detail/9-6-cu-in-4-bolt-hydraulic-spool-valve-geroler-motor/A-p8490062e to drive the input shaft on my 3PTH blower, using sprockets and a chain between the output shaft on the hydraulic motor and the input shaft on the blower, with a cross over relief valve between them. I plan to use a 20 tooth sprocket on the hydraulic motor and a 15 tooth on the blower input shaft, to up the speed to 540RPM. It seems to me that the motor will not have enough power to run the blower but I read another thread on this forum where someone did a similar conversion, with a similar motor and a tractor with a PTO output of 40Hp. The difference I see in the 2 setups is that the other person used a PTO pump rated at 20 GPM at 2200psi and a motor rated for 20gpm at 2200psi. My SS only puts out max 15gpm at 3050psi. So if I use the above motor and restrict the pressure to 2250psi will it still produce the rated HP? Or am I looking at a failure in the making?

 

[oldnslo]

15 GPM @ 3050 PSI is approximately 30 HP input. I would suggest finding a motor rated for full pressure to utilize all the power available. Dropping to 2250 PSI you lose around 8 HP

 

[mikester]

I did something similar except I ran a 5 foot blower

Using your specs
Horsepower Calculator - Metaris Hydraulics
15GPM @ 3000psi = approx 26 HP (should be ok - a little on the small side for 6 foot meaning you will have to take smaller/slower cuts with deep or wet snow)

15GPM -> 3465 cu.in/min / 9.6cu.in/rev = approx 360 RPM

I don't know if you will be happy with how far the snow gets blown for your speed/torque and gearing

Here's my blog on the hydraulic to front mount conversion

Snowblowers – Front and Rear PTO Driven Conversions for my Tractors – Part 1 – Divergent Stuff

I went with an electric chute rotator using a cheap electric winch because it was a lot cheaper than outfitting a diverter and solenoids.

 

[Hilbilly]

I think you guys are right. I need to get the most HP to the blower that I can. I'm trying to utilize a motor from Princess Auto because their prices are good but if it doesn't work then the price was bad because the money was wasted. They don't offer a motor with low flows and high pressures. I can get higher pressure ones but they require 20gpm, which I don't have. Seems like I need to find a different motor supplier in order to get the most out of my setup. I am a bit concerned that running the SS at full throttle and working it hard (like the blower will) may kill the poor old thing. More to think about. But first I need to see if I can find a motor that is a perfect match to my setup. If not, I guess I can either try the lower HP motor and hope it's good enough or just find another way to back up without killing my neck. I've tried mirrors but they just get covered with snow mist and then they're useless.

mikester, I was planning on getting the blower to run at 540 RPM by using larger sprocket on the motor than the blower.
I read your blog and found it very interesting. Nice job on the blower rebuild by the way.:thumbsup: I did find it odd that you went back to using the 3PTH with your new tractor. Was there something you didn't like about the front mounted ones you had previously converted?

 

[oldnslo]

Hillbilly,
The 20 GPM is the max rated flow for the motor. The will operate at less flow just run slower.

To figure motor displacement using RPM & flow Displacement in cubic inches per revolution = (GPM x 231) divided by RPM or 15 x 231 / 540 = 6.4 CIR motor @ 100% efficient. Personally I would shoot for 600 RPM possibly a little more to allow for speed loss do to inefficiencies.

or for metric displacement in cc/rev = LPM x 1000 / RPM

 

[Hilbilly]

Hillbilly,
The 20 GPM is the max rated flow for the motor. The will operate at less flow just run slower.

To figure motor displacement using RPM & flow Displacement in cubic inches per revolution = (GPM x 231) divided by RPM or 15 x 231 / 540 = 6.4 CIR motor @ 100% efficient. Personally I would shoot for 600 RPM possibly a little more to allow for speed loss do to inefficiencies.

or for metric displacement in cc/rev = LPM x 1000 / RPM

Thanks for the info Oldnslo. That got me pointed in the right direction and I think I've found a motor best suited for my setup. It's a 6.1 CIR and according to my calc's, with 15 gpm / 3000 psi input it will operate at 567 RPM, putting out 26 HP and 2887 in-lbs of torque. That's assuming my SS still puts out the specified flow and pressure. Also assumes running at full throttle and 100% efficiency. I think I will give this one a try and if it doesn't rotate fast enough I can change sprocket sizes to try to get the speed up. I'm pretty sure the blower will not perform as well as it did on the 3PTH since that is supposed to be 38 HP. But if it's works reasonably well, it will save my neck and I can go slower if need be.

 

[mikester]

I think you guys are right. I need to get the most HP to the blower that I can. I'm trying to utilize a motor from Princess Auto because their prices are good but if it doesn't work then the price was bad because the money was wasted. They don't offer a motor with low flows and high pressures. I can get higher pressure ones but they require 20gpm, which I don't have. Seems like I need to find a different motor supplier in order to get the most out of my setup. I am a bit concerned that running the SS at full throttle and working it hard (like the blower will) may kill the poor old thing. More to think about. But first I need to see if I can find a motor that is a perfect match to my setup. If not, I guess I can either try the lower HP motor and hope it's good enough or just find another way to back up without killing my neck. I've tried mirrors but they just get covered with snow mist and then they're useless.

mikester, I was planning on getting the blower to run at 540 RPM by using larger sprocket on the motor than the blower.
I read your blog and found it very interesting. Nice job on the blower rebuild by the way.:thumbsup: I did find it odd that you went back to using the 3PTH with your new tractor. Was there something you didn't like about the front mounted ones you had previously converted?

I now keep my firewood in 1000L totes. I prefer to keep the forks on my loader all winter for moving totes around.

The other problem with the unmodified 3PH blower up front is that it sticks way out forward. If you need to get into tight spots or have a curved driveway then its not as good.

If I was going to go forwards again I'd cut the 3PH arms off and mount a skidsteer QA plate directly to the blower. I'd also mount the hydraulic motor onto the blower instead of driving a PTO shaft.

Post pics when you get yours done!

 

[Rustyiron]

Good old Sruplus Center has these built for PTO operation. Ag PTO Output Hydraulic Motors | Hydraulic Motors | Hydraulics | www.surpluscenter.com
I don't know enough to tell you how to size these for your application. The psi is a bit low for your SS.

 

[Hilbilly]

I now keep my firewood in 1000L totes. I prefer to keep the forks on my loader all winter for moving totes around.

The other problem with the unmodified 3PH blower up front is that it sticks way out forward. If you need to get into tight spots or have a curved driveway then its not as good.

If I was going to go forwards again I'd cut the 3PH arms off and mount a skidsteer QA plate directly to the blower. I'd also mount the hydraulic motor onto the blower instead of driving a PTO shaft.

Post pics when you get yours done!

Makes sense. I just got a snow plow for the front of the tractor and have the blower mounted on the back. Seems like a good combo, except for the backing up part. I used the tractor that way yesterday and it worked well.

I plan on mounting the hydraulic motor beside the input shaft to the gearbox and use sprockets with a chain between them. That way I can leave all the 3PTH system in place. All I need to do is pull the driveshaft off and mount the sprockets to run it on the SS. I will make a 3PTH mount for the SS. That way I still have the ability to run it either way and I don't think the blower will stick out too far on the SS. I might get started on this next week. Biggest issue for me is trying to find the steel I need. It's all buried under 2 1/2' of snow and I'm not sure where the right size stock is, or if I have any.

Should have done this a few weeks ago. By the time I get this done, it probably won't snow again.:laughing: But that's OK, I've had enough anyways.

 

[Hilbilly]

Good old Sruplus Center has these built for PTO operation. Ag PTO Output Hydraulic Motors | Hydraulic Motors | Hydraulics | www.surpluscenter.com
I don't know enough to tell you how to size these for your application. The psi is a bit low for your SS.

Thanks for the link. I think the one I picked out is a better match because of the pressure capability. Plus Princess Auto has one in stock. All I need to do is go to the big city to get it. If this doesn't turn out I will probably use the motor to convert my rotary mower or flail mower to hydraulic. Maybe I should come up with some universal mounting system that would allow me to use this motor for all 3 implements. Food for thought anyways.