Hydraulic snowblower pump/motor calculations.

[oldnslo]

Why would he need an "axial or radial piston motor" vs a Geroler motor such as the one he linked to if the motor is rated for the same amount of torque?
Aaron Z

He wouldn't at 540 RPM but the problem is that typically geroler style motors are not very efficient. Most axial piston motors don't like to run that slow and radial piston motors that small are kind of rare. So in this case the geroler / geroter may be his best choice.

Now if he had a front mount meant to run at 2500 RPM he would be much better off with a good pressure side loaded gear motor or an axial piston motor since both of these will run well at this RPM.

 

[leonz]

1. The three point hitch will work without interference as far as the hoist cylinder at the mid point will raise it just like belly mower.


He has even less clearance when he sticks a pump and hoses under there.

The hitch is out in front otherwise it would not work.

2. Not possible; there is a reversing reduction gearbox that attaches to the three point hitch mounting frame and the short shaft that attaches to the snow clearer.

3. if the blower is used it will work no matter what.

4. the use of shear pins or roller chain also works very very well.

5 if you need to reverse the rotation you have lot of crap that should not be there anyway.

6. I cannot help that


7. What you mean is the critical angle of repose for the snowblower not the angle of attack.

Rolling over the snow clearer is counterproductive as the chute and spout will have limited movement, this is what drift cutters are for.

The front hitch systems are ment for tractors like his so it would be worth his while to call pronovost and ask them for a quote.



I am done with this.

 

[dkhntr04]

I'll entertain some of the questions that were brought up.

1. I want a loader mount unit. I want the flexibility to drop the blower in a minute or two and attach my plow, or put my bucket of forks on for other work, and also for many of the same reasons as the gentleman on here who has the sweet Kioti/ Quick Attach setup in ID. I also have a frame mounted, shaft-driven 59" Deere front blower. The blower is decent but narrow in width, and the changeover to the FEL takes longer than I'd like. I have carefully analyzed my needs and a loader mount blower is the best solution, in my opinion. Oh, and I've also used rear-pull blowers, not my cup-o-tea either.

2. I was looking at buying a Quick Attach brand blower and hydro power pack. I came to the realization that I didn't need to buy a blower as I already had one. What I needed was a hydraulic drive system. The blower I intend on converting is in excellent shape as I went through it last year and restored it to like-new mechanical condition. I have the time, tools, fab skills, experience, and funds for this project. The only thing lacking was experience designing a hydraulic motor circuit from scratch, hence my looking for verification on my calc's.

3. I chose to look into powering the pump off the mid PTO because the higher rpm gave more and less expensive pump options, and higher PSI capabilities than a standard 540 PTO pump. I still have not decided on a reservoir location, but I am debating between the merits of a 3-point mount or a side-saddle type configuration. The mid PTO idea may not work, I'm still in the concept stage at this time.

4. Gerotor type motors are the only ones I have even seen on commercial skid-steer blowers, so that's what I am trying to copy. They work for Frontier, QA/Erskine, Bobcat, and a host of others. Should work for me too, unless I am cursed.

Back on the original topic, I did more research last night and found the hydraulic motor HP formula on Surplus Center's webpage that I had overlooked. (Hydraulic motor power (Hp) = Torque (in-lb) x RPM / 63025) Staying within the confines of that particular motor's continuous torque limits and assuming 85% efficiency, the blower would only be getting 21hp, which is not going to do it.

So now I am out looking for a 6-7 CI motor that can handle 4000+ In/Lbs of torque continuous, or move to a larger displacement pump and motor.

Still looking for constructive input. Thanks!:thumbsup:

 

[RodNH]

A couple of thoughts to consider.

The hydraulic snow blowers used on skid steers are available with several different hydraulic motor packages that should be selected to match the hydraulic characteristics of the particular skid steer for best performance. The Bobcat one I use has a hydraulic motor that gives 734 rpm of the fan at wide open throttle of my skid - which is where I run it to get maximum HP. That's significantly greater than the standard 540 rpm of a tractor pto. Having used both a rear 540 rpm tractor blower and a 734 rpm skid steer blower, I much prefer the higher fan speed. The fan diameter of mine is 20 inches. I don't know if the construction is more heavy duty to accommodate the higher fan speed.

I'd recommend allowing a liberal amount for pressure drop in hoses and fittings between pump and motor. Several hundred psig is not unreasonable for that. Don't forget the back pressure on the motor. For motor performance calculations, use the anticipated pressure drop across the motor, not the nominal system pressure or the relief pressure.

Rod

 

[oldnslo]

I'll entertain some of the questions that were brought up.


3. I chose to look into powering the pump off the mid PTO because the higher rpm gave more and less expensive pump options, and higher PSI capabilities than a standard 540 PTO pump. I still have not decided on a reservoir location, but I am debating between the merits of a 3-point mount or a side-saddle type configuration. The mid PTO idea may not work, I'm still in the concept stage at this time.

4. Gerotor type motors are the only ones I have even seen on commercial skid-steer blowers, so that's what I am trying to copy. They work for Frontier, QA/Erskine, Bobcat, and a host of others. Should work for me too, unless I am cursed.

Back on the original topic, I did more research last night and found the hydraulic motor HP formula on Surplus Center's webpage that I had overlooked. (Hydraulic motor power (Hp) = Torque (in-lb) x RPM / 63025) Staying within the confines of that particular motor's continuous torque limits and assuming 85% efficiency, the blower would only be getting 21hp, which is not going to do it.

So now I am out looking for a 6-7 CI motor that can handle 4000+ In/Lbs of torque continuous, or move to a larger displacement pump and motor.

Still looking for constructive input. Thanks!:thumbsup:

3) Mid PTO with a side saddle reservoir would help reduce the hose length. As long as ground clearance for mounting the pump is not an issure I would definitly consider this option.

4) Yes gerotor/geroler motors are used extensivly in the Ag market. If possible look closely at the operating specifications for the motor. Make sure it is rated for continuous duty at the conditions you expect to operate at. Some companies actually publish charts showing speed Vs GPM and torque Vs pressure so that you can get a better idea on what the motor will do while in operation. reason I say this is that there are different grades of geroler/ geroter motors and some have very poor performance while others are fairly good. Inexpensive may equate to cheap.. For reference Look at the Eaton Char Lyn website. They have several different models with varing degress of performance. Eaton Char-Lyn was one of the originators of the geroter/geroler motors.

What is your total tractor engine power. What portion or percentage of that power is available for driving the blower? How much of the engine power is used to prepel the tractor or ryun the FEL hydraulics? You will have to balance available HP to drive the pump with the motor size.

I am all about saving money but like most of us ihave also been burnt by trying to cheap and then the machine does not perform as expected.

It may be easier to size the motor to run at 600 - 625 RPM theorectical and then let the inefficiencies of the pump and motor bring the RPM down closer to 540.

best of luck on this project.

Roy

 

[dkhntr04]

The last two responses got me thinking. Thanks to Ron and Roy, I started thinking about how 540 rpm is the limit because of the tractor driving it, not necessarily the max mechanical speed on the blower. I started looking for a higher RPM to compensate for volumetric efficiency losses and increase motor torque and power output. I spent some quality time with the Surplus Center website, the Vicker's Industrial Hydraulics Manual, and my TI-83. Here is what I came up with:

My 3720 puts out 35 hp at the pto. To get the full pto hp potential into the hydraulic system, I upsized the pump to a 2.01 CI Prince unit Surplus Center - 2.01 cu in PRINCE HYD PUMP SP25A32A9H1R . Using the formula hp= gpm x psi x 0.000583 to determine pump hp requirements, I determined I would need at 2100 pto rpm a relief valve setting of 2737 psi and a flow of 18.27 gpm to make maximum use of my 35 pto hp.

With the flow rate figured, I could calculate my rpm. 18.27 x 231 = 4220 / 7.1 (motor displacement) gives an rpm of 594. Assuming 85% volumetric efficiency I should land at around 505 rpm, which is a bit low. I also used an online calculator from Gates to roughly figure my pressure drop through the hoses. It came back with a pressure drop of about 11 for my diameter, length, fittings, and flow rate.

For motor power calculations, I calculated all in theoretical numbers, disregarding the likely 505 rpm due to volumetric efficiency. Fist was torque. Torque = (psi x displacement) / 2 Pi (aka 6.28)
My calculation was 2726 psi x 7.1 / 6.28 = 3081. So the motor should deliver a maximum of 3081 in/lbs of torque. Motor horsepower output is calculated by torque x rpm / 63025. Plugging in my values I get 3081 x 594 / 63025 = 29.04 hp (theoretical) for the motor output. Utilizing the 85% efficiency 505 rpm I come up with 24.7 hp.

If I calculated that all correctly, 24.7hp at 505 rpm isn't going to move the white stuff as well as I would want it too. Assuming I got my numbers right, main limitation to making this work is the available PTO horsepower of my tractor. For a 60" blower, this would work great, especially if you could increase the rpm by 30 to 40 with. 24-25 hp will run this 80" okay as I have ran it on 23 before, but it's way lower than I was looking for. Unless someone can find an error in my calculations, I'm filing this project away as an enjoyable learning experience that for once didn't actually cost me money.

Thanks again for all the input.

 

[oldnslo]

Duckhunter,
I did not physically check your math but what you could possibly consider is a slightly smaller motor to give you higher RPM'S and then possibly have to drive a little slower in heavy snow. Not sure if your tractor is gear drive or HST but how often where you at max power with the PTO drive while blowing snow? I lived in central MN for years and had an 8' rear mount blower on a Ford 5600 in the 55 - 60 HP range. HEavy snow or drifts feather the clutch or drop a gear. Moved up to a 2-85 White and still had to feather the clutch or drop a gear in heavy or drifts.

Possible options are using a two speed motor or a bent axis motor like rexroth A6VM or Sauer 51 series with hydraulic displacement control. With these motors they can be set at a reduced displacement to run at higher RPM and when the load / pressure increases to a set point they start increasing displacement which increases torque but lowers the RPM. These are used on mulcher heads to help power through tough work and then speed back up. Down side, you would have to look at their efficency curves in the 600 RPM range

Unfortunate reality is that hydraulics are not as efficient as mechanical drive is this application.

 

[dkhntr04]

Roy,

A 6.2 cubic inch motor would net me about 590 rpm after calculating for efficiency, but I would still be stuck at the 25hp level. I ran the blower on my McCormick gear drive with 23 PTO hp last season and it did ok. It could handle 6-7" of drifted snow fine at full width in low gear which was about 1 mph. Any more than that, full width was a no-go. 480 square inches of snow surface (depth x width) entering the blower in whatever configuration was the limit before you would need to clutch. One of my top 3 reasons for going to the 3720 was hp for snowblowing, even if I can get a good rpm the power is the deal killer for me. Those multiple displacement motors look neat, but spendy... though I could not find a price. Thanks again for the help.

 

[oldnslo]

Have you considered a back-up camera or mirrors and use the blower on the 3PH? Probably a lot less work and money and will give you full PTO power to the blower and save your neck.

For reference a 6.7 CIR bent axis motor with hydraulic displacement control lists for around $6000.

 

[dkhntr04]

I actually have a 59" Deere front blower that I'll be using as my primary with this one being my back-up. Loader mount front blower would have been the proverbial "better mousetrap" for me, same forward driving advantage as the 59" I have now, but a few features that would optimize performance for my situation.