PTO gearbox and pump for FEL snowblower

[Chaostamer]

All - thank you for your insight and wisdom. I am learning with the help of experts like you all. Turns our the pump is dead and rebuild is likely not an option (functionally and economically). I am waiting for my new pump and hoping no more snow for a week.

Best to you all in the coming year!

 

[RickB]

My tractor is only 45 hp and it operates my system like a champ. Why wouldnt you think his 60+ hp tractor wouldnt work.

I got the impression he was referring to 'reduced RPM' to get the full flow and pressure.

Exactly.

 

[Chaostamer]

Not the full flow...just stay in spec. It is a huge window.

 

[grsthegreat]

Thats just it. Numbers are numbers. I move lots of wet snow with my unit, but mines hydrostat transmission. I dont bog it down as i simply let off the peddle if needed. The reasion i dont have a tow behind unit is the 6 foot berms of snow i clear on my horse barns and sheds. I can lift my blower 7 feet in the air if needed to clear berms.

 

[Dave M7040]

Land Pride, now owned by Kubota makes a complete 3 pt hitch hydraulic system intended for front mounted blowers.

Model HRS-30

HRS3 Series Hydraulic Reservoir Systems | Land Pride

Min pto hp required 52

25 gpm and can operate up to 3,000 psi.

It is likely an expensive unit but its design features and spec's make a good target for you to copy.

The important consideration when matching an implement to a tractor is the engine's torque curve.

I know this is getting a bit technical/theoretical but plse bear with me.

A Torque curve is like a mountain on a graph. The highest torque value is at the peak of the mountain.

As the engine rpm's increase so does the torque output like climbing to the top of the mountain.

As the rpm's increase further, you are on the down slope of the mountain and the torque values start to decrease even though the power output in HP is still increasing.

If you are doing a job requiring lots of power like blowing snow or driving an electrical generator, you want to be operating the engine slightly past the peak of the mountain or the torque peak.

This becomes very important when the load on the engine starts to increase because of a deeper snow drift or a large electrical load on a generator.

As the engine starts to slow down, if it is operating on the down slope of the torque curve, its torque output increases as the rpm's drop as it retreats to the top of the mountain. This enables the engine to pick up the added demands and and not stall out even though the rpm's will have dropped a little.

The tractor designers carefully decide at what rpm the engine will operate to output 540 pto rpm. They deliberately establish that point past the engine torque peak by selecting gear ratios to drive the pto.

The convenience of a FEL mounted snow blower is very attractive. However, if the power requirements of your blower are close to the output of your tractor, the losses in the hydraulic system can be significant and lead to a frustrating operating situation.

Dave M7040

 

[majorwager]

Wow, lots to unpack with POST from PISTON. True, hydraulic power consumes more engine hp for same output than with traditional gear drive. But the goal is to maintain the RPM speed at the gearbox, without direct regard for engine speed. A horse power rating is the same regardless of how it is produced. Momentum is getting off into the tall weeds
So the GPM required to produce a hyd motor speed is the key. The cubic inch sizing of the pump determines the speed of the motor at specific RPM. Pressure remains a constant determined by the rating of the pump. Since most hydraulic pumps require 1500 RPM to meet their rated PSI capacity, a speed increaser is necessary for the 540 output shaft. Prince and several Chinese knock-offs offer a self contained unit mounted to tractor PTO shaft. Comer, Auburn Gear, others, offer a remote mounted increaser which I am using, discussed later. I believe that the confusion (for me anyway) is that the gearbox must operate at the required RPM. That result can be obtained by GPM pump size and the PTO shaft RPM's required to drive the pump. Remember pressure remains constant with an in-line pressure regulator valve which is an absolute mandatory system component. I am building a unit that will produce my required GPM at a slightly reduced PTO speed (417 =/-) and engine speed of 2250 RPM but closer to the peak torque band of the engine, which is more productive than the higher HP at 2700 RPM. Will save fuel, reduce engine wear and temperature

 

[CincyFlyer]

Wow, lots to unpack with POST from PISTON. True, hydraulic power consumes more engine hp for same output than with traditional gear drive. But the goal is to maintain the RPM speed at the gearbox, without direct regard for engine speed. A horse power rating is the same regardless of how it is produced. Momentum is getting off into the tall weeds
So the GPM required to produce a hyd motor speed is the key. The cubic inch sizing of the pump determines the speed of the motor at specific RPM. Pressure remains a constant determined by the rating of the pump. Since most hydraulic pumps require 1500 RPM to meet their rated PSI capacity, a speed increaser is necessary for the 540 output shaft. Prince and several Chinese knock-offs offer a self contained unit mounted to tractor PTO shaft. Comer, Auburn Gear, others, offer a remote mounted increaser which I am using, discussed later. I believe that the confusion (for me anyway) is that the gearbox must operate at the required RPM. That result can be obtained by GPM pump size and the PTO shaft RPM's required to drive the pump. Remember pressure remains constant with an in-line pressure regulator valve which is an absolute mandatory system component. I am building a unit that will produce my required GPM at a slightly reduced PTO speed (417 =/-) and engine speed of 2250 RPM but closer to the peak torque band of the engine, which is more productive than the higher HP at 2700 RPM. Will save fuel, reduce engine wear and temperature

Actually, flow[GPM] does control motor speed, but pressure controls motor torque. Since power is the product of speed and torque, simply spinning the pump at n rpm does NOT produce x power unless it has the requisite pressure. The pump RPM is totally irrelevant, as long as you can get the flow and pressure.
BTW, a healthy pump (gear type) can very nearly hit its peak pressure at extremely low speeds, perhaps 1/10, or less, of the 1,500 rpm you mention. Piston pumps can do it at just a few rpm. A PTO gear pump that is oversized (say, 20 GPM when you need half that) will allow you to run your engine at 1/2 PTO speed.

 

[majorwager]

CincyFlyer,
Guess we agree to disagree. Flow absolitely controls motor speed. Max pressure is an inherent feature of the pump design. If you read my post, I indicate the necessity of a pressure regulator IF the pump design pressure requires reduction. Also a safety feature. And the pump RPM is crucial to GPM production. If you look at manufactures specifications, they DO Not Rate their pump's performance (pressure) below a specified RPM, generally 1500. And over sizing a pump is just foolish , to utilize half the capacity? Further when you oversize, it is likely the engine hp driving the pump is woefully inadequate. That is voodo engineering. The pump manufacture publishes the output capacity and output begins at rated capacity. Again, reading my post, I acurately describe my appliation will satisfy the system requirement at less than max capacity but well within engine peak torque band. I do not know how your claim of operating a system at 20 gpm would produce zero pressure unles you employeed ,and abused the intended use of the pressure regulator at which point system failure would deliver inevitable failure in short order.