Calculating Hydraulic Requirements

BIG1RED9

Member
Morning everyone,

Because I need to consider the pump, loader spools as well as backhoe spools, I decided to come at this problem by gaining a basic understanding of hydraulics. I conclude there is no 1 size fits all. It is dependent on the size of and quantity of cylinders and therefore the total volume used and the max speed of which one want it to move. I am sharing the information I found in case others are trying to deal with it. The information comes from he Cylinder Pressure Chart from Baum Hydraulic Corporation.

The workup I have so far done is based on the 102 Davis loader and not the 185 backhoe. For the moment, I am assuming that the cylinders are either original or replaced with original spec'd parts. I will confirm this in the next day or two.

A major consideration is speed of lift.unit. looking around at new loaders, 3 to 5 seconds are some lift speed ranges. I am going to use 5 for now.

On the 102 loader
The bore of the lift cylinder is 2 1/4" (which is 3.97608 sq in)
The Stroke is 31"

3.97608 square inches x 31 (stroke) = 123.25848 cubic inches
to covert to gallons divide by 231 = .533586 gallons per lift cylinder.

.533586 x 2 lift cylinders = 1.067172 gallons to go to full extension

1. Speed 5 seconds
2. 1.067172 gallons (for both lift cylinders)
3. 1.067172 divided by 5 (speed) = .213434 gallons per second
4. .213434 X 60 (to get GPM) = 12.8 gallons per min

If I go with a joystick then I will need to also consider the dump requirements

4.909(sq inches) X 15.1875 (stroke) divided by 231(to get to gallons X 2 (2 dump cylinders) divided by 4 (speed for full extension of cylinders) X 60 (to ge GPM) = 9.68 GPM

Horsepower requirements
GPM X PSI divided by 1714 = HP required
One of the factory specs shows 17gpm at 2150 psi
That requires 21.3 HP to run the pump.

For myself I have not yet concluded what I am going to do. I need to understand the backhoe requirements.

Don
 
(quoted from post at 07:19:57 12/07/17) Sounds like you are going about things the right way in learning how it all works before spending any money.
This is the one I put on my 202 which runs the loader and power steering and the backhoe by itself with a valve pulled.
It's no longer available but you should be able to look up the specs.
https://www.surpluscenter.com/Hydra...r-Pumps/2-5-cu-in-Hydraulic-Pump-9-2149-A.axd

Hi Inno,

Thanks for the info. If you had to do it over again, would you select the same specs?

I am trying hard to not make mistakes. Safety time and money are all considerations. I did some work on the backhoe numbers and the number 12GPM keeps entering my mind. I think in part because the 185 parts book shows a Cessna 12GPM was used. To me that means it was adequate but not fast enough and later on they went to a 17GPM. My backhoe is #365 so its an early one and I would guess came with a 12GPM.

Assuming the engine is fine to operate at idle for long periods of time(need to study the Continental gas), my final step will be a HP and torque curve to see the HP on the Continental. If I could find a pump that at idle uses the 1/2 the HP available and at that RPM produced 12GPM and at operating RPM 15GPM to 17GPM, my thinking is it will be the most efficient and allow me to use some more speed once I gain experience.

Thanks
Don
 
I believe 12gpm is original spec yes. I think I upped it just a little bit but didn't notice a significant difference. It was maybe a little faster but everything on my tractor is either worn out or modified so it's hard to really quantify. I think my initial thought (this was in 2012) were that if I were doing it again I would try and get closer to the Cessna pump, not so much for the hydraulic specs but for the mounting. I had to do a fair bit of playing to make it fit and then had to cut out the front grille as it stuck out too far in the end.
There may be an old thread about the Cessna pump, something tells me there was some good info about it although there are no parts available for them.
 
Part of the problem with increased flow is also increased friction. Once the hyd fluid warms up I notice the backhoe being much weaker. Unless you plan on upsizing the valves and hoses it might be worse to go with higher flow than better, unless you plan for some sort of heat exchanger or radiator to cool the fluid.
Also, the governor on the 134 doesn't do much at idle, can't remember the threshold for operation but it's somewhere mid RPM that it starts having an effect.
 
Can't edit and I keep thinking of other things.....bear with me.

Even in stock form, those backhoes are plenty fast and have enough grunt to remove some pretty large tree stumps etc.
I believe my bucket is at least 18", perhaps larger and it will dig and lift a very full bucket of wet clay without too much problem.
If it were me, I'd try and stick within the designed parameters so you don't end up with other unwanted side effects.
 
(quoted from post at 09:11:30 12/07/17) Can't edit and I keep thinking of other things.....bear with me.

Even in stock form, those backhoes are plenty fast and have enough grunt to remove some pretty large tree stumps etc.
I believe my bucket is at least 18", perhaps larger and it will dig and lift a very full bucket of wet clay without too much problem.
If it were me, I'd try and stick within the designed parameters so you don't end up with other unwanted side effects.

Thank you. Had not thought about the governor, I am going to target 12GPM at an RPM/HP (assuming i can find the curve) that will run it or find the specs on the original Cessna and try to match those. The pump I am now running was switched to a 3.5 GPM Commercial Sear.
 
(quoted from post at 10:15:01 12/07/17) I would put some loss factors in you HP calculation.

Thank you Davis, I had not considered a HP Loss. How would you suggest I go about it?

The book says the operating pressure for the backhoe is 1750psi and the loader 1500psi

If I go with a 12GPM and 1750 PSI that setup will require about 13hp. At this point only for comparison (as I have no idea if the rest of the machine can handle it) 12GPM at 2000psi = 14HP and 15GPM at 2000psi = 18hp

Thanks
Don
 

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