Hydraulic pump?

[dipper]

ok here is the back hoe I bought a couple years ago. I got it cheap, of course and it didn't work. It's a 3pt, home made, and it has an independent hydraulic system that runs off the pto. All the Rams work except for the big one that controls the bucket. When I hook the ram directly to my tractor hydraulics, it works great.
So levers work, Rams work. When I spin the gears that turn the units hydraulic pump, there is virtually no resistance. I'm no expert but I'm pretty sure that my problem. The units pump, and they aren't cheap.
So I'm at the shop getting some hoses made for something different. A pump for $150. What? It's brand freaking new? Originally $1200?
What's the freaking catch I ask? Apparently this company is going tits up and they need to sell it. So I but it having no clue if it's going to give me the correct speed to make the backhoe functional.

So it's 75 liters/minute at 470 rpm. So that comes out to 19.7 gallons/ minute. The tractor pto is 540, but the pump has a seperate gear so I have to be going than 540? Right?
Here is a picture of the backhoe. Anyone smarter than me and think there is a chance this pump will give me reasonable operating speed?

 

[dipper]

The gear from the pto to the pump

 

[John-W-WI]

Looks to me like you could use the pump WITHOUT the gear. 19+ GPM is a lot of flow. Plenty to run that big cylinder IMHO.

If that chain drives the pump, it would only increase the flow (big gear on the drive side, small gear on the driven side). If the pump can take it, the increased RPM would only help.

For $150 I would buy it just to have it for future projects, even if it didn't work. Buy it, if it doesn't work I'll give you $150 for it.

-John

 

[Jim Timber]

Big sprocket on the driven shaft lets you run the PTO at a lower speed and still get the pump up to operating capacity for flow.

I'd buy the pump too.

 

[dipper]

Should work, but speed may be slow. How are you cooling the oil?

There is a revisor, I'm assuming that will keep it cooler. I don't have much concern on it being slow. I'm not a seasoned operator, so I work pretty slow anyway.

Looks to me like you could use the pump WITHOUT the gear. 19+ GPM is a lot of flow. Plenty to run that big cylinder IMHO.

If that chain drives the pump, it would only increase the flow (big gear on the drive side, small gear on the driven side). If the pump can take it, the increased RPM would only help.

For $150 I would buy it just to have it for future projects, even if it didn't work. Buy it, if it doesn't work I'll give you $150 for it.

-John

Ya that's why I just bought it. I have gambled with more than $150 before. It should work it's brand new. Good point on the gear, that makes sense about the gear making it faster. I'm gonna hook it up and see what happens.

 

[dipper]

Big sprocket on the driven shaft lets you run the PTO at a lower speed and still get the pump up to operating capacity for flow.

I'd buy the pump too.

So if the pump is too slow I could always increase the size of the sprocket to speed things up, and decrease to slow it down. I'm not an engineer, but I like playing.

 

[Jim Timber]

As long as your tractor has the torque needed to turn the pump at the engine RPM you're trying to run it at (you don't want to lug the engine either), you can make an over drive to bring the pump's speed up to it's rated output without matching that speed at the PTO. Be warned though, you need to make sure you don't run the pump too fast either, or it'll likely eat itself from exceeding the designed input forces.

I'm not a good engineer (I get by with "overkill" and "close enough for government work"), and it's been 20 years since I took physics so I'm not even confident in my math to be sure of my own hydraulic motor design problem I'm working on (skidding winch), but I can tell you with certainty that what the designer of that backhoe did was allow him to use the hoe without having the engine at PTO RPM.

If you needed 500 RPM for your pump to create it's rated flow - you'd need to calculate what the PTO output speed is based on 540 RPM at 2400-2600 RPM (it's different for different tractors), and then use that to determine how much faster the input shaft on the pump needs to spin to hit the 500 RPM.

So lets say our 540 PTO speed is @ 2400 engine RPM (because mine is :D ) which makes that have a 4.4444:1 reduction. If we wanted to run the backhoe at a fast idle of 1500 RPM, then the PTO shaft will only be turning 337.5 RPM; but we need 500. So now we'll add an overdrive gear train in between our PTO and the pump of 1.48:1 or 1.5:1 for ease of sourcing parts. So if your PTO driven sprocket had 45 teeth, your pump (load) would have 30.

An easy way to double check calculated gear ratios when you're trying to match speeds is to multiply the teeth by the RPM for both sides (337.5x45 and 500x30): they should be the same. ;)

Make sense?

 

[dipper]

Jim the pump says rpm of 470. Does that mean it shouldn't go faster than that?
Now when a tractor says it has a 540 pto, at what rpm is that? Because if I'm understanding you correctly, the rpm fluctuates with motor idle? Is a 540 pto at max throttle? I obviously don't want to run the tractor anywhere near that.
When I hooked that big ram directly to my tractor, the speed was reasonable. I'm pretty sure my tractor pump is 17 gallons/ minute so I should be about there with this pump.
Oh the suspense, now I have to find time to work on it.

 

[wiscwhip]

You run that pump too fast and it will blow the seals prematurely.

 

[Jim Timber]

I was just using easy numbers to set up the way you'd arrive at your solution. Since your pump is rated for 470 RPM, I'd run it a little slower around 450 just to give you a margin of error.

Your tach should have a spot indicated for the PTO speed. It's going to be at your peak HP, not max RPM. I agree, I wouldn't want to run my tractor that fast while moving dirt around either. The guy who built your hoe agreed too - which is why there's that big gear increaser off the PTO shaft. I'd start by calculating out the ratio you currently have, then finding out what speed that ends up at with your tractor's PTO, and you might be close enough already. The hubs and sprockets can be bought ready to weld at Fleet Farm for $5-15. It's really easy to roll your own drive gears for industrial chain.