Backhoe Design Ideas

[J_J]

Yes, it should as you are only using half of the flow.

10 GPM's - 3600 RPM = .6 cu in = 21 HP required
5 GPM's - 1800 RPM = .6 cu in = 10 HP required

So if you ran 10 GPM through a flow divider, and had a 50/50 split, each circuit would get 5 GPM, but the one leg would only go to tank, and the other side would have 5 GPM at 3000 psi

Maybe one of these.

https://www.surpluscenter.com/item.asp?UID=2009092314505827&item=9-5911&catname=hydraulic

 

[Brad_Blazer]

Is there a model number on the pump? If you can look up the rated flow or displacement it is not hard to calculate the power and torque requirements.

If you have a big pump and big cylinders you can reduce the relief pressure to prevent snubbing the engine or destroying the machine.

15HP at 540RPM (PTO) means about 146ft-lb of torque. Let's say you have at least 106ft-lb available at low RPM. That is enough to drive a 4 cubic inch gear pump at 2000psi.

Here is a link with some hydraulic calculators and tables.
Hydraulic

 

[J_J]

Iplayfarmer,

Did you mention whether that PTO pump was a 540 or 1000 rpm pump?

 

[Iplayfarmer]

Is there a model number on the pump? If you can look up the rated flow or displacement it is not hard to calculate the power and torque requirements.

If you have a big pump and big cylinders you can reduce the relief pressure to prevent snubbing the engine or destroying the machine.

15HP at 540RPM (PTO) means about 146ft-lb of torque. Let's say you have at least 106ft-lb available at low RPM. That is enough to drive a 4 cubic inch gear pump at 2000psi.

Here is a link with some hydraulic calculators and tables.
Hydraulic

There's no model number, but it has "Webster" stamped in two places on the housing.

You might have the answer: bigger cylinders and lower relief pressure. I guess that if I used bigger cylinders then I could simply adjust the relief pressure to match the power of the tractor. If I find that I have power to spare, I could simply increase the relief pressure and have more force to work with.

Flexibility and adaptability are big in my book.

Iplayfarmer,

Did you mention whether that PTO pump was a 540 or 1000 rpm pump?

It's 540.

 

[J_J]

Does this look like your pump?

 

[Iplayfarmer]

Does this look like your pump?

That Looks like it. Except mine has ports coming out the side.

 

[J_J]

I am used to seeing the PTO pumps like the ones by Prince. However, your Webster pump, looks like a regular hydraulic pump with a a PTO shaft adapter on it. What I am thinking, is that they are using a large cu in pump, and just running it at 540, or whatever the PTO rpm is. With 18 HP available, and a pump pushing 9 GPM, at 3000 psi, would require a pump with a displacement of 3.9 cu in. while turning at 540. If the pump displacement is larger, that means that you could use less rpm on the engine.

How much HP did the other guy have on his tractor, and maybe I can figure the size of the pump. The Prince PTO pumps also pump at 2000 psi.

 

[Iplayfarmer]

I am used to seeing the PTO pumps like the ones by Prince. However, your Webster pump, looks like a regular hydraulic pump with a a PTO shaft adapter on it. What I am thinking, is that they are using a large cu in pump, and just running it at 540, or whatever the PTO rpm is. With 18 HP available, and a pump pushing 9 GPM, at 3000 psi, would require a pump with a displacement of 3.9 cu in. while turning at 540. If the pump displacement is larger, that means that you could use less rpm on the engine.

How much HP did the other guy have on his tractor, and maybe I can figure the size of the pump. The Prince PTO pumps also pump at 2000 psi.

His tractor is a Massey 85. I think that's about 50 hp.

 

[Brad_Blazer]

You could put some short hoses on the pump, prime it, and turn it by hand say 10 revolutions to measure the output in a graduated bucket or big measuring cup. 1 cup = 14.44 cu in.

 

[J_J]

A 50 HP engine can run a 25 GPM pump at 3000 psi, at 540, and the pump displacement should be around 10.5 cu in.

 

[Iplayfarmer]

You could put some short hoses on the pump, prime it, and turn it by hand say 10 revolutions to measure the output in a graduated bucket or big measuring cup. 1 cup = 14.44 cu in.

I took your suggestion.

I turned it 50 revolutions and filled a 8" diameter bucket with 4 3/16" of fluid (I used heating fuel). I figure that's about 210 cubic inches or 0.91 gallons. That would make this a 4.2 cubic inch pump and the output at 540 rpm is going to be 9.8 GPM.

That sounds about right. At 2000 PSI that comes out to 11.5 Hp based on the formula on Wikipedia... Hp = GPM X PSI X 7/12,000. Even considering a large margin of error with my crude measuring, I should have no problem running the pump. I think I'll have room to throttle down if needed to slow things down a bit. I'll probably pass on the flow divider for now.

 

[Brad_Blazer]

Good to go! (and your pump is nice and clean )
2000psi should be enough that you don't need oversized cylinders.

 

[Iplayfarmer]

Good to go! (and your pump is nice and clean )
2000psi should be enough that you don't need oversized cylinders.

Cleaning the pump was another motivation for the exercise.

I agree that I don't need oversized cylinders. I have a couple of larger spare cyinders around though, and now that I have the flow I may use them vs. buying a smaller cylinder.

I'm fighting the temptation to hook up this pump temporarily to my loader. I'm currently running on about 2.5 GPM. 9.8 GPM may just be enough to actually launch something out of the bucket.

 

[J_J]

Where did the 2000 psi come from? I only stated that the Prince PTO pumps were 2000 psi. You will have to put a pressure gage on this pump to see the max pressure, but anyway, put an adjustable relief valve across the input and output, setting it at around 1500 to start with.

Do you know if this pump is designed to run at 540? Are there any numbers or letters on the pump.

 

[Iplayfarmer]

Where did the 2000 psi come from? I only stated that the Prince PTO pumps were 2000 psi. You will have to put a pressure gage on this pump to see the max pressure, but anyway, put an adjustable relief valve across the input and output, setting it at around 1500 to start with.

Do you know if this pump is designed to run at 540? Are there any numbers or letters on the pump.

Last I heard, 2000 PSI was the standard average that this size system uses. I'll have to steal my gauge back from my MIG gas bottle to test the actual pressure of the system.

There's nothing on the pump. I'm going with the fact that it came with a coupler that fits a standard 1 3/8" 6 spline 540 PTO shaft. I'm also taking the seller's word for it that it was the pto pump on the backhoe that I saw in his yard when I pulled up. I don't recall the make of the backhoe, but I do recall that it was a factory unit, not homemade.

 

[Iplayfarmer]

If I'm going to have a PTO pump, I'm going to need some way of defeating the safety switch so that the tractor will stay running with the PTO engaged but no operator in the seat.

How do most backhoe attachments accomplish this? My simple mind says to put a switch somewhere to override either the seat safety or the PTO safety. Is that the best way.

 

[Iplayfarmer]

If I'm going to have a PTO pump, I'm going to need some way of defeating the safety switch so that the tractor will stay running with the PTO engaged but no operator in the seat.

How do most backhoe attachments accomplish this? My simple mind says to put a switch somewhere to override either the seat safety or the PTO safety. Is that the best way.

Anybody?

How do backhoe attachments with PTO pumps work around the safety switches without an operator in the tractor seat and the PTO on?

 

[J_J]

Install a SPST switch across the seat switch. Off position, the switch is open to let the seat switch work as it should. Flip the switch on, and the switch is used to jumper across the seat switch.

 

[dfkrug]

How do backhoe attachments with PTO pumps work around the safety switches without an operator in the tractor seat and the PTO on?

First, the newest tractors seem to provide several interlocks that allow
some off-the-tractor PTO use. My latest will allow the engine to stay
running when you get off the seat if the parking brake is set. Starting
the tractor off the seat with the brake set simply requires you to push
with your finger on the middle of the seat while turning the starter switch.

Other tractors do it differently.

You can simply jumper the seat switch to disable that interlock. That move
is not really unsafe unless yours is a gear tractor. A HST tractor will not
run away when started off the seat.