Backhoe Connections - So Confused...

[mculik5]

I have a B2650 with a BH77 backhoe. Bought it like that. The backhoe connects/disconnects with two hydraulic lines which are looped when the backhoe is disconnected.

I want to add a three-spool valve on the back of my tractor and run it in line with the backhoe lines when the backhoe is disconnected. Simple enough, provided the valve I get has a power beyond outlet to continue the circuit to my 3PT lift, BUT...

Every single three-spool valve I've found a decent spec sheet for online says that it requires a tank return in addition to the power beyond outlet. So, three lines instead of two...

Clearly, a two-line connection can be done, because that's how my backhoe works.

So, the million dollar question - what valves don't require a tank return when power beyond is used?

Thanks!

 

[Matt Ellerbee]

Monoblock Directional Control Valve, 3 Spool, Joystick Handle, 11 GPM

Free Shipping Hydraulic Monoblock Directional Control Valve, 3 Spool, Joystick Handle, 11 GPM

summit-hydraulics.com

You'll also need the power beyond plug. They sell it too.

 

[mculik5]

@Matt Ellerbee - Thanks!

That valve would be perfect except all the connection examples show a line from the T port to tank in addition to the power beyond from the N port. I only have two lines back there, so if I bought this valve, it seems like I’d need to run a third line to tank.

Or can I just plug the T port?

 

[TheOldHokie]

@Matt Ellerbee - Thanks!

That valve would be perfect except all the connection examples show a line from the T port to tank in addition to the power beyond from the N port. I only have two lines back there, so if I bought this valve, it seems like I’d need to run a third line to tank.

Or can I just plug the T port?

You cannot plug the tank port. When the power beyond sleeve is installed all exhaust oil from the cylinders is routed to the T port. If it is plugged your cylinders will be hydraulically locked and will not operate. Simplest solution is to just run a tank return to some place on the tractor. Two possible locations for a tank return are a fitting on the hydraulic oil filler or a tee installed in the tank return line on your loader valve.

Dan

 

[mculik5]

@TheOldHokie - Thanks! That’s what I figured - that the T port can’t be plugged.

I’m just confused as to why there don’t seem to be any lever-actuated valves that don’t require a T line, when my backhoe has at least one and my third function also has one. Even the universal third function on Summit Hydraulic works that way - it has one outlet that can be used as either T or N.

At this point, I’m less concerned about finding such a valve (will just run a third line) and really just trying to understand hydraulics better.

Thanks!

 

[TheOldHokie]

@TheOldHokie - Thanks! That’s what I figured - that the T port can’t be plugged.

I’m just confused as to why there don’t seem to be any lever-actuated valves that don’t require a T line, when my backhoe has at least one and my third function also has one. Even the universal third function on Summit Hydraulic works that way - it has one outlet that can be used as either T or N.

At this point, I’m less concerned about finding such a valve (will just run a third line) and really just trying to understand hydraulics better.

Thanks!

I am going to risk the wrath of the purists with this response.

The valves you are shopping are designed for general purpose use in third party applications. They have a relief valve in the input section that regulates maximum pressure by venting input oil to the tank when the circuit pressure reaches the relief setting. Any back pressure on the tank port interferes with that operation so a power beyond sleeve and third port is used when the valve will be supplying pressure to a downstream device. The sleeve also isolates the tank port from the power beyond port. This provides a path to tank with minimal back pressure AND allows the cylinders and pressure relief to operate without interference from a down stream valve or cylinder.

Now to the heresy. If you do not install a power beyond sleeve and use the tank port to supply a down stream device it will work just like the back hoe valve. The relief in your valve will not protect the valve or down stream portion of the circuit and you will also be violating the valve manufacturers specifications for maximum pressure at the T port.

FWIW there are thousands of these valves being used in that manner by people who either don't know the difference, simply don't care, or have concluded there is no problem with that in their application. That said I strongly recommend you use the high pressure carry over (power beyond) feature provided by the valve. It eliminates all doubt as to the suitability and function of the valve in the use you are contemplating.

Dan

 

[mculik5]

@TheOldHokie - Awesome info! Thanks!

I definitely want to do it right, but would prefer fewer lines and fittings for cleanliness, less cost and less potential leak points.

I noticed that all of these valves seem to have reliefs built in and get why the relief needs a low pressure path to tank in order to work.

So here’s another heretical question…

If I remove the pressure relief and rely on the upstream relief on the loader valve and then plug the tank port, will the valve flow cylinder return oil out the PB port? I believe this is exactly how my third function works, since it only has four lines.

Also, separate question - do hydraulic motors always require a low pressure return? If I run a motor off my third function (solenoid duty cycle aside), where the outlet is PB to the backhoe and 3PT lift, will this be a problem for the motor or simply raise the temp of the fluid faster than a tank return because of higher pressure (resistance) downstream?

Again, thanks!

 

[TheOldHokie]

@TheOldHokie - Awesome info! Thanks!

I definitely want to do it right, but would prefer fewer lines and fittings for cleanliness, less cost and less potential leak points.

I noticed that all of these valves seem to have reliefs built in and get why the relief needs a low pressure path to tank in order to work.

So here’s another heretical question…

If I remove the pressure relief and rely on the upstream relief on the loader valve and then plug the tank port, will the valve flow cylinder return oil out the PB port? I believe this is exactly how my third function works, since it only has four lines.

Also, separate question - do hydraulic motors always require a low pressure return? If I run a motor off my third function (solenoid duty cycle aside), where the outlet is PB to the backhoe and 3PT lift, will this be a problem for the motor or simply raise the temp of the fluid faster than a tank return because of higher pressure (resistance) downstream?

Again, thanks!

There is no need to remove the relief cartridge to do what you are suggesting. If you do not install the power beyond sleeve all oil entering the valve will go to the T and N ports. The T port on your third function valve is rated at 2000+ PSI. Without the power beyond sleeve both the T and N ports on the Summit monoblock are rated at 300-500 PSI. The reasons for the lower rating are not provided by the manufacturer so you take it upon yourself to understand what you are asking of the valve.

Different hydraulic motors have different requirements but in general a motor spool should return direct to tank. You don't want to run the return from your motor into a downstream load. As long as the path to tank through the downstream device is not through any significant load there is only a minor concern with flow rate and heating.

Dan

 

[mculik5]

@TheOldHokie - Again, thank you!

If I'm following you correctly, the T and N ports are essentially the same thing without a PB sleeve. And when installed, the PB sleeve does two things:

1. It mechanically reinforces the N port so the port can officially handle a lot more pressure (whether this reinforcement is truly necessary is a different conversation)
2. It physically splits the T/N gallery so that pressure (and pump flow when there's no load) goes to the N port, and pressure relief and cylinder returns go to the T port

I've never seen a PB sleeve up close. For all the confusion and opinions around PB, I thought a PB sleeve had some kind of magical flux capacitor fluid dynamics trickery happening inside, but I'm now guessing it's basically just a specifically-sized nipple...?

Last question...hopefully...

I've read that with open center hydraulics that everything has to be in series. So, in practical terms, this means that I can only have one PB loop, starting from the loader valve, and anything I add to the tractor must be in that loop? Or can I run the loader valve PB port to a manifold and feed multiple sub loops from that? What's confusing to be about the whole "open center must be in series" thing is that it seems that I have two hydraulic loops as it is - my loader circuit (pump-valve-loader functions-return) and my PB circuit (pump-PB-third function-backhoe-3PT lift-return), which seems like two parallel circuits.

Really appreciate the help. I've learned more from this conversation than hours of googling. Thanks!

 

[TheOldHokie]

@TheOldHokie - Again, thank you!

If I'm following you correctly, the T and N ports are essentially the same thing without a PB sleeve. And when installed, the PB sleeve does two things:

1. It mechanically reinforces the N port so the port can officially handle a lot more pressure (whether this reinforcement is truly necessary is a different conversation)
2. It physically splits the T/N gallery so that pressure (and pump flow when there's no load) goes to the N port, and pressure relief and cylinder returns go to the T port

I've never seen a PB sleeve up close. For all the confusion and opinions around PB, I thought a PB sleeve had some kind of magical flux capacitor fluid dynamics trickery happening inside, but I'm now guessing it's basically just a specifically-sized nipple...?

Last question...hopefully...

I've read that with open center hydraulics that everything has to be in series. So, in practical terms, this means that I can only have one PB loop, starting from the loader valve, and anything I add to the tractor must be in that loop? Or can I run the loader valve PB port to a manifold and feed multiple sub loops from that? What's confusing to be about the whole "open center must be in series" thing is that it seems that I have two hydraulic loops as it is - my loader circuit (pump-valve-loader functions-return) and my PB circuit (pump-PB-third function-backhoe-3PT lift-return), which seems like two parallel circuits.

Really appreciate the help. I've learned more from this conversation than hours of googling. Thanks!

You are welcome and for a guy who is "so confused" you are showing remarkable insight.

Exactly how the power beyond conversion is done differs depending on the design of the casting. Prince Wolverine valves use a pipe plug installed inside the High Pressure Carry Over (PB) port to close the cast in passageway between the center and return gallerys. More commonly a steel sleeve is installed in the HPCO port. That sleeve creates a "tunnel" through the common exit cavity. It acts like a pipe connecting the center pressure gallery to the external port and isolates that flow from the return flow in the otherwise common exit chamber. Effluent oil from the cylinders or reliefs travels from one side of the casting to the other and ultimately the T port via an annulus around the sleeve. A picture may help visualize that. In the picture T is the two tank gallerys along the sides of the casting and E is the high pressure center gallery.

Your loader and backhoe valves are all in series. The high pressure flow goes from pump to loader, valve to third function, valve to backhoe valve to 3pt valve. When you disconnect the hoe and loop the hoses together you are just deleting the hoe valve from the series hookup. The tank line on the loader valve is only used to return exhaust oil from the work circuits when one of the spools is shifted and the center flow to downstream valves is blocked and the cylinder is moving.

You can split the flow in an open center system using a pressure compensated flow divider. - e.g. 1 in and 2 out. What you get is two new circuits each carrying a subset of the input flow. The flow divider takes care of matching the different flows and pressures and preventing reverse flows.

Clear aws mud?

Dan

 

[mculik5]

@TheOldHokie - So, so helpful! Thanks a ton!