Hydraulic "accessory" outlet

[hayden]

Hydraulic \"accessory\" outlet

Has anyone installed (or had installed) a hydraulic "accessory" outlet? I'm particularly interested in the B series with loaders, but I imagine the answers would be the same for the L's too.

As I understand it, the hydraulics on these machines is Open Center, which means the oil flows through the system at all times, and is diverted away to perform some task on demand.

To attach an accessory, you woudl then need two hookups, one for the oil to come out, and the second for the oil to return.

If an attachment is hooked up, then the oil flows out of one fitting, through the attachment, then back to the return fitting. This is all fine.

But what about when you disconnect the attachment? The oil can no longer flow out and the hydraulic circuit is plugged.

I think to work there has to be a bypass valve that eoither allows oil to bypass the accessory outlet, or diverts oil to the outlet with the expectation the what goes out will eventually come back.

I suppose alternately you coudl simply have a shunt hose that connects between the two fittings when an accessory is not in use.

Is this right or am I missing something?

How is your accessory outlet set up?

Thanks,

Peter

 

[TWINKLE_TOES]

Re: Hydraulic \"accessory\" outlet

Peter,

I think you have it correct.

This response is for the way the B21 is plummed.

From the Hydraulic pump, fluid flows to a flow priority valve which determines demand and diverts fluid to the power steering and hydrostaic transmission and to the loader position control valve and the backhoe. Priority is to power steering and HST. The loader and backhoe are connected in series as you stated. A selector valve is used to switch between front loader backhoe to frontloader three point position control. When the backhoe is removed the tractor supply and return line to the backhoe are connected togather.

 

[TomG]

Re: Hydraulic \"accessory\" outlet

Below is a description of a basic open centred system. The comment leaves out subjects like power beyond and regenerative circuits, as well as standard devices like priority and diverter valves.

A basic open centred system takes oil from a sump and pumps it in a loop back to the sump. Hydraulic devices are operated by control valves that are installed in the high-pressure line from the pump to the sump. Closing the centre of a control valve creates a high-pressure and a low-pressure side to the valve. The pump is on the high-pressure side, and the sump return is on the low-pressure side. Operating a control valve feeds pressure to one side of a cylinder and opens the sump return to the other.

The control valves used for double action cylinders (that are powered in both directions) have four ports; inlet, outlet and two for lines to cylinders. This type of control valve has three or four operating positions: 1) Centre, or neutral, where the centre is open and both lines are closed. 2) Closed centre with high pressure to one line and low pressure to the other. 3) The same as before but reversing the high and low pressure lines, and. 4) Float, which is an option that connects both cylinder lines together and leaves the centre open.

Control valves for double acting cylinders use both a pressure and a return line, because a double action cylinder contains oil on both sides of the cylinder. The cylinder could not move unless oil on the low-pressure side can flow out of the cylinder. In float position, both lines are connected but the centre is open. Float delivers no pressure to either side of the cylinder but allows oil to flow from one side of the cylinder to the other.

Cylinders are 'dead end' devices, and oil does not flow through them. When operated, cylinders extend to the limit of their travel or load. Then, system pressure is exceeded and the relief valve opens. When the valve is returned to centre, oil flows through the open center and both lines are closed. Removing an implement makes no difference to oil flow when the valve is centred. In effect, the open centre valve is the shunt tube mentioned.

As many control valves as desired can be installed in the high-pressure line in series with each other. Oil flows through the loop as long as all centres are open. However, when a valve is operated all other valves behind it in the high-pressure line are then on the low-pressure side and are inoperative.

 

[hayden]

Re: Hydraulic \"accessory\" outlet

Nice description - thanks.

I think you've identified a 3rd way to plum things, and it happens to be the way loader control valves are pummmed. The ways are (with what you've described first)

1) Leave the control value permanently installed and disconnect the cylinder lines, not the feed and return lines. The control valve provides bypass with or without the attachment.

2) Install a bypass valve so flow can be directed through the accessory outlet or bypass it based on the presence of an attachment and the valve position.

3) Connect the feed and return lines together when an attachement is not connected (TWINKLE_TOES B21 configuration)

I think for using arbitrary attachments, options 2 or 3 make the most sense because the control valve could be different for different attachments.

 

[Anonymous Poster]

Re: Hydraulic \"accessory\" outlet

I devised a relatively easy way to have an "accessory valve" to the rear of the tractor for very little cost. I have a kubota L3710 with 681 loader. I put quick connect couplers on one of the control valves (used the valve that controls the dump of the bucket) and on the corresponding loader hoses. I also ran two other accessory hoses to the back (or wherever you need them) of the tractor. These also have quick connect couplers. By changing hoses as needed, I can use either set of hoses. The down side is I have to have the loader on the tractor to use the loader hydraulic control valve and I can't use the loader bucket when using the accessory hoses. I use the accessory hoses infreqently (ie. hydraulic cylinder to lift grain auger, cylinder on small disc etc.) It would be nicer if Kubota would leave their hydraulic control valve on the tractor and not permanently mounted to the loader. My John Deere control valves are on the tractor. This would allow use of the hydraulic control valve with loader detached.

 

[Bird]

Re: Hydraulic \"accessory\" outlet

m dewald, it depends on which model Kubota you get. The control valves do stay on the tractor on some models, like the B2710, B2910, and I don't know how many others.

Bird

 

[TomG]

Re: Hydraulic \"accessory\" outlet

I have a rear hydraulic pair that I use for a hydraulic top link, snow blower, 3ph pallet forks or backhoe. Most implements with hydraulics just have double action cylinders. They are supplied with hoses that terminate in male quick connectors. The assumption here is that there is a control valve assembly with female quick connectors on the tractor, and the tractor supplies the control valve. However, backhoes have their own valve assemblies. The hoe controls can be thought of as an additional valve assembly inserted in series with the pressure line. I run the hoe by connecting it to the rear pair and use a bungee cord to hold the rear pair's control valve open. The open centre oil flow then goes through the rear pair pressure line, through the hoe, back to the valve assembly, the valve assembly's outlet, and to the reservoir.

The method perhaps isn't elegant, but it works and it's simple. I do have to make sure I know which hoe line is the pressure line, and which control valve line gets pressure when the valve lever is held forward. Connecting a hoe backwards can do a lot of damage. I suppose it's possible that routing the open centre flow through cylinder lines and control valves forces the oil to go through lines and orifices that are smaller than the main pressure line. If so, then the hoe may not have full power and speed, and the oil may over-heat. However, in quite a few hours of hoe operation, the hoe has done everything I want, and the oil doesn't get too hot.

Some unworkable alternatives for connecting the hoe would be: Use one leg of a diverter valve, which I don't have. Use an outlet on the 3ph. My 3ph lever has a detend above the full up position. When in the detend, the hitch can power an external remote. However, in the detend position, the hitch is full up. My hoe is a 3ph type, so that wouldn't work.

 

[Pks]

Re: Hydraulic \"accessory\" outlet

The valves on the B2400 with LA351 loader stay on the tractor too.

 

[Keoke]

Re: Hydraulic \"accessory\" outlet

Tom, I have the somewhat same setup for my hoe. What I did was have a male and female couplers on the tractor side going to hoe. That keeps me from crossing the pressure and return lines when I hook up.
george

 

[TomG]

Re: Hydraulic \"accessory\" outlet

That's a good idea. Myself, I used short plastic tie straps around the hoe's pressure line and the control valve line that I know gets pressure when the lever is held forward. I almost hooked it up backwards before I put the straps on.

Most people probably know this, but I'll pass along a tip a dealer mechanic told me for figuring out which hose gets pressure. He said: 'Just hold a hose in your hand and push the valve lever. You'll feel the hose that gets pressure stiffen.