Why is a diverter valve necessary?

[etpm]

I have a 1980 or '81 Yanmar YM2310. I bought the hydraulic cylinder/valve combo made for adding power steering to this tractor. It already has a Bulldog 285 loader so I will need to tee off of the hose that supplies the loader hydraulics. I also bought a diverter valve but now I kinda don't see the point. The power steering cylinder will only need oil when I'm turning and it will only use a small amount because it is pretty small in diameter. It seems to me that if I added another cylinder to the loader, for a grapple perhaps, I would just add a valve for it and not worry about a diverter valve that divides the flow in some way. Why couldn't I treat the power steering cylinder the same way? I know there must be a good reason but I can't see it and would really appreciate it if someone here could tell me the reason.
Thanks,
Eric

 

[RickB]

You don't need a diverter but you really should have a priority valve.

 

[rScotty]

You are on the right track, but it wouldn't hurt to think through the way that the flow in a typical open hydraulic system works.

Suppose that the system is just as it is originally. There is no power steering, and no diverter - just hydraulic flow through a hose to the FEL control valve stack.

When none of the control valves are moved from center position, the flow simply goes into the control valve body and out the return port and back to the sump.

Now suppose that you do put a "T" in the hose that supplies the loader hydraulics.... What happens then? Is there any reason for the flow to change it's mind and go some place other than where it has been going?

Remember, that there isn't any pressure in the hydraulic flow loop (other than simple fluid resistance) until the flow is blocked. Until some blockage happens, all we have is flow....no pressure.... and the flow just goes right on through the control valve body and back to the sump.

rScotty

 

[etpm]

You are on the right track, but it wouldn't hurt to think through the way that the flow in a typical open hydraulic system works.

Suppose that the system is just as it is originally. There is no power steering, and no diverter - just hydraulic flow through a hose to the FEL control valve stack.

When none of the control valves are moved from center position, the flow simply goes into the control valve body and out the return port and back to the sump.

Now suppose that you do put a "T" in the hose that supplies the loader hydraulics.... What happens then? Is there any reason for the flow to change it's mind and go some place other than where it has been going?

Remember, that there isn't any pressure in the hydraulic flow loop (other than simple fluid resistance) until the flow is blocked. Until some blockage happens, all we have is flow....no pressure.... and the flow just goes right on through the control valve body and back to the sump.

rScotty

Well duh, your explanation makes perfect sense. OF COURSE I NEED A DIVERTER VALVE ON AN OPEN CENTER SYSTEM. The power steering would not move at all, the fluid would just wave as it passed the tee. I feel pretty silly to not realize why the diverter is needed. But I'm tired.
Thanks,
Eric

 

[Harry in Ky]

So this diverter valve came with the steering assembly, came from the same supplier, or came from somewhere else entirely?

Hope you come back once it's up an running tell us how it all worked out.

 

[rScotty]

Well duh, your explanation makes perfect sense. OF COURSE I NEED A DIVERTER VALVE ON AN OPEN CENTER SYSTEM. The power steering would not move at all, the fluid would just wave as it passed the tee. I feel pretty silly to not realize why the diverter is needed. But I'm tired.
Thanks,
Eric

That's right, now you're thinking. Now that you can see what is happening, we can go into the three common types of diverter valves. The nice thing is that any of the three types of diverters will mount right there where you were going to put the tee, they aren't much bigger, and they all do the same thing as a tee but with more control.

1. A simple basic diverter valve has one inlet and two outlets. It is real inexpensive & either manual or run by an electrical switch and solenoid. You choose whether you want to power your steering or your loader. But it is an either/or thing. You only get one at a time; not both.

A priority valve is also a diverter and also has one inlet and two outlets. But it lets you split the flow between two outlets so that the PRIORITY outlet always has the same flow regardless of the load or pressure. So if your tractor flows 7 gallons/minute at full RPM you can set that prority valve so that the priority circuit to the steering always has 4 gallons/minute with the other 3 gallons/minute going to power the loader. That sounds fine until you throttle back to reduce the engine RPM to half, and now are only flowing 3.5 gallons/minute total. (RPM and flow rate are approximently a straight even relationship).
What happens as you throttle down is that greedy priority valve is still trying to feed 4 gallons/minute to the steering, which leaves it nothing but a memory left over for the loader. Yes, you could plumb to prioritize the FEL over the steering, but it only takes one incident to convince most folks that steering is more important.

Only a few dollars more buys you the third type of diverter valve. This one is called a PROPORTIONAL diverter valve. Again, it has the same single inlet and two outlets.
But on this valve you set the proportion (percentage) of flow that goes to the steering and to the loader. Suppose you choose 50/50 steering to loader....or better yet, 60/40 percent. Now it doesn't matter where the throttle is set, or whether the system is flowing at 3.5 gallons/minute or 7 gallons/minute. The proportional valve self-adjusts so that both systems get the same percentage share of the available flow. They may go slowly at an idle, but both systems always work

You can see that three types of diverter valves are plumbed the same. They are simply different types of a smarter tee, and allow you to adjust them for what you want. Some will require their own return line back to the sump, but you can Y into the existing return line.
There should be no pressure in a return line.
Enjoy!
rScotty

 

[etpm]

So this diverter valve came with the steering assembly, came from the same supplier, or came from somewhere else entirely?

Hope you come back once it's up an running tell us how it all worked out.

The diverter was indicated as a necessary part but was not sold to me by the vendor who sold the
power steering cylinder. As I build the parts and assemble them into a properly working power steering system I will be posting the process. Even though I own a machine shop I am going to try doing this as if I did not. I once had more time than money and still have some of the tools I built from scrap stuff more than 40 years ago. So I know how that goes. All kinds of folks have helped me through life, here I am asking for help again, so I really am obligated to post my progress. And who knows? Maybe the info I post will help someone else just like the info folks have already posted to this site is helping me.
Eric

 

[etpm]

That's right, now you're thinking. Now that you can see what is happening, we can go into the three common types of diverter valves. The nice thing is that any of the three types of diverters will mount right there where you were going to put the tee, they aren't much bigger, and they all do the same thing as a tee but with more control.

1. A simple basic diverter valve has one inlet and two outlets. It is real inexpensive & either manual or run by an electrical switch and solenoid. You choose whether you want to power your steering or your loader. But it is an either/or thing. You only get one at a time; not both.

A priority valve is also a diverter and also has one inlet and two outlets. But it lets you split the flow between two outlets so that the PRIORITY outlet always has the same flow regardless of the load or pressure. So if your tractor flows 7 gallons/minute at full RPM you can set that prority valve so that the priority circuit to the steering always has 4 gallons/minute with the other 3 gallons/minute going to power the loader. That sounds fine until you throttle back to reduce the engine RPM to half, and now are only flowing 3.5 gallons/minute total. (RPM and flow rate are approximently a straight even relationship).
What happens as you throttle down is that greedy priority valve is still trying to feed 4 gallons/minute to the steering, which leaves it nothing but a memory left over for the loader. Yes, you could plumb to prioritize the FEL over the steering, but it only takes one incident to convince most folks that steering is more important.

Only a few dollars more buys you the third type of diverter valve. This one is called a PROPORTIONAL diverter valve. Again, it has the same single inlet and two outlets.
But on this valve you set the proportion (percentage) of flow that goes to the steering and to the loader. Suppose you choose 50/50 steering to loader....or better yet, 60/40 percent. Now it doesn't matter where the throttle is set, or whether the system is flowing at 3.5 gallons/minute or 7 gallons/minute. The proportional valve self-adjusts so that both systems get the same percentage share of the available flow. They may go slowly at an idle, but both systems always work

You can see that three types of diverter valves are plumbed the same. They are simply different types of a smarter tee, and allow you to adjust them for what you want. Some will require their own return line back to the sump, but you can Y into the existing return line.
There should be no pressure in a return line.
Enjoy!
rScotty

Thanks Scotty. Is rScotty better? Nevermind. I'm not sure which kind of diverter I bought and if it can be changed if need be by adding or exchanging a part. I will contact the vendor and ask. Your third option looks like the best way to go and if I was designing a system from scratch it is the way I would go. I really appreciate all the help I have gotten from this site. Especially since my Yanmar YM2310 is not only my newest tractor to buy it is also my newest tractor. It replaced my oldest tractor, a 1939 Ford 9N. And it's my first diesel engined anything.
Thanks,
Eric

 

[rScotty]

Sounds good. I'll be curious to see how it goes.

Adding power steering to a small tractor - especially one with a loader - is one of the nicest things you can do for yourself. And it's cheap entertainment; for a few hundred bucks you can try every type of diverter on the market. They are all about the same size and use the same fittings. Most come with installation instructions.

Diverters tend to work best over a limited flow range, so figure out your max and min expected flow and buy accordingly.

A Ford 9N? Nice machine. I love those old gas engines. They could teach modern diesels a thing or two about reliability. That reminds me that you still see a lot of those old Fords, Masseys, and Farmalls that are running any extra hydraulic functions tend to have the type 1 diverter valve - which is the old manual lever either/or type. I don't really know why they chose that valve. It may be they used that valve instead of a priority or proportional because those old tractors had such tiny flow & relatively low pressure hydraulic pumps that the other types didn't work well in that range. Or maybe they just didn't know.

I probably don't need to remind a machinist about the dangers of modern high pressure hydraulics, but here goes anyway. Tractors today run 2000 to 3000 psi. A hydraulic leak can cut like a knife. You can use hose or hard lines on the high pressure side, but be sure to use hydraulic rated fittings, never plumbing fittings.

Oh, and "Scotty" is a nickname old friends call me.
As they say down south, "call me what you want, just don't call me late for dinner."