Auxiallry Hydraulics Setup Questions

[Rick Prentice]

Jim. I think I might throw out the challenge flag with these comments, unless I'm not understanding what you're trying to say.

You are correct, on both counts. Furthermore, if you do have a relief valve in the new valve and don't plumb it correctly, you still may in effect dead end the system. The return through the relief valve needs to go straight back to the reservoir, not the bypass block.

That Prince valve does not appear to be a power beyond valve. Any flow from the relief valve is evidently dumped to the "out" connection. As I said previously, that "out" needs to run directly to the reservoir. If it is plumbed back into the bypass block, there is a risk of over-pressuring the system.

If I bought the valve that SamsFarm showed and used it on my cub, I would plumb the "OUT" back to the bypass block return, not the reservoir. I must be missing something. If I plumbed the out to the reservoir, where are you picking up fluid to enter the bypass block to supply the T/C. Are you saying if you hit a hard stop on the new valve and hit a hard stop on the T/C unit, you could possibly damage something or are you just comparing apples and oranges with different valve setups.

[SamsFarm]

Here is the schematic from the Prince hydraulics.

It is showing in a round about way what Jim is describing in the 1000 loader hook-up!

http://www.princehyd.com/portals/0/tech ... erPbDA.pdf

The third drawing is the dangerous situation I've been trying to explain. The valves in the drawings appear to be drawn to include a pressure relief. Assume they are both set for 1,500 psi. If the downstream circuit hits a hard stop, the high pressure lines will all be at 1,500 psi. Now throw in the possibility that both valves are actuated and hit a hard stop at about the same time. You now have 1,500 psi on the line feeding the downstream valve. Since it is the same line as the return from the upstream valve, the upstream outlet pressure is 1,500 psi. The upstream pressure relief won't open until it senses ANOTHER 1,500 psi. So everything from that relief valve back to and including the pump has 3,000 psi. That is when things start exploding.

Jim, after spending some time on the Prince site, your right to say that a 3 line valve is required based on the valve manufactures recomendations.

Prince states that if pressure on the return side exceeds 300psi, that their valves may leak like in pic 3.

Maybe another valve is made different like on Gary S.'s tractor in post #2.

But your wrong to say the pressure will hit spike to 3000psi.

Each relief valve will open at the set limit, in this case 1500psi to let the fluid pass!

I would say that I dont have a problem with this on my Deere using the power beyond, because I dump the return oil back into the transmission housing (hydraulic oil tank)!

[SamsFarm]

Rick, according to Princes website the valve I posted would not work properly, they say they will leak. My bad!

You could use it on something like a log splitter where you take pressure from the cub diverter block and dump the return oil back to the touch control tank filler port.

While in use for a log splitter the touch control would not function though!

[Rick Prentice]

Another thought to think about. Back a few years ago when I made these bypass blocks with a special relief valve installed, allowing any control valve without a built in relief setup to be used, these relief valves were set at 1000psi and worked perfect. I tested a regular setup with a pressure gauge to determine what special relief valve to purchase. 1000psi seemed enough for the function of the angle blades to hold as well as the T/C to function properly. At only 1000psi, should be impossible to damage any parts or cause leakage.

[SamsFarm]

If you want to add a loader or hydraulic angle grader blade, it would probably be best to play it safe and add a 3 line valve like RickyRacer has posted in the beginning!

(Nice job on those custom bent hydraulic lines Ricky)

[Jim Becker]

. . .
If I bought the valve that SamsFarm showed and used it on my cub, I would plumb the "OUT" back to the bypass block return, not the reservoir. I must be missing something. If I plumbed the out to the reservoir, where are you picking up fluid to enter the bypass block to supply the T/C. Are you saying if you hit a hard stop on the new valve and hit a hard stop on the T/C unit, you could possibly damage something or are you just comparing apples and oranges with different valve setups.

There are a lot of apples and oranges in this discussion. I'm trying to keep from mixing them up.

I'm saying that particular Prince valve is not power beyond. It only has one outlet which should go straight to the reservoir. If you want pressure from the valve to feed another valve (like inside the Touch-Control), the valve needs another outlet port. Without the second outlet port, you don't have a supply to flow back into the bypass block. To feed the bypass block, the Prince valve needs to be a power beyond valve. That, quite simply, is the definition of power beyond.

Now with all of that said, there are a lot of systems hooked up in a fashion that amounts to running the outlet from that Prince valve back into the bypass block. Most of the time the system will work and usually without a problem. But it can cause some strange behavior. Some of it is just an inconvenience, others are outright dangerous.

. . .
But your wrong to say the pressure will hit spike to 3000psi.

Each relief valve will open at the set limit, in this case 1500psi to let the fluid pass!

I would say that I dont have a problem with this on my Deere using the power beyond, because I dump the return oil back into the transmission housing (hydraulic oil tank)!

I'm not familiar with your Deere and how the valves are configured. You may well be correct.

I may be wrong on the 3,000 psi scenario and am willing to be corrected by documentation straight from a valve manufacturer. But my belief is that any relief valve set for 1,500 psi will open when the pressure in the inlet is 1,500 psi greater than the pressure on the outlet. They will not open just because pressure on the inlet is 1,500 psi greater than atmospheric pressure. (It would be possible to build a valve that does that, but I can't imagine anyone doing it except maybe NASA). So as long as the pressure on the outlet side of the relief valve is near zero, pressure on the inlet side is limited to the 1,500 setting. But every pound of pressure held by the outlet side raises the inlet pressure required to open the valve by a pound. If the outlet side reaches 1,500 psi, as limited by a downstream pressure relief, the inlet side has to reach 3,000 psi before the valve opens.

[Rick Prentice]

Jim, after further review of all the facts and comments, I will agree that someone could have a unique situation where maybe the T/C relief valve malfunctions and builds pressure, which in turn would have pressure on both sides of the newly added control valve's relief setup( making it useless). Then if you possibly hit an object while angling your blade, causing a burst of added pressure, there could be situation that would cause that newly added standard valve(non power beyond) to burst.

With even a chance of that happening to anyone, I wouldn't want anyone to use the standard (non power beyond valve) control valve and then turn around and blame "farmallcub" because of the idea it was OK to use.

I will edit my post about power beyond yes or no,
Rick

[Gary S.]

I'm more confused than ever but that's ok. I like sausage but I don't need to know how it's made either