Bob if that were the case then why even have power beyond capabilities?
Also the Eaton 11 charge pump has NO relief at all.
The system pressure is relieved at the valve, this is why they squeal at full up and full down.
And if a valve is constructed with power beyond capabilities you better use it,as it has 2 circuits designed into it!! High pressure and low pressure or return pressure that is a max of 150 psi, any more would blow out hoses and coolers,and the valve body it self Depending on the brand,as some are tougher than others.
This can get quite complicated and lengthy, but doesn't need to.
You just need to follow recommended procedures, if the valve has this capability of power beyond, use it.
I stand corrected, the implement lift circuitry is a customer supplied option on Eatons. See the link in the first post of this thread for the flow diagram on page #11 of the PDF.
Keith, you're the one who taught me how a power beyond kit works. I just had to do a bit more research to get it locked in.
Relief valves work on the principle of pressure differential between the high side pressure from the pump and the low side pressure of the tank. In order for them to work correctly, they must have unobstructed flow directly to the tank. If another valve set is inserted into the system downstream from the relief valve, relieved flow meets an obstruction should a valve be cycled at the same time as a valve in the first (relieved) valve set setting up an additive pressure problem. Using acase of a 750 psi relief setting as an example, the first valve set has 750 psi to work with before the relief sends fluid back to tank via a second valve set. Should the second valve set be actuated, the pressure that it requires to do work is added to the relief pressure (differential pressure), and there is no relief protection since the pressure differential seen by the relief in the first valve set is zero. The same pressure exists on both sides of the relief valve. With relieved flow diverted to do work with the second valve set, pump breakage is pretty much guaranteed to happen at some point.
This issue crops up when the relief valve is in the valve set, not when it is at the pump as with an Eaton hydro and the relieved flow goes into the hydro case to drain back to the reservoir.
The return side of a valve set that can have a power beyond kit installed has a common chamber and two outlet ports, one for return to tank and the other for power beyond. Without the kit, either can be used for the return line.
The kit includes a plug designed (for that specific valve model) to separate that chamber into 2 chambers, one for discharging fluid going over the relief back to tank, and the other to send fluid on to successive valve sets in the primary circuit. The relief valve in the valve set ensures that maximum pressure allowed in the rest of the system is the relief setting, the same as in the case of the hydro with an implement relief.
Note: A valve set with no integral relief will not have provision for power beyond. It does not necessarily follow that a valve set with an integral relief will also have a power beyond capability. Some valves found on GT's, specifically FEL's, fall into the second category. Valve sets on the GT hydros rarely have an integral relief since there is a relief at the charge pump. Eaton 11's seem to be an exception.
Edited by TUDOR, May 28, 2015 - 03:08 PM.