Re: Hydraulics Questions

Posted by Tom R Ne on November 11, 2006 at 16:32:16 from (139.55.139.35):

In Reply to: Re: Hydraulics Questions posted by Allan In NE on November 11, 2006 at 05:58:52:

If you use tantem center spool valves such as you pictured, connected in series (the outlet of one valve connected to the input of the next valve). All valves except for the last valve must be rated for power beyond because when you operate any downstream valve the pressure that builds on the cylinder port to operate the load will be reflected back into the outlet of the proceeding valves. Valves that are not rated for “Power beyond” normally have the outlet tied to tank and all of the tank functions from the valves ports will be connected together, this usually involves subjecting a large area of the valve to the outlet pressure. Since the casting is fairly thin any back pressuring at this port can subject the outlet port of the valve to casting splitting forces.

Valves that are rated for power beyond may have a more complicated spool and porting design plus a stronger casting and only have one outlet port (many industrial valves are so configured).

Most of the time, with agriculture grade valves they supply a “power beyond sleeve” that separates the center port and the actual tank port function and creates 2 outlet ports, one for tank return and the other for center port fluid to pass on to additional valves for power beyond. This scheme separates the large area of the casting involved with the tank functions from the backpressure created by the operation downstream valves this reduces the chances of blowing out the casting of the valve. In addition backpressure on a non- power beyond valve can cause the backpressure to unbalance the spool and make the valve hard to shift under certain operating sutations.

Before you connect them as proposed you better check with Cross about the power beyond capabilities of the valves. It that is permissible then the relief valves need to be set so that the valve closest to the pump has the lowest setting and set the others to maximum so that in normal operation they do not function.

I am in agreement with those recommending the stack valve.

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