I regularly receive questions from owners of mobile hydraulic equipment in relation to the correct installation of an additional directional control valve using the 'power beyond' facility on an existing directional control valve.
What is power beyond?
Power beyond - also called high-pressure carry over (HPCO), is a facility on a mobile hydraulic directional control valve which enables the pressure gallery to be isolated from the tank gallery and be carried over to an additional valve - usually another directional control valve. The valve being installed must be sized to handle the rated flow from the pump.
The arrangement of the power beyond facility varies with valve type and manufacturer. However the most common arrangement is a facility to install a threaded plug or sleeve that blocks the drilling between the pressure and tank galleries inside the valve. The power beyond port is then used to supply pump flow to the additional directional control valve. If the existing directional control valve has an alternative tank port, this allows the tank line from the additional valve to be connected to tank via the existing valve (Figures 1 & 2).
Figure 1. Simplified line drawing showing pressure and tank galleries of a directional control valve (DCV) in open center arrangement.
Figure 2. Connection of an additional open center DCV using the power beyond facility.
Most mobile directional control valves can be made closed center by plugging the drilling between the pressure and tank galleries and leaving the power beyond port plugged (Figure 3). This means that if the existing valve is closed center, supplying pump flow to the additional valve only requires the connection of its pressure line to the existing valve's power beyond port (Figure 4).
Figure 3. Simplified line drawing showing pressure and tank galleries of a DCV in closed center arrangement.
It is important to note that if the existing valve is closed center, the power beyond plug or sleeve must be installed in the additional valve to make it closed center also(Figure 4).
Figure 4. Connection of an additional closed center DCV using the power beyond facility.
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