In the last hydraulics bulletin, we talked about a rarely considered way air can enter the high-pressure side of a hydraulic system.

Continuing on the subject of plumbing, I got this from one of our members:

“OK, I’ve done the research and read the results, and googled, but am still confused about ‘power beyond’ and its relevance when trying to hook up a second directional control valve. I’ve found nothing that explains exactly why it is needed and what it really does.

“I’m talking about simple three-position valves – up, neutral/hold, and down – which have pressure in, tank out, and working ports for a double-acting cylinder.

“In an open center system, I would simply put the second valve in series with the first one – the return line of the first feeds the pressure line of the second, and the return line of the second goes to the tank. This seems to be such a simple arrangement – and power beyond seems to be such a very big deal – that I have obviously missed some important point.”

Yes, he has.

Connecting the tank port of the first valve to the pressure port of the second will do two things. One, when the first valve is used at the same time as the second, there is no way for the return oil from the first valve to get back to the tank; and, two, when the second valve is used, the tank/return gallery in the first valve will be pressurized and blow the spool seals.

Power beyond is a facility in the valve where a plug is inserted between the pressure and return galleries.

Pump flow can then be “carried over” to another valve downstream – so when that valve is used, it pressurizes the pressure gallery in the upstream valve but NOT the return gallery. Watch this simulation video for a full explanation.

Yours for better hydraulics knowledge,

Brendan Casey