They saw that the hydraulic pressure was low and falling.

Finally losing its hydraulic pressure, the aircraft became impossible to control.

He'd also lost a bit of hydraulic pressure, and that was worrisome but not critical.

The loss of hydraulic pressure was a nagging worry, though.

Hydraulic pressure built up slowly until the door wheezed open.

Then he would stay indoors until hydraulic pressure utterly forced him outside.

The pump, however, is only engaged when hydraulic pressure needs to be generated.

This system will not engage during normal driving conditions, when hydraulic pressure is equal.

Hydraulic pressure was dropping; he had three yellow warning lights and a red.

Primary hydraulic pressure was on its way to zero.