An accumulator is a container with a floating piston inside; one end of the accumulator container is connected to system hydraulics, the other end filled with nitrogen with a charging valve.
The only time you can see nitrogen pressure is when there is no opposing hydraulic pressure, i.e no system pumps running and pressure part of the system vented to return. When this is the case you'll see true nitrogen pressure.
If accumulator pressure is down from a normal of say 1000psi to 500 psi for instance, the accumulator gauge attached to the accumulator will show 500psi and the system and brake gauges will show zero.
Start the pumps and system pressure will show on the system gauges and brake gauges. The hydraulic fluid on the hyd side of the floating accumulator piston will compress the 500 psi of nitrogen by moving the floating piston and you'll also see system pressure on the accumulator gauge. But you won't have as much volume of stored pressure. You can probably get down to a couple of hundred psi of nitrogen and when the pumps are on you'll see system pressure on the accumulator gauge. If you were to open the nitrogen charging valve when the pumps are on, you could bleed off the remaining nitrogen until the floating piston is pushed onto its stops, then the accumulator gauge will show true nitrogen pressure and eventually 0psi as its opened to atmosphere.
Last edited by itsresidualmate; 28th October 2012 at 22:32.