Here's some links to gntype.org for troubleshooting your brakes. As per the troubleshooting guide, the time it takes to recharge your system after pumping the brakes down is a pretty good way of telling if you need a new accumulator. If the time is too short (< 7 sec.) there is not enough gas space left in the accumulator, which causes the pump to cycle much more frequently. On my car the pump runs about every 2nd or 3rd time I hit the brakes.