TM10-3930-660-20 12-8. SERVICE BRAKE HYDRAULIC ACCUMULATOR -  REPLACE/REPAIR/TEST Cont’d) 5. IF PRECHARGE PRESSURE READING OBSERVED IN STEP 4 IS TOO LOW, ADD NITROGEN TO SERVICE BRAKE HYDRAULIC ACCUMULATOR  (1)  . a. Connect nitrogen charging bottle to charging and gauging assembly. b. Turn isolating valve on and admit nitrogen into diaphragm of accumulator (l). Do this slowly, checking the pressure gauge reading at regular intervals. c. Repeat step 5b, as necessary, until precharge pressure is 700 psi ± 50. 6. IF PRECHARGE PRESSURE READING OBSERVED IN STEP 4 IS TOO HIGH, BLEED NITROGEN FROM SERVICE BRAKE HYDRAULIC ACCUMULATOR (1). a. Open bleeder valve on charging and gauging assembly to vent nitrogen from the accumulator diaphragm as required. Leave the bleeder valve open for only a short period and then  close  it. b. Check the precharge pressure. C. Repeat steps 6a and 6b, as necessary, until precharge pressure is 700 psi ± 50. 12-27