MTS 318 Load Unit - Manual (Page 96)

318 Load Unit 96
Routine Maintenance Overview Checklist
Maintenance
2. With an open-end wrench, turn the locknut counterclockwise on the
accumulator valve assembly to open the valve. Read the pressure on either
the high or low accumulator charging kit pressure gage.
• If the pressure reading is other than the required pressure level recorded on
the accumulator, continue with the next subsection, “Change the Precharge
Pressure”.
• If the pressure level corresponds to the level recorded on the accumulator
label, turn the locknut clockwise to close the valve and continue this
procedure.
3. Open the bleed valve on the accumulator charging kit and remove the chuck
valve from the accumulator. Replace the valve stem cap and protective
cover on the accumulator.
Change the Precharge
Pressure
Often the precharge of an accumulator mounted on a hydraulic supply line is
increased to enhance system performance and reduce the transient HPS flow
demands. Accumulators may be precharged to 10 MPa (1500 psi) or more,
although amounts above 14 MPa (2200 psi) will have less and less performance
effect in most situations. Be sure that you read the following warning before you
charge your accumulator.
Accumulators have specific pressure ratings.
If the precharge pressure is too high, the accumulator can bottom out
causing the release of metal particles into the hydraulic fluid. Charging
accumulators above their rated level can damage system equipment.
Do not charge accumulators to pressures above their rated level. Charge
accumulators below their rated fatigue pressure of 21 MPa (3000 psi) for the
Model 111.11B and 22 MPa (3200 psi) for the Model 111.12C. Use a suitable
regulator and gage set to an accumulator’s charges.
Decreasing pressure
To decrease the precharge pressure:
1. Slowly open the bleed valve on the accumulator charging kit until gas
begins to escape. When the pressure reading on the appropriate pressure
gage drops to the level required, close the bleed valve.
2. Close the locknut (or close the chuck valve if you have a core-type valve).
Open the bleed valve on the accumulator charging kit and remove the chuck
valve from the accumulator.
3. Install the valve stem cap and protective cover.
Increasing pressure
To increase the precharge pressure:
1. Close the locknut on the accumulator (or close the chuck valve for a core-
type valve).
2. Open the bleed valve two turns.
WARNING