MTS Hydraulic Power Unit Model 506-92 - Manual (Page 20)

3-8 Service
Slow Turn-on
Accumulator Precharge pressure of the slow turn-on accumulator (Figure 3-2) must be
checked at regular intervals. To establish an interval time, follow this
procedure:
1. Initially, check the precharge pressure after 2 weeks or 100 operating
hours
.
2. If there is a pressure-level change of more than 50%, check the
precharge pressure every week or 50 operating hours.
If there is a pressure-level change of less than 50%, check the
precharge pressure every four weeks or 200 operating hours.
3 . 1 . 3 . 2 Precharging the Accumulators
If the pressure accumulator has a pressure-level change of
±
200 psi
between checks, recharge it. If the slow turn-on accumulator has a
pressure-level change of
±
50% between checks, recharge it.
The pressure and slow turn-on accumulators are typically precharged to
1000 psi (7 MPa) and 800 psi (5.5 MPa), respectively. These are the
recommended levels for an HPU output pressure of 3000 psi (21 MPa).
3 . 1 . 3 . 3 Changing the Accumulator Seals
When you have established a regular interval for checking the precharge
pressure, note the amount of pressure loss that occurs each time the
precharge pressure is checked. If an increase in pressure loss occurs
during the period between checks, the seals may require replacement.