MTS Series 505 SilentFlo Hydraulic Power Unit Model 505-11 - Manual (Page 41)

Recovering from an Interlock
Model 505.07/.11 SilentFlo™ HPU Operation 41
Recovering from an Interlock
This section describes how to reset each type of HPU interlock. If one of the
interlock indicators (Low Level, Overtemperature, Dirty Filter) is lit, the HPU
will not start. You must determine the source of the interlock (which indicator is
lit) and correct the cause before using the HPU.
Low level
The Low Level indicator lights when the hydraulic fluid falls below the setting
of the low level/overtemperature sensor which is mounted on top of the reservoir.
Perform the following steps to correct a low level interlock:
1. Add hydraulic fluid to the reservoir until the fluid level gage indicates the
proper level.
2. Press the Reset button to clear the interlock and turn the indicator off.
Overtemperature
The Overtemperature indicator lights when the temperature exceeds 55°C
(131°F). The temperature is detected by the low level/overtemperature sensor
mounted on top of the reservoir. The HPU cannot be restarted until the fluid has
cooled. Perform the following steps to correct an overtemperature interlock:
1. Check the temperature gage to ensure that the hydraulic fluid is actually
overheated. If not, the overtemperature switch may need replacement.
2. If necessary, cool the hydraulic fluid as described in this section.
3. Determine if the hydraulic fluid is receiving adequate cooling.
• Verify the operation of the Auto-Cooling Valve.
• The auto-cooling circuit provides a path for circulating hydraulic fluid
through the heat exchanger during periods of high pressure operation
with low demand by the system.
Note The cooling water inlet temperature affects the efficiency of cooling the
hydraulic fluid.
• Check the cooling water inlet-to-outlet pressure differential. It should be
between 0.24–0.34 MPa (35–50 psi). Adjust the water pressure at its source.
4. Press the Reset button to clear the interlock and turn the indicator off.
Cooling the
hydraulic fluid
If the HPU shuts down due to overheated hydraulic fluid, you may need to
perform the following procedure to circulate hydraulic fluid through the heat
exchanger to cool the fluid:
1. Open the HPU cover to monitor the temperature of the hydraulic fluid.
2. Turn the High/Low/Start switch to the Start position and hold it there. This
overrides the interlock and runs the pump motor.
3. Continue to hold the High/Low/Start switch in the Start position to
circulate the hydraulic fluid through the heat exchanger. Observe the
temperature gage.
4. Release the switch when the fluid temperature falls below 53°C (129°F).