MTS Series 248 Actuators - Manual (Page 38)

Series 248 Actuator Product Information 38
How to Relieve Nitrogen Pressure from the Static
Operation
How to Relieve Nitrogen Pressure from the Static Support
Nitrogen (N
2
) pressure must be relieved from the static support assembly before
you service the actuator or the static support assembly.
1. Ensure that system hydraulic pressure has been reduced to zero before
proceeding. To do this, turn off the hydraulic power unit and exercise the
actuator until it stops moving.
2. Remove the protective cap from the gas valve on the static support. Slowly
open the gas valve locknut on the pressure vessel until N
2
escapes.
3. Allow N
2
to gradually bleed off until pressure in the pressure vessel is at
zero.
4. Close the gas valve locknut and replace the protective cap.
Calculate Static Support Precharge
Determine the approximate static N
2
support pressure using the following
formula:
Where:
Ps =static N
2
pressure in MPa or psi.
W =weight the actuator is required to support in kg or lb.
A=piston rod end area cm 2 or in 2 .
For 248.0x models, A = 50.2 cm 2 (7.8 in 2 ).
For 248.1x models, A = 78.5 cm 2 (12.2 in 2 ).
For 248.2x models, A = 122.7 cm 2 (19.0 in 2 ).
K = a constant determined by the unit of pressure (for psi, K = 1; for MPa, K
= 0.098).
Note The calculated static support precharge could be high enough to prevent
the retraction of the actuator piston rod when the structure or component
is removed from the piston rod end. If this occurs, relieve gas bottle N
2
pressure to retract the piston rod.
Ps
W K 〈 〉
A
-------------- =