Weld on valves to allow regassing of the nitrogen gas side (not the hydragas fluid),
If your nitrogen pressure is low or zero the suspension will feel very hard and bounce off any bumps,
These require a hole to drilled in the gas sphere, welded on without overheating the unit, and then the valve fitted,
I recommend tig welding as this can be done with very minimal heat, brazing and soldering likely possible, Mig probably works but not usual on fine hydraulic type jobs,
These technically should be inflated with nitogen although i just used air from a motorcross/bicycle type shock pump, means they are servicable,
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Component Engineering