Austin,

Looks slightly different to mine, but wots under the plastic cover ?? What about on the other side??

Mine's got a 17mm spanner size nut locking a screw with a flat screwdriver slot in it. But AFAIK all hydraulic 2 posters will have an adjustment on them, your looking in the right area lol !!

If you have the exact make and model of the lift the instructions should be on the 'net.

Mine is a "Silent Technology" 4 tonne 2 poster, single phase.
Goes up just as quick as the 3 phase ones I had at the workshop in Kent, before I sold up and moved up here.

Regards Dave