Reassembling shower valve

[Gorners]

Can you please help me readable/ reseat this shower valve please (see photo’s), or at least explain how it works so I can try and figure it out myself. The shower type and valve are shown here. The mechanism has become stiff so took apart to add silicone grease. I’ve done this a few times before, the most recent two times including this I’ve had problems getting the on/off working, I did it by luck last time, but this time I’m well into double figures and it just will not work.

Basically the two brass parts with the o-rings screw together - it’s these that become stiff so undone them to apply grease. When I screw these together at various positions and then add the main sealing nut on top, whoever I turn the water back on, the shower is ‘on’. I then proceed to turn it off, which works, but then I can never turn it back on again because (I am pretty sure), the two brass parts have come apart in the process of turning it off. I’ve tried screwing it in at different points to no avail. I’m not sure if screwing on the sealing nut is also causing it to unscrew as well but there appears to be no way of preventing this.

Photo 1 is the sorts screwed fully together, photo 2 screwed half way-ish. When you screw a bit further they come apart and can never screw back together within the mechanism, only when I take it apart again.

Seems the water pressure is key to getting this working as well? Any help would be appreciated.

 

[Gorners]

After some more faffing about, I’ve come to the conclusion the valve is knackered and needs replacing. Seems as soon as the water pressure gets up, the valve comes apart. Shouldn’t need to set it in a certain position, should just be plug and play. Off to eBay to try and find a cheaper part !