Gate closer conundrum

[John Brown]

I have a gate closer exactly like this:
http://www.ebay.co.uk/itm/GARDEN-GATE-C ... 1420096810

It's been playing up a bit lately, I don't know why, but it seems to need a bit of tweaking every couple of years.
However, whilst adjusting it yesterday, I was trying to work out how the adjustment works. You open the gate to around 45 degrees and adjust the closing speed by turning a screw. Then you close the gate, and adjust the latching speed by turning the same screw - I know it's the same screw, as I have observed it while moving the gate.
I am at a loss to understand what the internal arrangement can be that allows this, so although it's not really a woodworking question, I thought I'd ask you clever sods.

 

[blackrodd]

Whenever possible I fit rising butts with any door closer units, as the rising butts will help to close the door, making the closer have a much easier life.
If rust is a concern, A pair of stainless butts is a good idea and a lot cheaper than galvanised.
Years ago, chippy's would "kick out" the bottom hinge about a 1/8" out of plumb, and up to 90 degrees, the door would close, and over 90 degrees, would go the other way and stay open.
If you "kicked" the top hinge out, the door would stay open, at 90 degrees.
This is with the door frame or lining perfectly plumb.
Regards Rodders

 

[John Brown]

Rising butts would not work well with this gate closer, as there is a small disc screwed to the gate that runs in a track on the closer.
Interesting re. kicking out the hinges, though.
Still doesn't get me any closer(NPI) to understanding how the adjustment works...

 

[blackrodd]

Rising butts would not work well with this gate closer, as there is a small disc screwed to the gate that runs in a track on the closer.
Interesting re. kicking out the hinges, though.
Still doesn;t get me any closer(NPI) to understanding how the adjustment works...

Yes, sorry I can't answer the original question, but reasoned that by having an easier life, as I said would help you're closer last longer between "adjustments".
Regards Rodders

 

[John Brown]

Well I am amazed! I really thought one of you clever chaps would have had a theory, at least!

You seem to know all about everything else!