It would seem that the 1/4 turn ceramic valve inserts used in older Damixa kitchen mixer taps are no longer generally available. (Nov 2016). You can get replacements from specialist suppliers like those mentioned previously, but at ludicrous prices - it's almost worth buying a new tap instead. However I have been able to use a replacement available from B&Q for less than £5 per pair to fix my Damixa tap in the photo below (this shows the tap after I repaired it) as follows:-
(Be warned however that it does require a degree of skill and care because if you mess up, tap replacement is almost certain!)
I used this product from B&Q
http://www.diy.com/departments/bras...-seal-thread1/2-dia8mm-set-of-2/913793_BQ.prd.
FIRST TURN OFF BOTH HOT AND COLD WATER SUPPLIES!! Then remove the coloured plug from the outer end of the knob shell (use a small screwdriver ro lever it out) to reveal the head of the brass securing bolt and put it somewhere safe. Using a cross-head screwdriver, unscrew the bolt and remove it. Carefully pull the shell aside. Note the position of the colour coded plastic shroud that fits ove the hexagonal part of the valve - maybe take a pic with your phone. This shroud provides the visible colour coding of the hot/cold sides of the tap in the photo above, and must fit snugly to the central body of the tap. Note too the orientation of the two nylon/plastic inserts in the shell of the tap knob. (It is possible that the inner one will be left on the splines of the valve when you remove the knob). If necessary remove it from the splines and set it aside. Remove the colour coded plastic shroud and put it aside. Using a suitable adjustable panner, extract the faulty valve from the tap and measure the spline length (8mm) and number of splines (20). I took the valve along to B&Q and compared the construction of the B&Q product above and the old valve. There are two main considerations: 1) will the colour coded plastic shroud that fits ove the hexagonal part of the valve fit (i.e. go on far enough to be flush with the tap body when the valve is fitted) If not, there will be an unsightly gap between the shroud and tap body, and 2) will the nylon/plastic part that fits on to the splines be able to slide on far enough to allow the outer shell to fit over it AND fit snugly to the outer side of the colour coded plastic shroud as it should do? If not, there will be an unsightly gap between the shroud andthe outer shell of the knob. The answer to 1) was 'Yes'. The answer to 2) was 'No'. The basic problem is that the brass shoulder of the B&Q part was higher than the original part, as illustrated below. The new B&Q part is on the right.
In my case, there was 3 to 4mm difference. The solution was VERY CAREFULLY to counterbore the INNER centre boss (arrowed above) of the nylon/plastic splined part. Measure the diameter of the brass shoulder of the B&Q part, in my case this was 10mm. Then, using a sharp twist-drill counterbore the centre to a depth of 3-4mm. I used a cordless drill, holding the part with my hand on a piece of wood. Do not try to drill too fast and do not apply too much pressure to the drill or the it may bite and wreck the part (new tap territory!). IT IS ESSENTIAL THAT YOUR DRILL BIT IS SHARP FOR A CLEAN AND ACCURATE CUT. This modification does of course reduce some of the load-bearing length of the spline, but thse valves do not require much torque to operate them and this should not be an issue. (I'll let you know if it is!!!)
In my case the
outer end of the splined hole of the nylon/plastic part had two interior flats; these need to be removed carefully using a sharp craft knife or Stanley knife. Insert the brass spline of the old valve into the nylon/plastic splined part from both ends to clear any swarf and use a soft brush to clear any other debris from the part. Fit the nylon/plastic splined part onto the brass spline and check that it goes on far enough that the brass spline end protrudes from the outer end of the nylon/plastic part sufficiently; if necessary increase the depth of the counterbore slightly. Fit the new valve into the tap body and tighten carefully. Fit the colour coded plastic shroud correctly and then the nylon/plastic splined part onto the brass spline. Then fit the outer shell, remembering the orientation. You may need to adjust the orientation of the shell by totating the shell slightly on the outer, finer, spline, then refitting to get the correct orientation. Basically that's it. Fit the securing screw and tighten, and then refit the colour-coded plug. Job done.