The main spindle at the centre of the valve assembly has just failed after 8 years of use. The point of failure is located between the plastic vertical spindle and the horizontal steel pin. The spindle has sheared as a result of me being heavy handed in attempting to rotate the handle when the valve becomes partly 'blocked' by the ingress of particles the size of sand. The same problem occurs each year during the the first use after the winter break. The winter debris cover prevents large items falling in the pool but allows grit/sand sized particles to enter. Vacuuming these out of the pool, in my case, causes the valve to jamb. The two key lessons to learn: don't force the handle and dismantle the valve immediately it becomes difficult to rotate.