I tested it again today. Its is pretty good, but needs improvement. it does not put out enough sand, after watching that video mr95gst suggested, i worked out why: my air valve down the bottom needs to be reversed, put on the other side on the 'T' before the sand valve, so that when you close the air valve slightly, pressure increases in the sand chamber, and more sand is pushed out.

So i will try and work that out today and tell you if it is better!

Thanks.
MRunknown.