Generally, the stopping up of the siphon blaster is caused by moisture in the air. If you've ever noticed, when you hold the nozzle close to the piece you are cleaning, you will see water droplets develope on the part. Two cures ,wait for a day with no humidity, or ocaasionally hold your gloved finger over the nozzel, then pull the trigger, this will back blow the sand and clear the nozzle. Humidity will also stop up large pressure blasters.Pressure blasters will clear themselves, but very anoyingly,they will slow down a lot,then will suddenly blow clean,then repeat the cycle.Hope this helps, I have had cheap siphon blasters and supposedly good ones,and big commercial pressure blasters and they all work the same, and have the same problems.Hope this helps, Fiddler