It depends on how washed the sand is and what it is blended like. The material cannot bleed water when transporting. i.e if it was conveyed along a pipe and bled water the material would become dean and block up the pipe. You can test this material by a couple of methods,
1 squeeze the mix through a clenched fist, if a ball of compacted sand remains the mix wont pump
2 leave a mix in a bucket for 15 mins if water comes to the top, the mix is not pumpable.
You can by superplasticisers which help make a material flowable.
The swing L will convey the mix to the end of the pipe, the material exits a gun which will have a spray cap about 12mm. the air is sent along a pipe that runs with the material pipe. it exits via a air tube just behind the spray cap in the gun. The air assists the material in projecting it on a wall. You can use the air on and off switch to control the machine coming on and off