[bombadier337]

You need two. If you just have one double, one side will always exhaust and then other will let air into the cylinder. There unfortunely isn't a way to turn the double solenoids "off", you can only change the direction of the airflow.
here's our code

if(p2_y>240)
{
relay7_fwd=1;
relay7_rev=0;
}
else if(p2_y<15)
{
relay7_rev=1;
relay7_fwd=0;
}
else
{
relay7_fwd=0;
relay7_rev=0;
}

please note that used the wiring method described in my previous post