How would I set the X, Y, or Z velocity of the player separately from the other 2?

Okay, so I think I figured it out; there is setVelocity method that can be used. But there's another issue: How do I make an action "run once" instead of continuing to run while the redstone circuit is powered? I'm trying to make Player Pistons (which push the player), and I'm setting the velocity of the player to a certain value depending on the redstone power level, but if I run into the front of the piston while the circuit is still active, it pushes me again. So how would I make it run the "push" code only once?

The method is in PlayerEntity I think; I had to edit the procedure's code to use it, but it turns out that ServerPlayerEntity doesn't have setVelocity, so it pseudo crashes your game when on a server. I fixed it by using a combination of getMotion() and setMotion(), using a Vec3d to get the motion and setting the other 2 motion(s) to the getMotion().x or z, like this:

Vec3d v3 = entity.getMotion();
entity.setMotion(v3.x, (double)world.getWorld().getRedstonePowerFromNeighbors(new BlockPos((int)x - 1, (int)y - 1, (int)z)) / 7, v3.z);

This is for the facing up player piston.

Still unsure how to make it only run once though, instead of while the redstone circuit is active, continually power the piston.