Gravel is more coarse than sand and depending on the size of the sand and gravel you want to separate, you need to find a strainer to do the job. In construction, the gravel runs through a series of different sized screens that are built onto a conveyor. The large rocks stay on top of the wire screen while the smaller particles fall through into waiting trucks. For the average person, you do not need elaborate equipment to separate the gravel from the sand. You can make your own screening device in a matter of minutes.
Lay a piece of plastic or tarp on the ground. On top of this, place several five-gallon buckets or a wooden box frame. The plastic will help catch what the buckets miss.
Find a heavy-duty wire mesh screen. The holes in the mesh need to be fine enough to separate the sand from the gravel. Choose a screen that will not buckle or bend beneath the weight of the gravel you put on it. If you don't have much sand and gravel to separate, use a window screen. Place this over the heavy-duty screen so it will not bend or come apart. A colander used for the kitchen also works.
Place the screen over several buckets or a makeshift frame to keep the screen off the ground.
Pour the gravel and sand mixture on top of the screen. Shake the screen to filter the smaller particles. Use your hands to spread the gravel around over the top of the screen. The smaller particles will fall through, leaving the bigger rocks on top. Wear gloves to protect your hands form sharp rocks.
Remove the larger pieces of gravel and place them where you want them.
Repeat the process until you have separated as much sand and gravel as you need.