It depends on the weight of the user. The best on the pump is at 15 psi and that is for the maximum weight person, and normally 12 psi is enough which is below the recommendation for full weight.
TIPS:
1.Make sure the knob on the double side at beginning because it can inflate when you push or pull it, it will be quickly when the board have no air inside. After the board full of air, change to single side, then it will inflate just when you push it, that can help us save energy and easy to put in the air to the end.
2.Check the board well before getting into the water. 1) Use the soapy water applied around the valve or the board side to check if it is leaking. 2) Inflate and wait for about 2 hours to see if the pressure can stay a normally time.