int motor = 6;  //
int inpin = 7;  // proximity sensor connected with the pin 2
int val = 0;    // this variable will read the value from the sensor
unsigned long sensorAir = 0;
unsigned long running = 2777; // how long the pump will run after seeing air

void setup()
{
  Serial.begin(9600);
  pinMode(motor, OUTPUT);
  pinMode(inpin, INPUT_PULLUP);
}

void loop()
{
  delay(10);  // just to cut down on printing.

  val = !digitalRead(inpin); // ! so val true == pressed
  unsigned long currentMillis = millis();

  running = analogRead(A0) * 3;

  if (val == HIGH) {
    digitalWrite(motor, HIGH);
    sensorAir = currentMillis;
    Serial.println(running);
  }
  else {
    if (currentMillis - sensorAir >= running)
      digitalWrite(motor, LOW);
  }
}