const byte out1 = 10;
const byte  in1 = 2;
const byte  in2 = 3;
const byte  in3 = 4;
const byte  in4 = 5;

const unsigned long actionDelay = 2500; // allowable time for flow to be distrupted without stoppage

void setup() {

pinMode(out1, OUTPUT);
digitalWrite(out1, HIGH);

pinMode(in1, INPUT_PULLUP);
pinMode(in2, INPUT_PULLUP);
pinMode(in3, INPUT_PULLUP);
pinMode(in4, INPUT_PULLUP);

delay(5000);

}

void loop() {
 
  static unsigned long readTime; // time at action
  unsigned long now = millis();  

  bool flowIsLow1= digitalRead(in1) == HIGH;  
  bool flowIsLow2= digitalRead(in2) == HIGH;  
  bool flowIsLow3= digitalRead(in3) == HIGH;  
  bool flowIsLow4= digitalRead(in4) == HIGH;  

  bool pumpFault = flowIsLow1 || flowIsLow2 || flowIsLow3 || flowIsLow4;

  // if flow is good and flow switches are closed
  if (!pumpFault) {
    readTime = now;
    digitalWrite(out1, HIGH);
  }

  // when (if!) the timer expires, turn ON the LED
  if (now - readTime >= actionDelay) {
    digitalWrite(out1, LOW);
  }

}