Archive for December 29th, 2008

How much water can you get out of your main water pipe?

December 29, 2008

A typical residential water service in our area has a dynamic water pressure of about 65 PSI, and a 3/4 or 1 inch supply line. This roughly translates to about 17 to 32 gallons per minute maximum water flow.

Well exactly how much water is that?

32 gallon = 512 cups = 4096 ounces = 24576 teaspoons

17 gallon = 272 cups = 2172 ounces = 13056 teaspoons

32 gallons per minute is the same as 512 cups per minute, 4096 ounces per minute, or 24576 teaspoons per minute. Which is 0.53 gallons per second, 8.533 cups per second, 68.26 ounces per second or 409.6 teaspoons per second.

17 gallons per minute is 0.2833 gallons per second, 4.533 cups per second, 36.2 ounces per second or 217.6 teaspoons per second.

I’ve a 3/4 inch supply line with 65 PSI dynamic water pressure and I was expecting the maximum of 17 gallons per minute. Based on my actual measurement, I was able to get about 12 gallons per minute.

I took three measurements from the closest water outlet to the water meter, and on average I was able to get 1 gallons per 5 seconds (12 gallons per minute or 3.2 cups per second). I’m sure that just after the meter, the rate will be closer to 4.5 cups per second. I also took a measurement at the water outlet furtherest away from the meter but still with minimum splits and turns, and as expected I was getting a lower flow rate — 1 gallon per 7 seconds.

Static Water Pressure is the water pressure measured as close to the water meter by hooking up a pressure gauge to the pipe before the meter.
Dynamic Water Pressure is the pressure that you’re left with after the water flows thru the meter, the back-flow device, and all of the pipes.


1 CCF = 748 gallons
1 gallon = 16 cups
1 cup = 8 ounces
1 ounce = 6 teaspoons

1 pint = 2 cups
1 quart = 2 pints
1 quart = 4 cups
1 gallon = 4 quarts

Here is how you can calculate the water flow rate

Q = V * A

where, Q is the Volumetric flow rate, V is the velocity of the water, and A is the cross-sectional area of the passage.

You can compute the velocity of the water

P0 - P = (rho) * V ^ 2

Where P0 is the total pressure calculated using a pitot-static tube, P is the static pressure, rho is the density of the fluid (water has a density of 1), and V is the Velocity of the water.

Most Water Utilities in North America and Britain charge water per CCFs (748 gallons per CCF). In our area a CCF is about $2.25.

1 gallon = 0.3 cents
1 cup = 0.0019 cents
1 toilet flush = 1.6 gallon = 0.48 cents

Posted in Water | 1 Comment »

Pulse Counter

December 29, 2008

The Arduino digitalRead function appears to be non-blocking. It reads either a LOW or a HIGH. If the pin you’re reading from is not connected to anything, it will read a random value. Here is a simple pulse counter that also measure the duration of the HIGH or LOW part of the pulse.

int pulsePin = 3;
int ledPin = 13;
unsigned long highCounter = 0;
unsigned long duration = 0;
int pulse = 0;
int lastPulse = LOW;
unsigned long timeNow = 0;
unsigned long lastTime = 0;

void setup() {
   pinMode(pulsePin, INPUT);
  // enable the 20K pull-up resistor to 
  // steer the input pin to a HIGH reading.
   digitalWrite(pulsePin, HIGH);   
   Serial.begin(9600);
   Serial.println("Pulse Reader - Version 2");
}

void loop() {
  pulse = digitalRead(pulsePin);
  if (pulse != lastPulse) { // pulse has changed
    timeNow = millis();
    duration = timeNow - lastTime;
    // blink the LED
    digitalWrite(ledPin, pulse);
    Serial.print(pulse);
    Serial.print(" ,");
    Serial.println(duration);
    lastPulse = pulse;
    lastTime = timeNow;
    if (pulse == HIGH) highCounter++;
  } 
}

Posted in Arduino | 3 Comments »

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