Poly Pipe Flow Rate Calculator

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Poly Pipe Flow Rate Calculator

Calculate the water flow capacity and friction loss for HDPE/Polyethylene pipes.

150 (New Poly Pipe) 140 (Standard HDPE) 130 (Older Pipe)

Calculation Results:

Flow Rate (Liters per Second): 0
Flow Rate (Liters per Minute): 0
Flow Rate (Cubic Meters/Hr): 0
Velocity (m/s): 0

Understanding Poly Pipe Flow Rates

When designing an irrigation system or a water transfer line using Polyethylene (HDPE) pipes, calculating the flow rate is critical. Unlike rigid metal pipes, poly pipes offer a very smooth internal surface, which minimizes friction and allows for higher flow velocities.

The Hazen-Williams Formula

This calculator utilizes the Hazen-Williams equation, which is the industry standard for calculating water flow in pressurized pipes. The formula is specifically optimized for water at ambient temperatures. The primary variables include:

  • Inside Diameter (ID): This is the actual internal space available for water, not the outside diameter (OD). Note that different SDR (Standard Dimension Ratio) ratings change the wall thickness and thus the ID.
  • Roughness Coefficient (C): For Poly/HDPE pipes, this value typically ranges from 140 to 150. A higher value indicates a smoother pipe.
  • Head Loss: This represents the energy lost due to friction or the elevation difference (gravity) driving the flow.

Example Calculation

Suppose you have a 100-meter run of 63mm OD poly pipe (with an internal diameter of approximately 51.4mm). If you have a 10-meter drop in elevation (10 meters of head):

  1. Internal Diameter: 51.4mm
  2. Length: 100m
  3. Head: 10m
  4. Coefficient: 150

Using the calculator, you would find a flow rate of approximately 4.8 Liters per second (L/s) with a velocity of 2.3 m/s.

Why Flow Velocity Matters

In poly pipe systems, it is generally recommended to keep water velocity below 1.5 – 2.0 meters per second for long-term durability. Velocities exceeding 3.0 m/s significantly increase the risk of water hammer (hydraulic shock), which can fatigue joints and fittings over time.

function calculatePolyFlow() { var d = parseFloat(document.getElementById('pipeID').value); var l = parseFloat(document.getElementById('pipeLength').value); var h = parseFloat(document.getElementById('headLoss').value); var c = parseFloat(document.getElementById('hazenC').value); if (isNaN(d) || isNaN(l) || isNaN(h) || d <= 0 || l <= 0 || h <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // Hazen-Williams Equation for Flow (Metric) // Q (m3/s) = 0.0000002788 * C * (D^2.63) * (S^0.54) // D is in mm, S is hydraulic slope (h/l) var s = h / l; var qLPS = 0.0000002788 * c * Math.pow(d, 2.63) * Math.pow(s, 0.54); // Results var lps = qLPS; var lpm = qLPS * 60; var m3h = qLPS * 3.6; // Velocity calculation: V = Q / A // Area in m2 = PI * ( (d/1000)/2 )^2 var radiusM = (d / 1000) / 2; var area = Math.PI * Math.pow(radiusM, 2); var velocity = (qLPS / 1000) / area; // Q in m3/s for velocity // Update UI document.getElementById('resLPS').innerHTML = lps.toFixed(2) + " L/s"; document.getElementById('resLPM').innerHTML = lpm.toFixed(2) + " L/min"; document.getElementById('resM3H').innerHTML = m3h.toFixed(2) + " m³/hr"; document.getElementById('resVel').innerHTML = velocity.toFixed(2) + " m/s"; document.getElementById('polyResult').style.display = 'block'; }

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