Piston Pump Flow Rate Calculation

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Piston Pump Flow Rate Calculator

Accurately calculate the theoretical and actual output of hydraulic piston pumps.

Calculation Results

Displacement per Rev: 0.00 cc/rev
Theoretical Flow: 0.00 LPM
Actual Flow Rate: 0.00 LPM
function calculatePistonFlow() { var bore = parseFloat(document.getElementById("boreDiameter").value); var stroke = parseFloat(document.getElementById("strokeLength").value); var pistons = parseFloat(document.getElementById("numPistons").value); var rpm = parseFloat(document.getElementById("pumpRPM").value); var efficiency = parseFloat(document.getElementById("volEfficiency").value); if (isNaN(bore) || isNaN(stroke) || isNaN(pistons) || isNaN(rpm) || isNaN(efficiency)) { alert("Please fill in all fields with valid numbers."); return; } // Calculation Logic // Area = PI * r^2 var radius = bore / 2; var areaSqMm = Math.PI * Math.pow(radius, 2); // Displacement per rev in mm^3 = Area * stroke * pistons var displacementMm3 = areaSqMm * stroke * pistons; // Convert mm^3 to cc (cm^3) -> 1000 mm^3 = 1 cc var displacementCc = displacementMm3 / 1000; // Theoretical Flow (LPM) = (Displacement in cc * RPM) / 1000 var theoFlowLpm = (displacementCc * rpm) / 1000; // Actual Flow = Theo Flow * (Efficiency / 100) var actualFlowLpm = theoFlowLpm * (efficiency / 100); // Update UI document.getElementById("resDisplacement").innerHTML = displacementCc.toFixed(2) + " cc/rev"; document.getElementById("resTheoFlow").innerHTML = theoFlowLpm.toFixed(2) + " LPM"; document.getElementById("resActualFlow").innerHTML = actualFlowLpm.toFixed(2) + " Liters/min"; document.getElementById("resultArea").style.display = "block"; }

Understanding Piston Pump Flow Rate

A piston pump is a type of positive displacement pump where high-pressure seals reciprocate with the piston. Determining the flow rate is critical for hydraulic system design, ensuring the actuators (cylinders or motors) receive the required fluid volume to operate at specified speeds.

The Calculation Formula

The total flow rate of a piston pump depends on the geometry of the pistons and the rotational speed of the pump drive. The formula used by this calculator is:

Flow (LPM) = [Displacement (cc/rev) × RPM × Efficiency] / 1000

Where displacement is calculated as:

Displacement = Area of Piston × Stroke Length × Number of Pistons

Key Factors Affecting Flow

  • Bore Diameter: The internal diameter of the cylinder. A larger bore increases the area, significantly increasing displacement per stroke.
  • Stroke Length: The distance the piston travels within the cylinder. Longer strokes displace more fluid.
  • Number of Pistons: Most axial piston pumps use an odd number of pistons (7 or 9) to minimize flow pulsation and pressure ripples.
  • Volumetric Efficiency: No pump is 100% efficient. Internal leakage (slippage) occurs, especially at higher pressures. Most high-quality piston pumps operate between 90% and 98% efficiency.

Practical Example

Suppose you have a 9-piston axial pump with a 20mm bore and a 25mm stroke, running at 1,800 RPM with a volumetric efficiency of 94%.

  1. Area: π × (10mm)² = 314.16 mm²
  2. Displacement: 314.16 × 25mm × 9 pistons = 70,686 mm³ (or 70.69 cc/rev)
  3. Theoretical Flow: (70.69 × 1800) / 1000 = 127.24 LPM
  4. Actual Flow: 127.24 × 0.94 = 119.61 Liters per minute

This calculator handles these conversions instantly, helping engineers and technicians select the correct motor speeds and pump sizes for their specific hydraulic applications.

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