Flow capacity of pipes/valves between pump and chamber (Liters/second).
Current pressure in the vacuum chamber (Torr/mbar).
Please enter valid positive numbers for all fields.
Effective Pumping Speed (Seff):–
Conductance Loss:–
Throughput / Flow Rate (Q):–
Performance Factor:–
function calculateVacuumFlow() {
// Get input elements exactly by ID
var pumpSpeedInput = document.getElementById('pumpSpeed');
var conductanceInput = document.getElementById('conductance');
var pressureInput = document.getElementById('pressure');
// Get values
var s_pump = parseFloat(pumpSpeedInput.value);
var conductance = parseFloat(conductanceInput.value);
var pressure = parseFloat(pressureInput.value);
var errorDiv = document.getElementById('vError');
var resultsDiv = document.getElementById('vResults');
// Validation logic
if (isNaN(s_pump) || isNaN(conductance) || isNaN(pressure) || s_pump <= 0 || conductance <= 0 || pressure <= 0) {
errorDiv.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
errorDiv.style.display = 'none';
// 1. Calculate Effective Pumping Speed (Seff)
// Formula: 1/Seff = 1/Spump + 1/Conductance
// Simplified: Seff = (Spump * Conductance) / (Spump + Conductance)
var s_eff = (s_pump * conductance) / (s_pump + conductance);
// 2. Calculate Throughput (Q) aka Flow Rate
// Formula: Q = Seff * Pressure
// Units will be [Pressure Unit] * [Speed Unit], e.g., Torr-L/s
var throughput = s_eff * pressure;
// 3. Calculate Loss Percentage
var loss = ((s_pump – s_eff) / s_pump) * 100;
// 4. Calculate Conductance Factor (Ratio of C to S)
var factor = conductance / s_pump;
var factorText = "";
if(factor < 0.5) {
factorText = "Poor (Conductance Limited)";
} else if (factor < 1) {
factorText = "Moderate Restriction";
} else {
factorText = "Good (Pump Limited)";
}
// Display Results
document.getElementById('resSeff').innerHTML = s_eff.toFixed(2) + " L/s";
document.getElementById('resLoss').innerHTML = loss.toFixed(1) + "%";
// Format throughput nicely based on magnitude
var qDisplay = throughput;
if (throughput < 0.0001) {
qDisplay = throughput.toExponential(3);
} else {
qDisplay = throughput.toFixed(4);
}
document.getElementById('resThroughput').innerHTML = qDisplay + " Torr·L/s";
document.getElementById('resFactor').innerHTML = factorText;
resultsDiv.style.display = 'block';
}
Understanding Vacuum Flow Rate and Effective Pumping Speed
In vacuum engineering, calculating the flow rate (throughput) and the effective pumping speed is critical for designing efficient systems. Unlike fluid dynamics in pressurized pipes, vacuum systems operate in regimes where the geometry of the connection pipes significantly restricts gas flow. This calculator helps engineers and technicians determine the actual performance of a vacuum pump when connected to a chamber via piping, valves, or manifolds.
Key Concepts: Pumping Speed vs. Effective Speed
When you purchase a vacuum pump, it comes with a nominal pumping speed (Spump), usually measured in Liters per second (L/s) or Cubic Feet per Minute (CFM). However, this is the speed at the pump's inlet. The moment you attach a pipe, elbow, or valve, you introduce resistance to the flow. This resistance is quantified as Conductance (C).
The Effective Pumping Speed (Seff) is the actual speed at the vacuum chamber, and it is always lower than the nominal pump speed. The relationship follows the rule of adding reciprocals, similar to resistors in parallel:
1 / Seff = 1 / Spump + 1 / C
This equation demonstrates that if the conductance of your piping is low (narrow or long pipes), the effective speed will be drastically reduced, regardless of how powerful your pump is. This is often referred to as being "conductance limited."
Throughput (Q): The Vacuum Flow Rate
Throughput, denoted as Q, represents the quantity of gas passing through a cross-section of the system per unit of time. It is essentially an energy flow rate. At a constant pressure, throughput is calculated as:
Q = Seff × P
Where P is the pressure at the point where the speed is measured. The units for throughput are typically Torr-Liters/second (Torr·L/s) or mbar·L/s. This metric is vital for determining if a pump can handle a specific gas load (such as outgassing from chamber walls or process gas introduction) while maintaining the desired pressure.
How to Use This Calculator
Nominal Pumping Speed: Enter the manufacturer's rating for your vacuum pump. Ensure units are consistent (e.g., L/s).
Connection Conductance: Enter the calculated conductance of your piping system. Long, narrow tubes have low conductance; short, wide tubes have high conductance.
Chamber Pressure: Input the target or current pressure of the system to calculate the mass flow rate (Throughput).
Conductance Regimes
It is important to note that conductance (C) changes depending on the flow regime:
Viscous Flow: At higher pressures (rough vacuum), gas molecules interact with each other. Conductance depends on pressure.
Molecular Flow: At high vacuum, molecules interact primarily with chamber walls. Conductance is independent of pressure but highly dependent on geometry.
This calculator assumes a constant conductance value, which is typical for specific operating points in system design.