.valve-cv-calculator-container {
font-family: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 0 auto;
background-color: #f9fbfd;
border: 1px solid #e1e4e8;
border-radius: 8px;
padding: 30px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.valve-cv-calculator-container h2 {
color: #2c3e50;
margin-top: 0;
border-bottom: 2px solid #3498db;
padding-bottom: 10px;
font-size: 24px;
}
.form-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
margin-bottom: 25px;
}
@media (max-width: 600px) {
.form-grid {
grid-template-columns: 1fr;
}
}
.input-group {
display: flex;
flex-direction: column;
}
.input-group label {
font-weight: 600;
margin-bottom: 8px;
color: #4a5568;
font-size: 14px;
}
.input-group input {
padding: 12px;
border: 1px solid #cbd5e0;
border-radius: 6px;
font-size: 16px;
transition: border-color 0.2s;
}
.input-group input:focus {
border-color: #3498db;
outline: none;
box-shadow: 0 0 0 3px rgba(52, 152, 219, 0.1);
}
.calc-btn {
background-color: #3498db;
color: white;
border: none;
padding: 15px 30px;
font-size: 16px;
font-weight: bold;
border-radius: 6px;
cursor: pointer;
width: 100%;
transition: background-color 0.2s;
}
.calc-btn:hover {
background-color: #2980b9;
}
.result-box {
background-color: #ffffff;
border: 1px solid #e2e8f0;
border-radius: 8px;
padding: 25px;
margin-top: 25px;
text-align: center;
}
.result-title {
font-size: 14px;
text-transform: uppercase;
letter-spacing: 1px;
color: #718096;
margin-bottom: 10px;
}
.result-value {
font-size: 42px;
font-weight: 800;
color: #2d3748;
margin: 0;
}
.result-sub {
font-size: 16px;
color: #718096;
margin-top: 5px;
}
.error-msg {
color: #e53e3e;
background-color: #fff5f5;
padding: 10px;
border-radius: 4px;
border: 1px solid #fed7d7;
margin-top: 15px;
display: none;
text-align: center;
}
.article-content {
margin-top: 40px;
line-height: 1.6;
color: #4a5568;
}
.article-content h3 {
color: #2d3748;
margin-top: 25px;
}
.article-content ul {
padding-left: 20px;
}
.article-content li {
margin-bottom: 10px;
}
.info-tip {
font-size: 12px;
color: #718096;
margin-top: 4px;
}
function calculateValveCv() {
var q = parseFloat(document.getElementById('flowRate').value);
var sg = parseFloat(document.getElementById('specificGravity').value);
var p1 = parseFloat(document.getElementById('pressureIn').value);
var p2 = parseFloat(document.getElementById('pressureOut').value);
var errorDiv = document.getElementById('errorDisplay');
var resultDiv = document.getElementById('resultSection');
// Reset display
errorDiv.style.display = 'none';
resultDiv.style.display = 'none';
errorDiv.innerHTML = ";
// Validation
if (isNaN(q) || isNaN(sg) || isNaN(p1) || isNaN(p2)) {
errorDiv.innerHTML = "Please enter valid numbers for all fields.";
errorDiv.style.display = 'block';
return;
}
if (q <= 0) {
errorDiv.innerHTML = "Flow Rate must be greater than zero.";
errorDiv.style.display = 'block';
return;
}
if (sg = p1) {
errorDiv.innerHTML = "Inlet Pressure (P1) must be greater than Outlet Pressure (P2) to generate flow.";
errorDiv.style.display = 'block';
return;
}
// Calculation Logic
// Formula: Cv = Q * sqrt(SG / (P1 – P2))
var dp = p1 – p2; // Pressure Drop
var sqrtTerm = Math.sqrt(sg / dp);
var cv = q * sqrtTerm;
// Output Results
document.getElementById('cvResult').innerHTML = cv.toFixed(2);
document.getElementById('dpResult').innerHTML = dp.toFixed(2);
resultDiv.style.display = 'block';
}
What is Valve Flow Coefficient (Cv)?
The Valve Flow Coefficient, commonly denoted as Cv, is a standardized measure used in fluid dynamics to define the capacity of a control valve. It represents the number of US gallons of water at 60°F that can flow through a valve per minute with a pressure drop of 1 PSI across the valve.
Engineers use the Cv value to size valves correctly for specific systems. Selecting the correct Cv ensures that the valve can handle the required flow rate without creating excessive pressure drop or instability in the system.
The Calculation Formula
For non-compressible fluids (liquids) like water or oil, the formula to calculate the required valve Cv is:
Cv = Q × √(SG / ΔP)
- Q: Flow Rate in US Gallons per Minute (GPM).
- SG: Specific Gravity of the fluid (Water = 1.0).
- ΔP: Pressure Drop across the valve (Inlet Pressure – Outlet Pressure) in PSI.
Why is Specific Gravity Important?
Specific Gravity (SG) compares the density of the fluid to the density of water. Since heavier fluids are harder to push through a restriction, the density affects the flow coefficient.
- Water: SG = 1.0
- Gasoline: SG ≈ 0.7
- Industrial Oils: SG ≈ 0.8 – 0.9
- Brine/Seawater: SG ≈ 1.03
Interpreting the Results
Once you have calculated the Cv, you can compare it to manufacturer catalogs.
- Undersized Valve (Calculated Cv > Rated Cv): The valve is too small. It will restrict flow, causing a higher pressure drop than anticipated, potential cavitation, or inability to reach desired flow rates.
- Oversized Valve (Calculated Cv << Rated Cv): The valve is too large. It will operate near the closed position, leading to poor control sensitivity ("hunting") and premature wear on the valve seat.
A general rule of thumb for control valves is to select a valve where the calculated Cv falls between 60% and 80% of the valve's maximum rated Cv capacity.