Calculate liquid valve pressure drop from Cv, flow, and specific gravity, or solve Cv and flow with metric units, head loss, and pump-loss power.

Clean, incompressible liquid estimate for non-choked flow. Gas, steam, viscosity corrections, cavitation and piping effects require a full sizing method.

Water default = 1; replace for your liquid and temperature.

Pump efficiency

Blank omits pump input power. Enter pump efficiency, excluding the motor.

Related Calculators

Cv To Pressure Drop Formula

The following formula is used to calculate the pressure drop for a given flow rate, Cv, and specific gravity (for incompressible liquids, with Q in US GPM and ฮ”P in psi).

ฮ” P = ((Q) / (Cv))ยฒ ร— SG

Variables:

  • ฮ”P is the pressure drop
  • Q is the flow rate
  • Cv is the flow coefficient
  • SG is the specific gravity

To calculate the pressure drop, divide the flow rate by Cv, square the result, and then multiply by the specific gravity.

Cv to Pressure Drop Conversion Table (Q = 10 GPM, SG = 1.00)
Cv (unitless) Pressure Drop (psi)
1100.000
1.544.444
225.000
2.516.000
311.111
46.250
54.000
7.51.778
101.000
120.694
150.444
200.250
250.160
300.111
400.063
500.040
600.028
750.018
1000.010
1500.004
*Assumes flow rate Q = 10 GPM and water (SG = 1.00). Formula: ฮ”P (psi) = (Q / Cv)ยฒ ร— SG.

What is Cv?

Cv, or flow coefficient, is a measure of the capacity of a valve to pass fluid. It is defined as the flow rate of water in gallons per minute (GPM) at 60ยฐF that will pass through a valve with a pressure drop of 1 psi. The higher the Cv, the greater the flow rate through the valve for a given pressure drop.

How to Calculate Pressure Drop?

The following steps outline how to calculate the pressure drop.

  1. First, determine the flow rate (Q).
  2. Next, determine the flow coefficient (Cv).
  3. Next, determine the specific gravity (SG).
  4. Finally, calculate the pressure drop using the formula ฮ”P = (Q / Cv)ยฒ ร— SG.
  5. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Flow rate (Q) = 10 GPM

Flow coefficient (Cv) = 5

Specific gravity (SG) = 1. Thus ฮ”P = (10/5)ยฒ ร— 1 = 4 psi.