U.S. Distributor of Quick Connect Coupling Systems
The Cv value of a coupling is defined as the volume of water in US gallons per minute that will flow through the coupling with a pressure drop of 1 psi.
Cv values are often listed in manufacturer's catalogs because it is a convenient way of characterizing the flow capacity of the part. For convenience, flow capacities for the most commonly used couplings are presented on graphs. Just follow the link on the table below. Pressure drops for all couplings can be quickly calculated using the formulas under the table. Calculated pressure drops are estimates only.
| LP Series | KL Series | UF Series | MD Series | HP Series |
|---|---|---|---|---|
| 06-003 | KL-006 | UF-006 | SG-006 | 02-003 |
| LP-002 | KL-012 | UF-007 | MD-006 | HP-004 |
| LP-003 | KL-030 | UF-012 | MD-007 | HP-006 |
| 07-003 | UF-019 | MD-012 | HP-010 | |
| LP-004 | UF-032 | MD-019 | HP-016 | |
| LV-004 | MD-025 | HP-020 | ||
| LP-006 | MD-032 | HP-032 | ||
| SP-006 | MD-050 | HP-050 | ||
| LP-007 | ||||
| SP-009 | ||||
| LP-012 | ||||
| LP-019 | ||||
| LP-032 | ||||
| LP-050 |
Approximate specific gravities of some common liquids are:
| Acetone = 0.78 | Benzene = 0.88 |
| Ethanol = 0.79 | Kerosene = 0.8 |
| Water (fresh) = 1.00 | Water (salt) = 1.03 |
An HP-010 coupling has a Cv of 1.85 flowing 8 gpm of benzine, the pressure drop will be approximately: 0.88 x (8/1.85)2 = 0.88 x 4.322 = 16.5 psi
Note: this relationship is widely published and commonly used in industry. It provides reasonable estimates liquids with viscosities similar to water. Please contact us for estimates for other liquids. Also check data on specific couplings for maximum flow rate restrictions
Calculating pressure drops for gases is much more complicated because of the compressibility of gases.
When the outlet pressure is greater than 0.5 x inlet pressure:
Q = 963 x Cv x ((p1 - p2) x (p1 + p2))½
(SG x T)½
When the outlet pressure is less than 0.5 x inlet pressure:
Q = 963 x Cv x 0.87 x p1
(SG x T)½
Approximate specific gravities of some common gases are:
| Air = 1.0 | Ammonia = 0.6 | Argon = 1.38 | Butane = 2.1 | CO2 = 1.53 |
| Chlorine = 2.49 | Ethylene = 0.97 | Helium = 0.14 | Hydrogen = 0.07 | H2S = 1/19 |
| Methane = 0.55 | Nitrogen = 0.97 | Oxygen = 1.15 | Propane = 1.56 | SO2 = 2.21 |
Gas formulae are suitable for gas temperatures between 30 and 150°F. All pressure drop calculations of this type are approximations. Fluid properties can be very significantly affected by pressure and temperature.