# Engineering Calculations

## Common Engineering Calculations

We have compiled a list of liquid flow and air flow formulae to allow users to calculate solenoid valve flow and pressure drop which are the key factors when choosing any solenoid, angle seat or process valve. This helps make sure systems will have sufficient flow, the correct valve size so avoiding additional costs or valve failure.

A complete media viscosity cross reference guide as liquid media thickness can be measured in various formats so in this way engineers will avoid installing a solenoid or process valve that would not be compatible with the media being controlled.

### Liquid Flow Formulae

Q=Kv x Square Root of (DP/d) or DP=d(Q/Kv)2

• Q = Flow L/Min
• DP = Pressure Drop (Bar)
• d = density i.e. Water = 1
• Kv = flow factor coefficient of valve (L/Min)
• (N.B. DP 5 - 10% is preferred)

### Air Flow Formulae

Where DP less than P1/2 : Q=1.69Kv x Sq Rt (DPxP2)

Where DP equal to P1/2 : Q = 0.84Kv x P1

• Q = Flow (M3 Hr)
• DP = Pressure Drop (Bar)
• Kv = flow factor coefficient of valve (M3 Hr)
• P1 = inlet pressure + 1 bar
• P² = absolute downstream pressure =(inlet pressure + 1 bar - DP)
Saybolt Universal (seconds) Engler (degrees) Kinematic (centistokes) Saybolt Universal (seconds) Engler (degrees) Kinematic (centistokes)
- 1.05* 1.5 103 3.0 21.3
34 1.15* 2.5 109 3.2 22.8
37 1.25* 3.4 115 3.4 24.1
40 1.3* 4.2 125 3.7 26.7
42 1.4* 5.0 137 4.0 29.2
45 1.45* 5.7 148 4.3 31.7
50 1.6* 7.5 160 4.6 34.2
57 1.8* 9.4 171 4.9 36.8
62 1.9 11.0 183 5.2 39
68 2.1 12.6 205 5.9 44
74 2.2 14.2 242 7 50
79 2.4 15.5 256 7.3 55
85 2.6 17.0 285 8.1 62
92 2.7 18.6 313 8.9 68
98 2.9 20.0 342 9.8 74

#### Pressure

• 1 Bar = 14.5 PSI
• 1 Bar = 100 kPa (Kilopascal)
• 1 PSI = 6.9 kPa
• 1 Kg/cm² = 0.98 Bar
• 1 Atmosphere = 1.013 Bar
• 1 Inch Water gauge = 2.49 mbar
• 1 mm Mercury = 1.33 mbar
• 1 Ton / in² = 154 Bar

#### Volume

• Gallon (UK) = 4.54 Litres
• Gallon (USA) = 3.79 Litres
• Pint (UK) = 0.57 Litres
• Pint (USA) = 0.47 Litres
• Fluid Once (UK) = 28.4 cm³
• Fluid Once (USA) = 29.6 cm³

#### FLOW

• 1 CFM = 0.472 Litres a second
• 1 CFM = 0.000472 m³/Sec
• 1 CFM = 28.32 Litres a minute

#### Temperature

From °F to C° : Add 40 then multiply by 5 then divide by 9 then -40

From C° to F° : Multiply by 9 then –40 divide by 5 then +40

#### Length

• 1 Inch = 25.4mm
• 1/16” Inch = 1.5875mm
• 1 foot = 0.305 Meters
• 1 Mile = 1.609 Kilometre

#### What is the Kv Value?

Kv value is the metric measure for the flow of a valve. It is defined as: The volume flow in cubic metres per hour of water at a temperature of between 5° and 40° Celsius with a pressure drop across the valve of 1 bar.

#### What is the Cv Value?

Cv is the imperial measure for the flow of a valve. It is defined as: The volume flow in US gallons per minute of water at a temperature of 60° Fahrenheit with a pressure drop across the valve of 1 psi.

#### What is the Qn Value?

Qn value is used in pneumatics to define the flow of a valve. It is defined as: The volume flow in litres per minute of air at a temperature of 20° Celsius, with an input pressure of 6 bar and a pressure drop across the valve of 1 bar.

#### Conversion : Kv, Cv & Qn

• Kv = 0.86 x Cv
• Kv = Qn / 1078
• Cv = Kv / 0.86
• Cv = Qn x 0.0008
• Qn = Kv x 1078
• Qn = Cv / 0.0008