# Useful Formulas

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# Convert Kilowatts to Horsepower KW to HP

Posted by **Ed Powell** on

KILOWATTS per HP = .746 watts

Multiply horsepower 25 by .746

*25HP compressor is 18KW*

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# Convert Kilowatts to Horsepower KW to HP

Posted by **Ed Powell** on

# Conversion of scfm to acfm

Posted by **Ed Powell** on

ACFM = SCFM x x Ps – (RHs x PVs) Where: Pb – (RHa x PVa) Ta Ts x Pb Pa

Where:

Ps = Standard pressure (PSIA)

Pb = Atmospheric pressure – barometer (PSIA)

Pa = Actual pressure (PSIA)

RHs = Standard relative humidity

RHa = Actual relative humidity

PVs = Saturated vapor pressure of water at standard temperature (PSI)*

PVa = Saturated vapor pressure of water at actual temperature (PSI)*

Ts = Standard temperature (°R) NOTE: °R = °F+460

Ta = Actual temperature (°R)

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# Conversion of scfm to acfm

Posted by **Ed Powell** on

ACFM = SCFM x x Ps – (RHs x PVs) Where: Pb – (RHa x PVa) Ta Ts x Pb Pa

Where:

Ps = Standard pressure (PSIA)

Pb = Atmospheric pressure – barometer (PSIA)

Pa = Actual pressure (PSIA)

RHs = Standard relative humidity

RHa = Actual relative humidity

PVs = Saturated vapor pressure of water at standard temperature (PSI)*

PVa = Saturated vapor pressure of water at actual temperature (PSI)*

Ts = Standard temperature (°R) NOTE: °R = °F+460

Ta = Actual temperature (°R)

#### Read more

# Heat and Horsepower

Posted by **Ed Powell** on

rejected heat from an air-cooled compressor is equal to total machine horsepower x 2,545 BTU per hour

Example: 50 HP compressor with 3 HP fan motor will produce:

53 HP x 2,545 = 134,885 BTU per hour

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# Heat and Horsepower

Posted by **Ed Powell** on

rejected heat from an air-cooled compressor is equal to total machine horsepower x 2,545 BTU per hour

Example: 50 HP compressor with 3 HP fan motor will produce:

53 HP x 2,545 = 134,885 BTU per hour

#### Read more

# Pressure Drop and Horsepower

Posted by **Ed Powell** on

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# Pressure Drop and Horsepower

Posted by **Ed Powell** on

# Compressor Pump Up Time (Minutes)

Posted by **Ed Powell** on

= V (tank size) x (final pressure – initial pressure)

7.48 x atmospheric pressure x pump delivery (CFM)

Example: 7.5 HP compressor rated at 24 CFM with an 80 gallon tank, unit starts at 100 PSI and turns off at 150 PSI

80 gallons x (150 PSI – 100 PSI) = 4000 = 1.51 minutes

7.48 x 14.7 x 24 CFM 2638

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# Compressor Pump Up Time (Minutes)

Posted by **Ed Powell** on

= V (tank size) x (final pressure – initial pressure)

7.48 x atmospheric pressure x pump delivery (CFM)

Example: 7.5 HP compressor rated at 24 CFM with an 80 gallon tank, unit starts at 100 PSI and turns off at 150 PSI

80 gallons x (150 PSI – 100 PSI) = 4000 = 1.51 minutes

7.48 x 14.7 x 24 CFM 2638