Imperial Gallons per Minute (imp-gal/min) to Gallons per second (gal/s) conversion

What is the Imperial Gallon per Minute?

The imperial gallon per minute is a unit of volumetric flow rate, measuring how many imperial (UK) gallons of liquid pass a point each minute. It is common in British and Commonwealth plumbing, pumping, and irrigation specifications.

Definition

One imperial gallon per minute equals one imperial gallon (4.54609 litres exactly) of volume flowing every 60 seconds:

$$1\ \text{imp-gal/min} = 0.0757682\ \text{l/s}$$

Because the imperial gallon is defined as exactly 4.54609 L, the exact relation is $4.54609 \div 60 = 0.0757681\overline{6}$ L/s. Note that the imperial gallon is about 20% larger than the US liquid gallon (3.785411784 L), so an imperial gpm is a larger flow than a US gpm.

Origin and History

The imperial gallon dates to the British Weights and Measures Act of 1824, which fixed it as the volume of 10 pounds of distilled water. It was redefined in 1976 (effective 1985) as exactly 4.54609 litres. The "per minute" flow rate arose naturally from waterworks and pump ratings, where minutes are a convenient interval for reading meters and sizing equipment.

Law and Notable Facts

The imperial gallon remains a legal unit in the United Kingdom and several Commonwealth nations, though the litre per second and cubic metre per hour are the SI-based standards for engineering. A tap flowing at 1 imp-gal/min delivers about 4.55 litres every minute; UK water-efficiency guidance often rates fittings in litres per minute, where 1 imp-gal/min corresponds to roughly 4.55 L/min.

Real-World Examples and Conversions

• A typical domestic kitchen tap or shower flows around 2 to 3 imp-gal/min (about 9 to 14 L/min).
• 1 imp-gal/min equals 60 imperial gallons per hour, or approximately 4.546 cubic metres per hour when multiplied out over an hour ($0.0757682 \text{ l/s} \times 3600 = 272.77$ litres/hour, i.e. 0.27277 m³/h).
• To convert to US gallons per minute, multiply by 1.20095: 1 imp-gal/min ≈ 1.201 US gpm.
• A small garden pump rated at 10 imp-gal/min moves about 0.758 litres per second, enough to fill a 200-litre water butt in roughly 4.4 minutes.

What is Gallons per Second (GPS)?

Gallons per second (GPS) is a measurement unit that tells you how many gallons of a liquid are moving past a certain point every second. It's a rate, showing volume over time. It is commonly used in the US to measure high volume flow rates.

How is GPS Formed?

GPS is formed by dividing a volume measured in gallons by a time measured in seconds.

$$GPS = \frac{Volume (Gallons)}{Time (Seconds)}$$

For example, if 10 gallons of water flow out of a pipe in 2 seconds, the flow rate is 5 gallons per second.

Conversions and Relationships

GPS can be converted to other common flow rate units:

• 1 Gallon ≈ 0.00378541 Cubic Meters
• 1 GPS ≈ 0.00378541 $m^3/s$
• 1 GPS ≈ 3.78541 Liters/second

Real-World Applications and Examples

• Firefighting: Fire hoses and sprinkler systems are often rated in GPS to indicate their water delivery capacity. A typical fire hydrant might deliver 500-1000 GPS.
• Pumping Stations: Large pumping stations, such as those used in water treatment plants or flood control, can have flow rates measured in thousands of GPS.
• Industrial Processes: Many industrial processes, such as chemical manufacturing or oil refining, involve the movement of large volumes of fluids, and GPS is used to measure flow rates in these processes.
• River Flow: While not a direct measurement, river discharge rates can be expressed in terms relatable to GPS (e.g., converting cubic feet per second to GPS for easier understanding).
  • The average flow rate of the Mississippi River is around 600,000 cubic feet per second, which is approximately 4.5 million GPS.
• Pool filling: Average garden hose has 5-10 gallons per minute. This means it will take around 30 minutes to fill a 150 gallon pool. This is 0.08 - 0.17 GPS.

Historical Context and Interesting Facts

While no single person is specifically associated with the "invention" of GPS as a unit, its use is tied to the development of fluid mechanics and hydraulics. Understanding flow rates became crucial with the rise of industrialization and the need to efficiently manage and transport fluids.

The measurement of flow rates dates back to ancient civilizations that developed aqueducts and irrigation systems. However, the standardization of units like GPS is a more recent development, driven by the need for precise measurements in engineering and scientific applications.