Imperial Gallons per Minute (imp-gal/min) to Pints per second (pnt/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 the pint per second?

Pints per second (pint/s) measures the volume of fluid that passes a point in a given amount of time. It's a unit of volumetric flow rate, commonly used for liquids.

Understanding Pints per Second

Pints per second is a rate, indicating how many pints of a substance flow past a specific point every second. It is typically a more practical unit for measuring smaller flow rates, while larger flow rates might be expressed in gallons per minute or liters per second.

Formation of the Unit

The unit is derived from two base units:

• Pint (pint): A unit of volume. In the US system, there are both liquid and dry pints. Here, we refer to liquid pints.
• Second (s): A unit of time.

Combining these, we get pints per second (pint/s), representing volume per unit time.

Formula and Calculation

Flow rate ($Q$) is generally calculated as:

$Q = \frac{V}{t}$

Where:

• $Q$ is the flow rate (in pints per second)
• $V$ is the volume (in pints)
• $t$ is the time (in seconds)

Real-World Examples & Conversions

While "pints per second" might not be the most common unit encountered daily, understanding the concept of volume flow rate is crucial. Here are a few related examples and conversions to provide perspective:

• Dosing Pumps: Small dosing pumps used in chemical processing or water treatment might operate at flow rates measurable in pints per second.
• Small Streams/Waterfalls: The flow rate of a small stream or the outflow of a small waterfall could be estimated in pints per second.

Conversions to other common units:

• 1 pint/s = 0.125 gallons/s
• 1 pint/s = 7.48 gallons/minute
• 1 pint/s = 0.473 liters/s
• 1 pint/s = 473.176 milliliters/s

Related Concepts and Applications

While there isn't a specific "law" tied directly to pints per second, it's essential to understand how flow rate relates to other physical principles:

• Fluid Dynamics: Pints per second is a practical unit within fluid dynamics, helping to describe the motion of liquids.

• Continuity Equation: The principle of mass conservation in fluid dynamics leads to the continuity equation, which states that for an incompressible fluid in a closed system, the mass flow rate is constant. For a fluid with constant density $\rho$, the volumetric flow rate $Q$ is constant. Mathematically, this can be expressed as:

  $A_1v_1 = A_2v_2$

  Where $A$ is the cross-sectional area of the flow and $v$ is the average velocity. This equation means that if you decrease the cross-sectional area, the velocity of the flow must increase to maintain a constant flow rate in $m^3/s$ or $pint/s$.

• Hagen-Poiseuille Equation: This equation describes the pressure drop of an incompressible and Newtonian fluid in laminar flow through a long cylindrical pipe. Flow rate is directly proportional to the pressure difference and inversely proportional to the fluid's viscosity and the length of the pipe.

  $Q = \frac{\pi r^4 \Delta P}{8 \eta L}$

  Where:

  • $Q$ is the volumetric flow rate (e.g., in $m^3/s$).
  • $r$ is the radius of the pipe.
  • $\Delta P$ is the pressure difference between the ends of the pipe.
  • $\eta$ is the dynamic viscosity of the fluid.
  • $L$ is the length of the pipe.