Understanding Water Meter Flow Rates (Q1, Q2, Q3, Q4) and R-Ratio

1. What is Water Meter Flow Rate？
1.1Flow Rate Calculation
1.2Testing Water Meter Flow Rates
2. What is R-Ratio in Water Meters?
2.1Calculating Flow Rates Using R-Ratio
2.2R80/R160/R200 Datasheet

What do a water meter’s Flow Rates (Q₁, Q₂, Q₃, Q₄) represent? What does R: Q3/Q1 stand for? Are you curious about this writing question? Let’s take a look at some water meter expertise.

What is Water Meter Flow Rate (Q₁, Q₂, Q₃, Q₄)？

Water meter flow rates are fundamental parameters that define a meter’s operational range and accuracy.

Q1 (Minimum Flow Rate)
Q₁, also known as Q_min, is the lowest flow rate at which the water meter is required to operate within the maximum permissible error (MPE). This flow rate is critical for detecting small leaks and measuring low water usage accurately.

Lowest flow rate at which the meter is to operate within the maximum permissible errors — ISO 4064

Q2 (Transitional Flow Rate)
Q₂, or Qt, is the flow rate that divides the meter’s range into two zones: the upper(Q₃) and lower(Q₁) flow rate zones. Each zone has its own MPE characteristics. Q₂ is always 1.6 times Q1, as per international standards.

Flow rate between the permanent flow rate and the minimum flow rate that divides the flow rate range into two zones, the upper flow rate zone and the lower flow rate zone, each characterized by its own maximum permissible errors — ISO 4064

Q3 (Permanent Flow Rate)
Q3, also referred to as Qn or Qp, is the highest flow rate within the rated operating conditions at which the meter is expected to function accurately over a long period. This is typically the flow rate used to designate the meter size.

Highest flow rate within the rated operating conditons at which the meter is to operate within the maximum permissible errors — ISO 4064

Q4 (Overload Flow Rate)
Q₄, or Q_max, is the highest flow rate at which the meter can operate for a short period while maintaining its metrological performance. It’s usually 1.25 times Q₃.

Highest flow rate at which the meter is to operate for a short period of time within the max imum permissible errors, while maintaining its metrological performance when it is subsequently operating within the rated operating conditions — ISO 4064

Additional Flow Rate Terminology:

Qs (Starting Flow Rate): The flow rate at which the meter’s pointer begins to move.

Qx (Combination Meter Changeover Flow Rate): Applicable to compound meters, it’s the flow rate at which the larger meter stops or starts operating.

Flow Rate Calculation:

The volumetric flow rate (Q) is calculated as Q = dV/dt, where V is the volume of water and t is the time taken for this volume to pass through the meter.

Testing Water Meter Flow Rates:

Using a DN15 water meter as an example, here’s how different flow rates are typically tested:

Starting Flow Rate: Gradually increase flow from zero until continuous pointer movement is observed.
Minimum Flow Rate: Pass 1L of water at Q₁(Minimum Flow Rate) and calculate the error.
Transitional Flow Rate: Pass 2L of water at Q₂(Transitional Flow Rate) and calculate the error.
Permanent Flow Rate: Pass 50L of water at Q₃(Permanent Flow Rate) and calculate the error.
Overload Flow Rate: Pass 100L of water at Q₄ (Overload Flow Rate)and calculate the error.

Note: Water volumes may be adjusted based on the precision of the water meter testing bench.

What is R-Ratio in Water Meters?

The R-ratio, a crucial indicator of water meter accuracy, is the permanent flow rate (Q₃) ratio to the minimum flow rate (Q₁). It effectively represents the meter’s measuring range and precision. R=Q₃/Q₁

Calculating Flow Rates Using R-Ratio:

Let’s consider an example of a meter with R160 accuracy class

Q₃(Permanent Flow Rate) = 2,500 l/h:
Q₄ (Maximum Flow Rate) = 1.25 × Q3 = 3,125 l/h
Q₁ (Minimum Flow Rate) = Q₃ / 160 = 15.625 l/h
Q₂ (Transitional Flow Rate) = 1.6 × Q₁ = 25 l/h

R80/R160/R200 Datasheet

크기	mm	Dn15	Dn20	Dn25	Dn32	Dn40	Dn50
		R80
Q4	l/h	3,125	5,000	7,875	12,500	20,000	31,250
Q3	l/h	2,500	4,000	6,300	10,000	16,000	25,000
Q2	l/h	50	80	126	200	320	500
Q1	l/h	31.25	50	78.75	125	200	312.5

크기	mm	Dn15	Dn20	Dn25	Dn32	Dn40	Dn50
		R160
Q4	l/h	3,125	5,000	7,875	12,500	20,000	31,250
Q3	l/h	2,500	4,000	6,300	10,000	16,000	25,000
Q2	l/h	25	40	63	100	160	250
Q1	l/h	15.63	25	39.375	62.5	100	156.3

크기	mm	Dn15	Dn20	Dn25	Dn32	Dn40	Dn50
		R200
Q4	l/h	3,125	5,000	7,875	12,500	20,000	31,250
Q3	l/h	2,500	4,000	6,300	10,000	16,000	25,000
Q2	l/h	20	32	50.4	80	128	200
Q1	l/h	12.5	20	31.5	50	80	125

Please note that these are the results when measured according to the standard. If the measurement is performed under non-standard conditions, the results will be different. For example, testing a vertically installed water meter in a horizontal test bench will result in reduced accuracy and a wider error range.

BMAG offers R80-R400 water meters to meet your needs.

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