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Volume Flow Rate of KM Drain Pans

Drain Fittings

Volume Flow Rate of KM Drain Pans

Killarney Metals is dedicated to providing solutions that help. This resource is admittedly technical. Please know our intention is to assist you in selecting the correct drain fitting for your specific application. To get started, use the formula below to find the Flow Rate of Liquid (water) draining from a container (drain pan).

*Note: Unit measurements included are in inches and seconds. You can use other units for this formula; just make sure you are converting the units as needed.

V̇ : Volume Flow Rate (in3/s)

  • ↳ V̇ = Cd A (2 g H)½

Cd: Discharge Coefficient

  • ↳ Cd = Cc Cv
  • ↳ Cd = 0.79 (for our pans, with water as the liquid)

Cc : Contraction Coefficient

  • ↳ Cc = sharp edge aperture: 0.61, sharp edge aperture with tube 0.81, well-rounded aperture: 0.98

Cv : Velocity Coefficient (depends on liquid)

  • ↳ Cv = water: 0.97

A : Area of Aperture (in2) (area of the circle drain opening in this case)

  • ↳ A = π r2

r : Radius of a Circle (in)

  • ↳ r = half of the diameter of a circle

g : Acceleration of Gravity (in/s2)

  • ↳ g = 386 in/s2

H : Height of Liquid (in) (volume flow rate is calculated based on the current height of the liquid)

  • Lateral Aperture Drain Pan Configuration
  • ↳ Lateral Apertures: For drains on the side of the pan, use the distance from the base of the pan to the bottom of the drain hole. Because the flow rate depends on the current height of the liquid, we are calculating the most common height at which liquid will flow from the drain pan: at the bottom of the drain hole once the liquid fills up to it. This point is relatively the same for all of our lateral aperture drain pans at about .6” from the base of the pan.
  • Base Aperture Drain Pan Configuration
  • ↳ Base Apertures: The fittings used on a base aperture drain pan will extend vertically from the base of the pan at a specific height, dependent on the fitting used. Our fittings will extend ⅝” - 1” up from the base. This is the height at which the water will fill up to before going over and into the bottom drain.
  • ↳ *Note: The flow rate will increase as the water height increases.

Once you have made your calculations, convert the resulting Volume Flow Rate from cubic inches/second (in3/s) to gallons/minute (GPM) for a standard flow rate representation using a liquid unit of measurement.

Below are the four drain fitting options we offer:

3/4” Drain Coupling
1” Drain Fitting
1” Drain Coupling
1 1/4” Drain Coupling

*Note: The threaded end of the fitting will generally always be on the inside of the pan. KM-00663 is an exception to that. With the non-threaded side being so short in length, it would be more advantageous to use this fitting on a base aperture (with the short end on the inside) than any of the other fittings. The short end likely wouldn’t impede on any appliances in the pan as much as another fitting might. KM-00663 is not a coupling or an adaptor, but if the threaded end is used on the outside (or underside) of the pan, then a hose can be attached to it for draining.

Using these measurements we are able to determine the GPM for each drain, based on where the aperture is placed on the pan-- lateral or base. Please refer to the table below for these results.

Drain FittingDescriptionLateral Aperture GPMBase Aperture GPM
KM-04591 ¾" - ¾" Coupling 1.94 GPM 1.98 GPM
KM-00663 1" Fitting 3.49 GPM 1.59 GPM
KM-00662 1" - 1" Coupling 3.49 GPM 4.5 GPM
KM-04592 1¼" - 1¼" Coupling 5.43 GPM 6.07 GPM

According to Compact Alliance, the Average Flow GPM for washing machines is 2.0 GPM. The average for sinks is 1.5 GPM. This means you can rest assured when using a Killarney Metals drain pan for your average household applications.

As always, if you have any questions, please feel free to Contact Us or check out our FAQ!

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