What Is a Flow-Limiting Cartridge or Automatic Balancing Valve?

RL Deppmann
January 26, 2017
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The flow-limiting cartridge is the heart of the automatic balancing valve and lets the valve act as the maximum flow rate controller.  This maximum flow rate is preset at the factory and the flow-limiting cartridge will limit the flow rate to +/- 5% even when system pressures change. This is different from a manual balancing valve, where the flow rate will vary with system pressure changes.

Flow-limiting cartridge

The stainless steel design of the cartridge body and internal spring resists corrosion and is the industry standard material. The parabolic shaped ports are cut by a computer-guided laser for 100% consistency to provide a smooth flow curve across the spring range.

How to Select Flow-Limiting Cartridge Spring Ranges

There are multiple spring ranges to choose from, and it is best to be in the middle half of the yellow range in the picture below.

Diagram showing cartridge at various flow rates

Common ranges:

  • 1-14 PSID
  • 2-32 PSID (Most HVAC applications use this)
  • 4-57 PSID
  • 8-128 PSID

Ranges for special flow rates:

  • 1-20 PSID
  • 4-20 PSID
  • 8-32 PSID
  • 3-18 PSID
  • 5-32 PSID

You will need to ensure that you select the proper range for your application to stay within the spring range. A few special applications are given below.

  • Boiler feed or condensate pump
  • Terminal units close to high-head pumps or very distant terminal units

Spring ranges can be mixed and matched in a system, depending on proximity to pumps. If you have questions on choosing the proper spring range, please contact your Deppmann salesperson.

How to Verify the Flow Rate

A balance contractor will most likely verify the flow rate of each valve in the system as part of the test and balance portion of the project. They will use the method below to check the flow rate. The flow rate can also be checked at any time if there may be a heating or cooling deficiency.

  1. Using a gauge with a needle, read out both ports of the valve.
  2. Determine which PSID control range the valve is set for. Nine ranges are available. (Note: the fourth number of the valve model denotes the control range. #3522 means the valve has a 2-32 cartridge.)
  3. If the differential pressure (high pressure minus low pressure) read across valve is within the spring range, you are within +/- 5% of flow-limiting cartridge flow rate. If not, use the table below to calculate flow rate as it becomes a fixed orifice.
  4. Use the following formula to calculate flow rate:

Flow rate formula and table for calculations

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