Step-by-Step Guide

Understanding Flow Sensor Types and Technologies

When selecting a flow sensor for your irrigation project, you'll be choosing between three main types of flow sensor technologies, each with distinct characteristics and applications.

The T-style flow sensor has been the industry standard for many years. These are the sensors you'll typically inherit on properties that already have flow monitoring installed. Examples include Industrial Scientific sensors and Creative Sensor Technology (CST) products. T-style sensors have been widely used throughout the industry and serve as a reference point when comparing newer technologies.

The hydrometer-style flow sensor, known as the WeatherTRAK Flow3, combines three devices into one unit: a water meter, a master valve, and a flow sensor. This design makes it easier to install and is considered the workhorse of the WeatherTRAK flow sensor lineup.

The ultrasonic-style flow sensor uses a different measurement technology than traditional impeller-based sensors. Instead of mechanical impellers, ultrasonic sensors use sound waves to measure water flow. This technology provides significantly higher resolution and gives visibility into flow ranges that other types of flow sensors cannot accurately manage.

Flow Range Specifications by Sensor Type and Size

Every flow sensor comes in a variety of sizes, typically ranging from 1.5 inches to 4 inches. Each size has its own unique specifications with two critical variables: the minimum gallons per minute (GPM) it can accurately measure and the maximum GPM it can handle.

For T-style flow sensors, a 4-inch device starts measuring flow accurately at approximately 40 gallons per minute. This relatively high minimum flow rate can be a limitation for certain applications.

The Flow3 hydrometer-style sensors offer improved low-flow detection. A 4-inch Flow3 device starts measuring flow at approximately 21 gallons per minute, which is nearly half the minimum of a comparable T-style sensor.

The ultrasonic flow sensors provide the highest resolution. A 4-inch iron ultrasonic sensor can start measuring flow at less than 1 gallon per minute, while a 4-inch HD plastic ultrasonic sensor begins accurate measurement at approximately 4 gallons per minute. This high-resolution data allows water managers to identify inefficiencies and detect issues that would be invisible to other sensor types.

Common Pitfalls in Flow Sensor Selection

The most common mistake when selecting a flow sensor is matching the sensor size to the meter size, backflow size, or master valve size. Many installers assume that if a system has a 1-inch meter and 1-inch backflow preventer, the flow sensor should also be 1 inch. This approach often leads to poor performance.

The correct approach is to understand what the irrigation system is actually doing—specifically, the flow ranges it operates within—and then select a flow sensor that can accurately measure those ranges. The sensor size should be based on performance requirements, not simply on matching pipe dimensions.

A specific example of this problem occurs with 2-inch sensors that have a minimum flow threshold of 10 gallons per minute. Many modern irrigation applications, such as MP Rotator stations, tree stations, and bubbler stations, operate correctly at less than 10 gallons per minute. When these stations run, the flow sensor cannot detect them accurately, forcing irrigation teams to turn off flow monitoring for those stations entirely. This results in losing all the performance benefits and features that flow monitoring provides for those zones.

Analyzing System Requirements Before Selection

When choosing a flow sensor, begin by analyzing the actual performance characteristics of the irrigation system rather than relying solely on design specifications.

1. Identify the flow range of all stations in the system. Determine the lowest GPM any station will produce and the highest GPM any station will produce.

2. Consider the available installation space. Different flow sensor technologies have different straight pipe requirements. T-style and HD plastic sensors typically require specific distances of straight pipe before and after the sensor (often expressed as multiples of pipe diameter, such as 10 times the diameter upstream and 5 times downstream). If you cannot meet these straight pipe requirements, a hydrometer-style sensor may be the better choice, as it has more flexible installation requirements.

3. Evaluate water pressure conditions. Water pressure can force you to choose brass or cast iron sensors over PVC options. PVC sensors are rated for specific pressure tolerances and are suitable for different applications (outdoor versus indoor). In areas where water pressure exceeds 150 PSI, pressure regulation or upgraded sensor materials may be necessary to prevent equipment failure.

4. Assess water quality. In areas with clean water sources, including relatively clean recycled water, standard materials are typically sufficient. However, water quality can affect sensor selection and longevity.

Selecting Between Standard and High-Resolution Sensors

The choice between traditional T-style sensors (such as the 228 series) and newer high-resolution options depends on your system's specific needs.

Traditional sensors like the 228 T-style and Creative Sensor Technology (CST) products have been industry standards for 10 to 15 years. They provide reliable performance within their specified ranges and are often selected when the system's flow ranges fall comfortably within their capabilities and when proper installation space is available.

High-resolution sensors, particularly ultrasonic models, should be selected when you need to monitor low-flow stations accurately, when you want to detect small leaks or inefficiencies, or when you need comprehensive data across a wide range of flow rates. The improved resolution allows you to monitor stations that would be below the detection threshold of traditional sensors.

Retrofit Considerations: FlowHD Plastic Inserts

When retrofitting existing systems that already have T-style flow sensor installations, the FlowHD plastic insert offers a way to upgrade to higher-resolution sensing without completely replacing the installation.

The FlowHD plastic sensor can insert into existing 228-series T-style installations. Early versions had some compatibility issues with existing tees, but these have been resolved. The FlowHD insert provides better performance than traditional T-style sensors, particularly for low-flow detection.

When deciding between keeping a traditional sensor and upgrading to a FlowHD insert during retrofit projects, the improved performance of the FlowHD typically makes it the preferred choice, especially when you need to monitor stations operating at lower flow rates.

Installation Requirements and Common Mistakes

Proper installation is critical for accurate flow sensing. Different sensor technologies have different installation requirements, and failure to meet these requirements is a common source of poor performance.

T-style and HD plastic sensors require specific straight pipe distances before and after the sensor. These are typically specified as multiples of the pipe diameter. Failure to provide adequate straight pipe can result in turbulent flow that affects measurement accuracy.

Common installation errors include using the wrong wire type, making improper wire splices, and entering incorrect K-factor and offset values in the controller. Each of these mistakes can compromise the accuracy of flow data.

The principle of "good data in, good data out" applies throughout the installation and configuration process. Respecting the equipment specifications, setting correct baselines, and properly configuring mainline thresholds in the controller will result in better system performance.

Verifying Flow Sensor Accuracy

After installation, verify that your flow sensor is reading accurately by comparing it against the mechanical water meter installed by the water district.

1. Confirm that the correct make, model, size, K-factor, and offset values are entered in the controller.

2. Run a station and compare the flow rate shown by the flow sensor against the reading from the mechanical water meter.

3. Verify that the flow sensor readings align with your expectations based on the system design. If your lowest station flow is 17 GPM and your highest is 55 GPM, ensure your sensor can accurately measure across that entire range.

Configuring Flow Monitoring in WeatherTRAK

Once you've selected and installed the appropriate flow sensor, proper configuration in the WeatherTRAK controller is essential to avoid false alerts and ensure accurate monitoring.

When a flow sensor's minimum detection threshold is higher than some stations' flow rates, you must exclude those low-flow stations from no-flow and low-flow alerts. For example, if you have a 2-inch flow sensor with a 10 GPM minimum and stations that operate at 7 GPM, those stations must be excluded from flow monitoring. Otherwise, the controller will detect zero flow intermittently (when the sensor misses pulses) and generate false no-flow alerts.

This exclusion requirement represents a significant limitation, as you lose monitoring capabilities for those stations. Selecting a flow sensor with a lower minimum threshold eliminates this problem and allows comprehensive monitoring across all stations.

Understanding High-Flow Limitations

While low-flow limitations receive significant attention, high-flow limitations are equally important and can cause serious problems if ignored.

Every flow sensor has a maximum GPM rating. Exceeding this maximum can result in inaccurate readings or equipment damage. This is particularly important in systems with looped mainlines or multiple points of connection.

For example, a system with two 2-inch points of connection and a 4-inch mainline might seem suitable for 2-inch flow sensors. However, in a looped configuration, either point of connection could potentially flow 120 to 130 GPM during certain operating conditions. A 2-inch flow sensor typically maxes out around 95 GPM, making it inadequate for this application despite appearing correctly sized based on the connection diameter.

Always analyze the maximum possible flow through your sensor location, not just the typical or average flow.

When to Relearn Flow

Flow learning establishes baseline flow rates for each station. Relearning is necessary whenever conditions change that would affect these baselines.

After preventive maintenance inspections (PMIs) and wet checks: Once you've identified and repaired all issues, performed a complete system inspection, confirmed all stations are operating correctly, verified no valves are passing water, and ensured the system is in optimal condition, relearn flow to establish accurate baselines that reflect the system's proper operation.

After station modifications: Relearn flow at the station level whenever you change nozzles, convert between sprinkler types (such as changing from Rain Bird MPR rotators to Hunter MP Rotators), modify the irrigation method, or alter the precipitation rate of a station or system.

When investigating anomalies: After learning flow, review the results for each station. If you see two rotor stations with the same precipitation rate irrigating the same turf area under the same conditions, but one shows significantly higher flow than the other, investigate before accepting the learned values. Verify the head count, check for blown heads by running the station with flow monitoring off, and look for other issues that might explain the discrepancy. Make any necessary repairs, then relearn flow for those stations.

Choosing Between Auto and Manual Flow Alert Response

WeatherTRAK controllers can be configured to respond to flow alerts either automatically or manually. The appropriate choice depends on your site conditions and management capabilities.

Automatic response is recommended when you have quality technicians on site, proper training programs in place, and reliable supervision. With automatic response, when a flow alert occurs, the controller will continue to check and reattempt that station. At minimum, with monitoring intervals of 3 to 6 minutes, you'll guarantee at least some water delivery. Even if there's a problem, the turf receives some irrigation, which can sometimes mask issues but prevents complete irrigation failure.

Manual response requires human intervention to clear alerts before irrigation resumes. This is more appropriate when you don't have the right supervisors or trained personnel in place, when labor availability is an issue, or when job sites are remote. The risk with manual response is that if alerts aren't cleared promptly, stations won't irrigate. A mainline break, for example, could stop all irrigation until someone manually clears the alert, potentially causing landscape damage due to missed irrigation cycles. Additionally, if you're picking up higher depletion rates and starting to experience depletion issues, manual response can compound the problem.

If you have visibility into system operations, adequate labor resources, and skilled personnel, automatic response is typically the better choice. Without proper supervision and resources, manual response provides more control but requires diligent alert management.

Setting Flow Alert Thresholds

Configuring appropriate high-flow and low-flow alert thresholds requires understanding your system's flow ranges and considering the accuracy limitations of your flow sensor.

A common approach is to use a percentage-based offset, such as ±30%. However, this percentage should not be applied uniformly across all stations without consideration of actual GPM values.

For a station with a 10 GPM baseline, a 30% threshold allows flow between 7 and 13 GPM (a 3 GPM swing). This range may be appropriate given sensor accuracy and normal system variation.

For a station with a 70 GPM baseline, a 30% threshold allows flow between 49 and 91 GPM (a 21 GPM swing). This wide range means three turf rotors could be run over by a truck without triggering an alert—an unacceptable situation for most water managers.

The solution is to start with percentage-based baselines (20%, 30%, or 40% depending on your comfort level), then review each station individually and adjust thresholds using user-entered values where appropriate. The more time you spend understanding your system, and the more pressure regulation you have throughout the system, the easier it becomes to manage these thresholds effectively and the tighter you can set them for better problem detection.

Alternative Connection Solutions

When traditional hardwired connections between the flow sensor and controller are not feasible, several alternative solutions exist.

Flow Link technology uses signal decoding to borrow existing station wires rather than requiring new trenching. Flow Link pulses the signals from the master valve, flow sensor, and station wire back to the controller through an existing healthy wire connection, then decodes these signals at the controller. To use Flow Link, trench from the point of connection to the nearest working valve, tone out the wire to confirm it's a good connection, then install the Flow Link system. This solution works even when traditional trenching is feasible but cost-prohibitive due to distance—in some cases, Flow Link is more economical than running new wire over long distances. Ensure your station wire is healthy, verify you're within manufacturer specifications, and use proper heat-shrink splices for reliable connections.

OptiFlow controllers can be installed at remote locations where electricity is available but communication wiring is not. An OptiFlow controller at the point of connection can monitor the flow sensor locally and communicate that data back to the main system, eliminating the need for a direct wire connection to the primary controller.

Wireless flow solutions exist but come with significant limitations. Most wireless flow systems operate on 900 MHz frequency and face challenges including line-of-sight requirements, total distance limitations, and interference from vehicles and other obstacles. A FedEx truck driving between the transmitter and receiver can disrupt the signal. Due to these reliability concerns, hardwired solutions or Flow Link technology are generally preferred over true wireless options.

Video Walkthrough

Video originally published April 2021.

If you have questions, here are 3 ways to get answers:

1. Search within this WeatherTRAK knowledgebase

2. Visit the WeatherTRAK support page

3. Call 800-362-8774 or email support@hydropoint.com, hours are Mon-Fri 3:00 AM – 6:00 PM PT and Sat 9:00 AM – 2:00 PM PT.