Portability and accurate sewer flow

FLOW MEASUREMENT in partially full pipes and open channels has always been hard. Unless it is possible to stop the flow and install a primary device, such as a flume or a weir, flow measurement in sanitary and storm sewers and industrial outfalls has been an interesting proposition at best. Recently the long-running lawsuit between what was Isco (now part of Teledyne) and what was Marsh-McBirney (the product line is now part of Hach Danaher) was ended when the judge noted that neither product was as good as its manufacturer stated. Independent testing on many flowmeter models for partially filled pipes has shown performance deviations from specifications by as much as 40% of indicated flow rate.

The problems these flowmeters have faced range from questionable theory to real maintenance issues with coating and plugging. The point velocity and line velocity theories that imply that a velocity measured near the pipe wall can be substituted for the average velocity throughout the cross section of the pipe have been significantly challenged. In addition, the need to install a sensor that sits in the invert of the pipe or that hangs down inside the pipe from the top has made installation difficult and dangerous, and provided a place for rags and other debris to collect, thus increasing the errors in measurement.

FIGURE 1: SCOPES OUT FLOW

Portability and accuracy join in battery operated wireless meter.

Flowmeter suppliers have tried for years to remedy these problems with little success. With the exception of the Datagator device, which never was adopted widely, no manufacturer of portable flowmeters has been able to marry the ease of installation of a velocity-area device with the accuracy of a primary device. In April (Out of the Box Flow Made Easy, p. 97) this magazine introduced the Cartridge Meter from Eastech Flow Controls, the successor to Badger Meters flowmeter division, that purported to do just that.

Now Eastech returns with a portable version of the Cartridge Meter called Flowscope.

The cartridge design, with its integrally mounted, factory-pre-aligned sensors can make installation faster and safer than a device with multiple parts, and can reduce maintenance requirements over the life of the flowmeter, says Frank Sinclair, president of Eastech. Because of the devices self-cleaning nature, Sinclair notes, requirements for additional entries over the life of the installation are reduced as well.

While most competitive designs measure velocity and infer flow, Flowscope measures flow directly and quotes accuracy in terms of flow rate. It can measure flow with an accuracy of ±2% of the actual flow rate over a 3:1 flow turndown, and ±5% of the actual flow rate over a 60:1 flow turndown. This flowmeter measures accurately without the installation and maintenance issues encountered when using alternative technologies.

Eastech claims to guarantee accuracy and cost efficiency by providing end users with a pre-engineered, field-ready flow measurement system requiring only 30 minutes for installation. Each component is aligned and calibrated at the factory and traceable to a primary flow standard.

The portable Flowscope electronics are supplied in a fully submergible, watertight enclosure with integral wireless communications, making it unnecessary to enter the manhole to retrieve data. Optional ADS Profile software is available for reports and reduction of data. Eastech also claims immediate cost savings of up to 40% by eliminating the labor-intensive requirements associated with flume installation, mounting brackets and internal sensor hoops.

At low flow rates, when the liquid occupies less than 1/3 of the pipes diameter, Flowscope measures the volume of fluid using a stainless-steel, trapezoidal flume with an ultrasonic level sensor. The ultrasonic level sensor, mounted in a nonfouling, Teflon housing above the normal flow stream, is pre-aligned, calibrated and programmed according to its dimensional relationship with the flume.

At high flow rates, when the liquid occupies more than 1/3 of the pipe diameter, Flowscope deploys an area-velocity algorithm that uses the same ultrasonic level sensor in conjunction with a pair of non-fouling, transit-time velocity sensors that measure the chordal velocity of the fluid from which the average velocity is calculated. This proven method (EPA Report 600/2-76/243) provides highly efficient measurement of bidirectional flow over changing operating conditions that may include backwatering or stagnation.

Product Exclusive Information

Eastech Flow Controls: 800-226-3569; www.eastechflow.com.