The PFS Sealed Metering System (SMS) was developed in the 1990’s in response to end users asking for an accurate and reliable flow meter that could be used on custody transfer or billing installations, particularly on contaminated flows such as sewage or sludge. While 25 years ago, the go-to meter type for contaminated applications was a magnetic flow meter, issues developed concerning their use where annual certification of the accuracy of the meter were desired or required. Over the years, the ability to provide a certified annual calibration report became more and more problematic for the end user given the difficulty in performing a “field calibration” of a magnetic type meter.
A Highly Accurate and Low Maintenance Solution
The ideal solution, given the long useful life, low maintenance requirements, high defendable accuracy was a venturi meter which, contrary to electronic type meters such as mags, can be field “bench calibrated” where an internal inspection can be performed without removing the meter from service via the build-in inspection port and, based on no change to the interior of the meter, a manometer is used as the calibration standard against which the differential pressure transmitter is field calibrated.
While the standard direct interface impulse lines that convey the high and low pressure to the DP transmitter work well on clean liquids, sewage and sludge can quickly plug the impulse lines and develop an inaccurate reading or no reading at all.
The PFS-SMS solution eliminates the direct interface between process flow and the DP transmitter and, instead, utilizes either a 2.0” or 3.0” diaphragm sealed sensor at the high and low pressure tap sensing points on the venturi meter.
To facilitate a simple field DP transmitter calibration process without stopping the flow or removing any equipment, the built-in SMS calibrator assembly allows for the primary checking device (manometer) to be connected and the DP transmitter calibrated to its readings. In addition, the SMS assembly includes an isolation ball or gate valve which allows for the removal of the sealed diaphragm system under flowing conditions.
5,000 SMS Installations in the USA
With over 5,000 SMS installations in the USA, the system continues to be used as a replacement for magnetic meter installations that cannot support current regulatory calibration requirements. One example of a Sewage Authority switching from mags to the PFS-SMS solution is a medium size mid-west utility that, since 2003, has installed the PFS solution throughout their sewage pump station system.