PMT-IPWyatt Lo-Loss Flow Tubes
Insert-Type Composite Primary Elements


  • Lowest Pressure Loss
  • Light Weight
  • Cost Effective
  • Short Laying Length
  • Best Documented Flow Tube on the Market


The Wyatt Lo-Loss® insert series of differential producers is designed for installation within a pipe, and is secured in place by the adjacent pipe flanges. Lo-Loss® insert venturi meters are available in two configurations: PMT-IP and PMT-IL. The standard PMT-IP is made entirely of engineered materials such as FRP, PVC, and other thermo-plastic compounds. The PMT-IL em-ploys similar construction, but offers a metallic throat section and mounting flange. Their permanent pressure loss, expressed as a percent of differ-ential pressure, is lower than any other venturi or flow tube on the market.


The PMT-IP and PMT-IL Lo-Loss® Meters can accommodate a wide range of flow rates, line fluids, and process conditions. They are designed to measure full-pipe, clean fluids and gases in virtually any pipe size. In applications where solids contaminate the line fluid, an auxiliary high pressure tap can be provided for installation in the upstream pipe. The Lo-Loss® insert meters have the advantages of minimal weight, low cost, and a short laying length.

Flow Measurement Accuracy

For pipe Reynolds numbers greater than 100 000 and a normalized piping configuration, the Wyatt PMT-IP and PMT-IL Lo-Loss® meters provide a flow measurement accuracy of ± 0.25% with independent flow calibration and ± 1.00% without flow calibration.

Lo-Loss® is a registered trademark of Wyatt Engineering.

PMT-IP Technical Specifications

Headloss comparison


Within the specified pipe Reynolds number range and a normalized piping configuration, the Lo-Loss® PMT-IP and PMT-IL provide flow measurement uncertainties of:
± 1.00% for standard meters and
± 0.25% for flow calibrated meters.

Pressure Loss

The permanent pressure loss of the Lo-Loss® meter, expressed as a percentage of the differential produced, is shown in Figure 1 and is the lowest of any differential-producing primary element.

Beta Ratio

Wyatt Engineering offers Lo-Loss® insert meters with a wider range of diameter ratios (d/D) than any other manufacturer. By custom designing a Lo-Loss® meter to your application’s flow conditions, Wyatt can provide an accurate and reliable primary element with the lowest permanent pressure loss.

Temperature Range

The insert series of Lo-Loss® primary devices is designed to operate within a process temperature range of 0 °F to +300 °F (-18 °C to +150 °C). Pressure Range/Flange Connections The allowable operating pressure for the PMT-IL is limited only to that of the adjacent pipe flanges. Pressures of 4000 PSIG to 6000 PSIG (27 500 kPaG to 41 350 kPaG) are not uncommon.

Piping Requirements

Designed for full-pipe flow, Lo-Loss® meters may be mounted horizontally or vertically. For recommended upstream piping, refer to the Wyatt Engineering Technical Manual for the Lo-Loss® meter.

Energy Considerations

Figure 1 compares the permanent pressure loss of the insert Lo-Loss® design with that of other primary flow elements. Figure 2 illustrates the substantial savings that are realized when a Lo-Loss® meter is used in a typical application. The pressure recovery of the Wyatt Lo-Loss® Meter means reduced pumping costs. High beta ratio Lo-Loss® meters will recover up to 97.5% of the differential pressure produced. This is two to four times better than typical classical venturi devices, as well as most modified venturi meters. Using venturi tubes instead of orifice plates can yield significant savings, and using the Lo-Loss® meter instead of venturi tubes can realize further savings. For over 40 years, engineers have given their clients the benefits of efficiency and accuracy by doing just that.

Annual Pumping Cost Savings

Comparison of Differential Producers

Lo-Loss ® vs. Orifice Plate $1704
Lo-Loss ® vs. Flow Nozzle $1544
Lo-Loss ® vs. Short-Form Venturi $327
Lo-Loss ® vs. Long-Form Venturi $52

12” (300mm) Water Line
Flow Rate: 7.5 CFS (212.4 LPS)
∆P = 100” (2540mm) H2 O
Line Temperature: 68°F (20°C)
Pump Efficiency: 100%
Energy Costs: US$0.07/kWh

PMT-IP Available Options

Materials of Construction

The Wyatt insert series of flow meters can be constructed of virtually any composite material, such as vinyl ester or isophthalic resin, reinforced with fiberglass or carbon fiber.PMT-IP: In the PMT-IP series, the body is typically constructed of vinyl ester resin reinforced with fiberglass (40% by weight). The throat can be constructed of polyvinyl chloride, FRP, or almost any other synthetic material.
PMT-IL: The meter body of the PMT-IL is generally constructed of vinyl ester resin reinforced with fiberglass, much like the PMT-IP. The PMT-IL incorporates a metallic throat (common materials are bronze or stainless steel) and, typically, an epoxy-coated, carbon steel mounting flange. Stainless steel and other materials are also available for the mounting flange.