May 2008

Focus on flow

A piece of flow history: In 1783, physicist Daniel Bernoulli published Hydrodynamica, and with it came a major milestone in the understanding of flow. Bernoulli introduced the concept of the conservation of energy for fluid flows. He determined an increase in the velocity of a flowing fluid increases its kinetic energy while decreasing its static energy. It is for this reason a flow restriction causes an increase in the flowing velocity and also causes a drop in the static pressure of the flowing fluid.

Vortex-shedding flowmeters

The P420 Series of vortex-shedding flowmeters meets requirements of water desalination, chemical, and water treatment operations for an inexpensive flow rate transmitter without moving parts that can stick, bind or coat when processing corrosive fluids. Applications include water, chemicals, brine, corrosives and low-viscosity pure liquids. P420 Series flow transmitters are electronic instruments with wetted parts entirely of polyvinyl chloride (PVC). The non-mechanical meters are designed to transmit low-viscosity liquids that are compatible with PVC.

The P420 flow transmitters are offered in five pipe sizes with maximum flow rates from 12 gallons per minute (45 liters per minute) to 200 GPM (750 LPM). The pipe sizes and maximum flow rates are: 1/2 inch (12 GPM, 45 LPM), 3/4 inch (25 GPM, 95 LPM), 1 inch (50 GPM, 190 LPM), 1-1/2 inches (100 GPM, 380 LPM), and 2 inches (200 GPM, 750 LPM). P420 vortex-shedding flow transmitters have no o-ring seals. Connection is made by either solvent welding PVC pipe into the socket port provided or threaded connection. Electronic output is from a 4-20 mA two-wire transmitter rated Intrinsically Safe when used with barriers.

Universal Flow Monitors


Precision turbine flowmeter

The HP Series precision turbine flowmeter, designed for demanding, high-pressure applications, is available in a wide range of sizes and features MS33514 end-fittings. It performs accurate liquid flow measurements across a wide flow range.  The meter is rated for pressures up to 5,000 psig (continuous), 7,500 psig (proof), and 25,000+ psig (burst).  It offers accuracy of +0.25 percent of reading, and response time of 2-3 mS or faster.

All HP Series flowmeter calibrations are directly traceable to standards established by the National Institute of Standards & Technology. With standard K-factor (10:1 flow ratio) calibration, the meter provides a frequency output linear to within ±0.5 percent over the entire flow range with liquids up to 1.26 centistokes viscosity.  With special calibration, ±0.5 percent linearity can be achieved at any one viscosity up to the meter's linear viscosity limit.  At higher viscosities, the output is non-linear, but repeatable. Standard K-ranges for the HP Series are available from 0.25-2.5 to 25-250 gallons-per-minute (GPM), depending upon meter size.  Standard constant K-Factor calibrations are available on MIL-C-7024C, Type 2, at 80°F only. 

With 20-point loop calibrations (10 points upscale and 10 points down-scale), ±0.5 percent linearity over extended flow ranges is available on fluids where viscosity does not exceed 1.26 centistokes. 

COX Instruments


Mass meters, controllers

The LIQUI-FLOW series mass meters and controllers for low flow rates are now available in compact, rugged design according IP65 (dust- and waterproof) and ATEX approved for use in Category 3, Zone 2 hazardous areas. The liquid flowmeters and controllers cover flow rates from 0.25 g/h to 1 kg/h and can be used in applications with pipeline pressures up to 100 bar (1500 psi). The stainless steel sensor has negligible internal volume and no moving parts.

Calibration of the mass flowmeters/controllers can be performed for virtually every liquid and up to eight calibration curves can be stored onboard the instrument itself. In addition, the digital instruments feature fast response (< 2 seconds) and high accuracy (1% FS or better). LIQUI-FLOW instruments have analog I/O-signals and also an RS232 connection as a standard feature. There is the possibility of integrating an interface board with DeviceNet, Profibus-DP, Modbus, or FLOW-BUS protocol. The basic pc-board incorporates PID control and various alarm and diagnostic functions.

Bronkhorst High-Tech B.V.