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Mechanical Turbine Water Meters
Hedland Variable Area Flow Meters

Flow Meter Selection Guide A simple guide to selecting the right Oval Gear Meter for your application...

Once you've decided that an Oval Gear Meter is the best flow meter for your specific application, there are a few key things you will need to know to narrow your selection down to a single oval gear flow meter. That list includes:

  • What is the flow rate (max and min)?
  • What liquid are you measuring?
  • What is the fluid viscosity?
  • Maximum pressure in the line?
  • What end connections are needed?
  • How do you want your data displayed, collected and/or communicated?

What is the flow rate (max and min)?

The maximum and minimum flow rates of the liquid measurement system are one the most important parameters for proper selection of a specific flowmeter. Referred to as "sizing the meter", we typically begin by determining your normal flow rate, along with a preferred line size (if any).

Using your that flow rate as a guide, a preferred line size is determined by finding a meter size where your normal flow rate is approximately 60% of the max flow rate. For instance, let's say your application has a minimum flow of 5 GPM and a maximum flow of 35 and a normal operating rate of 25 GPM. Start by dividing 25 by 0.6 to find what 25 is 60% of.

In this example, that's 41.7 GPM. Next, check out the available flow ranges on each of the available meter sizes to find one with maximum flow that's close to 41.7 GPM. The OM025 is a 1 inch meter with a range of 2.6 to 40 gpm making it a good match for the 60% test. Next determine if the min and max flows will work. In this example with an application range of 5-35 GPM and a meter capable of measuring from 2.6 to 40 gpm, we're good! As long as you can work with that 1 inch line size, the OM025 is a good match!

Remember that running the meter above the recommended max flow rates will drastically reduce rotor life, while running it below the minimum will cause accuracy to suffer so sizing the meter correctly from the start is vitally important!

What fluid are you measuring?

Check the compatibility between the liquid to be measured and the materials of construction of the flowmeter. The meter body, rotors, bearings and seals all need to be compatible.

For example most petroleum products are compatible with a meter constructed of an aluminum meter body, PPS rotors and Viton seals.

For more aggressive fluids that are not compatible with aluminum, Viton, etc... You might want to consider a meter with a stainless steel body and rotors, along with PTFE seals.

The examples given above are a good place to start, but before making a final decision on what materials would work best for your application, but sure to review one of the many material compatibility charts available on line. Click-Here to download the latest Chemical Compatibility Guide from GPI/Flomec.

Fluid Viscosity - How thick or thin is the fluid being measured?

Oval gear meters have the advantage of being relatively immune to changes in viscosity. This is as opposed to turbine meters where changing process conditions can affect the fluid's viscosity and ultimately its accuracy.

For liquids with viscosity in the range of 3-1,000cP, you typically don't need to consider the effect of the fluid viscosity on an Oval Gear Flowmeter.

For liquids below 3cP, like water (1cP), you need to allow for a slightly higher minimum flow rate to maintain the standard accuracy of your flowmeter due to slippage of the fluid between and around the rotors.

Above 1,000 cP the pressure drop across the meter must be considered, High Viscosity (Keishi Cut) rotors can reduce pressure without affecting accuracy.

Line Pressure - What is your maximum pressure?

Your maximum system pressure must be considered when specifying an Oval Gear Flow Meter (or any invasive type metering technology for that matter). The maximum pressure rating for an Oval Gear Meter is typically available in the respective product data sheets and is also available on the Data Plate attached to the meter itself. This rating is based on the maximum "non-shock" pressure at the maximum allowable process temperature for any given flow meter.

It's important to note that Oval Gear meters are precision instruments and accuracy can be affected by over pressurizing your meter. This is an important piece of information to consider when choosing an appropriate flow meter for any application.

End Connections

Make sure you select the appropriate process connection. The most popular connection types in our market area are NPT and 150lb ANSI Flanges. Flomec also offers BSP, 300lb ANSI Flanges, Sanitary and PN16 DIN Flanges.

Keep in mind that some connections may affect overall pressure ratings of the meter. For example, using the flange rule, a meter equipped with 150lb ANSI Flanges would be limited to a maximum pressure of 150 PSI. That same meter 316SS meter equipped with NPT Threads would be rated to 495 psi...

How would you like your data displayed and/or collected?

Like most flow meters, Ovals offer a number of different display/output options. First

Would you like to read rate on the meter, or transmit it into a remote unit somewhere else or a PLC? Would you like to record your volume on a mechanical register or electronic?

This determines what instrument you choose to accompany your meter.

Is the installation in a safe or hazardous area, which may require a flame proof or intrinsically safe instrument?

GPI/Flomec Electronic Options include the following:

Code Description
(Blank) Pulse Output Only, Combo Switch - Includes Reed Switch and Hall Effect Sensor
G5 GG-500 Rate & Total Display, available pulse output
G6 GX-500 Rate & Total Display, 4-20mA output
RS Reed Switch Only
E1 Ex-Proof IIB T4/T6 (IECEx & ATEX approved)
E2 Ex-Proof I/IIB T4/T6 (IECEx & ATEX Mines approved)
QP Quadrature Pulse (2 NPN Phased Outputs)
H1 Hi-Res Hall Effect, Ex-Proof (IECEx & ATEX approved)
PF Pulsating Flow, Hall Effect Pulse Output Only
P1 Pulsating Flow Option, Ex-Proof
B2 BT11 Totalizer w/Scaleable Pulse Output
B3 BT11 Totalizer (IS) w/Scaleaable Pulse Output
R0 RT12 Rate/Totalizer, Alloy Housing
R2 RT12 Rate/Totalizer, Plastic Housing
R4 RT40 Rate/Totalizer, Backlit LCD
E0 EB10 Batch Controller - 2 Stage Batcher/Totalizer
Mechancial Options include
M3 4-Digit Mech Totalizer - Liters
M4 4-Digit Mech Totalizer - US Gallons

Bottom Line... If you choose your flow meter carefully and correctly, with careful consideration given to all of the selection criteria mentioned above, your new Oval Gear flow meter should last for a very long time.

Make your choice using pricing and/or availability as your guide, paying little attention to what's required for your specific application and you are asking for a shortened meter life and inaccurate readings. Worse yet, you may be creating a safety hazard that could prove to be much more devastating in the long run, than what little you saved in cost and lead-time...

Remember, it's not always "all about the price". Experience matters!

Flow Specialist - Bill Michie Written By: Bill Michie  
Flow Applications Specialist
Cross Company
Instrumentation Group
Phone: (866) 905-9790 (M-F, 8am-5pm Eastern)
Contact the Experts

Special thanks to the Technical Team at GPI Austrialia for gathering, publishing and giving us permission to use the valuable information and images provided in this post.
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