by Jason Schoenbaechler • Sep 2, 2018
In recent years magnetic flow meters have replaced existing venturi in plants and in specifications. The reason for this is because they offer a lower entry cost and claim to be maintenance free. While this may be true, it doesn't tell the whole story.
There is no dispute that the purchase price of a magmeter is lower than that of a cast iron venturi. Now consider that many of the wastewater treatment plants built in the United States opened shortly after World War II. Those plants have been in operation for over 70 years. Even with an extended warranty options magmeters are only warranted for about 5 years compare that to the BIF Model 20181 standard warranty of 25 years. Many cast iron venturi meters installed in those 70-year-old plants are still working today.
The second claim of maintenance free operation should also be addressed. Magmeters are essentially an electronic device. Like your PC they don't need much maintenance maybe just a software update or reboot every once in a while. The downside is, like your PC they only have a lifespan of 5 to 10 years and then they need to be replaced. Venturi meters are physical devices, with no moving parts, that create a pressure difference. That difference is then measured by a differential pressure transmitter. The transmitter is an electronic device, but it has a much lower cost and is easier to replace than breaking into the main line to replace a magmeter. The BIF UVT is designed to be self-scouring or self-cleaning. The pressure taps and lines leading to the transmitter are the real area of concern in waste water applications.
To achieve reliable performance of a venturi in wastewater applications BIF offers 3 solutions
1. Vent Cleaners
2. Intermittent Purge System
3. Sealed probes
While vent cleaners do require manual operation by maintenance personnel, the other 2 options once installed are completely maintenance free.
These devices are installed directly to the venturi's instrument connections. The vent is essentially a rod that you push through the pressure port cleaning out and buildup. This is done on a regular interval by a plant employee.
The IPS offers a maintenance-free option for wastewater systems. The system uses clean water to flush the instrument lines keeping them free and clear of any solids.
BIF Model 20395 Intermittent Purge System
Another option is the use of seals on the transmitter impulse lines. Sealed probes are packaged with the DP transmitter at the factory. These systems are usually oil filled.
There is no doubt magnetic flow meters have come a long way and offer reliable flow measurement, but they still cannot compare to the robustness of a venturi. For more information on specifying the correct flow meter for your wastewater application contact your local BIF sales representative.