One issue that I run into relatively often with new technicians, or with some non-technical project managers is confusion over pipe sizing. A typical example looks like this: I ask a new technician-in-training to get me a count of 1-inch pipe that we have in storage. I take the info, and then later find out that what the trainee inventoried was the 3/4-inch pipe. The reason for this confusion lies in the way that pipe sizes are named. The 1-inch, 3-inch, 6-inch etc. pipe designations are closer to names than sizes. This is because pipe sizing goes by a nominal size standard which is somewhat non-intuitive.
For many people, if they are asked to locate pipe of a given size, 3-1/2” for example, they will take a tape measure and instinctually measure the outside diameter of the pipe, which will lead them to an incorrect identification. This has to do with the sizing conventions for pipes. Pipes are sized using a nominal pipe size (NPS) designation, and a pipe schedule (SCH) to fully define the size. The nominal size refers only to the approximate inside diameter, and the schedule refers to the wall thickness of the pipe. Because of this, the inner and outer dimensions from a pipe do not directly align with the “name” of the pipe size
In water treatment systems it is often important to measure the rate at which water is flowing through the system. Data from flow measurement devices can be used to control chemical dosing, set pump speeds, control filter loading rates, inform maintenance programs, and other tasks necessary for operation of a water treatment facility or on key components such as Degasification and Decarbonation systems or Biological Odor Control Systems. As with most types of instrumentation, there is an array of technologies that can be used for the task, each one with various strengths and optimal applications. For modern electronically controlled systems, the most common types of flow sensors used are axial turbine flowmeters, paddlewheel flowmeters, differential pressure / orifice plate flow transducers, and magnetic flowmeters. This article will briefly discuss the technology and features of each of these types.
A turbine flow meter,
consists of a tube that contains supports to hold a multi-bladed metal turbine in the center. The turbine is designed to have close clearance to the walls of the tubing such that nearly all of the water is made to flow through the turbine blades as it travels through the pipe. The turbine is supported on finely finished bearings so that the turbine will spin freely even under very low flows. As the turbine spins, a magnetic pickup located outside of the flowmeter housing is used to sense the tips of the turbine blade spinning past the pickup. An amplifier/transmitter is then used to amplify the pulses and either transmit them directly or convert the pulse frequency into an analog signal that is then sent to a programmable controller for further use elsewhere in the system. One advantage of a turbine flowmeter is that the electronics are separated from the fluid path. The magnetic pickup is the only electronic component, and it is installed outside of the turbine housing, reading the presence of the turbine blade tips through the wall of the sensor body. In clean water applications, this can be advantageous because the magnetic pickup can be replaced if needed without removing the turbine from service. However, the turbine itself covers most of the pipe area and creates back-pressure in the system, requiring increased pumping energy to move a given amount of water. In Industrial Water Treatment or Filtration Treatment, turbines can also easily become fouled or jammed if they are used to measure water or other fluids with entrained solids, algae or bacteria cultures which cause significant accumulation, or corrosive chemical components that can degrade the turbine bearings.
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