Totalizers, also referred to as total flow meters, typically measure the total flow volume within a closed pipe system. Today, many types of totalizers have several functions. Some may measure additional information, such as flow rate. While some totalizers operate mechanically, others use electrical power. Differences in type, design and material all affect the suitability of a totalizer for a particular function. When selecting a total flow meter, users typically want great function and cost-effectiveness. These attributes are not one-size-fits-all either, as they can be affected by the working environment, the substance being measured and the purpose of the meter. This article will provide a break down of the different types of totalizers in order to help you choose the best totalizer to suit your needs.
Direct and Indirect Volume Totalizers
Volume totalizers are among the most common and versatile type of total flow meter. They operate on the basic working principle of filling the meter with a specific volume, then measuring and integrating that volume to learn the total volume of the flow. A direct volume totalizer, also called a displacement meter, measures the flow by directing it through movable measuring chambers. This method works for both liquids and gases. Indirect volume totalizers include turbine totalizers, which use measuring vanes. Another method of volume totalization is the generation of a pulse total together with forced flow changes. As opposed to the measuring chambers, which measure a geometrically defined, specific volume, the pulse total measures the volume relative to function. For example, the total could represent the volume required to push a measuring vane totalizer for one revolution.
Oval Gear Totalizer
The oval gear totalizer is also fairly versatile and can be used in a wide range of environments. This meter operates via two oval gears, which rotate as the flow creates the torque necessary to move them. This mechanism is constructed so that a particular, defined volume will result in a complete rotation. Thus, the meter measures flow volume by counting the rotations of the gears. This number shows up on an indicator connected with a magnet coupling or with a magnetic pulse transmitter. While the operation of this meter results in wear and tear on the gears and bearings, advances in high-tech durable material production can reduce it substantially. If this totalizer will be placed in a high-temperature environment, its design should account for heat expansion as well. This meter’s measurements are highly accurate, although higher viscosity can reduce pressure and thus measurement precision. As the accuracy of the measurements depends on pressure, this meter is not suitable for larger pipes either.
Oscillating Piston Totalizer
An oscillating piston totalizer consists of a housing within which a hollow piston oscillates, allowing a defined volume of flow to enter and leave the totalizer. The measurements are calculated based on the rate of movement of the piston bearing. This meter is widely used to measure water and oil flow. The downside is that, due to the constant and rapid movement, the piston can wear out quickly if a highly durable material is not selected. This is especially important if the totalizer will operate with widely varying pressures. High-temperature precautions can necessitate additional adaptations such as an intermediate spacer. Unlike the oval gear totalizer, this meter’s accuracy is higher with increasing viscosity.
Lobed Impeller Totalizer
Lobed impeller gas totalizers are frequently used to measure gas flow volume. This type of meter uses two lobed impellers that look a little like a figure eight. The gas flow pushes on them and causes them to rotate in opposing directions. The impellers do not touch one another; instead, there is a constant gap between them. Each rotation moves four sections of flow volume through a measuring chamber. An external gear drive ensures the synchronicity of the impellers’ rotations. Pulsation, loud noise and contamination can all produce pressure drops and loss of accuracy. For optimal operation of this type of meter, use dampers to reduce any unavoidable pulsation or noise. Regular cleaning will reduce the chances of buildup or contamination that will reduce accuracy.
Turbine Meters Totalizer
Among indirect volume totalizers, turbine meters are widely used. This kind of totalizer consists of a rotating set of vanes, where total flow is measured using the number and frequency of the revolutions. Turbine totalizers come in several different designs. One is the rotary vane totalizer, which features a vaned wheel that is pushed by the entering flow. In a design used for liquid flow the wheel is connected to the totalizer via a gear train, and the totalizer is also located within the flow. In a dry design, the indicator is separated from the measuring chamber and receives the rotations through magnetic coupling. Turbine totalizers may have a single jet or multiple jets.
Another kind of turbine meter, the Woltman totalizer, has a rotor whose axle is parallel to the flow and connects to the totalizer with a low-friction gear train and magnetic coupling. In this design, the turbine wheel can be vertical or horizontal. A horizontal wheel allows for a larger flow and reduces pressure drops, while a vertical wheel offers higher sensitivity. This totalizer usually functions as a water meter.
A turbine flowmeter, or a turbine wheel totalizer, is built similarly to the Woltman. However, this type of totalizer measures the rotation electrically. It offers a higher level of sensitivity and is particularly effective in measuring flow with a high level of viscosity. This meter measures total volume, as well as the flow rate, through emitting a frequency based on the number of turbine revolutions.
Choose the Best Design for Your Purpose
Some of these totalizers, such as the lobed impelled totalizer, can only be used with one type of measuring medium. Others are more versatile. Optimal effectiveness of any totalizer depends on factors such as viscosity, likely pressure changes, temperature range and contamination quotient. A turbine totalizer should not be used for flow with mild contamination, while other types will need additional maintenance to cut down on the resulting wear and blockages. Many manufacturers also offer a range of options for housing and components. Choose based on durability in the expected environment. Some materials are designed to maximally resist chemical corrosion, while others are better suited to high temperature or pressure fluctuations. Direct flow totalizers work best for flows with irregular regimes, as their accuracy is least affected.
In addition to selecting a totalizer design that will most accurately measure your flow, consider environmental factors that could affect your meter’s performance. Ask your manufacturer about the best housing and component materials for your purposes, as well as about additional protection such as mesh for catching debris.
