Basics of Flow Meters

flow meter
Flow Meter

Measuring the flow rate of solids, liquids, and gases is referred to as flow measurement, and is a very important and widely used control variable. Many industries such as power, chemical, water, waste-water treatment, energy, mining and petroleum have many requirements for flow measurement and control.

A flow meter is a device that measures the rate of flow or quantity of a moving fluid in an open or closed conduit. There are two basic ways of measuring flow: volumetric basis and weight basis.

Flow measuring devices are generally classified into four groups:
  1. Mechanical type flow meters: Fixed restriction, variable head type flow meters using different sensors such as orifice plates, venturi tubes, flow nozzles, pitot tubes, quantity meters such as positive displacement meters, mass flow meters, etc. 
  2. Inferential type flow meters: Variable area flow meters (Rotameters), turbine flow meters, target flow meters, etc.
  3. Electrical type flow meters:  Electromagnetic flow meters, Ultrasonic flow meters, laser doppler anemometers etc.
  4. Other flow meters: Purge flow regulators, flow meters for solids flow measurement, cross-correlation flow meter, vortex shedding flow meters, flow switches, etc.
Flowmeters need to be integrated into existing piping or new installation. There are two methods for flowmeter installation: inline and insertion. With the inline method, connectors are provided for upstream and downstream pipes. For the insertion method, a sensor probe is inserted into the pipe.

Most flowmeters are installed with straight sections of pipe on either side for flow to normalize. For the inline method, the diameter of pipes should be same as the flowmeter size. Insertion design is easier to install and more economical in large diameter pipes.

To select the suitable flowmeters many factors should be taken in mind. The most important is fluid phase (solid, liquid, gas, steam) and the other is flow condition (clean, dirty, viscous, open channel etc.). The next important factor is line size and flow rate. Other properties that will affect the selection of flowmeter are density, pressure, temperature, viscosity etc. You should consult an application engineer before specifying a flow meter to assure proper installation, lowest installed cost and safety.

The Virtues of Angle Seat Valves

Gemu angle seat valve
GEMU Angle Seat Valve
“Angle valves” or “angle seat valves” are a family of on-off and control valves that have utilize a “Y” pattern body style, and a linear action to raise the disk from the seat to open and close the valve. By positioning the seat on an angle, the piston is pulled out of the flow path clearing the way for maximum flow. Angle valve provides tight shutoff, high cycle rate capability and very long service life. Here are other design features that make an angle valve a top performer:

The Importance of Auditing and Maintaining Your Steam System

Steam Trap
A blocked or leaky steam trap increases production times, reduce performance and wastes energy. By quickly identifying bad steam traps, you can save energy, optimize your process and improve safety. A well audited steam system reduces steam production costs, maintenance costs, repair costs, and possible environmental impact costs.

Saving money has always been a good thing and now saving energy is more important than ever. Going "Green" and staying "Green" is the mantra of todays eco-responsible organization. Improving the efficiency of your steam production and management system is an easy place to find big savings. Steam trap monitoring is a basic way to reduce waste, costs and environmental liability. It needs to be done.

Normal wear takes its toll and will cause steam traps to fail in either an open or closed configuration. Failed-closed traps create poor quality steam and effects steam efficiency, productivity, reliability and safety. Failed-open traps release live steam to atmosphere that wastes energy and money. Failed-open traps are very costly.

Statistics show 3 and 10 percent of steam traps fail each year, resulting in a 10 to 33 year life cycle. For a large facility with 10,000 steam traps, 300 to 1,000 traps may fail every year.

Below are tables that point out, in real terms, how much poor performing traps cost an organization.

Click for larger view (table courtesy of Spirax Sarco)
Click for larger view (table courtesy of Spirax Sarco)
As you can see from the data in the tables, it's very important to regularly audit your steam system and replace faulty or leaky steam traps. The short term costs of auditing and repairing will be repaid many times over in lower fuel costs, maintenance outages and environmental liability. 

Hydrostatic Tank Level Measurement

pressure transmitter
King-Gage pressure transmitter
One of the most proven and reliable methods of continuous tank level monitoring is remotely monitoring hydrostatic pressure.

Hydrostatic pressure is defined as "The pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity. Hydrostatic pressure increases in proportion to depth measured from the surface because of the increasing weight of fluid exerting downward force from above.

Pressure transmitters are a simple and accurate choice for measuring liquid level in storage tanks or processing tanks.

hydrostatic level
Typical hydrostatic level application
The principle behind hydrostatic, pressure-based, liquid level measurement is simple since pressure is proportional to the level of liquid multiplied by the specific gravity. The specific gravity of a liquid is the ratio of its own density to the density of water.

Alternatively, level equals the hydrostatic head pressure value divided by the density of the liquid.

Resilient Seated and High Performance Butterfly Valves

Lug Body Resilient
Seated Butterfly Valve
(Crane Centerline)

A butterfly valve uses a round, thin disk to control flow through a pipe. The disk is connected to the stem via a shaft completely through the disk, or at the top and bottom of the valve. 

The butterfly disk is continuously in the flow path, but because of its thin profile, has minimal impact on flow. Butterfly valves are popular because they offer very tight shut-off, are available in a wide range of materials and sizes, and can be automated inexpensively with many types of quarter-turn electric and pneumatic actuators.

Butterfly valves are used in many industrial applications today, from controlling the flow of water to handling much more severe industrial fluids. Butterfly valves are extensively used in water treatment, chemical processing, pulp and paper making, food processing, power generation and many other industries.

Swing Check Valve Operation - The Basics

check valve symbol
Check Valve Symbol
There are several types of industrial check valves such as piston, ball, diaphragm, wafer and swing. The following video introduces the viewer to the inner workings of the swing check valve.

According to Wikipedia, "Check valves are used in many fluid systems such as those in chemical and power plants, and in many other industrial processes.

Check valves are also often used when multiple gases are mixed into one gas stream. A check valve is installed on each of the individual gas streams to prevent mixing of the gases in the original source.

The swing check uses the directional flow to push open a swinging disk. As long as flow continues, the disk stays raised. But as flow stops, gravity allows the disk to re-seat itself and any reverse flow is prevented by the closed disk. As reverse flow pressure increases, the swing check valves seating increases as well.

A Fluid Velocity Tutorial

Here is another video describing the concepts of fluid velocity, pressure, and flow. It's from the Hydraulics collection offered by Columbia Gorge Community College.  In this video,  Instructor Jim Pytel, drives home fluid velocity concepts in a very entertaining and easy to understand way.  The video uses a humorous "application", where Mr. Pytel equates pressure to the system "strength", and flow as the system "speed". The video then goes on to explain the roles of pressure relief valves and flow control valves and how they allow for changes in force and speed of the sample system. It also introduces parallel and series hydraulic circuits, laminar and turbulent flow, flow rate, and flowmeters.