Flowmeter Application

Differential Pressure

Orifice Meter

Venturi Tube

Flow Nozzles

Pitot Tube

Dall Tube

Annubar

Target Meter

Rotameter

Flow Tube

Elbow Meters

Positive Displacement Meters

Rotary Meter

Sliding Vane Meter

Rotating Vane Meter

Reciprocating Piston Meter

Rotary Piston Meter

Velocity Meter

Turbine Meter

Vortex Meter

Electromagnetic Meter

Ultrasonic Meter

Mass Flowmeter

Thermal Meter

Coriolis Meter

 

About Peak Flow Meters, Water Flow Meters, Flowmeter Companies, Fuel Flow Meters and Flow Monitor Services.

Flow meters are used to measure the flow of air, fluids and gas. Some of the most popular flow meters are: peak flow meters, water flow meters, fuel flow meters, air flow meters, ultrasonic flow meters, and flow monitor services. Many flow meters measure the volume of the material while other flow meters measure the speed, and still other flow meters measure the mass of the materials. For the most part, flow meters are used to infer mass flow through calculations that flowmeter and flow monitor instruments make after taking various flow measurements such as absolute pressure, differential pressure, viscosity and temperature. Most flow meters including: peak flow meters, water flow meters, and fuel flow monitors, are made up of three parts: the primary device, transducer and transmitter. These three flowmeter parts are usually combined into one so that the flowmeter is only one instrument.

There are many different types of flow meters used for different measurements of flow. Thermal mass flow meters take measurements with two sensors that work together. A temperature sensor reference, and an active heated sensor take measurements by calculating how much heat loss occurs in the flowing liquid, and thus these flow meters can determine the flow rate based on this amount. Another type of flowmeter is the Coriolis mass flow meter, which operates on the basis of the Coriolis Effect. Basically, an excitation force is applied to the flowmeter tube, causing the fluid or gas to rotate because the acceleration is acting in opposite directions on both sides of the applied force. A flowmeter measurement can then be taken. Other kinds of flow meters operate using sound: these are called ultrasonic flow meters, and include several types like Doppler Effect flow meters and time-of-flight flow meters.

Because of their varied uses, flow meters are useful in a variety of fields. Medically, flow meters are used to measure a patients air intake. These types of flow meters are called peak flow meters and are particularly beneficial for asthma patients. In plumbing, water flow meters are used to measure the amount of fluid running through a tube for efficiency purposes. In general, flow meters are used in many industrial purposes for flow measurements to help companies determine profit gain or loss. Other industries that benefit from the use of flow meters, peak flow meters, fuel flow meters, water flow meters, and flow monitor services include the automotive industry, petroleum and gas industries, utility services, HVAC, food processing and raw materials industry.

Each type of flowmeter has specific guidelines that must be followed for proper use. For example, when using a gas flow meters, the flowmeter must remain full of gas. Liquid in gas flow meters can affect the flow meters accuracy. Similarly, in order for liquid flow meters to work properly, they must remain full of liquid. Gas in liquid flow meters can affect the accuracy of flowmeter readings. Generally, contaminants of any kind will cause an inaccurate reading of flow meters, so these flowmeter and flow monitor instruments must be treated with care and cleaned regularly.

Types of Flow Meters including: Peak Flow Meters, Water Flow Meters, Fuel Flow Meters, Air Flow Meters, Mass Flow Meters, Flowmeter Companies and Flow Meter Manufacturers.

Coriolis mass flow meters are used to measure the force of acceleration resulting from a moving object towards or away from the center of rotation.

Differential pressure flow meters are used to measure the flow of fluids and gases in a pipe by introducing constriction that causes the flowmeter pressure to drop. These flow meters must be kept clean to result in accurate measurements.

Insertion flow meters measure flow at one position in a pipe, and then, based on the flowmeter measurement, these flow meters estimate the flow rate for the entire pipe.

Magnetic flow meters measure flow by creating a magnetic field that is channeled into the liquid and causes a voltage signal to be sensed that is proportional to the flow of liquid.

Mass flow meters are used to measure gas flow and are one of the more popular types of flow meters. This flowmeter is relatively unaffected by changes in temperature or pressure in the mass flow meters tubes or mass flow meters pipes.

Open channel flow meters are used to measure the flow of liquids when the channel flow meters are open to the atmosphere.

Peak flow meters are used by patients with asthma or other lung disorders to measure the amount of air patients take into their lungs. Peak flow meters allow physicians to further determine the severity of any illness.

Positive displacement flow meters trap liquid to measure its flow by rotating parts that move between seals and the flowmeter body.

Sight flow indicators allow the operator to view the liquid as it is moving. Some flow monitor and flow indicator models come equipped with lights to enhance the visibility of the fluids.

Target flow meters measure the amount of force that is exerted on a target in a particular liquid or gas. Readings from target flow meters should not be used to measure high viscosity liquids because the target can be damaged.

Thermal flow meters are flow meters that use thermal properties of fluids to measure the flow. Thermal flow meters are heated and as the liquid flows by, it can tell the flow rate by the amount of heat lost.

Turbine flow meters consist of a rotor that measures the fluid when it passes through the blades. The blade speed of turbine flow meters is then translated into the speed of the fluid.

Ultrasonic flow meters use sound to determine flow rate. Both Doppler Effect flow meters and time-of-flight flow meters are two types of ultrasonic flow meters.

Variable area flow meters measure by letting the flow stream change the opening in the flowmeter with a movement of an internal flowmeter part.

Vortex flow meters and fluid flow meters generate oscillations as a result of the flow that allows a flowmeter measurement to be taken.

CONTROL VALVES is A final controlling element

Introduction : CONTROL VALVES is A final controlling element, through which a fluid passes, which adjusts the size of flow passage as directed by a signal from a controller to modify the rate of flow of the fluid. Valve Flow Coefficient (Cv) – The number of US gallons per minute of 60°F water that will flow through a valve with a one pound per square inch pressure drop

Rated Cv – The value of Cv at the valve full-open position

Rated Travel – The linear movement of the valve plug from the closed position to the valve full – open position
Leakage – The quantity of fluid passing through an assembled valve when the valve is in the closed postion
On-Off Service – When the valve is used to start / stop the flow by being cycled to the full open or to full closed position
Modulating Service – When the valve is being used to throttle or regulate the flow by varying the opening between open and closed positions
Maximum shut-off Pressure – The pressure of the fluid flowing into the valve against which the valve will have to close Service Temperature – The maximum and minimum temperature of the media
Supply Pressure – The plant air supply pressure available to operate a pneumatic actuator
Stem Torque – The force required at the valve stem to open or close the valve against system pressure and service conditions
Capactiy – Rate of flow through the valve under stated conditions
Fail close – The condition wherein the valve port remains closed should the actuating power fail
Fail open – The condition wherein the valve port remains open should the actuating power fail
Fail last – The condition wherein the valve port remains in the last position should the actuating power fail

Application : A Control Valve is a power-operated device used to modify the fluid flow rate in a process system. Well, what happens if the power is cut off? When a Control Valve is sized or selected to do a particular job, one of the first questions you should consider is how that valve will respond in the event of a loss of signal or power. This is called its “fail-safe mode” and knowing the fail-safe mode is the key to troubleshooting it. In most applications (about 80%), it is desirable for valves to fail closed. In other applications, you might want a valve to fail open or fail in place. Safety concerns and process requirements will mandate the fall mode of the valve. When a valve is not sitting in its fail position, is is being told how and when to move by some external signal. By the comments one hears, you would be led to believe that control valves sit around and think up things to do on their own. Perhaps this will some day be true when all control valves are “smart.” If a Control Valve is observed in an unstable condition or appears to not be responding correctly to an input signal, remember that something is telling the valve to behave that way.
A control valve is only as strong as its weakest link. When the 1965 Ford Mustang first appeared, it was powered by a 6-cylinder engine with a 3-speed transmission – but it had a 140 m.p.h.(225 k.p.h.) speedometer. The fact that it had a 140 m.p.h.(225 k.p.h.) speedometer did not mean it could actually travel that fast. In the same way, a control valve with a 600# rated valve body cannot throttle and shut off against 1440 pounds of pressure. There are two basic types of control valves: rotary and linear. Linear-motion control valves commonly have globe, gate, diaphragm, or pinch – type closures. Rotary-motion valves have ball, butterfly, or plug closures. Each type of valve has its special generic features, which may, in a given application, be either an advantage or a disadvantage

Butterfly Valves

Butterfly valves are throttling valves used to control flow through a circular disc by turning the valve’s main axis at ninety degree or right angles towards the direction of flow in the pipe. These valves use an inflatable seat to seal with air pressure, thus requiring less torque and a smaller actuator, resulting in lower overall valve cost.

The demand for actuated butterfly valves is growing because actuated butterfly valves can provide: precise, repeatable control for industrial process, complex automatic sequencing for process control. These important industrial fittings control the flow of gas or liquid by means of a disk, which turns on a diametrical axis inside a pipe or by two semicircular plates hinged on a common spindle, which permits flow in a single direction. These compactly designed valves offer a rotary system movement of less than 90 degree. The valves are manufactured in materials including stainless steel, plastic, ceramic and PVC.Advantage of Butterfly Valves
These valves can be used in areas where space is limited, this is so, because butterfly valves are available in small dimensions and are used in a variety of chemical services.

Types of Check Valves

Check Valves

A check valve is a mechanical device used as an industrial/plumbing fitting, which normally allows fluid or gas to flow through it in uni-direction. A double check valve is often used to prevent back flow and to keep potentially contaminated water from siphoning back. Clapper valves, a type of check valve is used in or with firefighting, and has a hinged gate (often with a spring urging it shut) that only remains open in the outflowing direction.

Types of Check Valves

• Single Disc Swing Valves : These valves can be mounted both vertically as ell as horizontally and are designed with a closure element attached to the top of the cap. This closure element can be pushed aside by the flow, but swings back into the close position upon flow reversal.
• Double Disc or Wafer Check Valves : These valves consist of two half-circle disks hinged together that fold together upon positive flow and retract to a full-circle to close against reverse flow.
• Lift-Check Valves : These valves can operate in either vertical or horizontal mounting.
• Silent valves : These valves are quite similar to lift check valves with a center guide extending from inlet to outlet ports.
• Ball-Check Valves : These valves are good for most services and can even handle fluids that produce gummy deposits. Since the disc is free to rotate, this all helps to keep the valve seats clean.
• Cone Check Valves : These valves use a free-floating or spring loaded cone resting in the seat ring as the closure element. Incase of a reverse flow, the cone is forced back into its seat preventing back flow.

Application of Check Valves

• Few types of irrigation sprinklers and drip irrigation emitters have small check valves built into them to keep the lines from draining when the system is shut off.
• Offshore Oil and Gas
• Civil Engineering
• Gas-Turbine Systems

Control Valves

A Control Valve is an important industrial fitting device used to modify and control the fluid flow rate in a process system. Also known as proportional valve, this power-operated device can be used to modify pressure rate in a process system.

There are various specifications and parameters which must be considered for these power-operated valves including diameter, working pressure and operating temperature. Available in choice of material including copper, brass, bronze, cast iron and stainless steel, and other plastic material such as PVC AND CPVC, these valves are the most used fittings.Types of Control Valves
Globe, Gate, Diaphragm, Needle, Butterfly, Ball and Plug Valves are all, kinds of control valves and are used for different applications in large number of industries.

Application of Control Valves

• Waterworks
• Fire Protection
• Irrigation
• Industrial
• Petroleum
• Aviation Fueling

Gate Valves

Gate valves, also known as Slide or Knife Valves, are named after a wedge-shaped internal plastic barrier, called a gate which rises and falls inside the valve as a handle is turned. These are linear motion valves in a which a flat closure element slides into the flow stream to provide shut off and are designed to minimize pressure drop across the valve in the fully opened position and stop the flow of fluid completely.

Knife valves effectively regulate flow rates from zero to full flow, they work well with solids-laden water, and these valves can be serviced in place. Knife Gate valves work well in applications involving slurries as the ‘gates’ can cut through the slurry, also these valves are advantageous in applications involving viscous liquids such as heavy oils, varnish, molasses etc.Types of Gate Valves

• Parallel Gate Valves: These valves use a flat disc gate between two parallel seats located upstream and downstream.
• Wedge-Shaped Gate Valves: These valves use two inclines seats and a little mismatched inclined gate allowing tight shut-off.

Application of Gate Valves

• Viscous liquids such as heavy oils, creams etc.
• Slurries

Globe Valves

Globe Valves

Globe valves derive their name from the rounded bodies/spherical shape and are widely used in fitting industry to regulate fluid flow in both on/off and throttling service. These linear motion valves consist of moving parts including disk, the valve stem, and the hand wheel.The stem is used to connect the hard wheel and the disk; the valves are threaded and fit into the threads of the valve bonnet. These specialty valves allow fluids to pass the spaces between the edge of the disk and the seat when open.

Types of Globe Valves
These valves are available in three main body types, namely : Angle Design, Y-design and Multi-piece Design. Angle valves are a type of globe valves, so designed, that the inlet and outlet are perpendicular, for transferring flow from vertical to horizontal. Y-design valves derive linear action from the incline between the axis of the inlet and outlet ports. The inlet and outlet are not of single piece construction. These valves offer precise throttling and control and have high-pressure limits. They also offer a low coefficient of flow and are however not good selections in applications requiring cleanliness or sterility.

Cavitation

Cavitation is a general term used to describe the behavior of voids or bubbles in a liquid. Cavitation is usually divided into two classes of behavior: inertial (or transient) cavitation and non-inertial cavitation. Inertial cavitation is the process where a void or bubble in a liquid rapidly collapses, producing a shock wave. Such cavitation often occurs in pumps, propellers, impellers, and in the vascular tissues of plants. Non-inertial cavitation is the process where a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. Such cavitation is often employed in ultrasonic cleaning baths and can also be observed in pumps, propellers etc.

nertial cavitation was first studied by Lord Rayleigh in the late 19th century when he considered the collapse of a spherical void within a liquid. When a volume of liquid is subjected to a sufficiently low pressure it may rupture and form a cavity. This phenomenon is termed cavitation inception and may occur behind the blade of a rapidly rotating propeller or on any surface vibrating underwater with sufficient amplitude and acceleration. Other ways of generating cavitation voids involve the local deposition of energy such as an intense focussed laser pulse (optic cavitation) or with an electrical discharge through a spark. Vapor gasses evaporate into the cavity from the surrounding medium, thus the cavity is not a perfect vacuum but has a relatively low gas pressure. Such a low pressure cavitation bubble in a liquid will begin to collapse due to the higher pressure of the surrounding medium. As the bubble collapses, the pressure and temperature of the vapor within will increase. The bubble will eventually collapse to a minute fraction of its original size, at which point the gas within dissipates into the surrounding liquid via a rather violent mechanism, which releases a significant amount of energy in the form of an acoustic shock-wave and as visible light. At the point of total collapse, the temperature of the vapor within the bubble may be several thousand kelvins, and the pressure several hundred atmospheres.

Inertial cavitation can also occur in the presence of an acoustic field. Microscopic gas bubbles which are generally present in a liquid will be forced to oscillate due to an applied acoustic field. If the acoustic intensity is sufficiently high, the bubbles will first grow in size, and then rapidly collapse. Hence, inertial cavitation can occur even if the rarefraction in the liquid is insufficient for a Rayleigh-like void to occur. High power ultrasonics usually utilize the inertial cavitation of microscopic vacuum bubbles for treatment of surfaces, liquids and slurries.

The physical process of cavitation inception is similar to boiling. The major difference between the two is the thermodynamic paths which precede the formation of the vapor. Boiling occurs when the local vapor pressure of the liquid rises above its local ambient pressure and sufficient energy is present to cause the phase change to a gas. Cavitation inception occurs when the local pressure falls sufficiently far below the saturated vapor pressure, a value given by the tensile strength of the liquid.

In order for cavitation inception to occur, the cavitation “bubbles” generally need a surface on which they can nucleate. This surface can be provided by the sides of a container or by impurities in the liquid or by small undissolved microbubble within the liquid. It is generally accepted that hydrophobic surfaces stabilize small bubbles. These pre-existing bubbles start to grow unbounded when they are exposed to a pressure below the threshold pressure, termed Blake’s threshold.

Cavitation Valve

If the speed through the valve is high enough, the pressure in the liquid may drop to a level where the fluid may start bubble or flash. The pressure recovers sufficiently and the bubbles collapse upon themselves.

control valve cavitation

Cavitation may be noisy but is usually of low intensity and low frequency. This situation is extremely destructive and may wear out the trim and body parts of the valve in short time.

* The Cavitation Number An introduction to and a definition of the Cavitation Number.
* Cavitation – an Introduction

Application Ratio

A common way to characterize potential cavitation conditions is the “applications ratio” (or “the incipient cavitation index”) and can be expressed as

AR = pi – po / (pi – pv) (1)

where

AR = Application Ratio

pi = inlet pressure, absolute

po = outlet pressure, absolute

pv = vapor pressure of the fluid, absolute

For application ratios above 1 – the fluid flashes. This is not the same as cavitation, but the closer the ratio is to 1, the higher the potential for cavitation.

Note! With an increasing fluid temperature the possibility for cavitation increases.
Example – Flashing Water

If we know the boiling point and the absolute pressure of a fluid (Steam Table with saturated steam properties) the minimum outlet pressure from a valve to avoid flashing can be calculated.

For an application ratio of one equation (1) can modified to

AR = 1 = pi – po / (pi – pv)

or transformed

po = pv

Using “Steam Table” with saturated steam properties we can conclude that

* for a water temperature of 17.51 oC and absolute inlet pressure of 1 bar – the minimum outlet pressure is 0.02 bar to avoid flashing
* for a water temperature of 81.35 oC and absolute inlet pressure of 1 bar – the minimum outlet pressure is 0.5 bar to avoid flashing
* For a water temperature of 99.63 oC and absolute inlet pressure of 1 bar – the minimum outlet pressure is 1 bar to avoid flashing

Note! Flashing is not the same as cavitation. Due to local conditions in a valve cavitation may start on much higher outlet pressures.
Multi Stage Control Valves

Cavitation can be avoided by using more than one control valve or more convenient – a multistage control valve.

Technical Principles of Valves

Risk, Reliability and Safety

Hazardous areas classifications, types of protection, rating systems and critical temperatures.
Sizing Steam and Condensate Pipes
GENERAL

Solenoid valves are used wherever fluid flow has to be controlled automatically. They are being used to an increasing degree in the most varied types of plants and equipment. The variety of different designs which are available enables a valve to be selected to specifically suit the application in question.

CONSTRUCTION

Solenoid valves are control units which, when electrically energized or de-energized, either shut off or allow fluid flow. The actuator takes the form of an electromagnet. When energized, a magnetic field builds up which pulls a plunger or pivoted armature against the action of a spring. When de-energized, the plunger or pivoted armature is returned to its original position by the spring action.

VALVE OPERATION

According to the mode of actuation, a distinction is made between direct-acting valves, internally piloted valves, and externally piloted valves. A further distinguishing feature is the number of port connections or the number of flow paths (”ways”).

DIRECT-ACTING VALVES

With a direct-acting solenoid valve, the seat seal is attached to the solenoid core. In the de-energized condition, a seat orifice is closed, which opens when the valve is energized.

DIRECT-ACTING 2-WAY VALVES

Two-way valves are shut-off valves with one inlet port and one outlet port (Fig. 1). In the de-energized condition, the core spring, assisted by the fluid pressure, holds the valve seal on the valve seat to shut off the flow. When energized, the core and seal are pulled into the solenoid coil and the valve opens. The electro-magnetic force is greater than the combined spring force and the static and dynamic pressure forces of the medium.

DIRECT-ACTING 3-WAY VALVES

Three-way valves have three port connections and two valve seats. One valve seal always remains open and the other closed in the de-energized mode. When the coil is energized, the mode reverses. The 3-way valve shown in Fig. 2 is designed with a plunger type core. Various valve operations can be obtained according to how the fluid medium is connected to the working ports in Fig. 2. The fluid pressure builds up under the valve seat. With the coil de-energized, a conical spring holds the lower core seal tightly against the valve seat and shuts off the fluid flow. Port A is exhausted through R. When the coil is energized the core is pulled in, the valve seat at Port R is sealed off by the spring-loaded upper core seal. The fluid medium now flows from P to A.

Unlike the versions with plunger-type cores, pivoted-armature valves have all port connections in the valve body. An isolating diaphragm ensures that the fluid medium does not come into contact with the coil chamber. Pivoted-armature valves can be used to obtain any 3-way valve operation. The basic design principle is shown in Fig. 3. Pivoted-armature valves are provided with manual override as a standard feature.

INTERNALLY PILOTED SOLENOID VALVES

With direct-acting valves, the static pressure forces increase with increasing orifice diameter which means that the magnetic forces, required to overcome the pressure forces, become correspondingly larger. Internally piloted solenoid valves are therefore employed for switching higher pressures in conjunction with larger orifice sizes; in this case, the differential fluid pressure performs the main work in opening and closing the valve.

INTERNALLY PILOTED 2-WAY VALVES

Internally piloted solenoid valves are fitted with either a 2- or 3-way pilot solenoid valve. A diaphragm or a piston provides the seal for the main valve seat. The operation of such a valve is indicated in Fig. 4. When the pilot valve is closed, the fluid pressure builds up on both sides of the diaphragm via a bleed orifice. As long as there is a pressure differential between the inlet and outlet ports, a shut-off force is available by virtue of the larger effective area on the top of the diaphragm. When the pilot valve is opened, the pressure is relieved from the upper side of the diaphragm. The greater effective net pressure force from below now raises the diaphragm and opens the valve. In general, internally piloted valves require a minimum pressure differential to ensure satisfactory opening and closing. Omega also offers internally piloted valves, designed with a coupled core and diaphragm that operate at zero pressure differential (Fig. 5).

INTERNALLY PILOTED MULTI-WAY SOLENOID VALVES

Internally piloted 4-way solenoid valves are used mainly in hydraulic and pneumatic applications to actuate double-acting cylinders. These valves have four port connections: a pressure inlet P, two cylinder port connections A and B, and one exhaust port connection R. An internally piloted 4/2-way poppet valve is shown in Fig. 6. When de-energized, the pilot valve opens at the connection from the pressure inlet to the pilot channel. Both poppets in the main valve are now pressurized and switch over. Now port connection P is connected to A, and B can exhaust via a second restrictor through R.

EXTERNALLY PILOTED VALVES

With these types an independent pilot medium is used to actuate the valve. Fig. 7 shows a piston-operated angle-seat valve with closure spring. In the unpressurized condition, the valve seat is closed. A 3-way solenoid valve, which can be mounted on the actuator, controls the independent pilot medium. When the solenoid valve is energized, the piston is raised against the action of the spring and the valve opens. A normally-open valve version can be obtained if the spring is placed on the opposite side of the actuator piston. In these cases, the independent pilot medium is connected to the top of the actuator. Double-acting versions controlled by 4/2-way valves do not contain any spring.

MATERIALS

All materials used in the construction of the valves are carefully selected according to the varying types of applications. Body material, seal material, and solenoid material are chosen to optimize functional reliability, fluid compatibility, service life and cost.

BODY MATERIALS

Neutral fluid valve bodies are made of brass and bronze. For fluids with high temperatures, e.g., steam, corrosion-resistant steel is available. In addition, polyamide material s used for economic reasons in various plastic valves.

SOLENOID MATERIALS

All parts of the solenoid actuator which come into contact with the fluid are made of austenitic corrosion-resistant steel. In this way, resistance is guaranteed against corrosive attack by neutral or mildly aggressive media.

SEAL MATERIALS

The particular mechanical, thermal and chemical conditions in an application factors in the selection of the seal material. the standard material for neutral fluids at temperatures up to 194°F is normally Viton. For higher temperatures EPDM and PTFE are employed. The PTFE material is universally resistant to practically all fluids of technical interest.

PRESSURE RATINGS – PRESSURE RANGE

All pressure figures quoted in this section represent gauge pressures. Pressure ratings are quoted in PSI. The valves function reliably within the given pressure ranges. Our figures apply for the range 15% undervoltage to 10% overvoltage. If 3/2-way valves are used in a different operation, the permitted pressure range changes. Further details are contained in our data sheets.

In the case of vacuum operation, care has to be taken to ensure that the vacuum is on the outlet side (A or B) while the higher pressure, i.e. atmospheric pressure, is connected to the inlet port P.

FLOW RATE VALUES

The flow rate through a valve is determined by the nature of the design and by the type of flow. The size of valve required for a particular application is generally established by the Cv rating. This figure is evolved for standardized units and conditions, i.e. flowrate in GPM and using water at a temperature of between 40°F and 86°F at a pressure drop of 1 PSI. Cv ratings for each valve are quoted. A standardized system of flowrate values is also used for pneumatics. In this case the air flow in SCFM upstream and a pressure drop of 15 PSI at a temperature of 68°F.

SOLENOID ACTUATOR

A common feature of all Omega solenoid valves is the epoxy-encapsulated solenoid system. With this system, the whole magnetic circuit-coil, connections, yoke and core guide tube – are incorporated in one compact unit. This results in a high magnetic force being contained within the minimum of space, insuring first class electrical insulation and protection against vibration, as well as external corrosive effects.

COILS

The Omega coils are available in all the commonly used AC and DC voltages. The low power consumption, in particular with the smaller solenoid systems, means that control via solid state circuitry is possible.

The magnetic force available increases as the air gap between the core and plug nut decreases, regardless of whether AC or DC is involved. An AC solenoid system has a larger magnetic force available at a greater stroke than a comparable DC solenoid system. The characteristic stroke vs. force graphs, indicated in Fig. 8, illustrate this relationship.

The current consumption of an AC solenoid is determined by the inductance. With increasing stroke the inductive resistance decreases and causes an increase in current consumption. This means that at the instant of de-energization, the current reaches its maximum value. The opposite situation applies to a DC solenoid where the current consumption is a function only of the resistance of the windings. A time-based comparison of the energization characteristics for AC and DC solenoids is shown in Fig. 9. At the moment of being energized, i.e. when the air gap is at its maximum, solenoid valves draw much higher currents than when the core is completely retracted, i.e., the air gap is closed. This results in a high output and increased pressure range. In DC systems, after switching on the current, flow increases relatively slowly until a constant holding current is reached. These valves are therefore, only able to control lower pressures than AC valves at the same orifice sizes. Higher pressures can only be obtained by reducing the orifice size and, thus, the flow capability.

THERMAL EFFECTS

A certain amount of heat is always generated when a solenoid coil is energized. The standard version of the solenoid valves has relatively low temperature rises. They are designed to reach a maximum temperature rise of 144°F under conditions of continuous operation (100%) and at 10% overvoltage. In addition, a maximum ambient temperature of 130°F is generally permissible. The maximum permissible fluid temperatures are dependent on the particular seal and body materials specified. These figures can be obtained from the technical data.

TIME DEFINITIONS (VDE0580) RESPONSE TIMES

The small volumes and relatively high magnetic forces involved with solenoid valves enable rapid response times to be obtained. Valves with various response times are available for special applications. The response time is defined as the time between application of the switching signal and completion of mechanical opening or closing.

ON PERIOD

The on period is defined as the time between switching the solenoid current on and off.

CYCLE PERIOD

The total time of the energized and de-energized periods is the cycle period. Preferred cycle period: 2, 5, 10 or 30 minutes.

RELATIVE DUTY CYCLE

The relative duty cycle (%) is the percentage ratio of the energized period to the total cycle period. Continuous operation (100% duty cycle) is defined as continuous operation until steady-state temperature is reached.

VALVE OPERATION

The coding for the valve operation always consists of a capital letter. The summary at left details the codes of the various valve operations and indicates the appropriate standard circuit symbols.

VISCOSITY

The technical data is valid for viscosities up to the figure quoted. Higher viscosities are permissible, but in these cases the voltage tolerance range is reduced and the response times are extended.

TEMPERATURE RANGE

Temperature limits for the fluid medium are always detailed. Various factors, e.g. ambient conditions, cycling, speed, voltage tolerance, installation details, etc., can, however, influence the temperature performance. The values quoted herein should, therefore, be used only as a general guide. In cases where operation at extremes of the temperature range are involved, you should seek advice from Omega’s Engineering Department.
Sizing of steam and condensate pipes and tubes, pressure loss in piping, recommended speed and capacities
Steam & Condensate Systems

Steam is an integral and essential part of modern industrial process technology. Without steam, food, textile, chemical, medical, power, heating and transport industries could not exist or perform as they do. In this section necessary information as steam properties, steam and condensate piping and much more is provided
Steam Thermodynamics

The basic thermodynamic of steam and condensate
Temperature Measurement

Measurement of temperature; probes, sensors and transmitters
Thermal Expansion of Pipes and Tubes

Thermal expansion of pipes and piping applications
Thermodynamics

Thermodynamics is the branch of physics which deals with the transformation of heat into mechanical work
Valve Selection Guide

An applications guide for selecting valves
Valves and Valve Standards

International standards common used for valves
Ventilation Systems

Systems for ventilation and air handling
Water Systems

Design properties for hot and cold water systems. Capacities, users consumptions, use of energy and more. Anyone involved in design, analysis, operation, maintenance or rehabilitation of water distribution systems will find practical guidance in this section. Hydraulics of pressurized flow, piping design and pipeline systems, storage issues and more