The temperature control valve is one of the most commonly used control valves. These valves are used in different industrial applications to control the temperature of the fluid. The efficient working of this valve is very important to achieve optimum efficiency. This article mainly explains the temperature control valve working, applications, and types.

What is a Temperature Control Valve?

A temperature control valve (TCV) is used to control the process temperature by regulating the flow or pressure of thermal fluid in a heating coil, tank shell, compressor, or other heating element. The temperature control valve is also known as a temperature regulator.

The temperature control valves are employed in processes that need to maintain a stable temperature when the ambient temperature changes.

The TCVs are useful in industrial, marine, and process control applications where liquids are diverted or mixed to attain the best operating temperature. They can also be used in a cogeneration system to regulate the temperature of the heat recovery loop to maximize heat recovery and ensure proper engine cooling. All of this helps to deliver the optimal temperature for your process and avoid costly downtime.

Valves for various applications are most commonly named by the number of their ports. For example, as the name suggests, a two-way valve contains two ports. A three-way valve contains three ports. A valve port is a valve connection point where fluids enter or exit the valve.

Sometimes, TCV can be used to moderate engine temperatures and a faulty TCV can even create the failure of car engines as suggested by some car accident attorneys.

How does a Temperature Control Valve Work?

Before delving into the workings of temperature control valves, it is vital to understand their design. The design of the temperature control valve consists of 4 major components parts:

• Temperature sensing element
• Sensor
• Power supply
• Controlling medium

The temperature-sensing element is responsible for sending a mechanical or electrical signal to an actuator. With this signal, the actuator then acts on a voltage supply that measures the position of the valve.

The temperature regulator is actuated by a mechanical temperature gauge. It contains a full lightbulb as the temperature sensor. Due to the thermal expansion properties of the material, it swells as the temperature rises. This expansion loads the actuator pressure. This pressure controls the valve position in the regulator that regulates the flow of refrigerant.

Temperature control valves use the following two common temperature control schemes:

Mixing of hot and cold process liquids:

In this case, the cold and hot process liquids are set at two dissimilar temperatures (Tx and Ty). A temperature control valve (TCV) is configured to physically mix these fluids to achieve the desired temperature. It is vital to observe that no chemical reactions take place between the liquids. The sensor installs in the hot process liquid. Ty calculates the thermal process fluid temperature and transfers it to the controller with the Tx setpoint. When the thermal process fluid temperature exceeds Ty, the controller recognizes the temperature change. The control valve mixes the cold process liquid with the hot process liquid until the desired temperature is gained.

Heat exchange between hot and cold process liquids:

In this process, instead of mixing the liquids, energy is transferred between two hot and cold process liquids. This means that the hot fluid flows through the heat exchanger shell while the cold fluid transfers energy through the tubes. The hot liquid transfers energy to the cold liquid and the temperature rise of the cold liquid is observed and regulated by a temperature transmitter and transferred to the temperature controller. As the temperature rises, the controller sends it to the temperature control valve to turn it on or off accordingly. It stays on until the desired temperature is reached, facilitating energy transfer.

Types of Temperature Control Valves

Broadly there are two types of temperature control valves;

• Thermostatic Control Valves, and
• Actuated Control Valves

Thermostatic Control Valves

Valves that work by detecting and regulating the temperature of the liquid inside are called thermostatic control valves. This temperature control valve is self-contained and requires no external power supply. The working temperature range is measured by the chemistry of the wax material and is preset at the factory or local dealer as recommended by the engine or equipment manufacturer.

When the thermostatic element is adjusted according to the specific temperature, it can’t be reformed without installing a new element. This rugged yet simple design stops operators from accidentally overheating or overcooling equipment, resulting in poor fuel economy, costly repairs, and downtime.

Actuated Control Valves

Unlike internal sensing valves, actuation control valves are typically part of a complete system that uses an external probe to sense temperature changes. The probe transfers a signal to the powertrain control module (PCM) to open and close the valve port using an external power supply. Normal system types include pneumatic, electric, or a combination of both.

However, this type of valve requires more components to function, it has several advantages. First, it tends to be more precise. So, if your application needs accurate temperature control, this method is the best option. Second, unlike a thermostatic valve, the actuated control valve permits flexible adjustments to the temperature range as operating conditions change.

Temperature Control Valve Applications

The temperature control valves are most commonly used for different industrial and residential applications. The following are the major applications of temperature control valves:

• Unit heaters
• Small jacketed pans
• Small heater batteries
• Tracer lines
• Ironers
• Small storage calorifiers
• Small tanks
• Acid baths

Some of the industries that use temperature control valves are

• Food Industries
• Oil and Gas sectors
• Chemical and Petrochemical industries.

Advantages and Disadvantages of Temperature Control Valve

Advantages of Temperature Control Valve

• These types of valves have low cost.
• They have small sizes.
• They are easy to install.
• The temperature control valve has one trade installation.
• It is very robust and reliable.
• Tolerant of imperfect steam conditions and of being oversized.
• It works on a self-acting principle which means that no external power is needed.
• You can easily select it according to your requirements.
• These valves are available in different designs different capillary lengths and temperature ranges.

Disadvantages of Temperature Control Valve

• These valves are available in limited sizes.
• They have limited pressure ratings.
• Sensors tend to be much larger than the pneumatic and electronic equivalents and also much slower acting.
• Limited turndown.

Follow this to learn the sizing of control valves.

The orifice flow meter is a device widely used for flow measurement applications in the Oil & gas industry. The orifice flow meter is capable to measure the flow rate of both services (Liquid & Gas) and steam service. An orifice plate is used to create the differential pressure in the process line by acting as an obstruction for flow. The flow rate passing through the orifice in the processing pipeline is directly proportional to the square root of differential pressure (Pressure Drop).

The orifice plate is fitted into line with the flanged connection in the pipe of the process line. The orifice bore diameter size is smaller than the pipe diameter, thus reducing the area which means a lower flow rate is passing through the orifice construction. The location at which the orifice meter cross-sectional area is minimum and fluid tends to regain energy after this point is called the Vena contracta. 

Principle of Orifice Flowmeter

The principle on which the orifice meter works is the differential principle. Flow rate is calculated when fluid (Liquid or gas) is passed through the Orifice flow meter, differential pressure is generated.

According to Bernoulli’s equation, the flow rate is directly proportional to the square of the pressure drop. The flow rate is calculated from the differential pressure indicated on the display of the orifice flow meter.

“Reduction in flow passage accelerates the fluid thus pressure difference is created. Measurement of flow rate is based on the inlet pressure and pressure reduction point to give a discharge flow rate of pipe”.

Important technical terms in Orifice Flowmeter

Some key terms are important terms for the understanding of orifice meter design and working principle.

Beta ratio (β):

The beta ratio is the ratio between the diameter of the orifice bore to the inside diameter of the pipe.

Beta (β) = Orifice Bore Diameter (d) / Internal Pipe Diameter (D)

The beta ratio has no standard range, recommended range for the beta ratio is between 0.2 – 0.7.

Case if the beta ratio is less than 0.2 (Beta ratio < 0.2):

In this case, the following observations are found:

1. The diameter of the orifice bore is small.
2. High-pressure drop, hence higher flow restriction.
3. Increase in uncertainty and decrease in accuracy.
4. Chances of cavitation and flashing take place, because higher pressure drop line pressure may go below the vapor pressure of the fluid.

Case if the beta ratio is greater than 0.7 (Beta ratio > 0.7):

In this case, following observations are found:

1. The diameter of the orifice bore is larger.
2. Low-Pressure drop, hence minimum the flow restriction.
3. Experiences difficulty in measuring low-pressure applications service.

Reynolds Number:

Reynolds number plays an important role in the selection of the type of orifice plate. Reynolds number is the ratio of inertial forces to viscous forces. 

At low Reynolds number flow geometry or profile gets disturbed, a Reynolds number greater than 10000 is recommended so that the coefficient of discharge becomes constant throughout the indicated curve below.

Selection of differential pressure transmitter range:

At full flow conditions differential pressure range between 0 to 2500 mm H₂O (0 – 25 KPA or 0 – 100 inch of water) is adopted very commonly for the orifices.

Refer below-shown figure shows that the 0 – 100 Inches DP range is sufficient in which curve minimum error, due to the change in density to the change in temperature. This range of differential pressure also indicates that accuracy is maximum than the other cases.

Installation of Orifice flow meter:

Orifice-type flow is directly installed in the process line using the flanged connection. The orifice meter consists of taps for pressure measurement which are connected to a pressure measuring device situated according to the design construction. 

Precautions during installation

Within a 1 or 1.5-meter distance, there is no requirement of fitting a nearby Orifice flow meter. The upstream and downstream run is required for the orifice flow meter for velocity distribution.

How does an orifice flow meter work?

Orifice flow meter installed with known coefficient of discharge. Air pocket removal from tubing is necessary before the operation of the flow meter. The orifice flow meter assembly consists of an orifice plate which creates the pressure drop. Process fluid is flowing through the line, and passed through the orifice meter construction. The velocity of process fluid in the pipeline is irregular during initial operation, in a later stage fluid velocity gets stable, and the created pressure drop is measured by the pressure gauge on the taps. 

Thus pressure drop is used to calculate the volumetric flow of the stream indicated in the display of the orifice meter. Fluid density is multiplied by the volumetric flow to calculate the mass flow rate of the Process fluid.

Types of Orifice Plates in Orifice Flowmeter

Orifice flow meters consist of mainly four types of orifice plates which are described below:

Eccentric orifice plate

Eccentric type orifice plate in which borehole is typically constructed off center, square edged. This type of construction is helpful to prevent the deposition of solid and other unwanted materials present in process fluid on the surface which can block the orifice bore. 

The eccentric orifice plate is capable of calculating the flow rate of fluid-carrying gas within the liquid phase (Mixture Phase). The degree of uncertainty is far greater in the Eccentric type in comparison with the concentric type orifice plate.

Concentric orifice plate

A concentric orifice with a center bore design is most commonly used in the application. The concentric orifice plate is a proven and reliable technology that is adopted at the global level. Manufacturing of concentric is also simply by machining a thin plate to create a circular hole in the middle portion of the plate. Concentric orifice plate consisting of a square edge.

Segmental Orifice Plate

In this type of orifice, the plate borehole is centered and consists semicircle shape, with a square edge. Segmental orifice plates are designed for a low amount of slurry and a high amount of solid concentration in the fluid. This type of orifice is an expensive and higher degree of uncertainty in comparison to an eccentric orifice plate.

Quadrant radius orifice plate

This type of orifice plate is designed like a nozzle in which upstream construction is lesser sharp in comparison to the downstream design construction. They are designed for flow containing Reynolds numbers less than 10000 and viscous media properties.

Advantages of Orifice flow meter

• Simple in construction 
• Low space requirement
• Relatively cheaper

Disadvantages of Orifice flow meter

• Poor pressure recovery
• Not suitable for low-pressure application
• Higher power loss

Click here to learn about types of flowmeters and their applications

Level measurement is a process of measuring/monitoring the fluid level within equipment (i.e. Vessel, Reactor, and Storage Tanks). Level measurement may be a Point level or continuous type which can be achieved with the help of a sensing element called the sensor.

Objectives of Level Measurement

There are several technologies available in the instrumentation Industry, Level Measurement is an essential activity in process engineering. The main objectives of level measurement are below mentioned with the possibility of Zero error. 

1. Online level measurement means a digital display of output data for alarm, trip, and record data as well.
2. Increases process Efficiency
3. Tackle or avoid Safety Related incidents

Types of Level Measurement

Level measurement techniques are mainly classified into two categories which are the following:

1. Point Level measurement
2. Continuous Level measurement

These two classifications of level measurement sensors are briefly described below:

Point Level Measurement:

Point level Measurement referred to as the instrument will produce the output or measure value when the level reaches a certain level (up to or greater than the Sensing element of the Level Instruments) within the equipment. Selected media (fluid type) used for level may be liquid, solid, or slurry.

Examples of Point level measurement sensors: Capacitance, Conductivity, Tuning fork

Level Indication basis in Point level measurement: This type of measurement detects high/low-level points where high is set to keep the equipment safe from future overfilling incidents & low to keep the plant safe from downtime.

Types of Point level measurement techniques:

Working of capacitance type sensor:

Capacitance-type sensors are rod-shaped like level measurement which is inserted from the top of the equipment. This type of level sensor works over the principle of change in capacitance.

Capacitance is directly dependent upon the amount of Fluid present within the Equipment. The thermal capacitance of process fluid gradually increases as the level inside the equipment increases and vice versa. Installation of this type of sensor is usually top-mounted.

Advantages of Capacitance type sensor: 

1. Suitable for liquid & solids.
2. Cost-effective solution
3. Used for Viscous media
4. No mechanical or moving parts
5. Small in construction

Working of Conductivity type sensor:

This type of sensor is also rod-shaped consisting of a pair of electrodes with the probe. An alternating current from an external source is supplied to the sensor. When the fluid level inside the equipment reaches up to the sensor, supplied alternating current helps to complete the circuit which causes current to flow. Thus fluid levels are calibrated from the output current value. Installation of this type of probe switch is usually top-mounted.

Advantages of Conductivity type sensor:

1. Available at low cost
2. Easy to use
3. No mechanical or moving parts

Working of Optical type level sensor:

Working of optical type level sensors based on the emission of infrared light towards the application media. The principle used by the optical type level sensor is total internal reflection.  

IR Light is emitted from the LED source called the sender, and the source which collects back IR light is called the receiver this all activity takes place within a prism arrangement. As emitted IR light from the sender gets absorbed or reflected in the application media, thus remained IR light is sent back to the receiver. Reflection of the IR light helps to detect the present liquid level.

Advantages of Optical type level sensor:

1. Compact Size
2. No Moving
3. Inexpensive & Effective Solution

Working of Tuning fork type sensor:

Tuning forks have been used in level measurement since the 1970s. The working principle of the fork sensor is dependent on the application media which completely uses vibrations.

Case-I (Applicable for solid Media): The amplitude of the Vibration principle is used in the case of solids where a fork continuously vibrating at constant intervals gives an amplitude value let’s say X, this amplitude value acts as the threshold value.

When the solid material present inside the equipment contacts with the vibrating fork, the oscillation of amplitude gets changed from X. When this amplitude value goes below X which is the threshold value with the help of an inbuilt electronics system causes changes in output (Calibration or calculation of media level). 

Case-II (applicable for liquid media): The principle is used “Frequency of operation” the in which frequency threshold value is generated due to the vibration of the tuning fork.

The natural Frequency of the fork gets reduces when the liquid media increases inside the equipment. Level measurement is calibrated in the condition when the natural frequency matches the threshold frequency.

Advantages of tuning fork type level sensor:

1. Compatible with high-temperature fluid
2. Not affected by the flow behavior (i.e. turbulence, foaming, etc.)
3. Small in size & easy to installation

Continuous Level Measurement:

Continuous Level measurement refers to the measurement in which media is present in the equipment from the ground level to the peak (top) Level. Continuous Level measurement can be used for liquid or solids.

Level Indication basis in Continuous Level monitoring: In this type of level measurement, each output value changes as fluid rises or down. The set Point can be decided from the range measured.

Types of continuous-level measurement techniques: 

Working of Ultrasonic level sensor:

Ultrasonic type level sensor working principle based on the ultrasonic waves. Ultrasonic waves are emitted by the head of the sensor which is passed through the fluid media and finally gets received by the receptor of the sensing element after striking the bottom surface of the equipment. The time difference between ultrasonic wave emission & reception is used to calculate the distance (i.e. level). Ultrasonic waves used are sound waves for level measurement.

The level can be calculated by the equation:

Distance L = 1/2 × T × C

Where, 

• T is the time difference between the emission & reception of waves (1/2 is used in the equation for wave travel for both emission & reception path).
• C is sonic speed 
• L is distance 

Advantages of Ultrasonic level sensor:

1. The sensing element does not come in direct contact with application media
2. Low cost-effective solution
3. Not affected by the environmental condition (moisture, high ambient temperature)

Working of Radar type level sensor:

The radar-type level sensor working principle remains the same as in the ultrasonic-type level sensor case. Radio waves are responsible for level measurement instead of sound waves used in the ultrasonic-type level sensor. Radio waves are released from the antenna which is placed at the top of the equipment after striking the bottom surface these returned signals are received by the antenna as well. 

Level measurement is achieved by the time difference between emission & received signals.

Advantages of Radar type level sensor:

1. Non-contact type with application media
2. Gives high-accuracy measurements.
3. Suitable for vacuum & high-pressure applications.

Working of DP Type level sensor:

This type of level sensor work on the pressure difference. Two sensors are placed at low-pressure & High-pressure regions. The level is measured from the equation

Pressure = Density of fluid * acceleration due to gravity * Height 

Rearranging equation;

Height = Pressure / (Density of fluid * acceleration due to gravity)

The density of process fluid remains constant for an accurate result.

Advantages of DP Type level sensor: 

1. Easy to install & removal
2. High accuracy
3. Easy maintenance & testing (block valves provided to keep instrument isolated from process fluid).

Causes / Impacts of Incorrect Level Measurements

• Case – I: If the measured level is lower than the actual level. It may produce an impact on the equipment (may damage).

• Case – II: If the measured level is High than the Actual level. Safety (instruments with their alarm, trip interlocks) & environmental Norms or standards are halted.