A control valve is the most commonly used to regulate fluid flow in the process.
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The international society of automation defines the control valve as a power-operated device that operates a fluid flow rate in a process control system.
Control Valve Accessories
The following list shows the most commonly used accessories with the control valve, as per the requirements.
If a control valve is equipped with proper accessories can become more useful for process control also provide smooth and efficient operation. Pneumatic control valve accessories help ensure optimal performance and are an essential component in a process control system.
Purpose of Control Valve AccessoriesThere are five basic reasons that accessories are added to a control valve:
Image Credits: Fisher
I/P Transducer
An current to pressure uses a converter module that converts a 4 to 20 mA current input to a proportional 3 to 15 psi pressure output.
In some applications, where a high level of positioning accuracy by a positioner is not required. In these applications, an electro-pneumatic (I/P) transducer only can be used.
Read: I/P Converter Principle
Volume Boosters
When the actuator volume is very large, the control valve positioning speed of response becomes less.
Volume boosters are used to provide additional pneumatic thrust output capacity to a valve assembly.
Single-acting actuators typically use one volume booster. Double-acting actuators require at least two volume boosters.
Read: Volume Booster Principle
Position Transmitter
The purpose of a position transmitter is to provide independent, separate valve position feedback to the control system. Position feedback of the control valve often becomes necessary as it is used for process monitoring, troubleshooting, or startup/shutdown verification from the control room by an operator.
Image Credits: Emerson
The position transmitter is mounted directly to the valve yoke and measures the position of the valve stem or shaft.
Read: Positioner Principle
Solenoid Valve
In some applications, the solenoid valve will trap air in the actuator to lock the valve in its current position.
In some applications, the solenoid valve will vent out the air from the actuator to allow the valve to move to its no air position.
Read: 2 way Solenoid Valve
Limit Switches
The purpose of a limit switch is to provide a discrete open or discrete close input signal to the control system when the valve reaches a specific position within its range of travel.
Image Credits: Titanindustech
Limit switches, which are mounted on the control valve and on the yoke are also used for process monitoring, troubleshooting, or startup/shutdown verification from the control room by an operator.
These switches will only provide specific valve position feedback. These can be mounted on the control valve to get additional feedback signals to the DCS or PLC systems as per our requirement.
Trip Systems &#; Airlock relay
Trip systems such as air lock relays are used in control applications where a specific actuator action is required in the event that air supply pressure is lost. These are used with double-acting actuators that do not have an inherent air, fail state, or with single or double-acting actuators to provide pneumatic lock-up.
When the instrument air supply pressure falls below the trip point, the trip valve causes the actuator to fail up, lock the control valve in the last position, or fail down.
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For double-acting applications, an air volume tank provides the reserve air capacity to operate the valve in case of air supply failure and until the supply pressure is restored. When once the air supply pressure restores, rises above the trip point, the trip valve automatically resets, turns normal, and allowing the system to return to normal operation.
Read: Air Lock Relay Principle
Handwheel
Handwheels for diaphragm actuators of the control valve are often used as adjustable travel stops. They also provide a manual means of positioning the control valve in an emergency.
They are arranged in two ways to a control valve.
The side-mounted handwheel can be placed to limit travel in any direction, but not both directions at the same time. By keeping the handwheel of the control valve in the neutral position, automatic operation is possible throughout full valve travel.
Top-mounted handwheels are used for &#;infrequent service&#; to manually stroke the valve.
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Those seemingly simple valves employ a lot of physics inside those metal bodies of theirs. What you may think of as a simple open-and-close system is about to be a bit trickier than you thought. In this post, we&#;ll talk about the most important valve components and their functions.
If you&#;re an automotive detailer or industries from industrial and residential cleaning who&#;s trying to understand more about valves, you&#;ll find this post useful.
You&#;d also be happy to know that our shop at MTM Hydro powered by Veloci has more than what you need. Let us know if you have any questions, and make sure to check the tips and tricks to keep our products safe.
The Basic Valve: An Overview
A valve is a device that can regulate or control the flow of a fluid through pipes. For a device to be able to do that, it&#;ll need to withstand pressure, prevent fluid leaks, and have a mechanism that allows for fluid control. All of this leads to a plethora of components working together to provide the final result.
There are different types of valves out there. A few examples are:
Globe valves
Gate valves
Butterfly valves
Needle valve
Ball valves (sometimes referred to as plug valves)
Non-return valves
Diaphragm valves
Each of these valves controls the flow of fluids differently. Some of them share the same function but with a different design, like gates and globe valves. Nevertheless, there are a few basic components that are found in all valves. These are:
Body and bonnet
Disc and seat
Actuator
Stem
Packing
Trim
Valve Components: Explained
Here&#;s what each component does in detail:
The valve&#;s body is the valve&#;s main pressure boundary and the primary housing that contains all other parts of the valve.
The bonnet is the valve&#;s cover, making it another pressure boundary element. Some valves don&#;t have valve bonnets. Instead, the body is split into two parts that are threaded, bolted, or welded together.
In some valves (like globe and stop check valves), the bonnet can have an opening where the valve stem passes, giving you access to the valve&#;s internal parts. This is useful when you need to repair any damage inside the valve.
Together, the body and the bonnet resist the fluid pressure and, if properly constructed, should prevent any leakage.
Valve bodies can be made into various shapes and from various materials depending on the intended use. Some of these include:
Stainless steel
Bronze
Iron
Plastic
If the design includes a bonnet, the bonnet is often made from the same material as the body.
The disc is the valve part that controls the water flow. As long as the disc is seated in place, it&#;ll be exposed to the full system pressure until the outlet is opened again and the disc leaves its place.
Because of the constant pressure applied on discs, they&#;re often made from hard materials to resist wear.
The seat (sometimes known as the seal ring) acts as the disc&#;s seating surface. Not every design will have seal rings, as some of them have the body machined to act as the seating surface.
The expression &#;close the water valve&#; that people use is practically incorrect. You don&#;t close the valve; you operate the actuator (also known as the handle) in a linear and rotary motion to close the valve.
When you use the actuator, you put the disc in or out of place, which, in turn, controls the fluid flow.
Actuators could be manual handwheels or levers, but they could also be operated via motor operators, pneumatic operators, and hydraulic rams.
Unlike the valve body, bonnet, and disc, the actuator is often outside the pressure boundary. The exception lies in some hydraulic or pneumatic cylinders.
The stem is the connector between the disc and the actuator. When you operate the actuator, the stem puts the disc in or out of place to connect the fluid flow. Much like the actuator, it also lies outside the pressure boundary.
Oftentimes, stems are forged and threaded or welded to the disc. This connection allows for some slight movement range to facilitate the disc&#;s seating on the seat or the valve&#;s body.
Some designs also manufacture the stem to be more flexible to allow the disc to position itself on the seat. However, these designs are more likely to damage the valve disc because of constant fluttering.
Note that stems have two types:
Rising stems
Non-rising stems
The difference between both types lies in the movement of the stem as the actuator is operated.
Rising stem designs will have the stem screw above the actuator during usage. That rise is because the stem is threaded to a yoke that&#;s mounted to the bonnet. Alternatively, non-rising stems won&#;t rise above the actuator since the stem is internally threaded to meet the disc.
Leakage can happen outside or inside the valve. The inside leakage is prevented by filling the space between the bonnet and stems with packing.
This packing can be composed of various materials like flax and teflon. The point is to seal the internal parts of the valve to minimize leakage.
The trim is a collective term used to describe all removable internal valve parts. These parts include:
Spacers
Discs
Valve seats
Guides
Springs
Valve Applications
The quickest example of using valves in most people&#;s minds is using a water tap valve. However, they can be utilized in many other clever manners.
For example, car detailers often use consolidated guns and lance systems to clean cars. This system usually uses a three-way ball valve. However, this would result in a lot of dismantling, wasted time, and lost spray.
A smarter application would be to use a two-way shuttle valve that allows the user to keep both the nozzle and the foam cannon in one place. With a single click, the user can switch between water or foam.
One of the latest wash systems that utilize this design is the Mezzo Wash System by MTM Hydro powered by Veloci.
The Verdict
As an automotive detailer, understanding valve components is among the many things you need to learn.
And if you&#;re looking for smart applications of valves and various other auto detailing equipment, make sure to check MTM Hydro powered by Veloci.
If you have any further questions, don&#;t hesitate to contact us today. We&#;re only a few clicks away.