What Valves can be Used for Throttling?

Pipeline systems are not complete without industrial valves, which come in different sizes and styles to cater to different needs.

Industrial valves can be classified according to their function. There are valves used to stop or start the flow of media, control or change the media flow.

Choosing the right kind of valve is crucial to an industrial operation. A wrong type would mean system shut down or system under performance.
 
What Are Throttling Valves

A throttling valve can open, close and regulate media flow. Throttling valves are regulator valves. Some people use the term "control valves" to mean throttling valves. The truth is, there is a distinct line between the two. Throttling valves have discs that do not only stop or start media flow but also regulate the amount, pressure and temperature of media to pass through in any position prescribed.

Throttling valves will have a higher pressure at one end and a lower pressure at the other end. The valve will be closed depending on the degree of pressure. One such example is a diaphragm valve.

On the other hand, control valves will control the flow of media with the use of actuators. The valves cannot function without the actuator.

Pressure and temperature disrupt the flow of media so control valves regulate them. Also, these valves can change the flow or pressure conditions to match the required piping system conditions.

In this sense, control valves are specialized throttling valves. That being said, control valves can throttle but not all throttling valves are control valves.

The best example is the hydraulic system where an outside force has to release the vacuum so gas can enter the valve.

The Throttling Mechanism

When the throttling valve is used for the pipeline, the media flow rate changes. When partially opening or closing the valve, there is a restriction in the flow of fluid, hence the control of media.

This, in turn, compacts the media in that partially open valve. Molecules of the media begin to rub to each other, which additionally slows down media flow as it passes through the valve.

To better illustrate, think of the pipeline as the garden hose. Turning on it, the water goes straight out the hose without any restriction. The flow is not strong. Now, think of the valve as the thumb partially covering the mouth of the hose.

The water that comes out changes in velocity and pressure because of the obstruction (the thumb). The water is much stronger than the one that has not passed the valve yet. In the basic sense, this is throttling.

To apply this in the pipeline system, the system needs the cooler gas to be at the required hotter condition. With the throttling valve in place, gas temperature increases. This is due to molecules rubbing each other as they try to get out of the valve through a limited opening.


Throttling Valve Applications

There is a broad range of uses for the throttling valves. Often one can find throttling valves in the following industrial applications:
    ● Air conditioning systems
    ● Refrigeration
    ● Hydraulics
    ● Steam applications
    ● High-temperature applications
    ● Pharmaceutical applications
    ● Chemical applications
    ● Food processing applications
    ● Fuel oil systems
 
Valves that can Be Used for Throttling

Not all valves are for throttling. Different valve designs are one of the major reasons why some valves are unsuitable throttlers.

Globe Valves

Globe valves are one of the most popular valves. The globe valve is primarily used as a throttling valve. It belongs to the linear motion family. The disk moves up or down in relation to the stationary ring seat. Its disk controls the amount of media that can pass through.

The space between the seat and the ring allows the globe valve to function as a great throttling valve. There is less damage to the seat and disk because of its design.

Limitations

Due to the design of the globe valve, when used in high-pressure applications, it needs an automatic or powered actuator to move the stem and open the valve. Pressure drop and range of flow control are the two considerations for efficient throttling capabilities.

There is also the possibility of leakage due to damaged seat as this comes in full contact with the flow media. This valve is also prone to the effects of vibration, especially when the media is gas.

Butterfly Valves

Butterfly valves look like the gate valve. But, one of their distinct differences is the butterfly valve belongs to the quarter-turn valve family. 

An outside force acts on the actuator. This actuator is attached to the stem which connects to the disc.

Among the most common valves, the butterfly valve is the most suitable for throttling. The valve can be opened or closed with a full quarter turn.

For throttling to happen, it only needs to be opened a bit for the media to pass.

Limitations

One of the limitations of the butterfly valves is that the disc is always in the path of the media flow. The entire disc is more susceptible to erosion. Also, because of this design, cleaning the internal parts is difficult.

For the butterfly valve to be effective, it is necessary to identify the maximum flow and pressure requirements with proper calculations.

Gate Valves

The gate valve belongs to the linear motion valve. Gate valves have gates that move up and down for the opening and closing of the valves. They are primarily used for on-off services. Gate valves have limitations as throttling valves.

In an almost closed aperture, throttling happens as it limits the flow of media. This increases the velocity of the media as it goes out of the valve.

Limitations

The only time that you should use gate valves for throttling is when the valve is 90% closed. Closing it to just about 50% won't achieve the desired throttling capabilities. The downside to using the gate valve is that the flow media can easily erode the face of the disc.

Additionally, gate valves should not be used as throttling valves for long durations. The pressure produced by throttling can tear the gate seat so the valve can no longer completely shut off. Another, if the medium is liquid, there is vibration, which can also affect the seat.

Pinch Valves

Considered as one of the simplest designs, the pinch valve has a soft elastomer liner. It is pinched to close using fluid pressure. Hence its name. Belonging to the linear motion family, the pinch valve is lightweight and easy to maintain.

Pinch valves are very effective when sterility and sanitation are the priorities. The elastomer liner protects the metal parts of the valve.

The stem attaches to the compressor which is lined exactly above the liner. The pinch valve closes when the compressor lowers to the liner. 

The effective throttling range of a pinch valve is usually between 10% and 95% of the rated flow capacity. The best flow control is at the last 50% of the stroke.

Limitations

This valve does not work best when the media has sharp particles, especially when the valve is 90% closed, which can cause tears in the elastomer liner. This valve is not suitable for gas media, and high pressure and temperature applications.

Diaphragm Valves

The diaphragm valve is quite similar to the pinch valve. However, its throttling device is an elastomer diaphragm instead of an elastomer liner.

In the pinch valve, the compressor lowers into the liner and then pinches it to stop the media flow. In the diaphragm valve, a diaphragm disk presses against the bottom of the valve to close it.

Such a design allows larger particles to move through the valve. Between the straight way diaphragm valve and the weir diaphragm valve, the latter is better for throttling.

Limitations

Although it can provide a leak proof seal, diaphragm valves can only withstand moderate temperatures and pressures. Additionally, it cannot be used in multi-turn operation.

Needle Valves
 
The needle valve is similar to globe valves. Instead of a disc, the needle valve has a long tapered point at the end of the valve stem. This is more suitable for applications that need precise regulation.

Additionally, needle valves are better valve control regulators for smaller quantities. The fluid goes in a straight line but turns 900 if the valve is opened. Because of that 900 design, some parts of the disk passes through the seat opening before a complete close of the valve.

Limitations

The needle valves are for delicate industrial applications. That being said, needle valves are unsuitable for thicker and viscous media. The opening of this valve is small and particles in slurries become trapped in the cavity.
 
How to Choose Throttling Valve



Each type of throttling valve has its pros and cons. Understanding the purpose of implementing throttling valve always narrows down the choices for the right kind of throttling valve.

Valve Size

The right valve size means doing away with future valve issues. For example, a valve too large means limited throttling capacity.
Furthermore, the valve that is too big would have additional fittings as an adjustment to the pipes. The fittings are costly.

Material of Construction

The valve body material is an important aspect when you choose the throttling valve. It should be compatible with the type of media that would pass through. For example, chemical mediator should pass through a non-corrosive valve. Media that tends to reach high temperature or pressure should pass through the valve body of a strong alloy with internal coating.

Actuation

Actuation also plays a big role in choosing the right throttling valve. In pipeline applications, there are instances that strong pressure is present. Because of that, a manual actuator may not be efficient in opening or closing the valve.

Connections

How the valve is connected to the pipes is also worth considering. It is important for valves to adapt to the existing pipe connections rather than the pipes adapting to the valves. 

It is more cost effective to suit the valve to the existing pipe requirements. For instance, when the pipe ends is flanged, the valve should also be flanged.

Industry Standards

Industry standards are just as important. There are standards for the type of material for a particular media. There are also standards on end connections or the thickness of the metal for the valve.

Such standards bring safety to applications. There is often an increase in temperature and pressure when the throttling valve is used. By that, it is vital to understand such standards for the safety of everyone.
 
In Summary

While most valves have limited throttling capabilities, one does not simply use them as so. For the valve to last longer, it is best to know which valves is suitable for a particular throttling application.