TECHNOLOGY ANALYSIS OF STEAM TRAP

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PHUC MINH is a distributor of steam traps and specialized valves and equipment for steam systems, boilers, boilers of industrial steam systems. Through consulting a series of projects on the selection of steam traps as well as industrial valves for steam systems and equipment for steam systems, we have gained a lot of valuable experience in terms of structure, operating principles from which to choose and advise on suitable steam traps for each application according to customer requirements.

To help customers understand more about steam traps, to choose for themselves the best steam traps, the most suitable for their system, we present the most in-depth article on steam traps to help customers understand more about steam traps. You have more information, knowledge about this field. In case you need advice on steam traps, please contact PHUC MINH via Email: info@pm-e.vn – Hotline: 0902800728 / 0766226161 for advice.

 

PHUC MINH is a distributor of TLV Industrial Valves & Steam Traps, Samyang Korea

1. What is a steam trap? Why install a steam trap?

A steam trap is a type of valve that automatically filters condensate (i.e. condensate) and non-condensable gases such as air without allowing steam to escape. In industry, steam is frequently used for heating (heating) or as a driving force for mechanical energy. Steam traps are used in such applications to ensure that steam is not wasted.

According to ANSI, the definition of a steam trap is as follows: Steam Trap - A self-contained valve that automatically drains condensate from a steam-filled enclosure while keeping live steam sealed or, if necessary, allowing steam to flow at a controlled rate. control or adjust. Most steam traps will also pass through non-condensable gases while still being held tightly to live vapor.

Steam is formed when water evaporates to form a gas. For vaporization to occur, the water molecules must be energized enough for the intermolecular bonds (hydrogen bonds, etc.) to break. This energy provided to turn a liquid into a gas is known as 'latent heat.

What is a steam trap? Principle and How to install the most standard steam trap

Diagram of installation of steam traps, industrial valves for steam systems and equipment for steam systems in industrial steam systems

Steam-based heating uses latent heat and transfers it to a certain product. When the job is done (i.e. the steam has removed its latent heat), the steam condenses and becomes condensate. In other words, condensate is incapable of doing the job that steam does. As a result, heating efficiency will be affected if condensate is not removed as quickly as possible, whether in a steam conveyance pipeline or in a heat exchanger.

 

2. What's wrong with using a mechanical valve?

It is sometimes believed that the condensate load can be adjusted with a conventional valve instead of a steam trap by simply adjusting the valve opening manually to match the amount of condensate generated.

Theoretically, this is possible. However, the range of conditions required to achieve this is so limited that in practice it is not a practical solution.

The biggest problem with this method is that setting the valve opening to discharge a fixed amount of liquid means that it is not possible to compensate for fluctuations in the condensate load. Indeed, the amount of condensate produced in a given system is not fixed. In the case of equipment, the load of condensate at start-up is different from the load during normal operation. Fluctuations in the product load also lead to a difference in the amount of condensate produced. Similarly, in the case of steam pipelines, the condensate load can vary depending on the outdoor air temperature or due to heavy rain or snow.

If the unit cannot respond to fluctuations in condensate load, the condensate will be discharged inside the unit/pipe instead and heating efficiency will be affected. On the other hand, when the condensate volume is reduced, steam leakage will occur and the steam will be wasted.

 

3. Steam traps have many different mechanisms.

Various types of steam traps (operating principles) have been developed for automatic discharge of condensate and non-condensable gases. The most widely used mechanisms are those based on differences in temperature, specific gravity, and pressure. Each of these types of steam traps has its own advantages and applications.

 

4. How do mechanical steam traps work? Consider the mechanism of action and use.

Mechanical traps are steam traps that operate on the principle of specific gravity (specifically, the difference in specific gravity of water and steam), unlike other types of steam traps that rely on temperature changes or changes. speed/phase change. In a mechanical trap, the valve opens and closes due to the movement of the float rising and falling with the condensate flow.

Mechanical traps can operate in precise response to condensate flows without their performance being affected by most external factors. This is one of their distinct advantages over thermal and thermodynamic steam traps, whose performance can be affected by external factors such as rain, wind or even insulation.

 

5. Two types of design: Float steam trap and reverse bucket steam trap.

There are two main types of mechanical steam traps: float traps and reverse bucket steam traps. Float steam traps typically use a sealed spherical float, while inverted bucket traps use a cylindrical cup with a float, upside down.

Floating force is the main force operating at the core of both types of mechanical traps, but their structure and operating principle are quite different.

 

5.a. Floating steam trap

In a float steam trap, the position of the float is directly affected by the level of condensate in the trap. The float reacts to the condensate flow, opening and closing the valve to compensate accordingly.

There are two basic designs used for float traps: lever floats and free floats.

In the lever float trap design, a float is attached to a lever that controls the valve. As condensate flows into the trap, the float floats and moves the lever, causing the trap valve to open. However, due to the limited movement of the arm, the valve head is often in the condensate flow path, which can result in an additional pull acting to close the valve in high flow conditions.

In Samyang's float trap, the float is not attached to the lever, and the float itself acts as the valve for the trap. The float can extend out of the drain hole independently, allowing condensate to be drained without clogging. In addition, the natural rotation of the steam trap allows an almost infinite number of contact points to seal the air outlet, greatly reducing localized wear of the valve.

 

5.b. Inverted bucket steam trap (inverted barrel type steam trap)

In a reverse bucket steam trap, the bucket inside the trap is attached to a lever that opens and closes the trap valve according to the movement of the bucket. As steam or air flows into the bottom of the inverted bucket and condensate surrounds it on the outside, the steam causes the bucket to float and rise. In this position, the bucket will cause the trap valve to close. There is a vent on the top of the bucket that allows a small amount of steam to be released on top of the trap, where it is discharged downstream. As steam escapes through the vent, condensate begins to fill up inside the barrel, causing it to sink and allowing the lever to open the trap valve and release the condensate (along with any steam trapped in the trap).

 

Continuous drainage: The important advantage of float traps

A key difference in the operation of float traps and reverse bucket traps is the type of condensate drainage they provide; The float trap provides continuous drainage, while the reverse bucket trap provides intermittent drainage.

In a steam trap, which has a continuous condensate discharge function, the float rises and falls based on the amount of condensate entering the trap, allowing the valve to automatically adjust the level of condensate in the trap. When condensate flows in, the valve opens just enough to drain the condensate, closing when the condensate flow stops. This allows the trap to respond quickly to fluctuations in condensate loads.

On the other hand, in intermittently drained steam traps, condensate is not drained until a significant amount of steam has been released from the bucket, thereby causing the bucket to sink and the valve to open. Therefore, when the valve is closed, the valve can close completely, with no condensate escaping until a certain amount of steam is released from the inside of the barrel.

The flow of condensate from the equipment and steam lines is essentially continuous, regardless of how the steam trap operates. Therefore, in intermittently drained steam traps, condensate will accumulate in the trap as long as the valve remains closed.

 

Trap selection affects operation in low condensate systems

Steam traps are necessary in any system where condensate forms, even if it forms in very small volumes, such as in systems using superheated steam. It is therefore important to understand how steam traps work in environments where condensate loads can be extremely low.

In superheated systems there is usually little condensate. In such operations, there may not be enough water inside the reverse bucket trap to generate buoyancy. As a result, the bucket fell to the bottom of the trap, leaking a large amount of superheated steam. This is not only costly but can also increase back pressure.

Float traps are also affected during use in superheated systems. In a lever float trap, the valve head is very close to the valve seat. Low-flow operations can cause condensate to flow through the valve at extreme velocities, causing erosion of valve components known as "drawstrings". However, the float rotates away from the top of the seat during low traffic service. Since the valve head is not directly in the flow path, wire withdrawal is impeded even in low flow conditions.

 

Number of holes indicates maximum operating pressure

A notable feature of mechanical traps is that there are different hole sizes based on differential pressure available for each Model type. The hole size is designed to match the maximum operating pressure of the trap.

It is important to understand that if the trap is used above its maximum operating pressure, the trap valve may not open. In this situation, known as a "pressure block", the trap remains closed and condensate will not be allowed to escape.

 

6. Mode of operation of the steam trap (Steam trap): Mechanism and Use of the steam trap

Thermodynamic steam traps are appreciated for their compact size and versatility over a wide pressure range. The disc steam trap, also known as the coin steam trap, has a simple structure and works in both horizontal or vertical positions. These features make thermodynamic steam traps a preferred choice for many traced, drip and certain light steam process applications.

 

6.a. There are two types of traps: Disc Steam Traps and Thrusters

There are two basic types of thermodynamic steam traps: Thermodynamic Discs and Thermodynamic Pulses. Of the two, coin steam traps also called disc steam traps are more commonly used, perhaps because impulse traps can leak conductive steam and can fail when small amounts of dirt block the channel. guide. For these reasons, this article will only cover disc traps (coin steam traps).

With a thermodynamic disc steam trap, the condensate flow is controlled by a circular valve head (disc) that opens and closes against the base of the valve. The valve disc is disconnected from all other parts of the trap and rests on top of the valve stem.

The valve stem consists of two concentric rings (gaskets): the inner ring and the outer ring. The inner ring separates the liquid inlet from the outlet(s) and prevents shorting of the vapor inlet. The outer ring controls steam leakage from the pressure chamber above the disc to the outlet.

 

Benefits of the Thermodynamic Disc Trap

 

Limitations of Thermodynamic Disc Trap

 

6.b. Working mechanism of disc steam trap (coin steam trap)

Thermodynamic disc steam traps feature intermittent, cyclic operation. The valve mechanism - consisting of a disc and washers - opens to drain condensate in seconds; and then close for a generally longer period of time until a new discharge cycle begins.

The opening and closing action of the thermodynamic disc trap is caused by the difference in forces acting on the bottom and top faces of the valve disc. These forces are basically based on the changes in kinetic energy and pressure of typical liquids involved: air, condensate and steam.

At start-up, the incoming fluid consisting of air, and/or condensate (and sometimes even steam) at line pressure will create an Opening Force (Elevator) on the bottom of the valve disc; thus making it rise and open. This opening force lifts the disc from the seat to allow condensate flow. The next section explains how the disc mechanism closes after it is opened.

 

Scenario 1: From Open to Closed Position (Explanation of Thermodynamics)

When in the open position, there are two main forces acting on the disc valve: steam in the pressure chamber on the top of the disc and steam running through the underside of the disc. This steam that works to open and close the valve is known as Control Steam.

As steam flows rapidly under the valve disc, the pressure under the disc decreases. The valve disc is then "pushed" onto the valve seat due to the greater pressure in the cavity. This closes the valve.

Controlled steam can be rapid steam or direct steam. It is vapor when water condenses into the trap and undergoes a period change due to a decrease in pressure. It can be direct steam in the case of small amounts of condensate, or if the design can be compromised and not prevent unnecessary steam loss. The best designs minimize or eliminate direct steam use and operate with fast steam whenever possible.

The control vapor in the pressure chamber acting on the top of the valve disc is the result of pressure multiplied by area. Controlling steam on the underside of the disc causes a pressure drop under the disc because of the high velocity (as long as the disc is in the open position).

The valve is designed to close at a vapor temperature close to the condensate wall, which occurs when the condensate that has accumulated is discharged to the outside. When the Closing Force is large enough to overcome the Opening Force (Lift), the valve will close.

The operating mechanism causes the condensate to be released almost instantaneously, making more noise than many other types of steam traps

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