Table of Contents
Valve trim refers to the operating parts of a valve that are usually exposed to the process fluid. In this article, we will explore what valve trim is, examine a valve trim chart, delve into material selection processes, and compare common trims such as Trim 5 and Trim 8.
How much you know about Valve Trims
1. What is Valve Trim?
Choose the correct answer:
Explanation: Valve trim includes the internal components of a valve that come into direct contact with the process fluid. These components are crucial for regulating the flow and pressure of the fluid.
2. What is a characteristic of a Quick Open plug profile?
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Explanation: A Quick Open plug profile significantly increases the flow with a minor initial change in stem travel, achieving near maximum flow with a small stem lift. It is ideal for on-off applications.
3. Which plug profile is used in systems where the valve pressure drop is a significant fraction of the total system pressure drop?
Choose the correct answer:
Explanation: The Linear plug profile is used in systems where the valve pressure drop is a significant fraction of the total system pressure drop, providing a consistent change in flow per unit of valve stroke.
What is Valve Trim?
Valve trim includes the internal components of a valve that come into direct contact with the process fluid. These components are crucial for regulating the flow and pressure of the fluid. The key parts of the valve trim include:
- Stem: Transfers motion from the actuator to the valve plug or disc.
- Plug: Controls the flow of the fluid.
- Disc: The part that opens, throttles, or closes the flow path.
- Seat: Provides a surface against which the disc seals.
The trim’s configuration and material play a significant role in the valve’s performance, durability, and suitability for various applications.
Valve Trim Plug Characteristics
The plug profile in a valve trim influence how the valve performs under different operating conditions. Here are the common plug profiles:
Quick Open
A quick-opening valve plug significantly increases the flow with a minor initial change in stem travel. It achieves near maximum flow with a small stem lift, making it ideal for on-off applications.
Linear
The linear profile provides a consistent change in flow per unit of valve stroke, regardless of the valve position. This profile is used in systems where the valve pressure drop is a significant fraction of the total system pressure drop.
Equal Percentage
The equal-percentage valve plug changes the flow by a fixed percentage at each point along its characteristic curve. This type is used in high-precision applications where consistent flow control is necessary.
Check your Knowledge on Valve Trim Parts
1. Which valve trim part provides a seal when the valve is fully open, preventing leakage into the packing chamber?
Choose the correct answer:
Explanation: The Back Seat provides a seal when the valve is fully open, preventing leakage into the packing chamber.
2. What is the function of the Seat in a valve trim?
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Explanation: The Seat is the component that the disc seals against. It can be permanent or removable and made from metal or non-metallic materials.
3. Which part connects the actuator or handwheel to the disc in a valve trim?
Choose the correct answer:
Explanation: The Stem connects the actuator or handwheel to the disc, controlling its movement.
Valve Trim Parts
Understanding the parts of valve trim helps in selecting the right trim for specific applications. Common valve trim parts include:
- Disc: Can be forged, cast, or manufactured. It needs a smooth surface to minimize friction with the seat.
- Seat: The component that the disc seals against. Seats can be permanent or removable and may be made from metal or non-metallic materials.
- Back Seat: Provides a seal when the valve is fully open, preventing leakage into the packing chamber.
- Stem: Connects the actuator or handwheel to the disc, controlling its movement.
Valve Trim Chart
Valve trims are categorized and assigned numbers based on the materials used for different parts. This chart helps in selecting the appropriate trim material for different service conditions.
| API Trim No. | Material | Seat | Disc | Backseat | Stem | Notes |
|---|---|---|---|---|---|---|
| 1 | 410 | 410 | 410 | 410 | 410 | |
| 2 | 304 | 304 | 304 | 304 | 304 | |
| 3 | F310 | 310 | 310 | 310 | 310 | |
| 4 | Hard 410 | Hard 410 | 410 | 410 | 410 | Seas 750 BHN min. |
| 5 | Hardfaced | Stellite | Stellite | 410 | 410 | |
| 5A | Hardfaced | Ni-Cr | Ni-Cr | 410 | 410 | |
| 6 | 410 and Cu-Ni | Cu-Ni | Cu-Ni | 410 | 410 | |
| 7 | 410 and Hard 410 | Hard 410 | Hard 410 | 410 | 410 | Seas 750 BHN min. |
| 8 | 410 and Hardfaced | Stellite | 410 | 410 | 410 | |
| 8A | 410 and Hardfaced | Ni-Cr | 410 | 410 | 410 | |
| 9 | Monel | Monel | Monel | Monel | Monel | |
| 10 | 316 | 316 | 316 | 316 | 316 | |
| 11 | Monel and Hardfaced | Stellite | Monel | Monel | Monel | |
| 12 | 316 and Hardfaced | Stellite | 316 | 316 | 316 | |
| 13 | Alloy 20 | Alloy 20 | Alloy 20 | Alloy 20 | Alloy 20 | |
| 14 | Alloy 20 and Hardfaced | Stellite | Alloy 20 | Alloy 20 | Alloy 20 | |
| 15 | 304 and Hardfaced | Stellite | Stellite | 304 | 304 | |
| 16 | 316 and Hardfaced | Stellite | Stellite | 316 | 316 | |
| 17 | 347 and Hardfaced | Stellite | Stellite | 347 | 347 | |
| 18 | Alloy 20 and Hardfaced | Stellite | Stellite | Alloy 20 | Alloy 20 |
Material Selection Process
Choosing the right material for valve trim is essential for ensuring optimal performance and longevity. Here’s a brief overview of the material selection process:
- Stainless Steel: The most commonly used trim material due to its resistance to corrosion and wear. It is available in various grades and provides a good balance between cost and performance.
- Monel: An alloy that offers excellent resistance to corrosion and is used in highly corrosive environments.
- Alloy 20: Known for its resistance to sulfuric acid and other corrosive chemicals.
- Cu-Ni: Offers good resistance to seawater and is used in marine applications.
Hardened Trim
For high-pressure applications, hardened trims are preferred. They can be made of solid hard materials or feature a hard coating. This type of trim is suitable for services involving high temperatures or abrasive fluids.
Example of Trim Selection Criteria
When comparing different trims, such as Trim 5 and Trim 8, it’s important to consider factors like material hardness, suitability for the process conditions, and cost. Here’s a comparison of these two trims:
| Details | Trim No. 5 | Trim No. 8 |
|---|---|---|
| Nominal Trim | 410 – Full Hard faced | 410 and Ni-Cu |
| Trim Code | F6HF | F6HFS |
| Stem and Other Trim Parts | 410 (13Cr) (200-275 HBN) | 410 (13Cr) (200-275 HBN) |
| Disc/Wedge | F6+St Gr6 (CoCr Alloy) (350 HBN min) | Monel 400® (NiCu Alloy) (250 HBN min) |
| Seat Surface | 410+St Gr6 (CoCr Alloy) (350 HBN min) | Monel 400® (NiCu Alloy) (175 HBN min) |
| Trim Material Grade | 13Cr-0.5Ni-1Mn/Co-Cr-A | 13Cr-0.5Ni-1Mn/Ni-Cu |
Trim 5 is ideal for high-pressure, slightly erosive, and corrosive services, providing robust performance. Trim 8 is suited for moderate pressure applications and offers a longer service life. Trim 5 generally outperforms Trim 8 in terms of hardness and durability.
Conclusion
Understanding valve trim is crucial for optimizing valve performance in various applications. The valve trim chart, material selection process, and specific trim profiles all play a significant role in ensuring that the valve meets the operational demands of your system.
FAQs
1. What is valve trim?
Valve trim refers to the internal components of a valve that interact with the process fluid. It includes parts such as the stem, plug, disc, and seat, which are essential for controlling fluid flow.
2. How do I select the right valve trim material?
Material selection depends on factors like the fluid type, temperature, pressure, and environmental conditions. Common materials include stainless steel for general use and Monel or Alloy 20 for corrosive environments.
3. What is the difference between Trim 5 and Trim 8?
Trim 5 is designed for high-pressure, erosive, and corrosive services with a higher degree of hardening. Trim 8 is suitable for moderate pressure applications and provides a longer service life.
4. Where can I find a valve trim chart?
Valve trim charts are available from API and various valve manufacturers. They list different trim numbers and the materials used for each part of the valve trim.
5. What does “trim” mean in a valve?
In a valve, “trim” refers to the operating components that regulate fluid flow, including the disc, seat, stem, and plug. The trim’s design and material affect the valve’s performance and suitability for different applications.
By understanding these concepts and using the provided resources, you can make informed decisions about valve trim for your specific applications.
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