Spring-Loaded and Pilot-Operated Safety Valves and Their Industrial Uses

Here's a detailed explanation of spring-loaded and pilot-operated safety valves and their industrial uses.

Spring-Loaded Safety Valves

• Description: These safety valves feature a simple, self-contained design consisting of a valve body, a valve seat, a disc (or poppet), a spring, and an adjustment screw. The spring actively exerts a force on the disc, keeping it pressed against the valve seat and the valve closed under normal operating conditions. You can adjust the spring tension using the adjustment screw, enabling customization of the set pressure of the valve.
• Operation: When the system pressure exceeds the set pressure, the pressure forces the disc away from the valve seat by overpowering the spring force, opening the valve, and allowing excess pressure to vent out. Once the system pressure drops below the set pressure, the spring forces the disc back onto the seat, closing the valve.
• Applications: Industries use spring-loaded safety valves in various applications such as boilers, pressure vessels, and different piping systems, especially where the fluid is gas or steam. These valves respond quickly to sudden increases in pressure.
• Advantages: Spring-loaded safety valves are self-contained, straightforward, and reliable. They operate without the need for any external control or power supply.
• Disadvantages: These valves have limited capacity, might not handle extreme pressure fluctuations effectively, and can suffer from issues like "chattering" (rapid opening and closing), which can damage the valve.

Pilot-Operated Safety Valves

• Description: Pilot-operated safety valves are more intricate than spring-loaded valves. They comprise two main components: a main valve and a pilot valve. System pressure and a smaller spring close the main valve, acting on a larger surface area. The pilot valve, essentially a small spring-loaded safety valve, controls the opening and closing of the main valve.
• Operation: When system pressure surpasses the set pressure, the pilot valve opens first, reducing the pressure on top of the main valve. This action opens the main valve, venting the excess pressure. As the system pressure drops below the set pressure, the pilot valve closes, and the main valve reseals.
• Applications: Industries commonly use these valves in high-capacity and high-pressure applications such as chemical processing plants, power plants, and oil and gas facilities. They are ideal for liquid-based applications because they can handle large pressure fluctuations and higher flow capacity.
• Advantages: Pilot-operated safety valves offer greater capacity, improved performance with liquids, and increased stability compared to spring-loaded valves. They can accommodate more significant pressure fluctuations and are less susceptible to chattering.
• Disadvantages: These valves are more complex and costly compared to spring-loaded valves. They might also need periodic maintenance to ensure proper functioning.

Both types of safety valves play a crucial role in maintaining safe operating conditions in industrial systems. They prevent equipment damage and protect workers from potentially dangerous situations. The choice between spring-loaded and pilot-operated safety valves depends on the application's specific needs, such as the fluid type, operating pressure, and flow capacity.

CTi Controltech

https://cti-ct.com

925-208-4250

API 6D & API 6A Valves

API 6D and API 6A are two different valve standards developed by the American Petroleum Institute (API) to guide the design, manufacturing, and application of valves in the oil and gas industry. Both standards are widely used in the industry, but they have different scopes and cover different types of valves.

API 6D (Pipeline Valves): This standard primarily focuses on pipeline valves, which include gate, plug, and ball valves. These valves are specifically designed to transmit and distribute oil, gas, and other hydrocarbons in pipeline systems. API 6D covers the following aspects:

1. Valve design: Specifies the requirements for valve design, including materials, dimensions, pressure ratings, and testing criteria.
2. Manufacturing: Provides guidelines for manufacturing processes, ensuring consistent quality and performance of the valves.
3. Application: API 6D valves are typically used in onshore and offshore pipelines to transport oil, gas, and other hydrocarbon products.

API 6A (Wellhead and Christmas Tree Equipment): This standard focuses on wellhead and Christmas tree equipment installed at the surface of an oil or gas well to control the flow and pressure of the produced fluids. API 6A covers a wide range of valves, including gate, needle, choke valves, and other wellhead equipment, such as flanges, connectors, and fittings. API 6A addresses the following aspects:

1. Valve design: Specifies the requirements for valve design, materials, dimensions, pressure ratings, and temperature classes.
2. Manufacturing: Provides guidelines for manufacturing processes, quality control, and valves and wellhead equipment performance verification.
3. Application: API 6A valves are typically used in onshore and offshore oil and gas production and processing facilities, including wellheads, Christmas trees, and surface production equipment.

In summary, the main difference between API 6D and API 6A is the application and scope of the valves they cover. API 6D focuses on pipeline valves for oil and gas transportation systems, while API 6A focuses on wellhead and Christmas tree equipment for oil and gas production and processing facilities. Both standards provide valve design, manufacturing, and application guidelines to ensure safe and efficient operations in the oil and gas industry. 

https://cti-ct.com
925-208-4250

What are API 526 Safety Valves?

API 526 is a standard published by the American Petroleum Institute (API) that covers safety valves for use in the petroleum and natural gas industries. API 526 safety valves are designed to protect against overpressure conditions in piping systems, vessels, and equipment by automatically relieving excess pressure. They are used to protect against hazards such as explosions, structural damage, and injury to personnel. API 526 covers the design, materials, testing, and installation requirements for safety valves in these applications.

API 526 is a purchasing specification for "API safety valves" that specifies nominal diameters, flange pressure ratings, center-to-face dimensions, flow areas, body and spring materials, and service restrictions. API safety valves are utilized in the petrochemical sector globally, both on and off-shore. Standardized plants, blow-down systems, and large pipework sections distinguish these applications. The LESER type 526 combines the API standards and the ASME Code requirements with the LESER range's established and tested service reliability.

https://cti-ct.com
925-208-4250

Happy Holidays from CTi Controltech

When You Need an Extremely Durable 4.5 Inch Process Gauge

The Series PT45P process gauge from REOTEMP is an exceptionally durable gauge that can withstand pulsation and vibration, as well as corrosive atmospheres and media. It was built specifically for use in the process industries. The combination of the solid front and the blowout back provides a very high level of user safety. Note: A diaphragm seal should be installed for any highly corrosive application, operates at high temperatures, or put through strenuous use.

For more information about REOTEMP products in Northern California and Northwestern Nevada, contact CTi Controltech by calling 925-208-4250 or visit https://cti-ct.com.

Happy 4th of July!

Control Valve Application Notes

Using an incorrectly applied or sized control valve may have significant ramifications for operation, productivity, and, most importantly, safety. Here is a brief list of fundamentals to consider: 

Control valves are not isolation valves: 

Control valves do not isolate a process and do not offer a bubble-tight seal, and utilization in a shutoff capacity is unwise. 

Choose the suitable materials for the job: 

The valve body, seat, and wetted materials must all be compatible with the process under control. Before selecting a valve, evaluate the pressure ratings, operating temperatures, and material compatibility. 

Sensor placement: 

Place the flow sensor upstream of the control valve when configuring the control loop. When the flow sensor placement is downstream of the control valve, exposure to an unstable fluid (bubbles) created by the flashing and turbulence of the flow in the valve cavity is possible.

Control precision and mechanical constraints: 

Consider the degree of controllability you need and the inherent Deadband produced by your valve and associated components. Deadband is the built-in movement that occurs in a control valve between the signal change and the direction of the valve, which exacerbates by worn or poorly designed couplings between valve and actuator, mechanical sensor tolerances, friction in the valve stems and seats, or an undersized actuator. Due to opening/closing oscillations, too much deadband leads to poor controllability (hunting). 

Stiction: 

Stiction is the "stickiness" in valve action induced by packing gland, seat, or force against the disk friction. It may happen if the valve sticks in one position for a prolonged time or is constantly traveling in a minimal range for an extended period. The actuator must apply more force to break the disk free, resulting in overshoot and poor control. 

Tuning the loop controller and/or positioner: 

A poorly configured loop controller or positioner is often the source of poor control and loop instability. Advanced auto-tuning capabilities in PI (proportional with integral), PD (proportional with derivative), and PID (proportional with integral and derivative) controllers have replaced human (often trial and error) loop tuning. 

Valve sizing should be correct: 

Control valves are often oversized, permitting maximum flow at just a tiny percentage of total travel. Minor adjustments in valve position have a significant impact on flow. A high valve-position-to-flow ratio promotes continual "hunting," which leads to excessive valve wear. A decent rule of thumb is to size a control valve at around 70% to 90% of its travel. 

What sort of flow characteristics does your valve produce: 

The flow characteristic of a control valve is the connection between the position of the valve disk, gate, or globe and the change in flow rate through the valve under normal circumstances. A linear flow characteristic is desirable. However, different valve designs have varying flow characteristics, some of which are linear and others that are not. Globe control valves have linear flow properties, while butterfly and gate valves have non-linear flow characteristics. Manufacturers will often create specifically shaped disks or orifices to "characterize" the valve's flow to improve linearity.

The above is a brief list of the most common things to consider when applying control valves. There are many other criteria to consider. It is suggested in the strongest terms to consult with an experienced application expert before selecting or using a control valve.