What is the best valve for pressure control?

Hello everyone,

I am seeking advice on selecting the most suitable type of valve for my application. My specific situation involves a compressor that supplies a constant flow, while my clients require a variable flow that maintains a constant pressure. To achieve this, I aim to install a valve in a bypass to ensure stable pressure levels. Currently, I am using a butterfly valve, but I’ve encountered issues since opening it to 50% results in approximately 70% of the flow being discharged.

Could anyone offer insights on this matter?

Thank you!

It's essential to consider the flow rate and available pressure drop when selecting a valve type. These are critical factors in pressure control applications. A globe valve with equal percentage trim is typically effective unless a low-pressure drop is necessary or the flow rate is excessively high. Additionally, there are V-ball valves that may provide better performance compared to the butterfly valve currently in use. It would be beneficial to consult with your local Fisher representative for expert guidance on valve selection.
Good luck,
George Griggs
Sr. Process Controls Engineer

Initially, I planned to recommend a globe valve with a pressure regulator but realized that your system might involve air (or gas). The line size and the frequency with which the valve must change positions are also important considerations. Could you provide more details?
Best,
Patricia Lougheed

ConservAir pressure control valves are ideal for this application. Their pressure fluctuation is narrow, typically around 2 psi. Regular pressure relief valves may work, but they generally experience higher pressure drops.
It's important to install these valves in the main line rather than in a bypass line; only consider the bypass if there are issues with the mainline valve.
Regards,

To clarify, is the flow rate in m³/hr referring to the compressor's output, the user's needs, or both? Understanding the physical configuration of your system is crucial. In addition, the valve turndown ratio—maximum and minimum flow along with associated pressures and temperatures—should also be evaluated.
If your customer requires a steady supply of air, place a control valve in-line with a controller monitoring downstream pressure. As demand fluctuates, this control valve will adjust to maintain a consistent pressure.

When regulating pressure with a control valve, it remains necessary to have a bypass line. A single control valve can restrict flow during reduced demand, potentially causing upstream pressure to rise and creating problems with your pump.
Installing a bypass line allows you to use a back pressure regulator in the bypass, ensuring the line pressure remains within desired limits. As demand increases (lower pressure), the BPRV will close, and it will open when demand decreases (higher pressure) for relief.

With proper configuration, a butterfly valve can also offer good control. Here are a few installation strategies:

1. Ensure the valve size is appropriate for typical operating conditions.
2. If operating conditions extend outside the valve’s control range (20-70° open), consider adding another valve in parallel.
3. Choose an actuator control offering the required performance characteristics.
4. For detailed information about our closed-loop control actuator which is currently under development, please visit our website. This electronic actuator features built-in PID control and high-speed performance. The Emech ceramic disc valve is designed to resist cavitation and maintain ANSI Cl. IV seal integrity, even with dirty fluids.
For further discussions on your applications, feel free to reach out.

Pressure control valves are integral in pneumatic and hydraulic systems, preventing damage, power wastage, and overheating. Circuit designers utilize various efficiently designed pressure control valves to manage maximum system pressure and pump flow during inactive periods. Many of these valves are compact and easy to install. Depending on the design, some valves can relieve system pressure, while others maintain it within designated limits. This article outlines the various types of pressure control valves.

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Below, we will highlight the major types of pressure control valves.

1. Pressure Relief Valve (PRV)

A pressure relief valve regulates system pressure to prevent equipment failure. When pressure builds up, these valves release excess fluid to maintain safety. They typically operate to open at a predetermined set pressure. The difference between the set pressure and the reseating pressure is referred to as the blowdown, which can vary between 2-20%, with some valves offering adjustable blowdowns.

2. Pressure Reducing Valve

This valve automatically regulates high inlet pressure to a stable, lower outlet pressure, often referred to as a pressure-reducing regulator. They’re compact, require no external power, and are widely used in industries like gas and steam. They can be classified as direct-acting or pilot-operated, with direct-acting valves being more economical for smaller loads.

To ensure optimal performance, these valves can also act as bypass systems to guard against power failures.

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3. Sequence Valve

These valves manage the flow of fluids in a predetermined order, facilitating operations in various industrial settings. They enable pressurized fluids to transition to secondary circuits only after completing tasks in the primary circuit.

4. Counterbalance Valves

Counterbalance valves, or load-holding valves, naturally prevent loads from dropping by maintaining backpressure. They permit fluid flow in one direction while restricting it in the opposite direction. This feature provides an essential safety mechanism in hydraulic systems.

5. Unloading Valve

Unloading valves are specifically designed to divert flow as required, ensuring that system pressures remain stable and fail-safe.