Control Valve Noise Level Standard and Noise Reduction

Ambient noise at worksites needs to be controlled to reduce potential damage to people’s hearing but also to meet each country specified standards. Read on to find out the main causes of control valve noise and how to reduce it with MASCOT solutions.

What Causes Control Valve Noise?

The three main causes of noise generated by valves are:

1. Vibration. The mechanical vibration of the valve, its components e.g., valve actuator, or connected piping or steelwork.
2. Turbulent gas flow through the valve. This is known as aerodynamic noise and is generated within the valve trim, and at the valve exit. Aerodynamic noise results from the sheer forces created as the gas hits obstructions in the flow stream e.g., the valve trim, where it decelerates, expands, or changes flow direction.
3. Cavitating liquid flow through the valve. This is known as hydrodynamic noise, and similar to aerodynamic noise it is generated within the valve trim and, at the valve exit. Cavitation is the formation and collapse of vapour cavities in the flowing liquid. You can read more about cavitation in our article here.

Why is Valve Generated Noise an Issue?

Legislation and company standards often limit the noise allowed in a working environment to eliminate potential hearing damage to plant operators and maintenance crews. The noise generated by valves can contribute significantly to the overall plant noise.

Legislation and standards differ, however typical limits are:

• For continually operational control valves noise shall not exceed 85 dBA one meter downstream of the valve and one meter out from the valve,
• For intermittently operated atmospheric discharge vent valves noise shall not exceed 90 dBA at a point four meters downstream from the vent exhaust.

Control valve noise can introduce process control issues, and if left untreated lead to costly repairs to valves, pipes, field mounted instrumentation and surrounding equipment.

How To Estimate Valve Noise

It is better to avoid installing a noisy valve rather than trying to retrofit noise abatement solutions to an existing valve. Therefore, estimating valve noise at the design stage is good practice. The ISA and IEC organizations have developed a method of calculating valve noise in the international standard IEC 60534-8-3, "Industrial process control valves – Part 8-3: Noise considerations – Control valve aerodynamic noise prediction method".

All reputable valve suppliers will provide noise estimates for the given service conditions when they quote for supply of a valve. You will receive this as part of any MASCOT quote.

How to Reduce Control Valve Noise

The two basic approaches for reducing valve noise are source treatment and path treatment. Source treatment attempts to curb excessive noise that would have been generated within the valve, while path treatment attempts to reduce noise after it has been generated.

Reducing Control Valve Noise at Source

The common source treatments include:

• Proper sizing of valve trim
• Selection of low noise valve trims
• Use of an inline diffuser
• Use of a vent diffuser
• Multistage trim designs.

Path Treatment Options

The principle of path treatment is to reduce the propagation and transmission of sound to the external sound field. The common path treatments include:

• Increasing pipe wall thickness, or as it is more commonly referred to pipe schedule. The use of a heavier walled pipe downstream of a valve can reduce noise. A method not over popular with piping engineers due to the increased complexity of the piping design.
• Use of acoustic (or thermal) insulation. When correctly applied this can be a very effective method of reducing noise. However, this method can lead to Corrosion Under Insulation (CUI). CUI is a form of localised, external corrosion of pipe resulting from water trapped between the pipe and insulation. Undetected CUI on pipes can result in leaks. Consequently, acoustic insulation is not popular with the plant maintenance team.

MASCOT Solutions for Noise Reduction and Noise Attenuation Control Valves

The MASCOT MEGAFLO trim for control valves is used to reduce control valve noise to acceptable levels in high pressure drop gas applications.

The MEGAFLO attenuator design consists of a series of retainers which can reduce noise levels by up to 30 dBA. Noise attenuation is achieved by staging the pressure drop not just across the plug and seat but also across the holes in each of the retainers and by controlling the turbulence carried into the downstream piping using the following mechanisms:

• Staged Pressure Drop
• Small Flow Streams
• Acoustic Impedance

Need help choosing or specifying control valves? Get in touch with us today.

MASCOT Industrial engineers have over 100 years of combined experience in providing high quality equipment to the Global Continuous Process Control Industry. Our core products and services include control valves, choke valves, actuated and commodity valves, and associated equipment for both standard and severe service applications.

MASCOT’s Engineering & Manufacturing expertise allows us to provide tailored solutions to our customers’ needs with timeliness and accuracy no matter the process. We aim to exceed our expectations with Better Value highly engineered products, faster delivery (-times) on any process, offering support from first contact through to after-sales and beyond.

For more information about our services, please call us at +61 3 9608 6400 or get in touch via sales@mascot-au.com