Question 1

Can a Cv or Kv value be specified for a silencer?

Accepted Answer

In principle, a Cv or Kv value can be specified for a Glaunach Silencer or Dump Tube, but it serves only as a rough reference.

Silencers / Dump Tubes are not designed for flow regulation; instead, they are selected according to the valve manufacturer’s specifications or the design value of an orifice plate.

The silencer’s Cv/Kv must not restrict the required system flow and is therefore not an independent design parameter.

For diffuser-silencers, the design is not comparable to that of valves or orifice plates.

Since silencers are intended to pass a defined flow with minimal loss, specifying a Cv/Kv value is usually not meaningful in practical applications.

Question 2

What is the maximum allowable liquid content in the gas?

Accepted Answer

A gas may become two-phase (liquid and vapor) due to pressure drops, temperature fluctuations, or insufficient separation.

We assume that the medium is free of liquid components in our products. In practice, however, a liquid content of up to 10% by mass is generally tolerated without impairing operation.

Please note that we do not accept any liability for damage resulting from the presence of liquids. It is the responsibility of the system operator to ensure that the medium is free of liquid water.

If the steam is additionally cooled, for instance by water injection (spray cooling), the system operator must ensure that no liquid water enters downstream components such as silencers, diffusers, or steam dump tubes.

Question 3

What is the maximum allowable flow velocity in the silencer inlet?

Accepted Answer

Flow velocity significantly affects both pressure losses and noise generation. It must therefore be calculated specifically for each medium.

As a rule of thumb, the flow velocity at the silencer inlet should not exceed 0.3 Mach - that is, 30% of the speed of sound in the respective medium.

Question 4

What influence does the mass flow have on the backpressure in the silencer inlet?

Accepted Answer

Mass flow has a significant impact on the backpressure that develops within the silencer. As the mass flow increases, so do flow velocity and associated pressure losses due to friction, turbulence, and redirection within the silencer.

Note:
In subcritical flow (v ≪ Mach 1), the mass flow rate varies approximately linearly with back pressure, since the flow is not constrained by sonic conditions.

Question 5

What is the advantage of a higher inlet pressure in the silencer inlet?

Accepted Answer

A higher allowable inlet pressure offers several advantages:

At a given mass flow rate, the volumetric flow rate of the medium decreases due to higher density, which in turn reduces flow velocity.

This results in lower aerodynamic noise and may allow for smaller pipe diameters upstream of the silencer. Additionally, part of the overall pressure drop can be shifted from the control valve to the silencer, where it can be managed in a way that optimizes acoustic performance.

Each Glaunach Diffuser is designed for a specified operating pressure during normal operation and a defined maximum allowable working pressure (MAWP or PS) for upset or fault conditions. This pressure is present directly at the silencer inlet and is referred to as inlet pressure or back pressure.

⚠️ Warning:

An increase in operating pressure significantly affects both the flow characteristics and the acoustic performance of the silencer. The most notable effects include:

Higher noise potential:
 Increased inlet pressure corresponds to higher energy content in the medium, which can lead to more intense discharge noise and greater sound emissions.

Increased pressure drop:
 While higher pressure increases gas density and can reduce flow velocity, it may also allow for higher mass flow rates, potentially leading to increased pressure loss across the silencer if not properly designed.

Greater mechanical stress:
 Higher pressure subjects the silencer housing and internal components to greater mechanical loads.
 It is therefore essential that the maximum allowable working pressure (MAWP/PS) is never exceeded.

For these reasons, the silencer must always be selected and designed based on the highest expected inlet pressure to ensure safe, reliable, and acoustically effective operation.

We are happy to assist you in selecting the optimal operating pressure.

Question 6

What should be considered when using silencers with multiple inlets?

Accepted Answer

When using silencers with multiple inlets, it is important to ensure that unwanted backflow between connected lines is avoided. For example, if a control valve opens while a safety valve remains closed, steam or gas can flow backward through the common discharge system toward the safety valve. This may lead to issues such as apparent leakage or corrosion, even though the valve itself has not activated.

Glaunach can implement specific design measures to significantly reduce the risk of backflow. However, with multi-inlet silencers, backflow cannot always be completely prevented due to the nature of the design.

For critical applications where any backflow must be avoided, we recommend:

using separate silencers for each source (e.g. one for the control valve and one for the safety valve), or
installing check valves in the inlet lines to block reverse flow.

We are happy to support you in selecting the most suitable solution for your system.

Question 7

Why is hydrogen a particularly demanding gas for silencer applications?

Accepted Answer

Hydrogen has unique physical properties that set it apart from other gases:

Extremely high flow velocity: Up to 2000 m/s (≈ 6600 ft/s) – several times higher than that of air.

Shock wave formation: When released into the atmosphere, highly underexpanded jets form, generating intense shock waves – a frequently underestimated phenomenon.

Thermodynamic challenges: Low density, high thermal conductivity, and rapid diffusion require a deep understanding of fundamental physical principles.

Why can't standard silencers be used?
Conventional silencers are typically designed for steam or gases with significantly lower flow velocities. In the case of hydrogen, incorrect design can lead to poor sound attenuation, increased wear, or even safety risks.

Why is Glaunach particularly well suited for this?
Glaunach combines many years of experience with deep expertise in fluid dynamics, thermodynamics, and acoustics – essential for the accurate design and safe operation of silencers used with hydrogen.

Question 8

Is a GLAUNACH Vent Silencer a pressure vessel?

Accepted Answer

Yes and no.

The silencer includes a pressure-bearing diffuser that can maintain a certain pressure at the inlet during operation. This pressure not only enables effective noise reduction through physical principles, but also helps minimize the diameter of the upstream piping and the silencer itself.

However, the downstream silencer housing is typically not pressurized, as it is open to the atmosphere.

Therefore, a vent silencer is partially considered a pressure vessel and is certified in accordance with applicable regulations.

Frequently asked questions