Chapter 10.21 - Control Valve Features: Valve Features to Reduce Noise

Valve Features to Reduce Noise

Silencers and Diffusers

A diffuser is a pressure reducing device that is installed downstream from a control valve. The total pressure drop needed for flow control of a flow control loop is divided between the valve and diffuser. This enables the valve to operate at a lower pressure ratio (Δp/p₁) and greatly reduce the control valve noise level generated by steam, gas or vapor flow. A properly selected diffuser valve combination can result in up to a 40 dBA noise reduction.

The diffuser or silencer differs from other types of path treatments because it does actually absorb some of the noise energy. For control valve applications operating at high pressure ratios (Δp/p₁ greater than 0.8), a series approach, which splits the total pressure drop between the control valve and a fixed restriction such as a diffuser, downstream from the valve, can effectively minimize the noise.

The diffuser must be designed for each unique installation so that the noise levels generated by the valve and diffuser are equal. Valve manufacturers that offer diffusers will design for the conditions. Diffuser and silencer design are covered in Chapter 8.

Vent Diffusers

Control applications venting to atmosphere are usually very noisy because of the high ratios of delta p/p_l and the excessive exit velocities involved. A vent diffuser or silencer may be used to divide the total pressure drop between the actual vent and an upstream control valve. A vent silencer and control valve combination can reduce the predicted or potential overall system noise by as much as 60 dba.

Figure 10-40 shows a vent diffuser venting to atmosphere, downstream from a control valve.

Noise Abatement for Butterfly Valves

For rotary valves, noise attenuation devices are also available. Depending on the intended pressure drop ratios, a fixed restriction installation downstream from the butterfly valve, can consist of one or more stages of perforated plates. Its purpose is to absorb the maximum possible portion of the system pressure drop.

Valve Features to Reduce Noise

Silencers and Diffusers

A diffuser is a pressure reducing device that is installed downstream from a control valve. The total pressure drop needed for flow control of a flow control loop is divided between the valve and diffuser. This enables the valve to operate at a lower pressure ratio (Δp/p₁) and greatly reduce the control valve noise level generated by steam, gas or vapor flow. A properly selected diffuser valve combination can result in up to a 40 dBA noise reduction.

The diffuser or silencer differs from other types of path treatments because it does actually absorb some of the noise energy. For control valve applications operating at high pressure ratios (Δp/p₁ greater than 0.8), a series approach, which splits the total pressure drop between the control valve and a fixed restriction such as a diffuser, downstream from the valve, can effectively minimize the noise.

The diffuser must be designed for each unique installation so that the noise levels generated by the valve and diffuser are equal. Valve manufacturers that offer diffusers will design for the conditions. Diffuser and silencer design are covered in Chapter 8.

Vent Diffusers

Control applications venting...