Viewed From X X

FIGURE 3 Cutwater of a spiral casing and impeller (Reference 9)

FIGURE 4 Effects of gap width between cutwater of a spiral casing and trailing edge of the impeller blade (Reference 9)

Control of Noise Paths These approaches consist of system modifications and treatments to disrupt the conduction of sound, whether borne by the structure, liquid, or air. They include approaches other than those that directly affect the originating source of oscillating energy (Figure 6).

LIQUID PATH Noise generated in the region of the pump is conducted both upstream and downstream by the liquid in the piping system. Such paths are most effectively reduced by acoustic (pulsation) filters or other pulsation control equipment, such as side branch accumulators (see Section 3.6).

STRUCTURE-BORNE NOISE Obvious paths for solid-borne noise are the attached piping and pump support systems. Oscillatory energy generated near the pump by pulsation, cavita-tion, turbulence, and so on, can be conducted as solid-borne noise for substantial distances

FIGURE 5 Reduction in sound pressure level with influences on head and efficiency at 100% flow for various impeller blade and casing tongue configurations (Reference 10)

before it is radiated as acoustic noise into the atmosphere. Some success in controlling solidborne noise propagation can be achieved by the use of flexible couplings in the piping systems, mechanical isolation (vibration mounts and so on) for the pump and drive systems, and resilient pipe hangers and supports.

Techniques for the vibration isolation of mechanical equipment are well known and available from many suppliers of vibration isolators or mounts. These may consist of resilient supports at each mounting point of the machine, although it is often necessary to mount the pump and drive system on a single rigid skid (to assure alignment) and then isolate the skid from its support system. For best isolation, the lowest resonant frequency of the supported system should be well below the minimum operating frequency, and none of the higher resonant modes should be coincident with running speed or multiples thereof.

The application of elastomeric coatings to the exterior surface of the pump or piping to damp pipe wall vibrations is normally ineffective except on very thin conduit. However, such coatings may have a small acoustic effect in confining or absorbing high-frequency noise that would otherwise be radiated by the pipe wall vibrations. (See the following discussion on pipe wraps.)

(a)

Noa* 0wmnitng m*m cmjmi

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

Get My Free Ebook


Post a comment