Water hammer systems

E. B. Wyhe and co-workers. Fluid Transients in Systems, Prentice Hall, New York, 1993 J. Zarbua, Water Hammer in PipeEine Systems, Elsevier Science Pubhshing Co., New York, 1993. 

With a better understanding of the nature and severity of the water hammer problem, we can avoid its destructive forces. This greater understanding should also help with the introduction of more preventive measures into system designs and installations, which will help provide maximum safety for personnel, lower maintenance cost and reduce system downtime. 

Where Water Hammer Occurs. Water hammer can occur in any water supply line, hot or cold. Its effects can be even more pronounced in heterogeneous or biphase systems. Biphase systems carry water in two states, as a liquid and as a gas. Such a condition exists in a steam system where condensate coexists with live or flash steam in heat exchangers, tracer lines, steam mains, condensate return lines and, in some cases, pump discharge lines. 

Water hammer arrestors, if correctly sized, placed, and maintained, will reduce water hammer by providing a controlled expansion chamber in the system. As the forward motion of the water column in the pipe is stopped by the valve, a portion of the reversing column is forced into the water hammer arrestor. The water chamber of the arrestor expands at a rate controlled by the pressure chamber and gradually slows the column, preventing hydraulic shock. 

To control differential shock, the condensate seal must be prevented from forming in a biphase system. Steam mains must be properly pitched, condensate lines must be sized and pitched correctly, and long vertical drops to traps must be back-vented. The length of lines to traps should be minimized, and pipes may have to be insulated to prevent water hammer. 

High-pressure fluid flows into the low-pressure shell (or tube chaimel if the low-pressure fluid is on the tubeside). The low-pressure volume is represented by differential equations that determine the accumulation of high-pressure fluid within the shell or tube channel. The model determines the pressure inside the shell (or tube channel) based on the accumulation of high-pressure fluid and remaining low pressure fluid. The surrounding low-pressure system model simulates the flow/pressure relationship in the same manner used in water hammer analysis. Low-pressure fluid accumulation, fluid compressibility and pipe expansion are represented by pipe segment symbols. If a relief valve is present, the model must include the spring force and the disk mass inertia. 

The amount of moisture that air can hold is inversely proportional to the pressure of the air. As the pressure of the air increases, the amount of moisture that air can hold decreases. The amount of moisture air can hold is also proportional to the temperature of the air. As the temperature of the air decreases, the amount of moisture it can hold decreases. The pressure change of compressed air is larger than the temperature change of the compressed air. This causes the moisture in the air to condense out of the compressed air. The moisture in compressed air systems can cause corrosion, water hammers, and freeze damage. Therefore, it is important to avoid moisture in compressed air systems. Coolers are used to address the problems by moisture in compressed air systems. 

The pressure that can develop from the shock wave can be destructive to the containing system hardware, particularly in long pipe. Examples of conditions that can develop water hammer are ... 

Steam traps are automatic mechanisms that remove low heat-content air and condensate from the steam delivery system. The lack of steam traps or use of traps that fail to function properly leads to a gradual decline in heat-transfer efficiency, waterlogged heat exchangers, and water hammer (which may in turn result in ruptured pipes). When adequate maintenance of steam traps is neglected, this ultimately leads to a serious overall loss of operating efficiency. There are various types of steam traps, each designed for a specific function. Some common variations are discussed in the following sections. 

Where condensate forms from the wet steam and drips back through the system, water hammer may develop and cause severe damage. 

Instantaneous surges of water under pressure caused by sudden interruptions in water flow in a pipe or water system, producing a hammering sound and leading to metal stress and possible eventual failure. Water hammer can develop where a steam main is incorrectly pitched, has un-drained pockets or where steam flows up and meets draining condensate flowing down causing a temporary interruption in both flows. 

It creates steam or water hammer in the condensate collection system. 

Steam, or water hammer (more properly called hydraulic hammer), is one process plant phenomenon familiar to the general public. I well remember trying to warm up the steam system of a large amine plant in Texas City in 1980, and feeling more than hearing, the crescendo of crashes, due to steam hammer. The cause of steam hammer is illustrated in Fig. 8.7. 

Figure 8.8 Avoiding water hammer in a condensate collection system.

Pressure surges in liquid service Violent, multiple closing cycles cause liquid water hammer and place undue stress on companion piping, piping supports, internal components in pressure vessels, metering systems, and so on. 

Hammer, M. J. (1986). Water and Wastewater Technology. John Wiley Sons, New York. Kotov, A. 1. (1998). Water treatment system is one of the most important elements of the ecological safety of the plant. Tyazheloe Mashinostroenie, 7, 58-60. 

Water hammer arrestors, if correctly sized, placed, and maintained, will reduce water hammer by providing a controlled expansion chamber in the system. As the... 

Current practice to install piles has been by using a system of chasers and an above-water hammer (Figure 10.25). A chaser is a pipe of the same diameter and wall thickness as the... 

The only possible cause of water hammer in the process-.water system would be an instantaneous closing of the 24-in. main proceS s-water-control valve. If this valve, closed in less than 0.2 sec, the maximum possible increase in pressure. .would be 385 psi if the closing time were 16 sec, the maximum pressure.would be 4 psi. However, since the Valve is designed to close in 30 sec, the. possibility of water hammer is eliminated. Failure of the pumps lifting water to the working reservoir will not cause water hammer because the reverse momentum of the water is quite low. 

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