Water hammer control

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. 

Anotlier cause of water hammer is lack of proper drainage ahead of a steam control valve. When the valve opens, a slug of condensate will enter the equipment at a high velocity, producing water hammer when it impinges on the walls. In addition to this, the mixing of the steam that follows wifli the relatively cool condensate will... 

Water hammer can also occur in steam mains, condensate return lines, and heat exchange equipment where steam entrapment can take place (Fig. I). A coil constructed and installed as shown here, except with just a steam trap at the outlet, permits steam from the control valve to be directed through the center tube(s) first. Steam then gets into the return header before the top and bottom tubes are filled with steam. Consequently, these top and bottom tubes are fed with steam from both ends. Waves of condensate are moved toward each other from both ends, and steam can be trapped between the waves. 

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. 

Buildup of condensate in a heat exchanger can cause operating problems as well as water hammer. If the steam supply is controlled by a motor valve and the valve is not fully open, the steam pressure may be too low to expel the condensate, and its level will rise. This will reduce heat transfer, and ultimately the steam supply valve will open fully and expel the condensate. The cycle will then start again. This temperature cycling is bad for the heat exchanger and the plant and may be accompa-... 

The above unit is economical, avoids water hammer, has excellent control, and is easy to start up. Contrary to popu-... 

Closure at the instant of flow reversal is most nearly attained with tilting-disk, dual-plate, and specialty axial-flow check valves. However, quick closure is not the solution to all noise, shock, and water hammer problems. External dashpots are available when a controlled rate of closure is desired. Nonmetallic seats are also available. 

Water Hammer and Condensate Backup Steam-Side Reboiler Control... 

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

The shock wave may he several times the normal pressure and will travel to the end of the Une where it wUl he reflected back. The cycle will be repeated until all the energy is dissipated or relieved. The rapid closing of valves and piping layouts that are conductive to water hammer should be avoid. Surge tanks, pneumatic chambers, relief valves, or shock absorbers and arrestors are sometimes used to control water hammer concerns. Water Reactive Chemical... 

Main feedwater flow during plant startup is only delivered to the economizer inlet feedwater nozzles of the steam generators at temperatures at or above 200°F, which minimizes the probability of condensation-induced water hammer in the economizer sections of the generators. Below a predetermined power level, main feedwater is delivered to the downcomer feedwater inlet nozzles. Changeover to the economizer nozzles at this power level is effected by the Main Feedwater Control System. Emergency feedwater is always delivered to the downcomer inlet nozzles. (See CESSAR-DC, Sections 10.4.7.2.ID and 7.7.1.1.4.)... 

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