Water hammer is often a main concern in pumping systems and must be a consideration for designers for a quantity of causes. If not addressed, it can cause a host of issues, from damaged piping and supports to cracked and ruptured piping parts. At worst, it may even cause damage to plant personnel.
What Is Water Hammer?
Water hammer occurs when there’s a surge in strain and flow fee of fluid in a piping system, inflicting fast adjustments in pressure or force. High pressures may end up in piping system failure, corresponding to leaking joints or burst pipes. Support components also can experience strong forces from surges and even sudden circulate reversal. Water hammer can happen with any fluid inside any pipe, but its severity varies depending upon the circumstances of both the fluid and pipe. Usually this occurs in liquids, however it can also occur with gases.
How Does Water Hammer Occur & What Are the Consequences?
Increased stress occurs each time a fluid is accelerated or impeded by pump condition or when a valve position modifications. Normally, this pressure is small, and the rate of change is gradual, making water hammer virtually undetectable. Under some circumstances, many pounds of stress could also be created and forces on helps may be nice sufficient to exceed their design specs. Rapidly opening or closing a valve causes stress transients in pipelines that can lead to pressures properly over steady state values, inflicting water surge that may critically injury pipes and process management tools. The significance of controlling water hammer in pump stations is well known by utilities and pump stations.
Preventing Water Hammer
Typical water hammer triggers embrace pump startup/shutdown, energy failure and sudden opening/closing of line valves. A simplified model of the flowing cylindrical fluid column would resemble a metallic cylinder abruptly being stopped by a concrete wall. Solving these water hammer challenges in pumping systems requires either decreasing its effects or stopping it from occurring. There are many options system designers want to remember when creating a pumping system. Pressure tanks, surge chambers or comparable accumulators can be utilized to soak up stress surges, that are all helpful tools in the struggle against water hammer. However, stopping the stress surges from occurring within the first place is often a greater strategy. This may be achieved by using a multiturn variable velocity actuator to manage the pace of the valve’s closure fee on the pump’s outlet.
The development of actuators and their controls provide alternatives to use them for the prevention of water hammer. Here are three cases the place addressing water hammer was a key requirement. In all circumstances, a linear characteristic was essential for circulate control from a high-volume pump. If this had not been achieved, a hammer impact would have resulted, doubtlessly damaging the station’s water system.
Preventing Water Hammer in Booster Pump Stations
Design Challenge
The East Cherry Creek Valley (ECCV) Southern Booster Pump Station in Colorado was fitted with high-volume pumps and used pump check valves for move control. To avoid water hammer and potentially serious system injury, the appliance required a linear flow characteristic. The design challenge was to obtain linear circulate from a ball valve, which typically reveals nonlinear flow characteristics as it is closed/opened.
Solution
By using a variable speed actuator, valve place was set to realize totally different stroke positions over intervals of time. With this, the ball valve could be driven closed/open at varied speeds to realize a more linear fluid flow change. Additionally, within the occasion of an influence failure, the actuator can now be set to shut the valve and drain the system at a predetermined emergency curve.
The variable velocity actuator chosen had the capability to manage the valve place primarily based on preset occasions. The actuator might be programmed for as much as 10 time set points, with corresponding valve positions. The pace of valve opening or closing might then be managed to make sure the specified set position was achieved at the appropriate time. This superior flexibility produces linearization of the valve characteristics, allowing full port valve choice and/or considerably lowered water hammer when closing the valves. The actuators’ built-in controls were programmed to create linear acceleration and deceleration of water during normal pump operation. Additionally, in the event of electrical power loss, the actuators ensured fast closure by way of backup from an uninterruptible power supply (UPS). Linear flow rate
change was additionally supplied, and this ensured minimal system transients and easy calibration/adjustment of the speed-time curve.
Due to its variable velocity capability, the variable pace actuator met the challenges of this set up. A travel dependent, adjustable positioning time supplied by the variable speed actuators generated a linear flow by way of the ball valve. This enabled fantastic tuning of working speeds via ten different positions to forestall water hammer.
Water Hammer & Cavitation Protection During Valve Operation
Design Challenge
In the realm of Oura, Australia, water is pumped from multiple bore holes into a group tank, which is then pumped into a holding tank. Three pumps are each outfitted with 12-inch butterfly valves to regulate the water flow.
To defend เครื่องมือวัดความดันคือ from injury brought on by water cavitation or the pumps from running dry in the event of water loss, the butterfly valves must be able to speedy closure. Such operation creates huge hydraulic forces, known as water hammer. These forces are adequate to cause pipework damage and must be prevented.
Solution
Fitting the valves with part-turn, variable speed actuators allows completely different closure speeds to be set during valve operation. When closing from totally open to 30% open, a speedy closure fee is set. To avoid water hammer, during the 30% to 5% open section, the actuator slows all the method down to an eighth of its previous speed. Finally, in the course of the last
5% to complete closure, the actuator accelerates again to scale back cavitation and consequent valve seat harm. Total valve operation time from open to shut is around three and a half minutes.
The variable pace actuator chosen had the capability to change output pace primarily based on its place of journey. This advanced flexibility produced linearization of valve traits, permitting simpler valve selection and decreasing water
hammer. The valve velocity is defined by a most of 10 interpolation points which may be exactly set in increments of 1% of the open position. Speeds can then be set for as much as seven values (n1-n7) based mostly on the actuator type.
Variable Speed Actuation: Process Control & Pump Protection
Design Challenge
In Mid Cheshire, United Kingdom, a chemical firm used several hundred brine wells, every using pumps to switch brine from the properly to saturator units. The flow is managed utilizing pump delivery recycle butterfly valves pushed by actuators.
Under normal operation, when a decreased move is detected, the actuator which controls the valve is opened over a period of eighty seconds. However, if a reverse flow is detected, then the valve needs to be closed in 10 seconds to protect the pump. Different actuation speeds are required for opening, closing and emergency closure to ensure protection of the pump.
Solution
The variable pace actuator is ready to provide as much as seven totally different opening/closing speeds. These may be programmed independently for open, shut, emergency open and emergency shut.
Mitigate Effects of Water Hammer
Improving valve modulation is one solution to think about when addressing water hammer concerns in a pumping system. Variable velocity actuators and controls present pump system designers the flexibility to continuously control the valve’s working velocity and accuracy of reaching setpoints, another task other than closed-loop control.
Additionally, emergency protected shutdown can be provided using variable speed actuation. With the aptitude of continuing operation utilizing a pump station emergency generator, the actuation technology can provide a failsafe option.
In different phrases, if a power failure happens, the actuator will shut in emergency mode in various speeds using energy from a UPS system, permitting for the system to empty. The positioning time curves may be programmed individually for close/open path and for emergency mode.
Variable velocity, multiturn actuators are also an answer for open-close responsibility conditions. This design can present a delicate start from the start position and delicate cease upon reaching the top position. This degree of control avoids mechanical stress surges (i.e., water hammer) that can contribute to premature part degradation. The variable pace actuator’s capability to supply this management positively impacts maintenance intervals and extends the lifetime of system parts.
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