Water hammer can be a main concern in pumping techniques and should be a consideration for designers for several reasons. If not addressed, it can trigger a number of issues, from damaged piping and supports to cracked and ruptured piping parts. At worst, it could even cause injury to plant personnel.
What Is Water Hammer?
Water hammer happens when there is a surge in stress and flow price of fluid in a piping system, causing rapid modifications in stress or pressure. High pressures can lead to piping system failure, similar to leaking joints or burst pipes. Support components can even experience sturdy forces from surges and even sudden circulate reversal. Water hammer can occur with any fluid inside any pipe, but its severity varies relying upon the circumstances of both the fluid and pipe. Usually this occurs in liquids, but it could additionally occur with gases.
How Does Water Hammer Occur & What Are the Consequences?
Increased pressure happens every time a fluid is accelerated or impeded by pump situation or when a valve position changes. 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 additionally be created and forces on helps may be nice sufficient to exceed their design specs. Rapidly opening or closing a valve causes strain transients in pipelines that can outcome in pressures properly over steady state values, causing water surge that may critically damage pipes and process management equipment. 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 metal cylinder abruptly being stopped by a concrete wall. Solving these water hammer challenges in pumping systems requires both lowering its effects or stopping it from occurring. There are many solutions system designers need to remember when developing a pumping system. Pressure tanks, surge chambers or similar accumulators can be used to absorb pressure surges, that are all helpful instruments in the battle against water hammer. However, preventing the stress surges from occurring within the first place is usually a greater strategy. This can be completed by utilizing a multiturn variable speed actuator to regulate the pace of the valve’s closure fee at the pump’s outlet.
The advancement of actuators and their controls present alternatives to make use of them for the prevention of water hammer. Here are three circumstances where addressing water hammer was a key requirement. In all cases, a linear characteristic was essential for move 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 flow management. To keep away from water hammer and probably severe system damage, the application required a linear move attribute. The design problem was to acquire linear circulate from a ball valve, which generally exhibits nonlinear move characteristics as it is closed/opened.
Solution
By utilizing a variable velocity actuator, valve position was set to realize different stroke positions over intervals of time. With this, the ball valve could possibly be pushed closed/open at numerous speeds to attain a more linear fluid circulate change. Additionally, within the event of a power failure, the actuator can now be set to close the valve and drain the system at a predetermined emergency curve.
The variable speed actuator chosen had the capability to manage the valve place primarily based on preset occasions. The actuator might be programmed for up to 10 time set factors, with corresponding valve positions. The speed of valve opening or closing might then be managed to make sure the desired set position was achieved on the correct time. This advanced flexibility produces linearization of the valve traits, allowing full port valve choice and/or significantly decreased water hammer when closing the valves. The actuators’ integrated controls had been programmed to create linear acceleration and deceleration of water throughout regular pump operation. Additionally, within the occasion of electrical power loss, the actuators ensured rapid closure via backup from an uninterruptible power supply (UPS). Linear move fee
change was additionally provided, and this ensured minimum system transients and simple calibration/adjustment of the speed-time curve.
Due to its variable pace functionality, the variable velocity actuator met the challenges of this installation. A journey dependent, adjustable positioning time offered by the variable pace actuators generated a linear move by way of the ball valve. This enabled fantastic tuning of operating speeds via ten totally different positions to prevent water hammer.
Water Hammer & Cavitation Protection During Valve Operation
Design Challenge
In the world of Oura, Australia, water is pumped from multiple bore holes into a collection tank, which is then pumped into a holding tank. Three pumps are each outfitted with 12-inch butterfly valves to control the water circulate.
To protect the valve seats from injury attributable to water cavitation or the pumps from running dry within the occasion of water loss, the butterfly valves should be able to fast closure. Such operation creates large hydraulic forces, often recognized as water hammer. These forces are adequate to trigger pipework injury and have to be avoided.
Solution
Fitting the valves with part-turn, variable pace actuators permits completely different closure speeds to be set throughout valve operation. When closing from fully open to 30% open, a speedy closure rate is ready. To keep away from water hammer, during the 30% to 5% open phase, the actuator slows right down to an eighth of its previous velocity. Finally, through the final
5% to complete closure, the actuator hastens again to reduce cavitation and consequent valve seat harm. Total valve operation time from open to shut is round three and a half minutes.
The variable pace actuator chosen had the capability to alter output speed based on its place of journey. This advanced flexibility produced linearization of valve characteristics, allowing less complicated valve choice and decreasing water
hammer. The valve velocity is defined by a most of 10 interpolation factors which may be precisely set in increments of 1% of the open position. Economical can then be set for as much as seven values (n1-n7) based mostly on the actuator kind.
Variable Speed Actuation: Process Control & Pump Protection
Design Challenge
In Mid Cheshire, United Kingdom, a chemical firm used a number of hundred brine wells, each using pumps to transfer brine from the well to saturator items. The circulate is managed using pump delivery recycle butterfly valves driven by actuators.
Under normal operation, when a reduced flow is detected, the actuator which controls the valve is opened over a period of 80 seconds. However, if a reverse move is detected, then the valve must be closed in 10 seconds to guard the pump. Different actuation speeds are required for opening, closing and emergency closure to make sure safety of the pump.
Solution
The variable pace actuator is in a position to provide up to seven totally different opening/closing speeds. These can be programmed independently for open, close, emergency open and emergency shut.
Mitigate Effects of Water Hammer
Improving valve modulation is one solution to consider when addressing water hammer issues in a pumping system. Variable pace actuators and controls provide pump system designers the flexibility to continuously control the valve’s operating pace and accuracy of reaching setpoints, one other activity apart from closed-loop management.
Additionally, emergency safe shutdown may be offered utilizing variable velocity actuation. With the potential of constant operation using a pump station emergency generator, the actuation expertise can offer a failsafe option.
In other phrases, if an influence failure occurs, the actuator will close in emergency mode in varied speeds using energy from a UPS system, allowing for the system to empty. The positioning time curves can be programmed individually for close/open course and for emergency mode.
Variable velocity, multiturn actuators are also a solution for open-close responsibility situations. This design can provide a gentle start from the start position and soft stop upon reaching the top place. This stage of control avoids mechanical pressure surges (i.e., water hammer) that may contribute to untimely component degradation. The variable speed actuator’s capability to supply this control positively impacts maintenance intervals and extends the lifetime of system components.
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