Preventing Water Hammer With Variable Speed Actuators

Water hammer could be a major concern in pumping techniques and must be a consideration for designers for a quantity of reasons. If not addressed, it could trigger a bunch of points, from broken piping and supports to cracked and ruptured piping components. At worst, it could even trigger injury to plant personnel.
What Is Water Hammer?

Water hammer occurs when there is a surge in strain and move rate of fluid in a piping system, causing rapid adjustments in pressure or force. High pressures can lead to piping system failure, similar to leaking joints or burst pipes. Support elements also can expertise strong forces from surges and even sudden flow reversal. Water hammer can happen with any fluid inside any pipe, but its severity varies relying upon the situations of both the fluid and pipe. Usually this occurs in liquids, but it might possibly additionally occur with gases.
How Does Water Hammer Occur & What Are the Consequences?

Increased strain occurs each time a fluid is accelerated or impeded by pump situation or when a valve position adjustments. Normally, this pressure is small, and the rate of change is gradual, making water hammer practically undetectable. Under some circumstances, many kilos of pressure may be created and forces on helps can be great enough to exceed their design specifications. Rapidly opening or closing a valve causes pressure transients in pipelines that can lead to pressures properly over steady state values, inflicting water surge that may critically harm pipes and course of control gear. 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 steel cylinder suddenly being stopped by a concrete wall. Solving these water hammer challenges in pumping methods requires both reducing its results or stopping it from occurring. There are many options system designers want to remember when growing a pumping system. Pressure tanks, surge chambers or comparable accumulators can be used to absorb strain surges, that are all useful tools within the fight in opposition to water hammer. However, stopping the pressure surges from occurring in the first place is often a better technique. This can be completed by using a multiturn variable velocity actuator to manage the velocity of the valve’s closure fee at the pump’s outlet.
The development of actuators and their controls present opportunities to use them for the prevention of water hammer. Here are three circumstances where addressing water hammer was a key requirement. In all instances, a linear characteristic was essential for flow management from a high-volume pump. If this had not been achieved, a hammer impact would have resulted, potentially 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 circulate control. To avoid pressure gauge octa and probably critical system harm, the application required a linear circulate attribute. The design challenge was to acquire linear flow from a ball valve, which generally displays nonlinear move characteristics as it is closed/opened.

By utilizing a variable velocity actuator, valve place was set to attain completely different stroke positions over intervals of time. With this, the ball valve could be driven closed/open at various speeds to realize a more linear fluid circulate change. Additionally, in the occasion 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 pace actuator chosen had the capability to manage the valve place based mostly on preset instances. The actuator might be programmed for as much as 10 time set factors, with corresponding valve positions. The velocity of valve opening or closing may then be managed to make sure the desired set place was achieved on the appropriate time. This advanced flexibility produces linearization of the valve characteristics, allowing full port valve choice and/or significantly lowered water hammer when closing the valves. The actuators’ built-in controls were programmed to create linear acceleration and deceleration of water during regular pump operation. Additionally, within the occasion of electrical energy loss, the actuators ensured fast closure by way of backup from an uninterruptible energy provide (UPS). Linear circulate rate

change was additionally offered, and this ensured minimum system transients and easy calibration/adjustment of the speed-time curve.
Due to its variable velocity capability, the variable speed actuator met the challenges of this installation. A travel dependent, adjustable positioning time supplied by the variable speed actuators generated a linear flow by way of the ball valve. This enabled nice tuning of working speeds via ten completely different positions to forestall water hammer.
Water Hammer & Cavitation Protection During Valve Operation

Design Challenge

In the world of Oura, Australia, water is pumped from a number of bore holes into a collection tank, which is then pumped into a holding tank. Three pumps are every equipped with 12-inch butterfly valves to control the water move.
To defend the valve seats from harm caused by water cavitation or the pumps from operating dry in the event of water loss, the butterfly valves should be capable of speedy closure. Such operation creates huge hydraulic forces, generally known as water hammer. These forces are sufficient to trigger pipework injury and have to be averted.

Fitting the valves with part-turn, variable pace actuators allows different closure speeds to be set during valve operation. When closing from fully open to 30% open, a speedy closure price is about. To avoid water hammer, during the 30% to 5% open phase, the actuator slows all the way down to an eighth of its previous speed. Finally, in the course of the last

5% to complete closure, the actuator speeds up once more to reduce back cavitation and consequent valve seat damage. Total valve operation time from open to close is round three and a half minutes.
The variable velocity actuator chosen had the capability to change output velocity based mostly on its position of journey. This superior flexibility produced linearization of valve characteristics, permitting easier valve selection and lowering water

hammer. The valve velocity is outlined by a most of 10 interpolation points which can be exactly set in increments of 1% of the open place. Speeds can then be set for up to 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 company used several hundred brine wells, each using pumps to transfer brine from the properly to saturator items. The flow is managed using pump delivery recycle butterfly valves pushed by actuators.
Under regular operation, when a lowered flow is detected, the actuator which controls the valve is opened over a interval of eighty seconds. However, if a reverse move 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 safety of the pump.

The variable speed actuator is ready to provide up to seven completely different opening/closing speeds. These could be programmed independently for open, close, emergency open and emergency close.
Mitigate Effects of Water Hammer

Improving valve modulation is one answer to contemplate when addressing water hammer considerations in a pumping system. Variable velocity actuators and controls present pump system designers the flexibleness to constantly management the valve’s working pace and accuracy of reaching setpoints, another task aside from closed-loop management.
Additionally, emergency safe shutdown can be provided using variable velocity actuation. With the capability of continuing operation utilizing a pump station emergency generator, the actuation expertise can provide a failsafe choice.
In other phrases, if a power failure happens, the actuator will shut in emergency mode in various speeds utilizing power from a UPS system, allowing for the system to empty. The positioning time curves could be programmed individually for close/open path and for emergency mode.
Variable pace, multiturn actuators are also a solution for open-close duty conditions. This design can present a gentle start from the start place and delicate stop upon reaching the tip position. This stage of control avoids mechanical strain surges (i.e., water hammer) that can contribute to premature component degradation. The variable pace actuator’s capacity to provide this management positively impacts upkeep intervals and extends the lifetime of system elements.

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