NB: This article first appeared as part of the Talking the Torque series in Water Magazine
Martin Hardwidge shows how the benefits of variable speed actuation can be applied to eliminate water hammer, arguing that variable speed produces the Swiss Army knife of valve actuation and leaves us dazed and confused by a Led Zeppelin reference.
Anyone who knows me will know that I am a bit of a music head, have been since my parents bought me the first Led Zeppelin albums when I was 12 (In 1972!). So, I was delighted to find an entire album of music on Bandcamp (the music equivalent of YouTube) about water engineering, called Water Supply. It’s the creation of Dr Richard Collins, who also lectures in the subject at Sheffield University.
On the track Water Hammer, the listener is told to ‘require that the valve be closed slowly’, to avoid the elastic pressure wave that can damage the pipe and fittings. Absolutely right, but what if you don’t want to close the valve slowly? What if you need the option of faster operation or want to have tighter control of your process, but still want to avoid damaging pressure transients, cavitation and water hammer?
The benefits of using variable speed drives (VSD) in pumping operations are well understood, and VSD implementation has increasingly become standard practice. Better control, reduced energy usage, soft start and stop, significantly reduced inrush current and network calming, to name just a few benefits. AUMA’s SQRV and SARV variable speed valve actuators bring those benefits right down to the valve level; and add a few more.
A variable speed profile with as many as ten set points can be created for both the open and close cycle along with soft start and stop. What that means is that the valve can, for example, run at 100% speed for 80% of travel and then for the last part of the valve travel drop to 25% of full speed, reducing the upstream pressure transients in lab tests by as much as 85%, protecting assets and reducing the risk of non-revenue and other leakage. You maintain most of the speed of operation, and there’s an emergency function that will open or close the valve at full speed. If anyone would like to see the figures that back this up, please contact me through the magazine.
Variable speed actuation brings even more benefits: Soft stop control means that valve positioning is both fast and incredibly accurate. From the standpoint of standardisation, a single actuator that can deliver anything from 12 to 120 rpm with tripping torques between 40 – 120 Nm (SAR 10.2) will handle the majority of standard applications. Not only that, but the ability to add a variable speed profile means that a simple butterfly valve can be linearised, opening the possibility of using it in a more sophisticated flow control function than the more normal ‘nudge and wait’ approach.
Throughout AMP8, although the focus will rightly be on the megaprojects, there are thousands of smaller schemes to be delivered that will largely involve the use and upgrade of existing assets. VSD will be used extensively, in part because the low inrush current will allow existing cables to be used. The same thing applies with the actuators. Reducing the inrush current by using the soft start function reduces the need to pull new cables, and in fact opens new opportunities, for example in off-grid applications to take advantage of solar power.
Variable speed actuation is a bit like having a Swiss army knife. A single device that lets you reduce leakage, reduce energy, increase versatility and, above all, enhance control.