Water hammer prevention in pumping stations under power failure conditions.

With more than 30 years experience in the industry, Colin joins us today to talk about water hammer prevention in pumping stations under power failure conditions. Previously, we’ve talked about the methods of controlling water hammer during regular pump starts and shut downs, and some of the efficient solutions on offer.

In today’s episode, we’re going to dive into what happens in the event of a power failure at a pump station, and what are the consequences? Colin, you’re an expert in this area. Could you elaborate on what a power failure looks like and what the consequences might be.

The big issue with a power outage at a pump station is that if we think about typical pump stations, they’re used for water supply, irrigation, mining in buildings, they all play a critical role. And if the whole engineering behind the pump station, the pipeline and everything else, has to be safe and fit for purpose under all operating conditions. And that’s under normal pump starts normal shut down, but also in the event of power failure or instant shut down. The net effect is if there’s no control when the pump basically just stops, that water has been pumping up the hill or the building and has a lot of energy. And when we stop instantly, that energy is going to come racing back towards the pump station and creates a lot of water hammer.

I want to share one real story from many years ago when I was called to go to a pumping station in New South Wales and they had serious water hammer at this pump station. The operators took me into pump station building and they were explaining where the issue was and they asked me, and they said, Colin, before we demonstrate the water hammer, can we just move over to the side?

And I said, okay. So they turned the pump off and there was substantial water hammer. It came down and made a lot of noise. And I asked them, I said, why did you ask me to move? And they said, well, in the past, the water hammer has been so severe that when the check valve closed, one of the arms of the valves came off and went through the back of the building where you were standing.

So this was a real situation. So it’s not just about protecting the asset, the pump station, and everything else, but this was a rare event that could have had terrible consequences. I was awfully glad he did ask me to move to one side.

If that means that the pressure is going to double or triple, then I have to rate all of the components and the pipe to a much higher degree of safety. And that’s usually not terribly practical. So what a lot of the designers and engineers will look at and say, well, okay, what do we do in the event of power failure? And what are the things we need to do to make sure it’s going to be safe?

But the bottom line is that we’re going to experience water hammer here and we have to make sure we design it fit for purpose. Typically the stress that this is going to provide to everything is at its highest level. So the engineering has to be done really well and accurately, so we can really plan for what we need to do next.

So the best advice I could give everyone is to get some good reporting done and get some analytics done on what you know is going to happen. Now, most of the software today really has many, many years experience. We have limited software that gives us a very, very good snapshot. And I should stress that what we provide at BWT is not a full surge analysis, but it’s a very good and fairly accurate snapshot of what we think we’re going to see. So the best advice is to get good information before this happens, so we can plan for the right products.

And there really is a multitude of different options that we can use to try and mitigate that. So it’s about getting the right information. We know the right questions to ask, which is the important thing.

And so, say you received this surge report. What are the solutions that you can offer to reduce the effects of the water hammer?

We’re also looking very clearly at what the pressure is going to be at the pump station too as well. In many instances, if we’ve got a pump station that’s not generating a lot of pressure and it’s in relatively flat country; we can see column separation and column separation is when the pump stops, we see the pressure in the maine dropping to atmospheric pressure.

So if we had an air release valve there at that point, that’s where the air valve is going to allow large volumes of air to be drawn into the pipeline. And then as the column comes back to the pump station, that will release the air. If we have column separation and we can see that in the report, the very simple, easy and effective way to do is with what we call an anti-slam air release valve. We have spoken about these in previous episodes being used on the pipeline, but they can also be used at the pump station too. And what the anti-slam air valve does really simply and easily without any use of energy or power is when that pump stops, and the pressure drops to zero, large volumes of air are being drawn into the pipeline. So we now have a large bubble of air inside the pipe. And as this column is coming back towards the pump station, that air bubble now wants to release very quickly.

An anti-slam air valve lets it out at a very slow controlled rate, so we’re actually utilizing the air that’s been drawn into the pipe to come back out of the pipe very slowly. And so they were basically releasing at a very slow controlled rate. It’s enormously effective, and has been proven in a multitude of applications over many years. And importantly, it can be modeled in software and everything else to ensure that it’s going to be fit for purpose and it’s safe.

So anti-slam air valves are a very good option only if there’s column separation.

So from our perspective, there’s three key solutions that we can offer. One of them is called a fast-acting pressure relief valve. So for example, if we had a pipeline that was very short, and only 800 meters long, and we were experiencing this return wave to come back to us within 0.8 of a second; then we have very fast-acting relief valves that will instantly dissipate that energy as it rises above the normal condition.

For us, that’s the VRCA direct-acting relief valve, which is simple, very effective and works in that sort of condition very well. If it were a longer pipeline and we were experiencing maybe a return wave that came back in 3, 4, 5 seconds; we may use a valve called a surge anticipating valve. Now this is technology, which we’ve had at Bermad for many years. It’s really proven and very effective, and what it basically does, is that it anticipates this wave coming back, being a surge-anticipating valve. So it actually opens when we see a low pressure wave, and then as the return wave comes back, that energy dissipates through the relief valve, and then the valve shuts slowly.

It’s called a surge-anticipating valve, so there’s many ways we can configure it, but it’s very safe. It’s basically like a hydraulic fuse in the pipeline, basically, that’s just going to make sure that we’re going to anticipate that wave coming back, we’re going to release it, and we’re going to slowly close at a very controlled rate to make sure that it doesn’t regenerate a secondary wave. And it’s a very proven feature of how to overcome that issue.

The third way could just be that we’re experiencing a slight pressure rise, and it’s going to come back very slowly because the pipe may be PVC or poly, so the wave might come back to the pump station over 60-70 seconds. And then we’ve got the ability to put in a standard pressure relief valve, which for us, will open as much as it has to, to get rid of that energy and shut down really slowly and gently just to dampen out that surge.

So for us, there are 3-4 key solutions that are reasonably inexpensive. We know they work factually and that they can be modeled and put into software to anticipate the effects of how they’re going to work. And of course it’s all about the experience and knowing how to design them and put them in to as well.

So these are some very proven solutions for water hammer that we’ve certainly used.

Now, in some very complicated pipelines, we sometimes actually do put a battery backup and we’ll also put a solenoid on the valve. We do this if we know we’re going to see secondary waves that come back, because sometimes in very complex pipelines, this search is not a simple quick-fix answer, it can be quite complicated. But in general, we don’t require any backup of power. So it’s generally a purely a hydraulic solution from our perspective.

I can still go back to a situation where we had a surge anticipating valve and the water was running out through our valve through a large discharge pipe, some 50 meters below into the river. And when the valve actually was closing, when the surge had dissipated, we created so much vacuum in the pipe down stream that it collapsed the pipe. So you can overcome that very easily by putting a vacuum breaker and doing lots of different designs to ensure it’s going to be safe. The point I’m making is that experience counts for everything.

We’ve got so much experience in doing this and doing this well, the difference with Bermad is that, not only are we going to design and make the right product fit for purpose, but we’re going to help the designer make sure they install it correctly, put the correct associated isolation valves, pipe work, thrust blocks, and everything else to ensure that when this works, it works reliably. Because the net effect is if you get it wrong, you’re going to break something.

We learn through our mistakes, and I’m not saying we haven’t made mistakes before, but we certainly try never to make them a second time.

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