|Sarah||Hello and welcome to Controlling Water, a space for us to talk valves, water, meters, and interesting insights about the water industry. Each episode we’re joined in conversation by industry professionals that specialize in all things, valves, meters, and best practice knowledge in the water industry. We are here with Colin Kirkland, from Bermad water technologies, who is one of the engineers in Australia.
With more than 30 years’ experience in the industry, Colin is joining us today to talk more about water hammer. This time, we’re going to discuss water hammer prevention in pumping stations. Welcome back Colin. It’s always great to have you here.
|Colin||Good to be here. Thank you.|
|Sarah||So I’m sure this is a bit of a long question, but can you firstly, explain why water hammer occurs, especially in a pumping station?|
|Colin||Yes. Well, in previous episodes we’ve discussed actually what water hammer was, and of course, it’s a rapid increase in pressure generated by a very sudden change in flow. This is what a pump station does every day. So if we see we have many pumping stations where pumps can start and they can run for days and weeks at a time, or we can have pumps that will have 20, 30, 40 starts a day.
The net effect is, is that at a pumping station, when you start a pump you’re generating a change in flow. When you turn that pump off, you’re generating a rapid change in flow. So those conditions with controlled ramp up, controlled ramp down happen, whether you like it or not. It depends how you control that as to the net results.
So pumping stations are probably one of the biggest offenders in generating water hammer in all industries, whether you be in mining, water, irrigation, or whatever. The key thing here is really to understand what a pump station design is, and to make it work effectively under normal operating conditions, but also in uncontrolled conditions.
In other words, in the event of power failure, or in uncontrolled conditions. So pumping stations are the biggest offenders of water hammer for sure that I’ve come across in many years.
|Sarah||And so, how do designers typically minimize this condition?|
|Colin||Okay. So if we were designing a pump station itself, if we think about typical pumps, we might have an electric motor, we’ll have a coupling and we’ll have a pump. And when they’re designing these pumps, they’re generally designing a pump that can produce enough flow and energy to transfer the water to wherever it has to be. And most people when they’re putting this pump set together, and they’re considering an electric motor, they’ll also consider different ways of being able to start and stop that motor.
So there’s many processes that have been around for a long, long time. There’s what we call DOL, which is direct online, and direct online basically means when someone comes up and hits the start button, bang, pump starts straight away and off it goes, I had stopped and it instantly stops. No control, terrible for water hammer.
And then you have things like a Star-delta Starters. Star-delta Starter is like a staged set up and it will do it over a controlled period to ramp up. And usually the ramp down is very poor too, as well. But today there’s been so much work done on how to control pump starts. And there’s a lot of things called like soft starts or variable speed drives or they’re referred to as drives. And what these are, are electrical products that basically enable the motor to ramp up at a slow controlled rate.
And conversely, when they come to shut down, they allow them to ramp down. Now the thing that most people are looking at is that when they’re designing a pump station, they’re generally not looking at water hammer. That’s a secondary thing. What they’re looking at, is that they’re wanting to say, I want the pump to be as efficient as possible. And I know, if I start the pump very quickly, it draws a lot of power. So I need 30% more power to start the pump. But if I do it with a drive and I ramp it up nice and gently, I don’t require as much power. So the motor becomes smaller, the infrastructure is smaller, and it’s more efficient, you know, so there’s a lot of really good types of situations that can start and stop these motors effectively.
What we’re always looking at, from a water hammer perspective, is to see, well, how are you starting and stopping the pump? And we can see what the net effects are on how well that’s going to have on water hammer, but they don’t generally look at it from that perspective. They’re purely looking at it for, let’s make it work and let’s make it work efficiently.
So today, most of the designers, when they’re designing that pump station, will incorporate one of the starting procedures to start those pumps, whether it be a drive or a soft start or DOL. The key thing is, is that what we’re looking at from a water hammer perspective, so we want something that ramps gradually, and ramps down gradually, it’s soft in the system. Now some of these systems may be able to assist in water hammer prevention, but definitely not all of them.
|Sarah||Good to know. Good to know. Colin, I want to touch on something you said before. You mentioned that in many instances, the design may be able to minimise water hammer.|
|Sarah||I’m guessing that there are conditions though, where this design change may not actually work. What are some of these conditions?|
|Colin||Okay. If we talk about those basic starting devices that we spoke about – direct online, very fast starting rate, fast stopping, has no effect on water hammer at all really.|
|Colin||Direct Star-delta Starters has a slight effect because it has a slightly gradual increase in the RPMs of the pumps, which is not too bad, but soft starts can have a really good effect.
So a soft start or a drive can ramp up slowly and introduce flow and pressure into the pipeline gradually, which is a good thing. But the overall design that the operator’s thinking is – if I were to ramp that pump up over 60 seconds, the assumption is the flow is going to gradually increase over that 60 seconds, and that’s not always the case.
As a pump starts to increase its speed, it starts to develop pressure. Now, flow only starts to move once you’ve overcome the static head. So to keep it really simple, imagine I’m pumping up a hill and the hill is one kilometer away, and the hill is 50 meters in elevation. Until the pump generates 51 meters of energy, then it’s overcome all that static energy it’s sitting against the pump and the water starts to flow.
Now, if the pump ramps up over 60 seconds, but 50 seconds of it take that time to get to 51 meters, it’s not transferred any flow, it’s just ramped up and ramped up and done nothing. And all of a sudden, bang, it’s opened. So I’ve actually only had five seconds of transfer, which is kind of useless.
|Colin||So, to answer your question, if the static head that we’re talking about, in other words, that 15 meters of head, is very close to the running head, call it 60 meters, then it’s unlikely that’s going to have a good effect on water hammer, because it’s not going to ramp the flow up gradually. And more importantly, it’s not going to ramp the flow down.
As soon as you start ramping it down after 10 seconds, it’s going to stop the flow instantly. You know, so, in summary, if the static head is very close to the running head, it’s really ineffective from water hammer, and the drive’s not going to do much, if anything, at all.
|Sarah||Good to know. So under this condition, where the pressures are very similar, what can you do to achieve the same result? I’m sure that over the years with your experience, you’ve possibly found some solutions.|
|Colin||Yes Sarah, we do. We have a very good solution called the Bermad model 740 Pump Control Valve. It’s been around ever since I’ve been in the organization and has been a real benchmark of a product that has worked reliably over many, many years.
What this product actually does, is that irregardless of the ramp up speed of the pump, what we want to achieve, is a gradual increase in flow as we’re pumping up the hill. What the Pump Control Valve or the Bermad model 740 is, is a solenoid valve. So what it says is, when I start the pump, I energize the solenoid, and once it develops enough pressure, the valve opens at a very slow controlled rate and less water travel up the pipeline. So it’s exactly like an operator saying, I have a gate valve, and I’m going to start with that gate valve closed, and when I start the pump and the pump starts, I’m going to have the operator open the gate valve very slowly and I’ll induce water into the pipeline slowly and gradually. That’s wonderful for a pump startup and the Bermad valve does that really well, simply and reliably.
Really importantly, more of the water hammer happens when they turn the pump off. So if I were an operator and they say to me, make sure you turn the pump off and do it safely. I would keep the pump running and I would slowly close the gate valve over one minute or two minutes. I would reduce the flow, reduce the flow, reduce the flow. Once the flow is down to 10% of what it’s designed to be, I’ll turn the pump off, and there’s very little change of flow, and no water hammer. That’s what the Bermad valve does also.
So when the signal comes for the pump to stop, the pump keeps running, but the valve is de-energized the signer and the belt, the energized, and the valve says I’m going to slowly close at a controlled linear rate, and once I get to 90% closed, have a little micro switch that says, turn the pump off. It does it automatically.
|Colin||So it’s a really simple looking valve, which really is enormously effective in giving a gradual increase in flow, gradual decrease in flow, irregardless of the design. So in things like pumping and high rise buildings, or in mines that are transferring big distances or in water supply, or in irrigation, pump control is a really effective tool.
And, the net effect because it’s a double chambered hydraulic valve, it’s also a non-return valve. And what that, because each pump usually will have a non-return valve in there to ensure that when we turn the pump off, there’s no reverse flow. This function is also incorporated in the double chambered function of our valve. So it’s a slow opening, slow closing valve and a non-return valve all in the one function.
|Sarah||Wow. Let’s take a short break.
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Now, back to the show.
Colin, my brief understanding of most pump stations is that they always have a non-return valve on the pump discharge. Does this mean that you can remove the existing check valve?
|Colin||Yeah. It’s an important question, Sarah, because you don’t like to have check valves in series. Because our pump control valve is already a non-return, you’re basically putting a secondary product in for no real benefit.
The problem can be, if you have check valves that close at different rates, you can actually get a buildup of pressure between the two when they’re closing, which can generate bouncing and water hammer issues, which are not desirable.
So, to answer your question, we don’t like to use a secondary check valve when we’re using the pump control, cause it already provides that function. So it’s good to eliminate that. It’s one less thing you have to worry about with head loss and maintenance, et cetera, too as well.
|Sarah||Sounds good. And can the valve perform any other functions other than simply on-off and non-return functions?|
|Colin||Yes, so the valve is a diaphragm actuated control valve. So how it works is by applying water to the top chamber of the valve, which makes it close, and taking it off to make it open, we can incorporate many additional features all in the one.
And as a couple of examples, let’s say when the pump is up and running and it’s supplying a water distribution network, let’s say there’s a fire. And in that fire condition, there’s many fire trucks taking additional water out of the maine. Now, if you draw too much water out of the maine and the pump gets to the end of its curve or its end of its capacity, the more water you pump, the more energy that the motor draws. Now, if you get to a critical level and you keep wanting to draw more and more flow, you draw more and more energy. And once you get to too far, the motor is going to trip and turn off. Now that’s catastrophic in a case of a fire because all of a sudden they have no water pressure.
So in many cases we can provide what we call a flow control function. So if we know, for example, that the critical flow in this pump has 100 liters, a second, we’ll allow it to operate up to that value. But if the demand in the field starts drawing more than the pumps capacity, I will ensure that the pump doesn’t turn off, and that’s the flow control function.
Sometimes, depending what the pump curve looks like, if it’s a steep curve or a flat curve, we can also use a pressure sustaining function that has a somewhat similar effect to flow control, and keeps the pump on the curve because really importantly, what you’re trying to do with the pump all the time is to ensure that it works efficiently and it doesn’t work in a cavitation zone. If a valve cavitates, they can get premature failure and a lot of wear inside the pump and stuff too as well.
So, by putting these additional functions, we can also cap that. There could even be a function where you may have a situation that you’re providing water to a distribution tank, and maybe they’re going to turn part of that water supply off and supply another smaller tank. And all of a sudden, now I’m running half the amount of flow, the pressure has gone up too high – it’s a problem. So we could incorporate a pressure reduction function. We can add those additional functions at the time of installation or later down the track. It’s very versatile in summary. So basically the main things are, is that it’s a non-return, it’s a water hammer preventing valve by opening and closing slowly, and it can do flow control, sustaining or reducing if required as well. So it’s, um, it’s like a Swiss army knife with all the little tools.
|Sarah||Sounds like it. I love that.
So if someone’s considering the use of a pump control valve, does this generate any additional head loss at the pump station? Um, I’m under the assumption that pumping efficiency is critical in any design.
|Colin||Absolutely. Yes, completely Sarah. So we know that when you’re designing a pump and you’re looking at a network, what you’re trying to do is to get a pump that’s really efficient, uses a little amount of power, so you can keep everything fairly efficient and green. If I put something in the flow of the path, which generates a high head loss, and all of a sudden, this means I need a bigger pump in a bigger motor, that’s not efficient.
So we tend to always design the valve to suit the pump casing discharge pipe work, but ensure that the head loss is hardly noticeable at all. So the Bermad Y pattern design is enormously efficient in producing a low head loss. So it’s, it’s absolutely made for a pump control application to ensure that there’s virtually no, little, if any head loss at all.
|Sarah||And so it appears that the pump control valve is a flexible and efficient design that can reduce the effect of water hammer during every pump start condition. What happens if there’s a power failure at the pump station?|
|Colin||Okay. Okay. So, um, so what we’ve explained is what the valve can actually do, or the process can do, under normal controlled conditions. If the power is out, all the bits are off, the valve shuts and you don’t want to know what happens after that. So this is now talking about water hammer under uncontrolled conditions. So maybe that’s a topic for the next podcast. What do you think Sarah?|
|Sarah||Sounds like it might be Colin.
Well, that wraps up this week’s episode on preventing water hammer in pumping stations, valve checks, and the designs in place to minimize water hammer.
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