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Surge Tank Sizing
3

Surge Tank Sizing

Surge Tank Sizing

(OP)
Hi Guys

I am currently working on a pump Station for which I need to size a surge tank for Water Hammer/pressure variations, I know that we have some standards in AWWA m11 but if u guys have anything like an excel sheet or anything please help me out this is the first time I am sizing a surge tank

I've done expansion tanks for Air Conditioning Systems and Pressure tanks for VFD-Booster Pumps but here we are talking abt a pump station with really high flow like 5000 m3/hr and basically I need to size a surge tank please help me out even if u know any analysis software or manual calculations etc

RE: Surge Tank Sizing

Check AFT Impulse at http://www.aft.com/products/impulse

The software is ideal for surge analysis in 100% liquid systems. Quarterly lease cost for a standalone license was about 1,800 USD the last time I checked.

Dejan IVANOVIC
Process Engineer, MSChE

RE: Surge Tank Sizing

(OP)
Thanks Man I ll definitely Check the software if my company is willing to pay for it, you see we dont really have a big project like its just one pump station we dont have an entire site so I have to only size just this one tank do u know any manual calculations??? but I ll try to convince the company to buy the software anyway

RE: Surge Tank Sizing

First off work out the scenarios as to why you need to have such a valve and tank.

Without working this out first you won't be able decide whether your tank is 10/20/50/100 m3 or indeed that you don't need one.

Without a transient simulation of some kind, there is no real means to determine whether such an event occurs or how much fluid you need to take out of the system to prevent over pressure.

5000m3/hr is a decent flow and pipe size so the tank size might be quite a reasonable size, or it could be nothing,

If you don't want to spend the time get a flow consultant to run some numbers for you.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Surge Tank Sizing

A surge tank may not be necessary if you can setup a damped check valve downstream of each of the pumps and / or a slow closing downstream shutdown valve.

RE: Surge Tank Sizing

5000 m3/h flow, I'd guess that you will need a surge tank, or have real good, proven reasons why you would not. I don't think some XL sheet that somebody on the internet gives you will be up to it.

I'd also suggest that you take your little budget and hire a consultant that can factor a week of software time into the tiny bill. That will probably be a far more efficient price and you'll get some very badly needed expertise as well.

RE: Surge Tank Sizing

(OP)
Thanks folks!!! that was very helpful

RE: Surge Tank Sizing

(OP)
I ll talk to my Manager about the software or to hire the consultant

RE: Surge Tank Sizing

If you have a limited budget, it will be cheaper to hire a consultant. Otherwise you will spend more (1) on all the time yourself learning how to use the program and (2) trying to find out if the software is giving you reasonable answers, if you made an input error, or if you are simply interpreting the output correctly. And you might still need to convince your client that you have the necessary expertise to use it and make a design from it. If you only expect to do these kinds of projects once in awhile, or maybe never again, then there isn't much sense learning to be a transient hydraulics engineering specialist.

RE: Surge Tank Sizing

I'm more concerned about the fact that you think a surge tank is needed before you've actually finalised the design and operating system.

The aim should be to avoid having such a tank, not rely on what is effectively a pressure relief valve going off every time you stop the pipeline.

Pressure surges sufficient to exceed the design pressure + 10% on a regular basis are not normally a good news long term and results in fatigue, movement of pipes especially at bends.

You may end up with a very occasional situation where you need one, but it should be the exception rather than the rule IMHO.

That's why you need to see why and where you get high surge pressures and what you can do to reduce it so that you don't need a surge relief tank. That tank will then need emptying before you can start again to give you ullage in operation.

The design of large water pipelines may be different, but it doesn't sound like a good move to me.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Surge Tank Sizing

(OP)
I understand what you are saying but the thing is I have seen the pump station built by the other contractor who basically has the entire site and they used a Surge Tank for their System and it seems like the client wants us also to install the Surge Tank unless we can prove with references and computerized reports that they dont need a surge tank

My manager says that he dont wanna take responsibility for the sizing of this surge tank, I mean if we ask the company to buy a software then its really on our head like its gonna be on my head in particular, I believe I ll tell em to hire a consultant

RE: Surge Tank Sizing

(OP)
I also checked with some suppliers if they can suggest the size of the surge tank and it seems like they dont know

Guys do you know any manufacturers of really huge surge tanks for domestic water applications please share here so that I can contact em not particularly for calculations but at least to know if they have the tanks available.... here many companies I contacted they dont have the thing available

RE: Surge Tank Sizing

Start with scaling. It may have no relation, but you might try. What's the flow rate of the other pump station and how big is that surge tank?

RE: Surge Tank Sizing

I agree with BigInch and look at getting a consultant to model your system. We have installed a number of large pump stations and none have needed tanks. The model would include pump momentum and other effects that may reduce the need for a tank.

RE: Surge Tank Sizing

(OP)
What I have exactly is a sort of distrebution plant there is one inlet from saline water conversion plant and then water is stored in huge storage tanks and we got like 3 outlets from tanks two of em are directly going out of the site toward the city and one of em follows rather a long route but then again it goes out toward the city so thats about it, they need booster pumps here becouse its a long pipeine and there is only one pump station here but I went to the other site of the same customer and there they had one pump station with like 1.75 times our flow rate so I already did the scaling to get an Idea abt the Tank size ;) but u know it does not work that way and we know it seems like I've found some company who can do this transient analysis lets see......

BTW KevinNZ did u do the transient analysis??? plaese help me learn it if u know :)

RE: Surge Tank Sizing

(OP)
@BigInch man I wrote on my notebook but its on my work station I ll let you know once I get to the office


RE: Surge Tank Sizing

Physics Nerd

I am glad you are trying to get a consultant to work with you as it doesn't appear your really understand why you might need surge tanks and what the key issues are.

I sense English isn't your first language, but if you want to come over as a serious engineer, please avoid text talk and use proper words, e.g.

them not "em"
Want to not "wanna"
Going to be not "gonna"

Use engineering data - you're an engineer so act like one - not "huge", "big", etc.
My "huge tank" is 160,000 m3. I doubt your "huge" tank is so big...

We also don't know where you are (region, country) so its difficult for anyone to provide such advise.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Surge Tank Sizing

If a tank is needed, all high pressures should be dissipated within 15 minutes.
Then for estimating purposes only:
Volume of 15 minutes of your flow rate is,
5000m3/h 15/60 = 1250 m3

You will most likely need a tank as long as your pipe diameter is small and velocities are above 5m/s

If you can increase pipe diameter and get velocity below 1m/s, you might not have any surge problem at all.

RE: Surge Tank Sizing

(OP)
U guys have been very helpful Thanks a lot folks for helping me out :)

RE: Surge Tank Sizing

Physics Nerd.

I sense you're not really understanding what me and a few others here are saying.

1) First work out if you actually NEED a surge relief tank. Many places and designs you don't need one or can eliminate it by better control design or slowing down a main valve closure.

2) If you need one then you really need a transient hydraulic analysis to tell you what the volume is to avoid over pressure.

3) The volume for surge tanks is normally quite small as it is a short term event ( say 15 seconds) of fairly high flow ( possible 2-3 times your normal flow) and that's it.

4) You need to avoid having a pump discharge pressure which can exceed the design pressure of the pipeline otherwise you could end up pumping into the relief tank for a long time.

5) If the event causing such surge is common then you really need to do something to avoid it as surge relief like this should be an accidental or occasional event.

6) remember your surge relief is only for pressures above the design pressure by more than 10% normally and the valves will close once that pressure pulse goes away.

7) from what you describe, a tank of about 100m3 or lower should be sufficient to deal with pressure surges. If you need the tank for other events then it might need to be bigger.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Surge Tank Sizing

With the 1.75 m/s velocity he may not need a surge tank at all, but if he does, 100m3 will certainly not be enough. Maybe LI is thinking about hydrotest pressure in a closed pipe. I've filled a 10,000BBL tank off a 24" pipeline before lowering the pressure from 1750 to 1400 psig. True, that was on the end of a rather long pipeline dropping down from the mountains and your's is around a 40" ID.

It's good you don't have a real high velocity. I suspect you may not need a surge tank, but get that hydraulic analysis done soon. Only then will you know.

RE: Surge Tank Sizing

(OP)
@littleinch

I told u guys before this is the first time I am dealing with a project where there could be a problem of surge so yes I dont know much about it and I do not consider myself as highly qualified professional rather I am still just a stundent and will remain so forver, and thats why I am here so that experienced people like you could help me out

English is not my first language and I am sure that is not a problem, is this a rule of the forum that I must not use short words if so please let me know

Storage tanks are really huge man, this site is meant to distribute water in a city..... 163,457 m3 is the Volume of the storage tank (Diameter = 110m, Height = 18.6) and yeah you are right its awkward to use huge... big is better!!! I should not have used huge for surge tank though

I am from INDIA and working in Riyadh, KSA, but our company is ready to buy from abroad its not an issue

Thanks again for your help & apologies for using bad english

RE: Surge Tank Sizing

Your English is fine. No worries.

Try the Turkish pizza at that place on Thalateen Street, if it's still open.

RE: Surge Tank Sizing

Generally, if the flow rate exceeds around 30 L/s and the dynamic head exceeds 15 m, a surge control analysis should be prepared.

The surge vessel positioned downstream of the pump station is to provide protection against a loss of power to the pump scenario.

What is the elevation difference from the pump station to the discharge point?

Do you have a standby generator in case of power failure?

Is the power reliable?

Controlling a transient response may be less expensive. Possible measures include extending valve opening and closing time periods, coordination of multiple valve closures, addition of quick closing check valves, modifying and extending pump shutdown with motor starters, and/or use of an alternative power supply on some pumps so that the entire system can't fail on loss of power.

RE: Surge Tank Sizing

(OP)
@bimr

thanks for your help, the thing is I dont think client will agree on us not installing the surge vessel as it is included in the BOQ & there are other such sites and I saw one em had a very big pressure tank for surge.... and the thing is these pumps are meant to distribute water in the city and I have the drawing of the distribution plant and not the city.... I am attaching a picture of what I have at this stage as this also our end of contract but the thing is that pressure vessel is within our contract limits :( and I do not have the excavation details at this stage either

all I know is Water is coming from 6 Tanks (each 163,457 m3) into a header with 5000 m3/hr flow & then the pump station and then to the discharge point out of the plant toward the city.... and I need to install this surge vessel after the pump station..... I dont know the elevation difference as I dont have the excavation details

@BigInch

I ll definitely check that Turkish Pizza.... :)

RE: Surge Tank Sizing

PN -

Lets be clear here what it is you are thinking off.

Is this a Pressure vessel to accommodate surges / high pressure / fluctuations without removing any water ( like an expansion vessel on a closed loop system) or a large tank (not a pressure vessel) which is connected to relief valves which open at high pressure and dump water into the tank?

I'm beginning to think you mean the first one, which is a completely different thing than what we've been talking about so far. Please explain / define further.

Your picture of an empty space on the drawing is not helpful and provides no information, sorry.

BI - Was that the Turkish place where they baked an enormously long single piece of bread if you went in with a dozen people?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Surge Tank Sizing

(OP)
@littleinch

its not a closed system, its open.... this pump station will deliver water to the city & to some other reservoir (I am working on getting information on this reservoir)

RE: Surge Tank Sizing

I know that, my question is whether this "surge tank" is actually a pressure vessel (i.e. water goes in and out held under pressure or is it an atmospheric tank??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Surge Tank Sizing

That's the one. (Turkish pizza) I remember you being there on occasion. I always liked that place.

RE: Surge Tank Sizing

LittleInch,

This project is utilizing a closed pressure surge vessel to protect the pump station from power failure. It is shown on his sketch.



Physics_Nerd:

This pump station and pipeline are considered to be closed systems.

RE: Surge Tank Sizing

(OP)
This is the exact situation... this tank is not atmospheric.... so I did'nt know if it was a closed system but anyway thanks for the guidance so thats abt it..... @BIMr what are he most important points I would need to find an approximation of this tank size???

obviously I am still working on getting drawings of te city & the his other reservoir

@bimr thanks for the picture :)

@littleinch
bro that picture is exactly what I have :)

RE: Surge Tank Sizing

OK,

given we are now looking at a pressure vessel, you're in a completely different place than where I was originally coming from.

This is primarily there to inject water under pressure at a big flow rate ( so will need pipes close to the size of the delivery pipes) for a very short time if the pumps all turn off together.

In those circumstances, the water downstream of the pumps can create a low pressure / vacuum due to the water in the pipeline continuing to move. When that vacuum then collapses as water rushes back the pressures can be very high. Hence designers often require some means of putting water into the pipeline to avoid the low pressure.

It is not really possible to estimate this volume without proper transient analysis, but if you want an initial size work on flowrate of the pipeline for 30 seconds - in your case 40m3. However a lot of the tank will need to be pressurized gas (50% say) so the volume of your pressure vessel comes to around 80m3. Depending on the pressure that's a big pressure vessel which costs a lot of money (compared to a "tank").

Your use of a consultant will be well worth the money because he or she might say you don't need one, or the volume is only 10m3.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Surge Tank Sizing

(OP)
@LittleInch

Thanks a lot man

RE: Surge Tank Sizing

(OP)
@LittleInch

if you worked here in Riyadh then you should know abt DONGO & METITO, they are the people who are mainly involved in these projects, I saw their sites the surge vessel looks big man, its horizontal & super huge so you see we quote good price for the vessel we can pay for it no problem lets see, I am still trying to get full information on the pipeline this is NWC we are working for, they dont reply fast and DONGO wont help obviously unless you have a friend inside :)

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