branch line water hammer protection

[pumpmann]

What are the options of protecting a branch line from expected surge conditions from the main line?
We are only responsible for connecting onto the main line, not with the design of the main line which is the property of the local authority

 

[BigInch]

Put a soft starter on your pump, but watch that starting torque requirements are not defeated.
Start your pump against a closed or partially open valve, then open valve slowly. Be sure valve does not overheat.
You may have success with a cycle stop valve as shown here,

http://www.cyclestopvalves.com/products.html

Other direct type pressure set relief valve to relieve to suction or back to tank.
Install an accumulator type device.
Temporarily hut off branch line connection.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[pumpmann]

thks
we however do not dictate the design or operation of the main line
we have to opt for pressure regulation/ isolation options

 

[BigInch]

You can only do what you can do.

Simply advise the owner of problems he can expect, if he does't take full responsibility for authorizing such a poor design specification that fails to understand that one part of a hydraulic system cannot be isolated from another part simply because the owner wants to.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[stanier]

You may consider some of the means of mtigating the pressure surges shown in this presentation.

You may be in a position I found myself in where the pipeline is a common user facility that you wish to use. The owner takes the view that you may break it so you must pay to protect it. As a professional engineer you have no option but to analyse the whole pipeline to determine the impact of your operations and what measures need to be taken.

This will need the cooperation of the owner in providing all the information necessary. If the owner is a competitor they may be less than enthusiastic in helping. Then you may need to go into legal issues such as restraint of trade or the equivalent in the USA.

You cannot just guess what you can do!

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[rconner]

[I guess could add to what others have said, "Very strong pipes and restraints" (i.e. ones capable of handling the surges imposed on them)]

 

[stanier]

Very strong pipes suc as legacy ductile iron and steel have a high modulus compared to thermoplastic materials. Hence transient pressures and wave speeeds tend to be orders of magnitude higher.

Use of fully welded thermoplastics means no thrust blocks, reduced wave speeds and lower transient excursionss this provided that there is no column separation and re combining of the liquid columns.

You need to do the numbers or you are just guessing.

"In physical science the first essential step in the direction of learning any subject is to find principles of numerical reckoning and practicable methods for measuring some quality connected with it. I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science, whatever the matter may be." Lord Kelvin

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[pumpmann]

what is your opinion of installing a surge anticipating valve and pressure regulating valve at the t-off. surge anticipating valve to open and relief pressure and regulating valve to "control" downstream pressure

 

[BigInch]

Try one or the other, the cycle stop might be the best bet, definitely NOT both. I doubt the pressure control valve will act fast enough to give you any control of a true water hammer pulse. Pressure control valves are more suitable to step by step pressure control, not pulses. If they do work that fast, the gain is set too high and they will be overactive, overcontrolling and probably worsen the problem.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[rconner]

I believe the original poster is perceptive in that some branch and dead end lines can represent even more water hammer concern than e.g. looped delivery systems. I also like the “Lord’s” quote regarding “numbers” in a response; however, I will offer some further comments regarding the inference or suggestion made in the same response that the answer to greater transient pipe loadings on piping systems is weaker pipes. Looking at surge mitigation by way of weak or viscoelastic pipes at least on the surface in terms of simplistic application of conventional Logan-Kerr or Joukowski celerity or wave speed formulae approaches, and with at least low velocity assumptions, does appear to come up with relatively small calculated surge “numbers”, and this can be used to take a slap at stronger pipes. However, pressure-caused bursts of e.g. quite strong undamaged steel and ductile iron pipelines are very rare, and a quick search with a few key words e.g. using the advanced search feature of just these forums will quickly reveal that this is on the other hand not necessarily the case with some weaker types of pipes. Here are some specific “numbers” to consider, that are in part likely most responsible for these realities:
The comparative head-to-head pressure tests etc. published by the Professional Engineers of DIPRA at

http://www.dipra.org/pdf/DIPvsPVC.pdf

reveal that the very lightest AWWA pressure class 350 6” ductile iron pipe (there are many heavier classes available) held up to 4,150 psi(286 bars) pressure, whereas the same nominal size DR18 (not the lightest available) pvc pipe held (in even short term burst) 1,040 psi(71.7 bars) pressure, or about ONE FOURTH as much. In similar fairly high pressure comparative hydrostatic testing as revealed on this same website some actual 6” DR11 hdpe pipe (not the lightest available) failed by ballooning/movement and permanent deformation (no more pressure could be achieved in those tests) at 638 psi. [I suspect the also substantial and well-proven pressure strengths of steel pipes (though less common at least for most prevalent water and wastewater pipe applications) in like or common thicknesses would be comparable to ductile iron.]

It should also be understood clearly that any theoretical mitigation of surges with viscoelastic pipes is in reality only accomplished via more exaggerated MOVEMENTS i.e. circumferential expansion and/or in the case of only “welded” (not thrust blocked) systems “Bourdon” movements (or such rebating movements) of the restrained systems. For anyone not familiar with the latter term what is meant is a lengthening of e.g. the legs of a piping system near a bend or closed valve etc. due to unbalanced pressure thrust on its ends along with expansion (for some exaggerated illustration purposes one can envision what happens to a tubular latex balloon as it is blown up to tie a balloon “poodle”). Yet the “numbers” or other effects at least regarding magnitude etc. of these specific movements are rarely if ever presented or discussed. I do know that (quoting a published article from a manager of the Johns-Manville research lab many years ago, as I mentioned also along with much more detail in the prior thread at

http://eng-tips.com/viewthread.cfm?qid=125930

) stated some high surge pressures have been measured in actual plastic pipe systems and also indicated perhaps non-obvious axial movement may even occur with very short duration higher pressure spikes, “Since PVC pipe moves axially as well as circumferentially in response to pressure surges ("Poisson's ratio effect"), pipe may undergo scratching of the outside when buried and in contact with sharp stones in the backfill. This area requires further study."

I have noticed that over the years since some “study” has been done and published, at least from the standpoint of some pipe-weakening effects of “scratches” if not movements. To their credit(or at least some arguable protection to the pipe manufacturers?), I believe AWWA standards e.g. C900, C906 and C909 etc. now do contain at least some caveats on scratches e.g. new AWWA C909 specification for pvco water pipe, that is now touted as a new and improved/more damage resistant (I guess over prior pvcu and cpvc) type of plastic piping, includes in Section 4.3 Pipe Requirements) the caveat, “Pipe surfaces shall be free from nicks and significant scratches.*… and in a footnote to this, “*Scratches that extend 5 percent or more into the pipe wall shall be considered significant.” [I read from this that e.g. a 4” PC 150 pvco pipe with a scratch etc. 0.05x(0.145”) = 0.007”, or a 4” pipe with a seven thousandths inch deep scratch etc. would not be acceptable per this newest standard. That being said, I’m not sure what real value this knowledge is with regard to even aboveground inspection of pipes (unless perhaps someone has the human and equipment inspection resources to crawl all over all pipes right before they are put in to detect same), and furthermore may be of virtually no value at all to an Owner if such damage were to subsequently occur after a one year contractor warrantee period, for whatever reason or mechanism, in pulling installations or below ground.

I guess it should also be remembered that plastic pipelines once installed in reality do not somehow float homogeneously by themselves essentially in a vacuum, as it appears is assumed by some surge theory, but despite greater bedding care in some areas, like all pipelines they are subject to all kinds of encasements, embedments, and bearings etc. somewhere in the systems. It is virtually inevitable that they will also at some point be adjoining connections to much stiffer metallic piping or be encased in stiffer concrete encasements or walls etc.(this is not likely to change any time soon). These realities greatly strain, so to speak, the credulity of a theory that assumes e.g. that in the fluid of the steel or ductile iron portion the surge pressure would be say 100 psi (nearly 7 bars) whereas in the same fluid near immediately just down the line in the plastic portion, say a nanometer away, the pressure would only be 30-40 psi(just a couple bars)! [In other words it may be kind of hard to reconcile this theory with the “law” of Pascal, essentially that at any point pressure is equal and opposite in all directions!] While I noticed Mr. stanier (in talking about stronger pipes) mentioned, “… transient pressures and wave speeeds tend to be orders of magnitude higher.” what he didn’t mention is that with weaker, lower wave speed pipes the duration of the transient/higher pressure application is correspondingly longer with the weaker pipes.

Also, one should perhaps also be careful in assuming that surge events happen only in a too quick interruption of just normal low potable water service delivery velocity. In areas much higher water flow velocities, and maybe particularly in “branches” or dead end lines, may occur at times in their life cycle. While one example might be in a hubbub of well-meaning “rear ends and elbows” opening and closing valves in fire fighting or fire flow testing events in common combined water and fire protection systems(by all means, run these “numbers”, as determination at least of fire flow velocity assuming say a 1,500 gpm fire flow quantity in a common 6” or 8” delivery branch is an even simpler calculation for all engineers, and make sure you are comfortable as you can practically be with the literature and the chosen type of pipe operating at same), another might be a case where an improperly welded or otherwise joint cuts loose, or where someone plows through a water line, and slugs of water get propelled by vacuums, then unrestricted head from a tank, or even trapped pressurized air somewhere in the system(in “water rocket” fashion etc.!)

While there is certainly proven utility to “fully welded” pipeline systems(if not surge mitigation), such and maybe particularly with plastic pipes come with their own sets of issues and considerations. Fully welded plastic pipeline systems are in fact not “jointless” (as I have seen often quite blatantly and shamelessly promoted), nor is assuring the resulting quality of fusions in all kinds of environmental conditions and weather, equipment, and with whatever locally/widely available pipe construction labor quite as simplistic as has sometimes been portrayed. Even once effective fusions are made, some resulting fully-welded plastic pipe systems are more susceptible to a unique phenomenon called “rapid crack propagation”, wherein once a burst occurs instead of one stick of pipe bursting the splits can run for hundreds of feet or hundreds of meters of pipelines(see e.g. the multiple reported instances, investigations, and photographs of Table 1 and following photographs on pages 4-5 of the quite recent document now at

http://www.plasticspipe.com/docs/Paper.pdf

, I accessed this day). It may be one thing to deal with a somehow burst or leaking stick of pipe, and yet another to deal with hundreds of meters of split piping, particularly if same happened to be in a crowded utility corridor!

Finally, we engineers surely love numbers(otherwise we’d probably be in some other business!), but I guess we must also realize the extent of our knowledge and also what is within our direct control (I fear sometimes not much from behind our desks, or nowadays from in front of our computers) over factors that influence assumptions used when we crank same. In other words, are we really as smart as we sometimes think we are, so that we can trim real safety factors to much lower numbers? In the mean time, or if we are not sure of this, stout pipes are perhaps a reasonably well-proven way of sleeping a little better at night, particularly when they can be had for about the same installed cost of weaker alternatives. While I noticed Mr. stanier at least qualified what he said with the words, “…provided that there is no column separation and re combining of the liquid columns”, what really is to protect at least the bulk of the piping from any of the above mentioned possibilities or eventualities, other than the strength of what’s there? For anyone who has suffered through this admittedly long and scribbled post so late in the week, thanks for the patience and have a great weekend!

 

[stanier]

Surge anticipation valves have been oversold to the market. I dont know one that can account for all potential conditions in a system. The purveyors of such devices do not carry professinal indemnity insurance or take process risk. Thus you have to ensure that the surge anticipation valve will cater for all circumstances in the system. In a complex system with a mixture of owners or responsibilities, lack of information or reluctance to model the whole system, that is a big call.

Add to that it is a high maintenance device that needs the security and testing of a relief valve. In these days of depleted maintenance resources, particularly in the water industry, it would be courageous to rely upon such a device.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[BigInch]

I would agree, which is why I suggested that the owner take a beating first, however it seems that alternatives to valves in this case are also limited.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[stanier]

BigInch Depending upon the system design a gas bladder accumulator may protect the branch. But this is all pure guesswork without some system response data from modelling or physical testing. I come back to my mentor Lord Kelvin and his numbers.

We can see how the world has got into a terrible financial mess because economists guessed the future. Engineering is the last bastion, but I am constantly disappointed by those who want to guess what is going to happen just because its hard to calcualte something.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[BigInch]

Sometimes it is impossible to calculate an answer, but the economists, or fill in the blank ____ "scientists", think they can. Dark matter is not confined to the outer reaches of the universe. There is ample distribution of it across all disciplines. And guesswork isn't all bad either and can in fact be better. It depends on who's doing it and if it is based on good experience, but then it isn't really guesswork anymore is it.

I would not be so foolhardy to suggest that in any way this internet page (or any other) represents anything near the proper engineering study that would be necessary to verify any actual solution here, then again the OP is only asking for our thoughts and ideas. Let's don't get carried away any more than necessary.


Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[jmw]

One of the inexpensive techniques that used to be used in water lines was to include a blind vertical riser which trapped a column of air inside - length and diameter adjusted to give the best results (and in some gravity systems an open ended vertical riser, so long as it was such that it didn't spout like a whale!)
This would absorb some of the surge.
I'm not sure how acceptable this is today but it may be a useful temporary protection.


JMW

http://www.ViscoAnalyser.com

 

[BigInch]

In closed end form, they are called gas/liquid accumulators.
The open ended "standpipe" system is still in use in some areas, but it's effectiveness depends on the maximum pressure of the transient. At all but the lowest maximum pressures, these things can easily draw the attention of Captain Ahab.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[jmw]

Thanks BigInch, I might have guessed someone would have made up a name for them.....

JMW

http://www.ViscoAnalyser.com

 

[rconner]

I guess virtually all surge control devices, for some price of design, procurement, and maintenance etc., probably offer some degree of protection from surges e.g. as explained at

http://en.wikipedia.org/wiki/Water_hammer

and with regard to potable water application also at

http://water.epa.gov/lawsregs/rules...forhealthrisksfromintrusionofcontaminants.pdf

. However, the latter reference also explains that there are contamination hazards or risks associated with some surge control devices themselves i.e. some air valves, vaults and surge control devices such as tanks and standpipes. It thus reveals practical limitations of air vaults and valves etc. and also, “If water is stored in the tank for long periods of time the water quality may degrade and proper operation and maintenance is required to avoid poor quality water from entering the distribution system.” While conveyed potable water contamination obviously may not be a direct issue in other pipeline applications, there nevertheless also be other environmental etc. concerns with some devices as well in some.

 

[stanier]

rconner,

Waterhammer mitigation is not a simple subject and the solution does pose risks. it is not something an engineer picks up in a simpe training session. Buying the software and books by Thorley, Streeter, Wylie & Suo, Swaffield and Boldy are just a stepping stone to understanding this topic. They are an aid to analysis, risk assessment and engineering judgement performed by very experienced engineers.

There is not only the understanding of dynamic hydraulics but it involves the dynamic design of pressure components, valve selection, control and relief valve sizing, process engineering, noise emissions, environmental engineering, risks of explosions, etc etc.

I liken surge analysis and design of mitigation measures to the game of backgammon. Anyone can be taught to play the game in a couple of hours but it takes a lifetime to understand the nuances of what you are doing. Then you retire!

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/