Can I measure Water Hammer?
Can I measure Water Hammer?
(OP)
Is Water Hammer the resultant "Noise" from the shock of acceleration of water? If so, Water Hammer is nothing more than vibration.
Is there a point when Water Hammer is pressent and not detectable by the human ear? If so, would there be any damaging affect because of the seemingly small amout of Water Hammer?
Is there a method of measuring Water Hammer?
Darrell
Is there a point when Water Hammer is pressent and not detectable by the human ear? If so, would there be any damaging affect because of the seemingly small amout of Water Hammer?
Is there a method of measuring Water Hammer?
Darrell





RE: Can I measure Water Hammer?
No, it's not the resultant "noise." It is also much more than vibration. A water hammer is a "layman's term" for a pressure transient, often severe, usually caused by fluid rapidly changing direction in a non-full pipe. Just accelerating the fluid doesn't do it, you also have to rapidly change the direction of the fluid. Having a partially steam filled line with a rapidly increasing pressure also adds to problems.
Yes a water hammer can be present and not detected by the human ear IF THERE IS NOBODY THERE TO HEAR IT. It depends on how close people are to the location of the water hammer and what intervening material (distance, amount of concrete, etc.) as to whether someone will actually "hear" it. And yes there could be damage, even if no one hears it. You can often "see" the after-effects of a water hammer by the line of dust on the floor that was shaken off the pipe. However, the major concern is with the pipe supports that might be damaged.
Generally, you want to design against it, because of the very large pressure transients which can occur. However, if you think you have it going on, then some high-speed pressure gauges and accelerometers would allow you to measure it.
Why do you think it is water hammer and not cavitation?
Patricia Lougheed
Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.
RE: Can I measure Water Hammer?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
regards
RE: Can I measure Water Hammer?
Best regards
Morten
RE: Can I measure Water Hammer?
At any rate, Try 1-2 fps change in velocity in a long pipe and I believe you will see the resulting unbalanced forces are relatively high.
Regards
RE: Can I measure Water Hammer?
BTW going back to the original question: I believe that you can get both electronic pressure gauges that are fast enough to catch the peak pressure and mechanical gauges with "stickyness" so that the gauge wont drop back but stay at the max pressure.
Best regards
Morten
RE: Can I measure Water Hammer?
What seems to be a slow closing valve is relative. In a long pipe, such a valve can be considered fast closing.
For example, neglecting friction and flow velocity, and say 2 miles of pipe with a sound speed of 3000fps- under 3 seconds closing time is fast.
Regards
RE: Can I measure Water Hammer?
Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us
RE: Can I measure Water Hammer?
regards
RE: Can I measure Water Hammer?
I think it is time to give a little background.
I am building Valve/Actuator packages and I would like to design into the actuator a closing profile which slows the closing time toward the 100% close position. I have a fellow associate who feels that it isn't necessary.
The velocity in an 8” pipe with the valve fully open is approximately 20 ft/sec^, and the length of pipe varies from 50 ft to 500 ft.
From your comments, it appears that I should press forward with a closing time profile.
Of coarse I would like to eliminate the complexity of the closing time profile, so If I were to build a prototype and test it for water hammer, and found that there isn’t a need to change the speed of the valve’s closing, everyone would be pleased. But, I would need a definitive test method to determine the amount of water hammer.
RE: Can I measure Water Hammer?
"budt (Industrial)I follow your reasoning, but the gauge reading is now dependent upon the response time of the check valve."
I know its not perfect but gets close enough with available inexpensive equipment. It is also a way to get info without the machine operator or others knowing you are checking.
Try it, you might like it.
Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us
RE: Can I measure Water Hammer?
A 3 second total closing time on a pipeline is speed of light, 1 sec/inch being more reasonable, unless its an ESD valve. Great care is needed in selecting valves and actuators when velocities are above 5 fps, as many valves effectively open in the first few seconds, or close in the few seconds, even though their total opening time and closing times may be only 1 sec/in diameter due to poor Cv vs actuator position curves. One must be carefully in slowing down the mainline velocity well before a valve gets close to its shutoff point.
If there is a snap acting gas operated ESD valve in your pipelines, you must do a transient analysis.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
Depends on time for inital reflection and responding reflection to return to point of origin.
For a short lengths, 3 seconds may be a slow closure.
Regards
RE: Can I measure Water Hammer?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
The Jucowsky equation give a conservative estimate:
h(wh)=a*dV/gc
where
a=sqrt(1/((den/gc*(1/K+D/(bE))
Keep it strictly metric and it all works out (head in metre liquid column)
gc:gravitational acceleration
V:velocity
K:bulk modulus of elasticity of THE FLUID
E:bulk modulus of elasticity of THE PIPE
See e.g. Perry for reference
Best regards
Morten
RE: Can I measure Water Hammer?
Best regards
Morten
RE: Can I measure Water Hammer?
Caution, the Joukowsky equation is for a straight single level pipe filled with one product and closed on one end, so it does not tell the whole truth when applied to an operating pipeline that typically will cross one or two mountain ranges and river valleys, maybe with slack flows, wide variations in product density (due to +2800 meter differential elevations), or perhaps 10 products in the line at the same time, have open connections into other systems, pumps starting, stopping, check valves chattering, and control valves changing %Open at several (or many) points along its length and have multiple reflected (algebracially additive) transient waves moving back and forth between stations.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
Best regards
Morten
RE: Can I measure Water Hammer?
The Joukowsky equation is not limited to a pipe with a closed end. If used properly, it can include the effect of disturbances such as valve closure or opening as a function of time, the movement of a pig in a pipe, etc.
The stated equation,is an oversimplification of the results of the method of characteristics. In the form presented, it does not include friction. However, in rapid transients, friction is generally small, compared to the acceleration effects.
In addition to neglecting friction,the Joukowsky equation should only be used with highly incompressible fluids (and further assumes sound speed does not change).
The method of characteristics is the way to go for general solution of one dimensional transient flows of a homogeneous fluid.
Regards
RE: Can I measure Water Hammer?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
In the electric power industry, the main steam stop valve at the turbine inlet is a 12" NPS electro-hydraulically actuated valve, fail closed, that will close in 0.2 second total stroke time. Similar speeds are assocaited with the turbine bypass control valves. While the bypass control valves may haev a reduced speed of closure to limit steam hammer events, the turbine inlet stop valve has not such limits, as its objective of preventing turbine overspeed has a much higher importance than pipe reactions.
There are also other specialty stop valves that close faaster than 0.2 secons- I recall that Target Rock stop valves ( used in nuclear subs) advertise a much faster closer speed.
RE: Can I measure Water Hammer?
No it isn't, If the valve closes say 1/2 way prior to the first reflection coming back, the full instantaneous pressure is not reached.
Regards
RE: Can I measure Water Hammer?
Please don't think you must describe reflections to me. I may not describe things in a detailed manner that you can easily understand what point I am trying to get across, but in any case, I can see them quite well during the simulations I am working on, so no need to bother yourself.
Back to Morton's question.
The Joukowsky equation can underpredict the maximum pressures in certain cases. I often find 10% differences in simple cases, where equipment interactions are not considered. This is due to line packing effects, after the fluid has effectively stopped forward progress, the pipeline begins to expand due to the higher pressures, allowing more fluid into those segments and small forward velocities persist.
Other errors are common in the use of the equation. For example, a water pump station, 20 miles of flat pipeline, a 1000 foot elevation climb in 5 miles with a pressure on top of -5 psig, followed by a uniform decrease in elevation over the last 20 miles to the terminal, which is at the same elevation as the pump station. Flowing pressure at the terminal is 125 psig with a velocity of 6.8 fps. If the terminal's ESD valve closes, what is the maximum predicted pressure at the ESD valve inlet?
When other factors are considered, where velocities may go higher than design velocity, a higher percentage error can occur. Just a valve opening too wide at a terminal downstream from a 3000 foot mountian may reduce the mountaintop pressue to the product's vapor pressure and create a runaway column. It would have to be stopped at its maximum velocity, which might be as much as 4 times the design fluid velocity of 5 fps. A Joukowsky prediction would give only the pressure increase based on the 6 fps velocity (400 psi), and the actual pressure that might be seen at the terminal could be as high as maybe 1750 psi. The 400 psi, would have to be added to the full static pressure at the terminal (1300) to come close to what would actually be seen at the terminal, 1750 psig.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
best regards
Morten
RE: Can I measure Water Hammer?
The results for the example I gave above, I think were from a case I ran for a water column running away from a 1000 foot head in a 20 mile long 30 inch diameter pipeline. I recall seeing a velocity of about 20 fps before the valve responded and increased the pipeline's outlet pressure sufficiently to start slowing it down. So, there's nothing to say the velocity might have not gotten higher.
Perhaps a safe conservative result could be found by using the maximum velocity attained by dropping an object from the pipeline's high point elevation to the inlet elevation + minimum inlet pressure head equivalent, but that would be way too fast to give any useful result. Seems that frictional resistance and a terminal velocity must be determined in order to yield a useful velocity.
Do you have some thoughts on how to find the "terminal velocity" for a run-away column? Maybe using an equivalent spring derived from the products average bulk modulus??? For me, its easier to do a sim.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
The Joukowsky equation can be modified for highly incompressible fluids where flow flow velocity is low compare to sound speed as
a*delta U+delta p/rho +(or -)delta z=0
where a is sound speed, U is velocity, pressure, rho density and z elevation.
Note friction is not included.
What do you mean by run away column?
Regards
RE: Can I measure Water Hammer?
"Does the Joukowsky equation give conservative results and, if so, is there a partiular manner in how it must be applied to give conservative results?"
I believe that it does not give conservative results and yields pressures that are (at least) 10% lower when pipe expansion and water compressibility are considered. I have compared the differences using water only. Will a more compressible product, say for a bulk modulus of 2/3 that of water, such as diesel or gasoline, result in even a greater difference than what is seen for water? I have never compared the results from J. eq. for any product other than water.
A run-away column happens in liquid pipelines. It typically results from reaching the vapor pressure of the fluid the highest (or a local high) elevation point of the pipeline. When reducing pressure, and upon reaching vapor pressure, no further pressure reduction is possible, as any liquid in the low pressure segment vaporizes to fill any increasing void space. With the "siphon" effect lost, liquid on both sides of the mountain peak could accelerate down the sloping pipeline, due to gravity, if the inlet and outlet pressures drop for some reason or are not brought up to equal the static pressure plus that required to stop acceleration.
So the question now at hand is, "What velocity should be used with the J eq. to give conservative results for a run-away column condition? Or, in other words, what is the maximum velocity attainable in a pipeline (or any column of liquid) with only vapor pressure at the top, and to be conservative, with atmospheric pressure at the bottom, accelerating due to gravity, within a vertical or sloping pipe of length X?
In the few cases I have actually compared (using water), I have seen that the J eq. resulting dH, calculated using the pipeline outlet velocity predicted by my simulations for a instantantly closing valve at the outlet, must be added to the liquid column's static pressure to approximate the maximum pressure at the closed valve that is predicted by the simulation, but it is still a little low when compared to the simulation result.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
From the method of characteristics with a highly incompressible fluid and negligible friction
Utop=0
(Ptop-Pbottom =rho*c*Ubottom + (Xbottom - Xtop)*rho.
See below for derivation.
Generally for liquids, sound speed>>velocity of fluid.
If sound speed is based on rigid pipe, then results should be conservative. If liquid is single phase prior to closure of valve at top, then liquid should not flash in uphill portion. Down hill is another story.
Is friction important? It can be, however, at best most of us can only use an approximate friction factor which is based on steady state, not transients.
I would suggest that if transient pressure rise or reduction compares with the initial steady state friction, then somehow, friction should be included. If transient pressure rise>>friction, then neglect friction.
The dearivation below can include friction, however, I have left it out just for simplicity.
Regards
du +dP/(lambda *rho)+dt=0 where u = velocity, P= pressure, rho=density t, time and
lamda = +(or -)sound speed
Or
du +dP/(lambda *rho)+dX/(u+ lambda)=0
where dX/dt =u+lambda
and X =distance in flow direction
With flow uphill to an instantaneous valve closure at top of hill
u+ integral dP/( (lambda *rho)+ integral dX/(u+ lambda)
=constant
assuming constant sound speed and small velocity compared to sound speed along with negligible change in density.
Utop -U bottom +(Ptop-Pbottom)/(rho*c)+(Xtop-Xbottom)/c=0
Utop=0
(Ptop-Pbottom =rho*c*Ubottom + (Xbottom - Xtop)*rho.
RE: Can I measure Water Hammer?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
Its found in the PSIG website where many other articles also can be found. This is a link to the article mentioned:
http://www.psig.org/papers/1990/9505.pdf
Best regards
Morten
RE: Can I measure Water Hammer?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
Best regards
Morten
RE: Can I measure Water Hammer?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
Best regards
Morten
RE: Can I measure Water Hammer?
Slack flow can happen during steady or transient situations. Usually, if steady state, it represents the minimum flow operating range for a pipeline, as for an oil pipeline (such as Baku-Tbilisi-Ceyhan) from the Caspian region where only a 100 MBOPD production from the first few fields is being transported now, but the pipeline's maximum design flow condition will be reached during the next 5 to 10 years, when the pipeline share of the region's production could eventually reach 1 MMBOPD. During the first few years, only a very small pressure is needed for the 100 M flow abd slack flow operation requires the least power.
If its a transient situation, it was probably created by a trip of an upstream pump station and the line is still flowing and rapidly dropping pressure at the high point. Could also be caused by an outlet pressure control that went below normal outlet pressure settings when somebody turned up the outlet flow too much. If the pressure is increased too rapidly during recovery, the collapsing bubble of vapor can make for a really large pressure spike as the two columns impact each other as the vapor re-condenses.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
RE: Can I measure Water Hammer?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
The wave bouced back toward the customer but went away about half way there. The SCADA system updated every 3 to 10 seconds and we had good rosemount transmitters we calibrated quarterly.
The product was high pressure propylene. The parallel ethylene system would not water hammer, too compressible.
RE: Can I measure Water Hammer?
Best regards
Morten
RE: Can I measure Water Hammer?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
This may be off the thread, but there is a sonic wave sent through the system whenever a valve is opened or closed. The pipeline I refered to above had some test run on this theory by NASA (the line went through Friendswood) and they used highspeed pressure recorders to sense when a valve opened. Then by listening along the pipeline at different stations and using time differential they could pinpoint the valve opening location. The application was leak detection. the opening of the valve was a leak.
It worked. The hold back then was cost of the system. especially the time factor, all the locations had to have exact time to "triangulate". Today I'd bet they could use GPS to get the time very accurate.
RE: Can I measure Water Hammer?
Actually there have been a lot of ultrasonic leak detection packages on the market for quite awhile now. Its claimed they work rather well.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
The NASA stuff looked promising, but I never knew what happened to it.
RE: Can I measure Water Hammer?
The only thing I know that works is a hot real-time transient model comparison to second-by-second data for large leak alarms and detecting small leaks by long term differential volume summation, and following the big blue flies to a gas leak.
LIC is one of the good ones.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
I demonstrated this to an international oil company when they had transients as shown by the pipes jumping all over the place yet their SCADA didnt pick up the event.
Go to www.ventomat.com and read the articles there on how they developed their air release valve. Ventomat didnt understand the pressures being experienced unitl they used the right gear.
Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng
www.waterhammer.bigblog.com.au
RE: Can I measure Water Hammer?
Joukowsky does not give you the worst conditions. For a start it doesnt predict column separation and the reforming.
Prof ARD Thorley inhis book describes this phenomenon. Also trey Walters in the manual for AFT's Impulse explains why Joukowsky cannot be relied upon.
This is one of the common mistakes in the engineering world. Ignorance is bliss for some as they do a quick calculation and advise their clients that the worst pressure is X as a result of a pressure transient.
When you consider that the piping codes all say that the design pressure shall include surge pressure, this ignorance is unforgiveable. how many engineers avoid surge analysis because it is too hard?
See my papers on Risks & Surgee at www.pipingdesign.com or www.olaer.com.au/products/water-surge-vessels.htm.
Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng
www.waterhammer.bigblog.com.au
RE: Can I measure Water Hammer?
Stanier, do you have a link to Trey's AFT paper? I couldn't find it.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
The elasticity of piping should serve to reduce sound speed and with it peak pressures.
Yes column seperation is important and as you state should be considered. As I uderstand it, typical water-hammer anlysis assumes the water-void based on isothermal analysis. That too may not be conservative, since it is possible during an expansion to have flashing and pressure drop in the two phase region as the flashing temperature is reached.
Regards
RE: Can I measure Water Hammer?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
It wasnt a paper by Trey it was from the Impulse manual. I will get it to you.
Geoff
Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng
www.waterhammer.bigblog.com.au
RE: Can I measure Water Hammer?
With adiabatic and or heat transfer, the method of characteristic equations also require the additonal complication of solution on a particle path ( of dxdt=u, where u is the local velcity).
I'd be interested to know the available programs out there which handle the more complicated MOC solutions.
As a correction to my last post, The elasticity of piping should serve to reduce WAVE speed and with it peak pressures.
Regards
RE: Can I measure Water Hammer?
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
As an expanding fluid drops in pressure and as you state there is a reduction in vapor pressure. However there is an increase of quality for two phase homogeneous fluids.
What is your basis for slower vaporization?
Also, sound speed will radically change at the point of zero quality and in the two phase region as quality increases.
I'd be interested to know of water hammer programs which handle the varying sound speed for the two phase region.
Regards
RE: Can I measure Water Hammer?
Send me an e-mail and I can show you what the manual has on it.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Can I measure Water Hammer?
For sending the manual
sailoday_28@yahoo.com
Regards