Water Hammer in a Fuel Line

Seems like I read that for water plumbing you solve this problem by adding a vertical closed pipe at the end of the line. Any plumbers out there?

Water hammering is widely used in steam mains. When you say water hammering in a fuel line do you mean "hammering"? If so please define fuel media.

Hammering takes place due to undersized mains and increased velocities and increased bends and fittings also resulting in pressure drops.

To minimize you must then need to design your lines on the velocity & pressure drops.

What is your inlet pressure, what is the pressure at the end point, what is the media of fuel, what is the flow rate in gpm, what is the spedific gravity of the fuel, what is the main size, what is the distance Rft from starting point to ending point, what are the nos of valves, flanges, bends & fittings involved, what is the nos of heights & lengths during the travel.

The total heads need to be calculated to arrive at the back pressure being encountered before actual sizing is undertken to minimize velocity and hence, hammering.

Fuel media is jet fuel. SG of the fuel is similar to diesel fuel.

Yes, I mean hammering. No water involved.

The system has been designed by someone else and is in place now. I am not looking to re-design the piping system, I am looking for a product that will reduce or eliminate the 'hammering' that exists now. It would be far easier to add a device such as a 'surge tank' to the existing line than to tear out all of the existing lines and start from scratch I would think.

Since you are not interested in designing the only possible thing that I can think of is that you have air inside giving turbulence and propabably you install a couple of air eliminators (float-type) at various air collecting points(rising bends, end of main).

Check up air eliminators for liquids (Spirax Sarco/ Armstrong / Ayvaz sites).

Next if possible install vertical buffer vessels(like headers 3 times the pipe size x 3ft height with air eliminators on top) in between at 150ft-200ft.This will stabalize the pressure drops for onward distribution and will minimize the hammering.

Best of luck.

a hammer is cause by the sudden closing of a valve, with a non compressible fluid the sudden loss of water velocity shows up as a shock wave or hammer. This travels through the fluid part at high speed. bouncing back from close dead end lines and slowly ebbing away.

How do you stop it? You place something compressible in the path. In water they use a small vertical pipe about 2 feet long with air trapped in it. This blocks the hammer completely.

Now in your jet fuel you can do the same, but with dry nitrogen in the vertical pipe and you will need some way to replenish the nitrogen as it will gradually seep out. The fuel industry must make a product for this already. Just ask an experienced jet fuel plumber from the airforce or Navy

"Water" hammer can be distructive. I'm sure the pressures you generate are higher than average water line pressure; and in a 6" line very high surge pressures can be generated especially if the dispensing valve is closed too quickly. Slow opening and slow closing valves minimize pipe line hammer. Also, in multiple pump systems where the pumps are manifolded, slow closing check valves on the discharge side of the pumps are used. I certainly would not recommend using a surge chamber. You might check with the refueling company at Houston Intercontentinal Airport or Lockwood, Andrews and Newnam, Inc., Houston, Tx who designed the refueling system.

g scott

Re: Water Hammer in a Fuel Line

I will give you an Example of a real experience of water hammer and how it was solved. A friend of mine was a volunteer Fireman. One day after training it was his turn to refill the water tanks on the the pumper truck. He was in a hurry and hooked up the hose to a fire hydrant in a quiet neighborhood and began to pump water as fast as he could, when the tanks got full he shut the valve, removed the hose and returned to the fire station. The next morning the water dept in the city got over a hundred complaints about ruptured hot water tanks in this neighborhood with lots of water damage to many of these homes. What happened was my friend got the water traveling so fast when he shut the valve Quickly the water was still traveling so fast in the pipes and with nowhere else to go, it ruptured the weakest link in the system, about a hundred hot water tanks. This is the best learning tool I have found from experience explaining why valves need to be opened slowly and closed slowly in any process when pumping any liquids or on any steam systems. Even if a surge tank with air bellows is used, 4" of water flowing at 40 mph in a pipe will compress the air to a very high pressure and can blow any seal or gaskets in the systems. The best way is to Engineer the System which could be very costly or you can control the Flow by opening and closing valves slowly as this is the only safe way to use your present system without spending a lot of money I can think of. I have worked 43 years in the pulp and paper industry and automatic valves are now equipped with air flow controls valves on the air supply or discharged side than can be set to operate the valve at a speed that eliminates this problem when pumping millions gallons of liquid every day. DonnieH

DonnieH:

I agree with you.

The best way on his existing system is to look at what is feasible to do in terms of closing the flow off more gradually. In some cases, the pump can be shut down just prior to the valve closing (he furnished only a few overall details on the piping system).

In general, it is never a good idea to have valves operate in such a way as to produce a pressure hammer and/or depending on the location of the valve in the piping system, possible cavitation as well. Either or both can result in a hammering effect. In other words it could even be downstream of the valve, depending on the specific pipe and valve layout.

In some cases, various by-pass arrangements can be employed if the valve action cannot be slowed.

One such arrangement uses a pressure relief valve and valve, in series with each other but in parallel with the main valve. In operation the valve on the pressure relief bypass line is opened with the main valve, but shuts on a time delay after the main valve, allowing the relief valve to pass some fluid around the closed main valve. This has the effect of absorbing enough of the energy related to the momentum of the moving fluid to eliminate the hammer. The overall effect is like closing the main valve more slowly but add to the complication over "simply" adjusting, modifying, or replacing the responsible valves. There are also devices that can be added upstream of the valve (typically in his case containing pressurized N2) that will buffer the sudden pressure rise.

Yes, I totally agree with you and this is the type of valve he should use. i was not aware of his exact problem with valve quick closing & line size since he never mentioned it during the intitial stages of discussion.

HYDRAULIK SURGE; Syn: HAMMERING, WATER HAMMERING

I have seen similar problems in truck and rail loading systems. To reduce the hammering you can adjust the closing time (last bit slow) and stopping the pump first of the valves (but this is mostly a battle with the operator. They whant quicker closing valves to reduce the dead time).

Sometimes this is not enough and you might have to install some hydraulik buffers (e.g HYDAC N2 Preloaded Cylinder) to eliminate peaks. Another method is to install a large drum with a membrane which is also preload. It always depends on many factors and you have to try.

Tuning the valve (or replace by better ones) is mostly the best and cost effient solution.

For technical support see http://www.flowmaster.com

Don´t forget to inspect your lines in the meanwhile surge can damage them. Check pipe supports, flanges ...). If you have vessels (Filters, ...) in the stream they are maybe in danger. I have seen cracking in them created by the surge wave.

I definitely agree. And tunning the valves, even older ones, may not be a big issue. Please take a look at this: normally high capacity valves are made with some proportional or electric discrete control, piloting a large actuator. If you insert just a restrictor in the valve actuator supply pressure line, it may slow your valve down a little enough to avoid the problem.

BUT: If you're dealing with a direct jet fueling line, where the aircraft fueling valve closes when the fuel quantity is reached, so you do not have much to do, except installing hydraulic accumulators (bmuelle commented about it - chambers with a separator and pre-loaded with N2) or maybe installing a second parallel redundant line to reduce the fluid speed. But, as you stated, you are not supposed to change the line, so, nevermind.

Pressure variation caused by unsteady flow, known as "water hammer" is easily controlled by a surge vessel (Pressure vessel with known gas mass. A vessel with an internal bladder prevents loss of gas by disolution). The change in pressure can be calculated by ..

Δh = cVo/g where

h metres head

c Sonic speed of pipeline material, m/s

Vo Initial velocity of liquid m/s

g gravity m/s/s

We supply such vesels up to 100 m³

Most water (fluid) hammer can be negated by using a flexible pipe at some convenient point in the pipe line...

On washing machines they use a crude but effective solenoid to switch the hot and cold water inlets off and on...

To stop any water hammer they use flexible hose connections to the water pipes...

John.

Until you find an "idiot proof" solution (nothing against anyone, just a descriptive term) the best thing you can do is alter the operational procedure. Close the valves slowly, assuming that you have that kind of control or can get it. The vertical gas (air, N2) pipe does work but as pointed out the velocity of the fluid dictates the volume required to absorb the energy. Think of it as an airbag for your fuel. Cost justification is relatively easy. What are the ramifications of a broken fuel transfer line at full pressure and velocity at the worst possible time and location in the system. How much will it cost to repair? How long will it take? What is the cost of down time and clean-up? What if the mechanical reactions caused by the rupture ignite the fuel? What are the safety risks? Potential for loss of life?

As Harrison Ford said in "Six Days, Seven Nights", "All good questions!"

All you need to do is incorporate a "pocket" of trapped air in your circuit. Since the air is compressible (and fluid is not) the shock wave created by the appruptly stoping the flow of the fluid will be absorped by the compressible gas disapaiting the energy. An upright tube with a capped end will create such an air pocket. If you go to plumbing supply stores you will find prefabricated copper assemblies or you could solder your own. I belive there would be no compatibility isses with petroleum based fuels although you would have to look at galvanic compatibility with the rest of your fluid line.

You stated that the fuel is pumped from a tank. The hammer is being caused by closing the valves fast. You can't depend on the user to close the valves slowly, which would also reduce the hammer.

Look at ways to reduce the pressure that the pump is putting out. Change the pump, use VFD units to run the pump at a slower speed, install pressure reducing valves or hose end regulators.

If you reduce the pressure you will reduce the hammer. It will also mean that you won't be able to pump fuel as fast.

Pressure reducing valves would work but why pump to a high pressure then burn up energy thru a PRV.

Cla-Val makes a lot of valve and fittings for aviation. www.cla-val.com

I think you can educate a crew to rotate valves at the proper rate. These guys are fueling jets.

What is more likely is the use of electric or hydraulic valves with faster action than they should.

It seems to me that this water hammer problem is as old as the hills and the company that made the fueling carts should have known this and had a fix at the start...this the problem is not the moving carts, thus it must be part of the fixed tank and piping installation that was not done properly at the start. Inspect the valves. They may have a rate of closure adjustment. If not the only fix is the adding of an expansion pocket here and there...or a short section of flexible tubing in the system such that it expands slightly when the peak pressure hits....robbing it of the peak.

http://www.google.ca/search?hl=en&safe=off&lr=lang_en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=%22jet+fuel+piping%22&spell=1

I don't think closing the fuel line valves slowly is going to happen - the fueler needs to fuel the craft in a speedy manner and when it's full the valve must close quickly or somebody gets soaked in fuel - not always so deadly but the environmental types will nail you for it. The system should have a pressure relief valve at the pump so when the valve closes the excess pressure can be dumped back into the feed, just like in any powerful pump assembly like a fire engine pumper.

If the relief valve is set up correctly, any hammer from slamming the valve shut should be dumped into the relief before it hits the pump - the problem then remains the hammer possibly tearing up your plumbing between the hose and the relief valve. On a fire pumper, there isn't a lot of hard plumbing between the pump and the hose, but in your jet fuel plumbing system you may have fixed piping from the pump to an outlet where a flexible hose is connected. That fixed piping is where your hammer will do it's damage. You can engineer out the elbows with curves, but in an existing system you are likely stuck with what you have. Then your ROI will kick in - how many pumps do you replace before you rip up your plumbing and engineer it better, or how many times you tear up your pipe from under the asphalt for repairs before you get a better design?

By slow, I mean in 1/4 second or so instead of the 1/100 that can cause a hammer.

WHat you say is correct, a peak pressure bypass back to the tank seems sensible.

PatyO,

There are manufactured surge suppresor products specifically intended for this kind of application. See Young Engineering for an example: http://www.youngeng.com/surgesupressors.html This is not a bellows type, but a bladder tank.

The usual culprits in fuel system surge are rapid valve closure and emergency stop events. System design (or in your case, troubleshooting) generally includes use of software such as KY Pipe to model the system under a variety of upset conditions. The model can also be used to determine appropriate size for a surge suppressor.

jere.ferguson@westonsolutions.com

I STRONGLY suggest you install surge supressor accumulators on all the lines subject to this potentially destructive fluid 'hammer' . Widely used, standard application. not expensive, works.

A wealth of information, But one thing was maybe overlooked. Water Hammer ,in this case Jet fuel hammer, can also be cause by liquid rushing back towards the pumping station, when the pump is turned off. It maybe the case here as you describe your line as vertical, and you might even have a submersible pump in there. We have solved similar problem, by simply installing 2 or more check valves along the line, the first one being installed at the immediate discharge port of the pump. Make sure the pump's Q is sufficient to keep the discharge line FULL at all times, and that the pump is always primed.

Google : "Red Jacket" (Fuel pump manufacturers) They are experts in the subject.

Wangito.

There are a few things to keep in mind.....Pipe line hammer can be serious. To watch a 16 " sched 40 elbow split wide open because of hammer will certainly get your attention. Even before the surge reaches that kind of pressure-force, you can hear it "singing" down the pipeline. It's scarey to say the least. Prevention of hammer should be designed into the system and not fixed after the fact, with some of the suggested solutions. I would suggest that 'PatyO' bite the bullet and redesign the system to eliminate the hammer, by using slow closing valving, etc. There are many experts in the refueling industry who would be more willing to make suggestions for the redesign.

I would suggest that you install a pressure relief valve immediately upstream of the closing valve. The pressure relief valve ( or two consecutive relief valves )connects a flexible line back to the originating fuel tank. This will prevent the hammer from happening and leading the fluid back from being an outflow to being a back flow. You should also need to know the hammer pressure present in the line with some calculation. P_h=sp.wt.of fuel x velocity of the flowing fluid x celerity= xxxxkpa. Set the numeral of the celerity at 1400 m/s. ( I hope your line is not that long -1400 metres ). Choose a pressure relief valve set at a low relieving value. Consult your supplier's engineers to check its economics vs. other systems.

Oops! the right formula for hammer pressure is : P_h = Density of fluid x velocity of fluid x celerity = xxxxxx kpa.

To calculate the celerity (sonic speed) you'll need

bulk modulus and density of the liquid

elastic modulus of pipe material

pipe diameter and wall thickness

Ooowwwww you've got me there.... what is 'celerity'?

First time I've come across the term......

John.

the C in e=mc2 is the speed of light, celerity is loosely....speed

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

Same for me. I was able to figure this from the formula, but it's the first time I see it being used in this context... I prefer, for a change the good old "V".

Wangito.

Ooowwwww you've got me there.... what is 'celerity'?

First time I've come across the term......

Celerity is the speed of sound in the liquid being pumped. Varies in water from 300m/s for MDPE to 1400m/s for steel.

Slow down the closing of the valves.