HESCO ProactiView on Water Hammer and Pipe Bang

If you have been inside a pump station and heard the dreaded bang inside the pipes, you know that Pipe Bang caused by a Water Hammer sounds like someone took a sledge and pounded on the entire system.  Did it cause major damage or just sound terrible?  Either way, it is clearly not the way any manager wants his system to operate.

So what do you do about it?  First of all, there are two separate things that may be happening, and it is important to determine which one (or both) you need to deal with:  Water Hammer and Pipe Bang.  For each of these problems, there are effective control strategies that can be implemented to prevent them.

Whether your system currently has these issues, or if you’d like to avoid them all together, HESCO can assist you in designing or retrofitting a system that will avoid these problems.

Contents

Differences between Water Hammer and Pipe Bang
Prevention of Water Hammer and associated damage
Prevention of Pipe Bang
Follow up with HESCO regarding Water Hammer and Pipe Bang

Differences between Water Hammer and Pipe Bang

Water Hammer – Water Hammer refers to the force exerted by the surge of a water column that was flowing, and is quickly stopped, typically by shutting off a pump or closing a valve.  Energy is no longer being applied to the system, but momentum keeps the fluid column moving away from the pump station.  This causes an initial pressure drop within the vicinity of the pump station.  In some cases, the momentum is so great that the pressure can go negative or even cause a column separation.  Eventually the fluid column will come to rest and then reverse direction.  As the mass of water in the pipeline rushes back toward the pump station, incredible pressures can build up that can cause catastrophic failures.  The severity of the pressure is dependent upon the configuration of the force main, the material of the pipe and the velocity of the water.

Pipe Bang – Pipe Bang is often associated with stresses produced in a piping system by Water Hammer, but is actually caused by a reversal of flow that catches a check valve before it is completely seated, slamming the valve shut.  It is possible in many systems to have a severe Pipe Bang situation without having any appreciable issues related to Water Hammer or surge.

Water Hammer and Pipe Bang often occur together, but the presence of a large bang does not necessarily mean that you are experiencing Water Hammer.  The opposite is also true, wherein you could have a severe Water Hammer problem without loud noises, if the valve is successfully seated before a Water Hammer surge strikes it.

Prevention of Water Hammer and associated damage

Historically, pumps were steam driven, and large flywheels were gradually spun up to full pumping speed.  When steam drives were shut off, the flywheels also gradually spun down as they lost momentum.  Therefore, water movement gradually accelerated and decelerated naturally, and there were no significant surges or Water Hammers.  With today’s electric motor driven pumps, the water can go from standing still to full pumping speed (or vice versa) in a couple of seconds, which creates the Water Hammer surges.

Water Hammer can be controlled by employing any one of three techniques:

1) Employing a control system that starts and stops the pump motors gradually over a longer period of time.
2) Designing a pump control valve system that controls the velocity of the fluid column as the pump starts and stops.
3) Designing a surge relief system that diverts excess pressure into a surge tank or around the pump station.

Prevention of Pipe Bang

As we said above, Pipe Bang is caused when rapid reversals in water flow slam a valve shut.  The main way to prevent Pipe Bang is therefore using a valve that has a mechanism which will shut the valve smoothly and quickly before the water slams it, and without a forceful bang.  There are several designs on the market to accomplish this, including spring loaded valves, lever and weight loaded valves, valves with air cushions, and internally loaded valves.

Here is a basic comparison of valves and their ability to prevent Pipe Bang.  Please note that these are generalizations, and should not be the only basis for any application decision.

Follow up with HESCO regarding Water Hammer and Pipe Bang

HESCO is uniquely qualified to help you avoid problems associated with water hammer and pipe bang and can help to design an effective control system. HESCO uses a Surge Analysis Checklist that helps us to quickly understand individual situations.

There are two immediate ways that you can contact us:

1.  Call Kevin Livingston or Glenn Hummel at 586-978-7200 and mention that you are following up on the ProactiView on Water Hammer and Pipe Bang. We will be happy to work through the Surge Analysis Checklist with you, if appropriate.

2. Email Kevin Livingston or Glenn Hummel directly.  Be sure to include your name, contact information, and brief description of your situation, needs and questions. We can attach the Surge Analysis Checklist to our reply for you to complete, if appropriate.