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If All You Have Is A Hammer…

Hammer & NailIf all you have is a hammer….everything looks like a nail!

The etymology of this saying is up for debate, but the idea is well known and universal.

‘If a person is familiar with a certain, single subject, or has with them a certain, single instrument, they may have a confirmation bias to believe that it is the answer to/involved in everything’

As engineers, especially those of us with significant years of experience, the tools we have available to use are many.  While I may have a hammer in my metaphorical toolbox, I also carry a wrench, pliers, and an assortment of screwdrivers and other items to tackle just about any work that comes my way.

Licensed Professional Engineer In Both Pennsylvania And Texas

Note I said “just about any work”

As a licensed Professional Engineer in both Pennsylvania and Texas I am required to work only in areas that I have proven and verifiable competency.  My background in engineering allows me to work on industrial equipment, piping systems and pressure vessels, but ask me to design an elevator or a bridge and I am legally, and ethically, required to pass on that.

If I do not have the tools used in an industry, I have a responsibility to admit that.

So, what triggered me to write about this?  I’m glad you asked that, even if you didn’t.

I recently came across an article by a company that provides pumps which are supplied with pulsation control on the discharge (pump outlet) side of the system.  These are specifically large, high-powered positive displacement pumps that could be used for pushing drilling mud or performing other functions needed in getting oil out of the ground.

The article covered the differences between a gas-charged and a reactive style pulsation dampener.  Unfortunately, the author only had one tool in his toolbox.

A Gas-Charged DampenerFor those new to this subject, a gas-charged dampener is mounted to the discharge piping in what is called an appendage mount.  The unit has a single connection to the flow located at the bottom of the vessel.  Inside is a bladder that is filled with nitrogen and acts as a compliance volume when compared to the much denser fluid.

The reactive style units are vessels that are mounted “in-line” or flow-thru meaning there is a defined inlet and an outlet.  They are completely filled with the fluid being pumped.

Helmholtz Resonator

In the world of acoustic analysis, the gas-charged appendage unit is called a “Helmholtz Resonator” while the reactive flow-thru is called an “Acoustic Filter”.   Remember those terms as there will be a test later.

For reference and scale, the gas-charged unit shown above weighs about 2,750 lbs. while the reactive unit tips the scales at over 8,000 lbs.

Now, getting back to the article, it was clear from the outset that the author’s “single tool” was the sale and service of gas-charged units.  While I surmise there was a heavy dose of marketing in the article, I am only looking at this from an engineering perspective, and that’s what caught my attention.

The author unequivocally stated they would never specify a reactive dampener into a system.  While I can agree that a reactive unit is larger and heavier, it does give better control of pulsations in the discharge flow.  It’s those sort of factors that make me never say never like the author did.

And how can I say that?

Some time ago PPC endeavored to compare the performance between an appendage and reactive flow-thru dampener.  I will save the details for another post, but a test was devised to perform an apples-to-apples comparison.  A gas-charged unit was run and data from the discharge flow was taken.  The same conditions were then run with a reactive dampener.

Appendage versus reactive flow-thru dampener

The pulsation levels in the fluid, after the dampener, for the gas-charged unit were measured at just under 600psi peak-to-peak.  The levels in the reactive style unit were measured at less than 200psi peak-to-peak.  (Note to self…..write a blog post on what “peak-to-peak” means).

Suffice it to say that the reactive unit reduced the pulsation levels in the fluid significantly below what the gas-charged unit could accomplish.

Now while the results are conclusive that the reactive style does “perform better”, this is just part of the equation.  The reactive unit is larger, heavier, and thus initially more expensive when compared to gas-charged.  Gas-charged units, while being smaller and lighter, require regular maintenance and sometimes daily operational attention to check and/or adjust nitrogen levels.  What level of control does the specific application require?  I could go on and on about the differences and why one style is not the answer to every problem, but that is not really the point.

You see, I have a toolbox full of solutions, and I use the one that best meets the needs of my customer.

If all you have is a hammer……then everything gets the same solution even if it needed a different tool.

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