Working Together to Build the Best

Last month’s Blog I discussed how pumps get over-sized because of our failure to communicate and the possibility of cumulative error in the process. This month I will discuss ways to communicate together from the get-go so a better system may be built.

In last months blog I stated that the most common communication problem in piping system design is the failure to accurately state the process requirements when selecting a pump. In this month’s blog I will add commentary of what could be done to improve the communications. (Italics indicate quote from last month’s blog.) 

Sizing the Pump

Every system needs a pressure gain device or pump to move the fluid through the piping system. Choosing the right pump, motor sizing, correctly sizing pipes, and determining the best efficiency point all depend on knowing the capacity requirements for the system.

“The owner of the system design provides a capacity requirement based on future system needs knowing full well that the system will be operating at a lower capacity for an extended period of time until the market need catches up with capacity.”

The owner should clearly state in the design documents that the pump system is expected to be operating at 500 gpm for the first 5 years then increase to 1,000 gpm once product sales ramp up. Full disclosure on the system’s intended design and purpose should be stated from the beginning. 

“The engineer designing the system takes the capacity provided by the process group and adds a 20% design margins of flow (to allow for future capacity increases).”

Assuming that the owner has clearly stated their design requirements in the design documents, the engineer now knows from the beginning that the system will be operating at 500 gpm for the foreseeable future, and the possible future requirements of 1,000 gpm capacity. There is no need for the engineer to factor the additional 20% design margin increase in pump selection. The engineer can size the pipelines to meet both the immediate needs AND have a design flexible enough to meet the future needs as well. Once the pipelines are sized, the head loss in the system can be determined for both 500 gpm and 1,000 gpm. Based on this information, the total head for the pump can be determined for both conditions but selected from the current condition of 500 gpm.

Avoiding the Snowball Effect

It may start as a small over estimate but it can get compounded when others on the project try to compensate for the lack of specificity in the beginning.

“In addition, a design margin for head is added (to account for system uncertainties during the design process) when specifying the equipment. As a result the pump design point is 1,200 gpm and 200 ft of head.

The individual selecting the pump chooses a pump with the design point left of the pumps Best Efficiency Point (BEP) to allow the pump to better accommodate future system capacity increases.”

Since engineering is now initially designing the system to operate at 500 gpm, there is no need to add extra capacity for the future at this time. When it comes time to add the future capacity, the owner will have a better understanding of the actual production needs and can factor that into the selection when the increased process loads are known. The engineer submitting the pump specification to the supplier can provide information on the current needs as well as the future needs.

The options available to the engineer and customer can be:

• Select a pump that can meet the future needs with a variable speed drive. This allows the pump to meet both today’s needs (at a slower speed) as well as the projected future requirements (at a higher speed).
• Select a pump that has a sufficient range of impeller diameters to meet the 500 gpm flow rate, with sufficient additional diameter to meet the expected future flow. A new impeller will need to be purchased to meet the future requirements but the savings in pumping cost will more than make up for the difference.
• Design the system with multiple pumps in parallel. To meet the initial 500 gpm one pump can be operated, and to meet the future needs a second pump can be operated providing the proper head and flow for the future capacity.

The next step is for the engineer to submit a pump specification to the pump supplier. Since the system owner provided a detailed description of how the system will operate, the design engineer for the system is able to provide the known information in the pump specifications. Armed with the full details of how the system will be operated throughout the next 5+ years, the pump supplier is able to select the best pump meeting the stated requirements.

By being upfront with the design intentions and explaining the current needs and future vision in detail, each group in the process knows how the system will be operating in the foreseeable future along with the projected future capacity. No assumptions needed. If that information is shared with each individual, every step of the way, the design margins will reflect how the pumps needs to be run, not how it will be run in the future, and less of a chance of a snowball effect.

I have offered one example of a common area of miscommunication in the piping system design process. Please feel free to add your experiences to the comments below or offer advice to anyone starting out on their first design project. I appreciate all of your feedback.

Darcy's Fables II

Estimated Reading Time: 3 minutes 31 seconds. Read Later

I was reading to my grandchildren from Piping System Fundamentals, their favorite book, and enjoying some family time. We were talking about the pump curve, one of the most important documents dealing with pumped systems. They all had questions about reading the pump curve and understanding why it was so important to know where it is running on the curve. Since they had so many questions, I created this Darcy’s Fable to explain:

The Raccoon, Possum, Porcupine, and the Golden Map

Once upon a time was a Raccoon, Possum, and Porcupine lived in the Primeval Woods. Life was hard for the woodland critters, and the past winter was especially long and cold which put everyone in a foul mood. Moreover, food was in short supply and everyone was worried about the future.

As the Raccoon, Possum and Porcupine were sitting by the side of a brook complaining about how hard life was, a beautiful Water Sprite flew by on shimmering wings.

She said to the trio, “I have been listing to your worries and complaints so I thought I would help you out. I will give each one of you a Golden Map. With it, you can find your way to Westwood. There you will find the weather is mild, the food is plentiful and life is much better. Just follow the Golden Map and all will be well.”

Then the Water Sprite flitted off laughing, knowing that her gift would cause misfortune for some of the critters. You see, this sprite was quite mischievous, often tricking people. She then vanished as quickly as she had appeared.

Possum quickly looked at the Golden Map and said, “This looks very simple, I will put it in my backpack and start the journey right away!” However, as the Possum was putting the Golden Map into his backpack, a sudden breeze caught the paper and it fell into the brook where it was swept away.

Possum was undeterred and he said, “No matter, it looked so simple I can easily remember it and find my way to the Westwood,” and he promptly set off.

Then Porcupine looked at the Golden Map and said, “This map must be very important, so I will make sure it is safely in my backpack and I will only take it out if I really need it.” Then he too, immediately set off for Westwood.

After the other two had so quickly gone on their merry way, Raccoon looked at the Golden Map and said, “This must be important, and since Westwood is so very far away I think I will study and learn about this map before starting my journey.”

He then set out to find the Great Owl, the wisest animal in the forest. The Great Owl looked at the Golden Map and after a while, was able to unlock its secrets.

He shared the secrets of the map with Raccoon and showed him the blue line to follow from the Primeval Woods through the Spot of Sweetness and finally going Between the Emerald Peaks (Let’s call it BEP) then your journey to Westwood will be easy.

The Raccoon then set about getting ready and packing for the journey, starting off the following morning. Within two days journey, he made it to Westwood where the winters are mild, the mood bright, and the food is plentiful. Racoon was so thankful he had learned how to read his Golden Map!

But the poor Possum without the aid of the Golden Map went into the “Lowlands of Poor Operation” where there was turbulence, cavitation, and excessive noise. The Possum was so scared in this land that he got totally missed the truck coming down the road he was standing on. Unfortunately he was run over and can still be found by the side of the road.*

*(I always like it when a character dies in a story. It keeps them from being too sappy.)

Porcupine started his journey, but when he looked at the Golden Map, he could not unlock its secrets. He wandered about aimlessly in the “Land of the Rough Running.” The rocks and the thorny bushes cut his shoes and ripped at his cloths and the noise and thunder keeps him awake at night. He was constantly buying new shoes and wandering around with tattered clothing, a very miserable porcupine. 

Suddenly one of my granddaughters exclaimed “Now it get it Pop Pop, for every pump in the plant we should have a pump curve. We should know where each pump is running on its curve and try to operate Between the Emerald Peaks, I mean around the BEP. If we do that we can reduce both its operating cost and maintenance cost.”

Her sister, always the romantic said, “Pop Pop whatever happened to the Raccoon in Westwood?”

I said that he is currently in a long-term relationship with a very attractive girl raccoon and they are looking to have a litter of kits when the time is right. She seemed satisfied with that answer so I chose to leave it at that!

If you'd like to learn more about reading pump curves. Engineered Software Knowledge Base has a couple articles that might help.

Reading a Pump Curve and Pump Curve Landmarks are both very informative.

Let me know what you think of these Darcy's Fables. I have at least one more to share, but I'd like to know what you all think about them. (Read The First Darcy's Fable Here) Leave a comment below or send an email to blogger@eng-software dot com. Thanks for reading!