NOTHING CAN STOP PRESSURE DROP!
It's just not the same
Ooh, baby, I'm losing you
It's in the air
It's everywhere
Ooh, baby, I'm losing you
(Losing you)
["(I Know) I'm Losing You," by C. Grant, E.Holland, and N. Whitfield, sung with soul by The Temptations in 1966 and rocked by Rod Stewart in 1971]
BRAVO PTOA READERS AND STUDENTS!
YOU HAVE ALMOST COMPLETED
THE PTOA PV FLOWRATE FOCUS STUDY AREA!
The most brilliant PTOA Readers and Students ... meaning those who are reading the PTOA Segments in the intended, sequential order ... have almost completed the PTOA PV Flowrate Focus Study Area!
The PTOA PV Flowrate Focus Study Area first featured flowing fluid theory and then focused upon the hardware components that make it possible for the PV Flowrate to exist so that theories can be proposed about it.
One example of a fundamental fluid flow theory that every PTOA Reader and Student knows by now is what the PTOA calls "The PV Pressure ↔ Fluid Velocity Swap." This theory was first introduced in PTOA Segment #159 and thence appeared in the content of an additional 34 PTOA Segments, primarily those related to explaining how centrifugal Pumps and Compressors infuse mechanical energy (aka "Pressure) into fluids.
While flowing through a restricted diameter, a flowing fluid's velocity increases as its PV Pressure decreases, and vice versa as the diameter increases.
In PTOA Segment #207, "The PV Pressure ↔ Fluid Velocity Swap" was revealed to also be known as "The Venturi Effect." A dude named Venturi observed the relationship between the flowing PV Pressure of a fluid and its velocity as it flowed through a pipe with a temporarily smaller diameter.
Almost a century later, Venturi's theory was applied to the fabrication of flow meters as well as the dynamic pumps and compressors previously mentioned above.
Laminar and Turbulent Flow characterize the flowing profile of a fluid as it flows through a pipe. Laminar Flow is required for some flowmeters to accurately measure the PV Flowrate. A shell and tube heat exchanger needs Turbulent Flow to optimize heat transfer.
In the PTOA PV Flowrate Focus Study Area, PTOA Readers and Students have learned many other fluid flow theories, like the several ways the PV Flowrate can be classified (PTOA Segments #235 and #236) and how the properties of flowing fluids (for example, "Compressibility") can predict their behavior PTOA Segments #237 through #240).
A pipe's length and how it is connected to other pipe and what it is made from and how many elbows or tees are in The Piping Network all impact the magnitude of Pressure Drop.
The PV Temperature and the PV Pressure are not dependent upon hardware to exist. A human being can feel the ambient temperature change through the seasons. That same human being can feel changes in pressure on their ear drums while seated in an airplane that is making a steep descent or while swimming in the deep end of a swimming pool.
Unlike the PV Temperature and PV Pressure, the PV Flowrate would not exist in modern process industry were it not for the fabricated metal piping, tubing, and hoses that fluids flow through (PTOA Segment #245).
How a length of pipe is connected to another length of pipe impacts Pressure Drop.
The piping used to fabricate a Piping Network is made from common and specialty metals (PTOA Segments #246 through #248). Pipe joining techniques are used to connect piping and piping components (PTOA Segments #249 and #250).
The number of Pipe Fittings (like Elbows and U-Turns) and Valves a fluid flows through impacts Pressure Drop.
PTOA Readers and Students learned the form and function of common and specialty piping components.
Common Pipe Fittings and Specialty Pipe Fittings were featured in PTOA Segments #251 and PTOA Segment #261 and PTOA Segment #262.
Common Valves and Specialty Valves were featured in PTOA Segments #252 through PTOA Segment #259.
Which all leads up to the point of this PTOA Segment, Fred, so don't miss it!
PRESSURE DROP HAPPENS
The liquid level in each "barometer" illustrates the decreasing flowing PV Pressure as a fluid flows from left to right through the pipe.
The flowing PV Pressure of any fluid will decrease as that fluid flows through The Piping Network of the processing facility. Nothing can stop Pressure Drop!
Pressure Drop was the featured topic of PTOA Segment #165. The friction created when a flowing fluid contacts the interior pipe wall causes a loss in the flowing PV Pressure.
TOP PIPE RUN: Reducing a pipe's diameter from 3/4 inch to 1/2 inch will increase the Pressure Drop from 3 psi to 15 psi! LOWER PIPE RUN: Increasing the Pipe diameter from 1/2 inch to 3/4 inch will decrease the Pressure Drop from 15 psi to 3 psi! PIPE DIAMETER GREATLY IMPACTS PRESSURE DROP!
Every PTOA Reader and Student learned in PTOA Segment #158 and reviewed in PTOA Segment #241 that the loss of PV Pressure observed in any flowing fluid might be called any of the following terms:
- Pressure Drop
- ΔP
- dP
- Delta P
- Pressure Gradient
This is the new information to commit to memory:
What a pipe is made from, how it is made, and how it is connected to other lengths of pipe impacts Pressure Drop. Every pipe fitting and pipe Valve ... and what they are made from ... impacts Pressure Drop. All of the Flowing Fluid Properties that Predict Fluid Behavior previously featured in the PTOA PV Flowrate Focus Study Area also impact Pressure Drop.
THE PTOA DEPARTMENT OF REDUNDANCY DEPARTMENT repeats:
The PIPE DIAMETER (aka, its size) significantly impacts Pressure Drop.
The PIPE LENGTH and HOW THE PIPE IS CONNECTED TO OTHER PIPES impact Pressure Drop.
The weird "E" in the above chart is the Greek letter Epsilon. Epsilon quantifies the roughness of the material type listed in the leftmost column. The smaller the number=the smoother the material. Copper is significantly smoother than Aluminum. Galvanized Steel is a somewhat more rough than non-galvanized steel. Pipes can also become rougher as impurities attach to inner pipe walls.
WHAT MATERIAL A PIPE IS FABRICATED FROM impacts Pressure Drop.
HOW MANY PIPE FITTINGS ... like Elbows and U-turns ... are inserted into the flow path impact Pressure Drop. THE MATERIAL THE PIPE FITTINGS ARE MADE OUT OF impacts Pressure Drop.
HOW MANY VALVES a fluid must flow through, WHAT MATERIAL THE VALVES ARE MADE OUT OF, and HOW MUCH THE VALVE IS OPEN impact Pressure Drop.
Furthermore ...
The technology used to measure the PV Flowrate impacts Pressure Drop. The popular DP Flowmeters have High Pressure Drop. The Coriolis Flowmeter has Medium Pressure Drop. Ultrasonic and Thermal Mass Flowmeters have Low Pressure Drop.
The PHASE(S) of the flowing fluid(s) impact Pressure Drop.
The flowing fluid's HEAVINESS (aka "Specific Gravity") and STICKINESS (aka "Viscosity") impact Pressure Drop.
The ATTRACTION OF THE BONDS BETWEEN DIFFERENT TYPES OF FLOWING FLUIDS impacts Pressure Drop.
WHAT'S THE BIG DEAL ABOUT PRESSURE DROP
SINCE A ΔP IS NEEDED FOR A FLUID TO FLOW?
On the X-Axis of the graph, Q symbolizes and increasing PV Flowrate from left to right. This graph shows illustrates that as the Delta P on the Y-Axis increases, the Flowrate Q increases much faster ... by a magnitude that approximates the Flowrate squared! (Q multiplied by Q!).
Every PTOA Reader and Student first learned in PTOA Segment #158 and more recently reviewed in PTOA Segment #241 that a ΔP is needed for a fluid to flow.
No ΔP = No PV Flowrate!
Furthermore, the amount of flow that can be created by human beings ... a.k.a. a fluid's "Flowrate" ... depends upon the magnitude of the ΔP.
The greater the ΔP = the greater the PV Flowrate!
So ΔP is naturally a good thing, right?
In a processing facility the design challenge is to make certain that sufficient ΔP exists to get the desired amount of fluid from Point A to Point B in the expected time.
If the magnitude of the ΔP is depleted before the fluid can have more PV Pressure energy added via a pump or compressor, then the PV Flowrate will be insufficient and thus not able to accomplish the job of transporting, cooling, or heating.
Behold the Lube Oil Auxiliary System Graphic which first appeared in the PTOA Tribology Focus Study. The Suction Pressure sensed at the suction to the Lube Oil Pump (labeled "PUMPS" in the schematic) is the lowest PV Pressure in the system. The Discharge Pressure sensed at the Lube Oil pump's discharge is the highest PV Pressure in the system.
In every process unit of a processing facility, the discharge pressure of the compressor or pump is the highest pressure in that gas or liquid system, respectively. The suction pressure of the compressor or pump is the lowest pressure in that gas or liquid system, respectively.
The E&C firm that designed the processing facility sized and selected the optimal pumps and compressors with full knowledge of the hardware in the Piping Network and also had a fairly good idea of the fluid characteristics of each process fluid that would be flowing through The Piping Network.
The purchase of rotating equipment is not only a significant investment with respect to $$$ but also a specific investment with respect to making absolutely certain the selected rotating equipment can reliably and efficiently transport fluids through the processing facility at the desired PV Flowrate.
Therefore, Fred ... and this is the point of everything ...
The decision on whether or not to install a Valve or Fitting ... and what type of Valve of Fitting to install and what it will be made from ... IS NOT AN ARBRITRARY OR RANDOM DECISION!
Mucho design work goes into selecting the optimal hardware that can continuously operate reliably AND perform efficiently ... which means not eat up too much ΔP while the process fluid is flowing through The Piping Network.
Since the only way to replenish the pressure energy of a flowing fluid is via a pump or compressor, any unnecessary hardware in The Piping Network would result in an extra burden placed on the expensive rotating equipment that has been sized and selected for the process facility's original design.
Here's just one example of the point Your Mentor is trying to get across:
The fluid flowing through this Automatic Control Valve will have significant Pressure Drop sensed between the inlet and outlet flow. The Delta Pressure is created to make it possible to sense the PV Flowrate. Substituting any other type of Valve would not be a good idea for the process.
The Outside Process Operator who assumes any ole type of Valve could perform the same Open/Close function of the Globe Valve on a Double-Block and Bleed Assembly would be highly mistaken.
Each and every piece of hardware in the Piping Network was selected because it could reliably and safely do its job while not creating too much ΔP.
Overtime, Pipe Fittings and Valve parts will wear out. The Operators and Maintenance Techs who owned the knowledge of why a particular valve was chosen over a cheaper alternative will have retired.
In the best of processing facilities, a "Management of Change" procedure will be followed to evaluate and document any changes to the processing unit's hardware.
A thorough "Management of Change" protocol backed by a savvy management culture is the best way to pass on the legacy of the facility's intended operational integrity and efficiency.
TAKE HOME MESSAGES: Unlike the PV Temperature or PV Pressure that both exist in nature, PTOA Readers and Students have learned that the PV Flowrate is created when fluids flow through a Piping Network.
The greatest PV Pressure in a gas system will be sensed at a Compressor Discharge. The greatest PV Pressure in a liquid system will be sensed at a Pump's Discharge.
As the fluid flows through a processing unit, a drop in the PV Pressure will be evident. PTOA Readers and Students had already learned that Pressure Drop is caused by friction created between the flowing fluid and the walls of the pipe.
This PTOA Segment emphasized the many other contributors to Pressure Drop with a Piping Network:
- The length and size (aka diameter) of pipe and what the pipe is fabricated from and how it is attached to other segments of pipe.
- The number and type of Pipe Fittings and Valves and what these components are fabricated from and how they are attached to the Piping Network.
- How much a Valve is open/closed.
- The phase(s) of the flowing fluid and the fluid characteristics that predict fluid behavior (e.g., heaviness and viscosity).
The lowest PV Pressure in a gas system will be sensed at the Compressor Suction. The lowest PV Pressure in a liquid system will be sensed at the Pump's Suction.
The Outside Operator must be aware that the design of the processing facility took all of the contributing sources of Pressure Drop into account. No Valve or Fitting was inserted into the design arbitrarily. Each Valve and Fitting was chosen to perform a specific job and should not be replaced without a thorough and rigorous Management of Change procedure in place.
©2026 PTOA Segment 0262
PTOA PV FLOWRATE FOCUS STUDY AREA
PIPING NETWORK HARDWARE
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