But underneath that cold exterior
I know you've got a heart of gold

("Heart of Gold," by The Kinks, 1983)

 

DEFINITION OF PUMP CASING

PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order just learned that "the Pumping Side" of a Centrifugal Pump is the side that contacts the liquid that is being infused with the PV Pressure.

"The Power Side" of the Centrifugal Pump contains the hardware components that make it possible for the impeller to spin around in "The Pumping Side" of the pump.

"The Power Side" of the Centrifugal Pump includes

• the driver.
• the coupling, which is protected from the weather by a covering/housing.
• the bearings and their protective bearing Housing
• the leak-sealing area that butts up to "The Pumping Side" of the Pump and which is enclosed in a piece of hardware typically called the packing Box or stuffing Box and sometimes called ... "the gland."

 

The Centrifugal Pump in the nearby photo is experiencing an obvious leak-sealing failure.

Perhaps the seal hardware  failed because of excessive radial or axial movement caused by a bearing failure.

The bearing Housing on the right side of the photograph protects bearings that counteract axial thrust and radial vibration.

Yes, Indeedo!

The malfunctioning Pump shown in the above photo has a visually distinct "Pumping Side," exposed sealing gland, and stabilizing bearings that are each protected from the surrounding environment by their respective Casings.

Casings are sometimes called Housings.

Just like the house you live in ... a Casing must be sufficiently strong to protect and support the internal components contained inside that are busy performing a variety of functions.

Since the PV Pressure is going to be increased within the Pump, the Casing must also be able to withstand the internal PV Pressure that the Pump creates.

 

The Real World grown up lingo to substitute for "being able to withstand the Pressure" is something like ...

"The pump Casing must be fabricated so that it is rated to withstand the Pressure which is generated within the  Casing."

 

PUMP CASINGS MUST ACCOMMODATE THE NUMBER OF PUMP STAGES

The number of impellers defines how many stages a  Centrifugal Pump has.

The Centrifugal Pump in the nearby graphic has one impeller, so it is called "a Single-Stage Centrifugal Pump."

The vast majority of Centrifugal Pump graphics featured in the PTOA up to this point have been Single-Stage Centrifugal Pumps.

A pump with two impellers would be called "a Two-Stage Centrifugal Pump."

A pump with three or more impellers would be called "a Multi-Stage Centrifugal Pump."

 

THE EXTERIOR FEATURES OF CENTRIFUGAL PUMP CASINGS

Truth be known, it is easy to find pictures of disconnected Centrifugal Pumps and harder to find pictures of installed, operating and well-maintained Centrifugal Pumps!

The nearby photo shows a bank of real world operating Centrifugal Pumps connected to their respective Suction and Discharge Lines.

In this photo, the exterior of each Pump Casing that encloses "the Pumping Side" of the Pump, the gland sealing area, and the bearing Housing is painted silvery gray.

From the exterior, the Casing looks like a metal protective covering that connects the Pump to the Process and keeps the outside environment from entering the pump.

Righteeo! That's what the Casing exterior is and that's what it does!

The PTOA Department of Redundancy Department demands that PTOA Readers and Students repeat the Pump Casing identification exercise with a different photo of yet another detached Centrifugal Pump:

In the nearby photo ...

"The Pumping Side" Casing, the sealing area stuffing box/packing box, and the bearing Housing are all painted blue (as is the supporting structure for the  Pump and the  driver).

The protective Housing situated over the coupling is painted orange. And the driver (an electric motor) is painted black.

 

Suction and Discharge Flanges

Pumps are manufactured by whichever pump manufacturing company won the bid to provide the pump.

The Pump Casing must be fabricated with the means to connect the Pump Suction Flange to the Pump Suction Line and the Pump Discharge Flange to the Pump Discharge Line.

Who amongst the brilliant PTOA Readers and Students has noticed a "rim with spaced holes" on all those pictures of Centrifugal Pumps that have been shown disconnected from a processing service?

Those "rims-with-holes" are Flanges.

The Centrifugal Pumps used for industrial-sized processing are typically connected to the Suction and Discharge Lines with Flanges because the two mating faces of metal can be bolted together yet are still leak free ... as long as a gasket with the proper PV Pressure rating is inserted between them.

Flange connections can also be designed and rated to withstand high processing Pressures.

 

 

 

 

 

THE INTERIOR FEATURES OF A CENTRIFUGAL PUMP CASING

The interior of the pump Casing is much more interesting than the exterior because it must be fabricated to create The Volute and The Cutwater.

 

In a Multi-Stage Pump The Volute becomes a set of Diffusers.

PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order recently learned in PTOA Segment #173 that The Volute is where the pumped liquid's Velocity is swapped into the PV Pressure.

Correctamundo!

By now any PTOA Reader or Student can recite by heart that the liquid enters the pump via the Suction which is intentionally placed to deliver the liquid into the eye of the impeller.

The fluid gains Velocity whilst being flung to the edge of the spinning impeller via Centrifugal Force which is made possible courtesy of "The Power Side" of the Pump.

As stated above,The Volute is carefully manufactured to create an increasing volumetric area that the flung liquid flows into.

With more room to flow through, most of the Velocity of the liquid is swapped into the PV Pressure.

The pumped-up liquid exits the Centrifugal Pump via the Pump Discharge at a higher PV Pressure.

A pump can even be manufactured with a split or double Volute which strengthens the Casing.

 

The Cutwater (aka Tongue) 

Besides the specifically built diffusing area of The Volute, The Cutwater is another important feature of the Casing interior.

PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already learned in PTOA Segment #169, that The Cutwater is the edge fabricated into the Casing interior which determines if the rotating fluid will take another spin around The Volute or exit the pump via the Discharge Nozzle.

Areas of liquid recirculation can occur on either side of The Cutwater which negatively impact optimal Pump operations.

PTOA Readers and Students already learned that The Cutwater is sometimes modified by professional Pump Mechanics.

 

 

The Flow Path through Multi-Stage Centrifugal  Pumps

Major industrial processing plants will require a Discharge Pressure to be greater than the Discharge Pressure that can be generated with a Single-Stage Centrifugal Pump with its single impeller.

Adding more impellers increases the Discharge Pressure of the Centrifugal Pump because the discharged liquid from a leading impeller is fed into the eye of the next, following impeller.

The nearby cutaway photo shows a 5 stage Centrifugal pump because the Pump has 5 impellers.

The Pump Suction Flange is on the left pointing out at the Reader and the Pump Discharge Flange is on the right top side of the Pump.

The liquid flows "in series" from left to right through the 5 Impellers.

The graphic below could be a schematic of the cutaway 5-Stage Pump shown above because it also has 5 impellers and the flow path is from left to right.

• The internal Suction Nozzle targets the liquid that enters into the eye of the first impeller.
• The liquid is flung radially outward to the edges of the first impeller.
• The Velocity of the liquid is converted into the PV Pressure in the first Diffuser. A Diffuser is what a Volute is called in a Multi-Stage Pump.
• The pumped-up liquid exiting the first Diffuser is guided into the eye of the second impeller.

 

• The liquid is flung to the edges of the second impeller.
• The Velocity of the liquid is converted into even greater Pressure in the second Diffuser.
• The even-more-pumped-up liquid that exits the second Diffuser is guided into the eye of the third impeller.
• And so on and so on until the liquid exits the Pump Discharge Nozzle on the top right of the graphic at a high Discharge Pressure.

PTOA Readers and Students should note that the color legend situated on the right side of the graphic because it hints how the PV Pressure is built up as the liquid flows through the 5-Stage Pump.

Dark blue is the lowest PV Pressure and red is the highest PV Pressure.

The dark Blue color for the low PV Suction Pressure enters the 5-Stage Pump via the Suction Nozzle on the left side.

• The dark Blue Suction Pressure changes to a greater PV Pressure which is indicated by Light Blue shading where the liquid enters the eye of the second impeller  →
• White shading where the liquid enters the eye of the third impeller →
• Yellow shading where the liquid enters the eye of the fourth impeller→
• Orange shading where the liquid enters the eye of the fifth impeller→ 
• And then the liquid exits the Pump with a high Discharge Pressure indicated by the color Red at the Pump's Discharge Nozzle.

 

Yep!

The Discharged PV Pressure from this Multi-Stage Pump is much greater than the Discharge Pressure that could be achieved with a Single-Stage Centrifugal Pump.

 

Suction and Discharge Nozzles

Who amongst the brilliant PTOA Readers and Students noticed that the interior Casing of a Centrifugal Pump is fabricated to have Suction and Discharge Nozzles?

As the nearby graphic shows ... the Suction Nozzle is fabricated to direct the incoming liquid into the eye of the first impeller. The Suction Nozzle really does look like a funneling nozzle!

So who is surprised to learn that the Discharge Nozzle is fabricated in a nozzle shape that continues to develop the swap of Velocity for Pressure as the pumped-up liquid exits the Pump?

 

HORIZONTAL AND RADIAL PUMP CASINGS

Of course all PTOA Readers and Students have realized by now that a Centrifugal Pump involves many pieces of hardware that must work together to increase the PV Pressure in a liquid whilst intentionally creating and managing the impacts of Centrifugal Force.

Eventually, one of the hardware components in the Centrifugal Pump is going to need to be fixed or replaced ...preferably on a Preventative Maintenance program rather than a catastrophic failure emergency.

The choice and style of a Centrifugal Pump should include consideration of how the pump will need to be disassembled for maintenance.

If the Maintenance Department was consulted prior to pump design and purchase, the choice of Casing style will be made based on ease of access to the rotor.

The rotor is shorthand for all of the rotating parts of the Pump ... the shaft and various sealing, stabilizing, and lubrication hardware.

A Horizontally-Split Pump Casing (aka Axial-Split Pump Casing) is a Casing that allows access to the rotor after removing the bolts that connect the top half of the Casing to the bottom, stationary  half of the Casing.

Horizontally-Split Casings are easy to identify because of the many bolts that run down both sides of the Pump.

A Vertically-Split Pump Casing (aka Radially-Split Pump Casing) has a solid Casing around the rotor.

Therefore access to the rotor can only be made via disassembling "The Pumping Side" end of the Pump.

All of the Single-Stage Centrifugal Pumps shown in the PTOA have been manufactured with Vertically-Split Casings; access to the rotating hardware would be through the end of the Pump.

 

 

A nearby picture features a teal Ronda Multi-Stage Pump which also has a Vertically-Split Casing.

Fixing any moving part on the rotor would require disassembling the end of this Pump.

 

 

WARNING! POTENTIAL FOR TERMINOLOGY CONFUSION!

The Casing style of the Pump should not be confused with the orientation of the driver to the Pump, a topic that will be featured in a future PTOA Segment.

Drivers can be oriented horizontal to the pump ... or vertically placed to the pump ... and this happenstance causes jargon confusion!

Just be aware that the jargon related to Pump Casing style sounds the same but is not the same as the orientation of the driver to the Pump!

Finally, the Casing will provide some means to vent and drain "The Pumping Side of the Pump" and drain the lubrication/seal oil in an environmentally sound manner.

 

TAKE HOME MESSAGES: Casings are metal protective coverings that connect the Pump to the Process and keep the outside environment from entering the pump.

Casings protect and support the hardware enclosed in the  "The Pumping Side" of the pump, the gland sealing area, and the stabilizing bearings.

Casings are sometimes called "Housings."

The Casing must be rated to withstand the Pressures generated within the Pump.

The number of impellers defines how many stages a  Centrifugal Pump has; a Single Stage Centrifugal Pump has 1 impeller and a Multi-Stage Centrifugal Pump has more than 3 impellers.

The external, visual face of the Pump Casing includes these common features:

• Suction Flange fabricated to mate with the Suction Line Flange.
• Body to accommodate the number of pump stages/impellers.
• Horizontally-Split or Vertically Split construction for ease of access to the rotor.
• Discharge Flange fabricated to mate with the Discharge Line Flange.
• A means to vent and drain the Pump and lube/seal oil.

The internal side of the Casing must be fabricated to include:

• Suction Nozzle that feeds the liquid into the eye of the first impeller.
• A Volute or series of Diffusers that converts liquid Velocity into the PV Pressure.
• A Cutwater (Single Stage Centrifugal Pump) that determines if the liquid takes another turn around the impeller or exits the Pump.
• Discharge Nozzle that continues swapping the liquid's Velocity for Pressure up until it exits the Pump.

 

©2017 PTOA Segment 0175
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study

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