The more I learn, the less I know
And what I do ... it's all too much

("It's All Too Much," G. Harrison of The Beatles, 1969)

 

COMMON FEATURES OF ALL PUMPS

PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already know that pumps are rotating equipment which add the PV Pressure to liquid process streams.

The pump chosen for a process industry service might be a Centrifugal Pump, a Positive Displacement Plunger/Piston Pump or a Positive Displacement Rotary Pump.

Although the pumping service varies, there are common features of each pumping environment.

This PTOA Segment #163 and the upcoming PTOA Segment #164 familiarize PTOA Readers and Students with the "common pumping environment" ...while using Centrifugal Pump systems as an example.

 

Pump Discharge Pressure
is ALWAYS GREATER Than Pump Suction Pressure

The pipe that delivers flow into the Pump Suction is logically called "the Pump Suction Pipe."

There will always be a Pressure Indicator (PI) installed on the Pump Suction Pipe. 

This Suction Pressure PI logically measures and indicates the PV Pressure of the liquid that is flowing into the Pump Suction.

Likewise, there will always be a Discharge Pressure PI installed on the Pump Discharge Pipe that measures and indicates the Discharge Pressure of the pumped-up liquid.

The Pump Suction PI located on the Pump Suction Pipe will always indicate a Pressure that is less than the Pump Discharge Pressure ...

 

Because that's what pumps do!

That's their raison d'etre ...

their reason to exist!

Pumps add the PV Pressure to process stream liquids!

For example ...

The Suction Pressure PI on the Pump Suction Pipe in the below schematic indicates 50 psi.  The Discharge Pressure PI on the Pump Discharge Pipe indicates 250 psi.

 

 

 

 

So the schematic above conveys the following information:

• The pump has added 200 psi of PV Pressure into the liquid process stream that is flowing through the pump.
• The ISA symbol used in the schematic indicates that the pump is a  Centrifugal Pump.

 

ISA SYMBOLS FOR ROTATING EQUIPMENT

ISA Symbols for Centrifugal Pumps
and Centrifugal Compressors

This ISA symbol for a Centrifugal Pump is shown in the nearby photo.

A correctly drawn ISA Centrifugal Pump symbol will have a "backwards C" drawn in the center of the symbol.

Frequently the "backwards C" is omitted; sometimes it is drawn as a complete circle.

That's not very helpful ... but hey, that's life.

The "backwards C" or complete circle distinguishes the ISA Centrifugal Pump symbol from the ISA Centrifugal Compressor symbol ... the process industry equipment that adds the PV Pressure to gases.

The ISA symbol for a Centrifugal Compressor does not have the "backwards C" in the center ... it's just empty.

In the nearby symbol chart, the (correctly drawn) ISA symbol for a Centrifugal Pump appears in the top row.

The symbol for a generic Centrifugal Compressor appears in the bottom row, second column.

When a Centrifugal Pump is incorrectly drawn without a "backwards C" in the center and is therefore blank, PTOA Readers and Students must use their decoding skills to determine if the symbol represents a Centrifugal Pump or Centrifugal Compressor.

For example, when PTOA Readers and Students know the process fluid is a liquid, that will be sufficient information to assume that the symbol in a schematic is a Centrifugal Pump, not a Centrifugal Compressor.

 

ISA Symbols for Centrifugal Pumps, Plunger/Piston Pumps,
and Rotary Pumps

The top row on the below ISA symbol chart shows three typical drawings of Centrifugal Pumps labelled "Centrifugal Pump," "Centrifugal Pump 2," and "Centrifugal Pump 3."

However it is drawn, the Centrifugal Pump symbol is easy to distinguish from the symbol used for:

• Positive Displacement Plunger/Piston Pumps ... their symbol looks like a staircase and is in the middle row of the chart.
• Positive Displacement Rotary Pumps ... their symbols vary and some examples are the Screw Pump and Gear Pump ... which also appear on the middle row of the chart.

Who amongst the brilliant PTOA Readers and Students noticed that the first symbol in the Process Technology and Operator Academy logo is a Centrifugal Pump?

PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order are now aware of what three of the four ISA symbols in the PTOA logo represent.

 

ASSESSING THE PUMPING SITUATION

So far in this PTOA Segment #163, PTOA Readers and Students have learned:

• The casing of any Pump will be fabricated to create a Pump Suction and a Pump Discharge.
• The liquid that enters the Pump Suction will be delivered via the Pump Suction Pipe.  Here's new information: The Pump Suction Pipe is often called the "Pump Suction Line."
• A Pump Suction PI will measure and indicate the Pump Suction Pressure and a Pump Discharge PI will measure and indicate the Pump Discharge Pressure.
• The pumped-up liquid that exits the Pump Discharge will flow into the Pump Discharge Pipe. The "Pump Discharge Pipe" is often called the "Pump Discharge Line."

Guess what?

There's even more common features that will be found in the pumping environment, no matter what kind of pump is in service!

 

The Pump Will Be Placed Close To A Tank or Reservoir

PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order were introduced to the Lube Oil System block diagram below in the recent PTOA Segment #161.

To analyze the flow in the block diagram, locate the block labelled "Pumps" in the bottom right of the below diagram.

The plural form of the word "Pumps" implies there is a Primary Pump and an identical Back Up Pump represented by the block.

The block labelled "Reservoir" is a container or tank of some type that holds the liquid inventory of lube oil that is available to circulate through the Lube Oil System.

Note that the lube oil flows from the Reservoir into the Suction Line of the block labelled "Pumps."

In the real world, the Suction Pipe that delivers lube oil from the Reservoir to the Lube Oil Circulating Pump will be the shortest, straightest run of pipe possible.

From the Pumps Block, the lube oil flows through the Discharge Line to a Cooler → Filter → and finally to the Compressor Train that needs the lube oil to keep functioning.

The used lube oil is then drained from the Compressor and returned to the Reservoir.

The above Lube Oil System has a lot in common with the Cooling Water System shown below that was first introduced way back in PTOA Segment #40.

Instead of lube oil, cooling water is circulated in a Cooling Water System.

PTOA Readers and Students should recall that the "Heat Exchanger" labelled in the graphic represents several heat exchangers that use the circulated, cool Supply Water for heat transfer,

The warmer water effluent from the shell and tube heat exchangers collects in the Return Header that is piped to the top of the Cooling Tower.

Find the (Cooling Water Supply) Pump in the lower right of the above drawing. The ISA symbol indicates this is a Centrifugal Pump.

The water supplied to the Suction of this Centrifugal Pump comes from the Cooling Water Basin, which contains a large volume of water that will insure the Suction Line is always filled.

The basin of a real world Cooling Tower can be seen in the nearby photo.

 

 

Another nearby photo shows a bank of real world Cooling Water Supply Pumps that are drawing their Suction from the water basin shown above.

Aha!

PTOA Readers and Students should notice a common feature in both the Lube Oil and Cooling Water Systems:

A Tank ... or Reservoir ... or Large Container of some type CONTINUOUSLY supplies a steady process stream flow into the Pump's Suction. 

"Running a pump dry" will ruin the pump  ...

because pumps are made to add the PV Pressure to liquids ... not gases like air!

Any type of pump will always be associated with an identifiable holding Tank or Reservoir which contains an inventory of the liquid that is going to be pumped.

The Suction-side piping that connects any pump to the Tank/Reservoir will have common hardware components ... no matter what kind of pump is in service.

Likewise, the Discharge-side piping that connects the pump to its intended process industry service will have common hardware components ... no matter what kind of pump is in service.

The common hardware components that are found in the piping of the pumping environment are featured in the upcoming PTOA Segment #164.

 

TAKE HOME MESSAGES: Pumps are selected and matched to their specific process industry service. Common types of pumps are:

• Centrifugal Pumps.
• Positive Displacement Plunger/Piston Pumps.
• Positive Displacement Rotary Pumps.

No matter what kind of pump or process industry service, each pump will have:

• A casing that is fabricated to create a Pump Suction and a Pump Discharge.
• A Suction Pressure PI and a Discharge Pressure PI  ...(the Discharge PI will always indicate a PV Pressure that is greater than the pressure indicated on the Suction PI).
• A Pump Suction Pipe aka Pump Suction Line.
• A Pump Discharge Pipe aka Pump Discharge Line.
• A Tank or Reservoir.

The Tank/Reservoir insures that there is continuous process stream flow into the Pump Suction. Running a pump "dry" will ruin it.

Important pump service will be sustained by installing two pumps ... a Primary Pump and a Back Up Pump.

The ISA symbol for a Centrifugal Pump and Centrifugal Compressor are very similar; an accurately drawn Centrifugal Pump ISA symbol has a "backwards C" drawn in the middle, but sometimes it is omitted or drawn as a circle.

The ISA symbol for a Centrifugal Compressor is just like the symbol for a Centrifugal Pump but does not have anything drawn in the center.

Because of their similarity, PTOA Readers and Students will have to use decoding to distinguish between ISA symbols for Centrifugal Pumps and Compressors.

©2017 PTOA Segment 0163
PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study

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