Operating Characteristics of Positive Displacement Pumps

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Questions and Answers

What is the main principle of operation for positive displacement pumps?

Moving the fluid from the discharge inlet to the suction

Creating a void at the discharge inlet

Filling the void with compressible fluid

Creating a void at the suction inlet and filling it with incompressible fluid (correct)

What happens if the discharge valve of a positive displacement pump is inadvertently closed?

It has no effect on the pump operation

It increases the volume of fluid supplied

It can lead to extremely high pressures and potential damage to the pump or piping system (correct)

It causes the pump to stop functioning

Why must positive displacement pumps be equipped with a pressure relief device in the discharge line?

To reduce the volume of fluid supplied

To relieve high pressure and prevent damage to the pump or piping system (correct)

To prevent any fluid from being discharged

To prevent the formation of voids at the suction inlet

What distinguishes positive displacement pumps from centrifugal pumps in terms of clearance between the impeller and housing?

Positive displacement pumps have minute clearance Signup and view all the answers

What role does the pressure relief valve in the discharge line of a positive displacement pump serve?

It relieves fluid back to the storage tank when high pressure is reached Signup and view all the answers

What characteristic allows positive displacement pumps to develop considerable discharge pressure and vacuum at their suction inlet?

Small clearances between the pressure-imposing element and pump housing Signup and view all the answers

What is the reason that positive displacement pumps are considered self-priming?

They can develop great vacuum and draw fluids to considerable height Signup and view all the answers

Why is it advisable to manually prime rotary positive displacement pumps before starting?

They do not develop great suction lift like reciprocating pumps Signup and view all the answers

What is the purpose of running pumps when full of liquid?

To reduce wear on internal pump surfaces Signup and view all the answers

What should be done after starting a pump to monitor potential issues?

Checking the suction and discharge pressures Signup and view all the answers

When should the air vent be closed during the priming process of a pump?

When liquid flows out Signup and view all the answers

What should be ensured before removing a lockout from a positive displacement pump?

Gland lubrication supply is open Signup and view all the answers

What is one of the post-start checks that should be performed for all pumps?

Checking for leaks in mechanical seals or packing Signup and view all the answers

Why is it important to monitor suction and discharge pressures of a pump?

To identify problems in their early stages Signup and view all the answers

What is a routine check that should be performed during scheduled rounds for all pumps?

Monitoring lubricator levels, and adding oil when required Signup and view all the answers

What should be closed first when shutting down a pump?

The discharge valve Signup and view all the answers

What may indicate shaft misalignment in a pump, which should be corrected as soon as possible?

Pump vibration Signup and view all the answers

What is advisable to ensure that is secure and does not have excessive play before starting a pump?

The driver and pump coupling Signup and view all the answers

Study Notes

Positive Displacement Pumps

The main principle of operation for positive displacement pumps is that they capture a fixed volume of fluid and force it out of the pump chamber, creating pressure.

Operation and Safety Precautions

If the discharge valve of a positive displacement pump is inadvertently closed, the pump will continue to generate pressure, leading to a potential explosion or damage.
Positive displacement pumps must be equipped with a pressure relief device in the discharge line to prevent over-pressurization.
The pressure relief valve in the discharge line serves to prevent over-pressurization and potential damage by releasing excess pressure.

Characteristics

Positive displacement pumps differ from centrifugal pumps in that they have very small clearance between the impeller and housing.
Positive displacement pumps can develop considerable discharge pressure and vacuum at their suction inlet due to their ability to create a tight seal.
They are considered self-priming because they can create a vacuum at the suction inlet, allowing them to draw in liquid.

Priming and Startup

It is advisable to manually prime rotary positive displacement pumps before starting to ensure they are full of liquid.
Running pumps when full of liquid helps to prevent damage and ensures proper operation.
After starting a pump, it's essential to monitor potential issues by checking the pump's performance.

Shutdown and Maintenance

During the priming process, the air vent should be closed when liquid appears at the vent.
Before removing a lockout from a positive displacement pump, ensure it is safe to do so.
One of the post-start checks that should be performed for all pumps is to monitor suction and discharge pressures.
Monitoring suction and discharge pressures is crucial to detect potential issues and prevent damage.

Routine Checks

A routine check that should be performed during scheduled rounds for all pumps is to monitor temperature, pressure, and vibration.
When shutting down a pump, the discharge valve should be closed first.
Signs of shaft misalignment in a pump, such as vibration or noise, should be corrected as soon as possible.
It is essential to ensure the coupling is secure and does not have excessive play before starting a pump.

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Description

Explore the operating characteristics of positive displacement pumps, which create a void at the suction inlet, fill it with incompressible fluid, and move the fluid to the discharge. Learn about their ability to supply a constant volume of fluid and develop high pressures.