Positive Displacement Pumps on a Working Site
Where these pumps are found, what a competent technician or engineer does with them, and how the course fits together.
11 min
Activities: 0 of 2
Small pumps, large consequences
On most sites the big centrifugal pumps get the attention. They move the main process flow and they are easy to see. The positive displacement (PD) pumps are often smaller and hidden in skids, chemical sheds and package units. Yet they do some of the most critical work on the site. They inject chemicals that stop corrosion and scale. They push fluid into wells and pipelines at very high pressure. They move heavy crude, sludge and lube oil that a centrifugal pump cannot handle.
A PD pump fails in a different way from a centrifugal pump. When something goes wrong on the discharge side, it does not simply stop delivering. It keeps pushing, and pressure rises until something gives. This is why people who work on these pumps need their own set of skills.
Typical duties on a site
Small diaphragm or plunger metering pumps add corrosion inhibitor, scale inhibitor, demulsifier, biocide or methanol into a process line. The flow is tiny, often a few litres per hour, but the dose must be right every hour of every day.
What a competent person does
At this level you are expected to do more than recognise a pump type. You should be able to:
- choose the right pump family for a duty and explain the trade-offs;
- check that the system around the pump protects it, especially the relief path;
- calculate flow, power and suction margin well enough to spot a wrong number;
- operate the pump safely through start-up, changeover and shutdown;
- diagnose a fault from its symptoms and fix the cause, not only the part.
How the course is built
- 1
Module 1
Fundamentals
The numbers: displacement, slip, volumetric efficiency, power and torque.
- 2
Module 2
How they differ
Fixed displacement, the pump families, and choosing between them for difficult fluids.
- 3
Module 3
Suction, pulsation and installation
Net positive suction head, acceleration head, dampeners and relief valves.
- 4
Module 4
Operation and control
Flow control, start-up, changeover, dry-run protection and condition monitoring.
- 5
Module 5
Maintenance and metering
Wear parts, overhauls, seals and dosing accuracy.
- 6
Modules 6 and 7
Cases and consolidation
Real faults worked through from symptom to cause, then the complete picture and a personal checklist.
Which statement best describes why positive displacement pumps need their own competence?