Positive Displacement Pump Principles

Positive displacement pump principles are reciprocating pumps, rotary pumps, commonly used for metered chemical injection, pumping lean oil and amine

There are Several different types of pumps used in the petroleum industry. Two of the more common types are the centrifugal pump and the positive displacement pump. Centrifugal pumps are Discussed in another module of the Basic Operations Training Series. Positive displacement pumps are used in the petroleum industry for low volume applications or where high pressures are required to move a positive. fluids. In the field, you will find displacement pumps performing such diverse jobs as transferring oil from storage tanks to pipelines, re-injecting salt water into the reservoir, or pumping in a glycol dehydration unit. In gas plants, positive displacement pumps are commonly used for metered chemical injection, pumping lean oil and amine solutions, lubricating compressors, etc.
There are two types of positive displacement pumps :

(1) reciprocating pumps which the piston, plunger and diaphragm types and

(2) rotary pumps which include the gear, lobe and screw types. Reciprocating pumps have a piston plurger or diaphragm moving back and forth (reciprocating) in a cylinder. Rotary pumps have gears, lobes or screw-type rotors that rotate within a cylinder to move fluids.

Positive Displacement Pumps

Positive displacement pumps may be either direct-acting pumps or pumps. Power pumps have a separate driver, eg, electric motors, internal combustion engines, etc. Direct acting pumps do not have a separate driver. They are Often powered by steam, water or gas com- pressed.

Because of all the moving parts in the positive dis- placement pumps, lubrication is very important. The pumping components are normally cated by the fluids being pumped; however, some parts of the pump require oil or lubrication, eg, drip systems, splash systems, force-feed lubricators, etc. Discussion of Reviews These methods will be covered in another module.

In addition to lubrication, positive displacement pumps need to be cooled. Pumps may be either water-cooled or water-cooled. Air-cooling relies on ambient air to cool the pump while water-cooling requires the circulation of water or another coolant through the pump casing. In larger pumps or in pumps moving high temperature fluids, water jackets are commonly used. Water jackets are channels located in the casing around the hot sections in the pump, such as bearings and packing locations.

Operating Principle 

Positive displacement pumps work according to an old law of nature; that is, no two things can occupy the same space at the same time. An example: Fill a bucket to the top with water and then carefully drop a rock into the bucket. Some of the water is forced out of the bucket because the rock and water can not occupy the same space at the same time. The rock dis- places a volume of water equal to the volume of the rock.

Basically, the same thing happens in positive displacement pumps. Fluid is drawn into the cylinder, then displaced by a piston, plunger, etc. and the fluid is forced out the cylinder. Fluid pressure is increased in the pump by the piston, plunger, etc. pressing against the fluid in the cylinder.

If the discharge line becomes blocked,  the piston, plunger, etc. cannot displace the fluid in the cylinder and pressure will build up. Excessive pressure can cause the pump driver to stall or the pump casing and/or discharge piping to rupture.  For safety,  positive displacement pumps should always have a safety relief valve and bypass line located a short distance beyond the discharge port.

• [accordion]
• 1. Positive Displacement Pumps
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• 2. Positive Displacement Pump Types
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• 3. API 674 2010 2016 Positive Displacement Pumps - Reciprocating
• 4. API_674_Pump_Data_Sheet Positive Displacement Pumps - Reciprocating
• 5. API St 675-2012 (2015) Positive Displacement Pumps- Controlled Vol for Petroleum, Chem, and Gas
• 7. API St 676-2022 Positive Displacement Pumps - Rotary