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Glossary of pump terms: P

Packing: A manner in which to stepwise reduce the pressure from the pump so that by the time the fluid gets to the last step, the amount of leaking is acceptable. Usually implemented as a set of rings to produce the pressure gradient.

Packing ring: A seal composed of a set of rings that prevents leakage of the fluid into the atmosphere.

Parallel operation: As opposed to Series operation. Two pumps are connected to the same head and thereby provide twice the flow rate as a single pump.

Partial emission pump: Also known as a vane pump. A pump designed to handle corrosive chemicals at low flow rates. Developed in WWII to pump fuel into German Ram jet engines.

Pascal: The SI derived unit of pressure. Equivalent to one Newton/m2. One atmosphere of pressure is equal to a little over 100 kPa.

Passivated: A metal surface is said to be passivated when it has a protective oxide layer formed on its surface.

Pattern: Usually a wooden pattern to make a mold used for metal castings.

PD pump: Positive displacement pump. Pumps up to very high pressure, but low flow rates.

Performance curve: A graph depicting the plot of total head vs flow rate for a specific pump, with a specific impeller and set of characteristics.

Peripheral (regenerative) pump: Also known as regenerative or regenerative turbine pump. An alternative design to a centrifugal pump. In these pumps, fluid passes through the vanes many times (instead of once, in a centrifugal pump). The impeller has short vanes at the periphery and these vanes pass through a ring shaped channel. The fluid enters between two impeller vanes and is set into a circular motion, this adds energy to the fluid particles which travel in a spiral like path from the inlet to the outlet. Each set of vanes continuously adds energy to the fluid particle.

Peripheral speed: The velocity, or speed, at the periphery of some diameter (see peripheral velocity).

Peripheral velocity: Same as peripheral speed.

pH: The measure of how many H+ ions or OH- ions are in a solution. The scale is logarithmic and ranges from 0 (very acidic) to 14 (very basic).

Pickling: A process that cleans metals by immersion in a bath of nitric and hydrofluoric acids. The acids remove any impurities on the surface.

Pipe friction loss: The loss in head due to the friction between the process fluid and the walls of the pipes and joints.

Pipe roughness: A measurement of how rough the inside surface of a pipe system is. Many measurements are taken and averaged. It is the average size of peaks that are on the internal surface of the pipes producing friction.

Pipe strain: Pipe strain is the strain on the volute of a pump due to the piping attached. It can cause mechanical seal failure.

Piping pressure (maximum): Pipe systems have a maximum pressure rating to which they may be subjected. Otherwise they may burst due to excessive pressure. This also includes joins and flanges. The ASME pressure piping code B31.3 provides the maximum stress for pipes of various materials.

Pitot pump: A pump that contains a rotating casing that causes the fluid to rotate. At one point within the rotating cyclinder of fluid, there is a pitot tube, or pick up tube that captures a small amount of the rotating fluid and sends it to the discharge under high pressure.

Pitting: Erosion at the surface of a material as pits due to corrosion, erosion or cavitation.

Pitting resistance equivalent number (PREN): A characteristic given to a material that indicates how resistant the material is to pitting corrosion. Higher numbers indicate a greater resistance to pitting corrosion.

Plan 11: A mechanical seal single seal piping plan referenced by API 682, ISO 21049, and ASME B73.1& B73.2, for single seal arrangement using the pump liquid as medium. Plan 11 flush line originates at the pump discharge, or at a point on the pump casing where the pressure is higher than that at the seal chamber, and is piped through a flow control orifice to the flush port on the seal flange or seal chamber tap. The liquid flushes the seal face, flows around the seal, exists through a pressure reducing throttle bushing, and flows back into the impeller suction area.

Plastic range: Metals have an elastic range, where they “remember” what shape they were before you moved them, and a plastic range, where they won’t remember their prior shape.

Positive displacement pump: A type of pump that causes a fluid to move by trapping a fixed amount of the fluid and moving it into the discharge pipe.

Pour point: The temperature at which liquids cease to flow.

Power end: The section of a pump that attaches to the power source. Bearings are found here.

Power factor: In an AC circuit, the relationship between the real power flowing to the load and the apparent power in the circuit.

Precision bearing: Ball bearings and roller bearings are precision bearings, while sleeve bearings are not.

Press fit: Graphite, because of its softness, can be pressed into any irregular shaped holder and it will shear to fit the holder.

Pressure: Is the ratio of a force over an area over which the force is applied.

Pressure drop: The difference in pressure between two areas of a pump, or between the inside and outside of a container.

Pressure gradient: The pressure drop, when referring to mechanical seals, across the mechanical seal faces.

Pressure head: The pressure at the pump experted by atmospheric and other additional pressure that might be in the vessel.

Prime: In a centrifugal pump, if the source is lower than the pump, a small amount of process fluid is infused into the pump to start the suction process.

Progressive cavity pump: A positive displacement pump. Ideal for fluids with high viscosity (e.g. grease, pastes, etc.) They are also known as eccentric screw pumps.

Propeller pump: Also known as an axial flow pump. A pump in which the impeller imparts lift to the fluid propelling it along due the impeller’s shape.

Pseudoplastic: Any fluid whose viscosity increases slowly with the rate of shear is said to be pseudoplastic.

PT factor: A factor given to gaskets consisting of the operating pressure multiplied by the operating temperature at which the gasket can be safely used.

Pump curve: A graph supplied by the pump manufacturer depicting the relationship between the head and the capacity of a particular pump. Usually contains different curves for different sized impellers.

Pumping ring: In a mechanical seal to provide circulation between two mechanical seals. Required if oil is the barrier fluid, due to the oil’s poor specific heat.

Pump out vane: A feature of some impeller designs that lowers the stuffing box pressure.

Pumps as turbines (PAT): A pump running in reverse. That is, the fluid inside the pump moves and causes the pump to rotate.

Pure oil mist lubrication: A lubrication system for bearing that uses an oil mist, rather than a liquid in a sump.

Purge oil mist lubrication: A lubrication system where an oil mist purges only the bearing housing.

Pusher seal: A low quality design that uses a spring-loaded dynamic elastomer.

PV factor: A correlation between the pressure and the velocity at mechanical seal faces. The correlation does not hold up.

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