Internal gear pump: a positive displacement pump.
The internal gear pumping principle was invented by Jens Nielsen, one of the founders of

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Viking Pumps is a major supplier of these pumps

[link Point to another website Only the registered members can access] [hr][/hr] Jet pump: a jet pump is a commonly available residential water supply pump. It has an interesting clever design that can lift water from a well (up to 25 feet) and allow it to function without a check valve on the suction and furthermore does not require priming. The heart of the design is a

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see this article for

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[link Point to another website Only the registered members can access] [hr][/hr] K factor: a factor that provides the head loss for fittings. It is used with the following equation


The K factor for various fittings can he found in many publications. As an example, Figure 6 depicts the relationship between the K factor of a 90° screwed elbow and the diameter (D). The type of fitting dictates the relationship between the friction loss and the pipe size.

Note: this method assumes that the flow is fully turbulent (see the demarcation line on the Moody diagram of

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Figure 6 K factor vs. diameter of fitting (source: Hydraulic Institute Engineering data book)
Another good source for fitting K factors is the Crane Technical Data Brochure.

Figure 7 Values for the K factor with respect to the friction factor for a standard tee.


The Crane technical paper gives the K value for a fitting in terms of the term fT as in this example for a standard tee.



As is the case for the data shown in Figure 6, the friction loss for fittings is based on the assumption that the flow is highly turbulent, in fact that it is so turbulent that the Reynolds number is no longer a factor and pipe roughness is the main parameter affecting friction. This can be seen in the

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The term fT used by Crane is the friction factor and is the same as that given by the Colebrook or the Swamee-Jain equation.


When the Reynolds number becomes large the value of fT (using the

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furthermore the

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Therefore the value of the K factor is easily calculated based on the diameter of the fitting, the friction factor fT and the multiplication factor for each type of fitting.

[hr][/hr] Laminar: A distinct flow regime that occurs at low

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Figure 8 Laminar flow velocity profile.
[hr][/hr] Lobe pump: a positive displacement pump. Primarily used in food applications because they handle solids without damaging them. Lobes are driven by external timing gears as a result the lobes do not make contact. Liquid travels around the interior of the casing in the pockets between the lobes and the casing, meshing of the lobes forces liquid through the outlet port under pressure. They also offer continuous and intermittent reversible flows and can operate dry for brief periods of time. Typical applications are in following industries: food, pharmaceuticals, paper & pulp, beverages, chemical and biotechnology.



Viking Pumps is a major supplier of these pumps

[link Point to another website Only the registered members can access] [hr][/hr] Low NPSH pump: a pump designed for application with a low

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[link Point to another website Only the registered members can access] [hr][/hr] Mechanical seal: a name for the joint that seals the fluid in the pump stopping it from coming out at the joint between the casing and the pump shaft. The following image (source: the Pump Handbook by McGraw-Hill) shows a typical mechanical seal. A mechanical seal is a sealing device which forms a running seal between rotating and stationary parts. They were developed to overcome the disadvantages of compression packing. Leakage can be reduced to a level meeting environmental standards of government regulating agencies and maintenance costs can be lower.

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[hr][/hr] Mercury (Hg): A metal that remains liquid at room temperature. This property makes it useful when used in a thin vertical glass tube since small changes in pressure can be measured as changes in the mercury column height. The inch of mercury is often used as a unit for measuring vacuum level or pressures below atmospheric pressure.


The relationship between inches of mercury, psi and psia units of pressure.
[hr][/hr] Minimum flow rate
Most centrifugal pumps should not be used at a flow rate less than 50% of the B.E.P. (best efficiency point) flow rate without a recirculation line. (

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How is the minimum flow of a centrifugal pump established (answer from the Hydraulic Institute

[link Point to another website Only the registered members can access] The factors which determine minimum allowable rate of flow include the following:

* Temperature rise of the liquid -- This is usually established as 15°F and results in a very low limit. However, if a pump operates at shut off, it could overheat badly.

* Radial hydraulic thrust on impellers -- This is most serious with single volute pumps and, even at flow rates as high as 50% of BEP could cause reduced bearing life, excessive shaft deflection, seal failures, impeller rubbing and shaft breakage.

* Flow re-circulation in the pump impeller -- This can also occur below 50% of BEP causing noise, vibration, cavitation and mechanical damage.

* Total head characteristic curve - Some pump curves droop toward shut off, and some VTP curves show a dip in the curve. Operation in such regions should be avoided.


There is no standard which establishes precise limits for minimum flow in pumps, but "ANSI/HI 9.6.3-1997 Centrifugal and Vertical Pumps - Allowable Operating Region" discusses all of the factors involved and provides recommendations for the "Preferred Operating Region".