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[hr][/hr] Vane pass frequency: when doing a vibration analysis this frequency (no. of vanes times the shaft speed) and it's even multiples shows up as a peak which can indicate a damaged or imbalanced impeller.
Figure 15 Noise vibration spectra showing vane pass frequency (source: The Pump Handbook publ. by McGrawHill)
see articles on pump vibration sources on this web page: [link Point to another website Only the registered members can access]
[hr][/hr] Vane pump: [link Point to another website Only the registered members can access]
[hr][/hr] Vane pump (hydraulic): a positive displacement pump. Vane pumps are used successfully in a wide variety of applications (see below). Because of vane strength and the absence of metal-to-metal contact, vane pumps are ideally suited for low-viscosity, non lubricating liquids up to 2,200 cSt / 10,000 SSU. Such liquids include LPG, ammonia, solvents, alcohol, fuel oils, gasoline, and refrigerants.
1. A slotted rotor or impeller is eccentrically supported in a cycloidal cam. The rotor is located close to the wall of the cam so a crescent-shaped cavity is formed. The rotor is sealed into the cam by two sideplates. Vanes or blades fit within the slots of the impeller. As the impeller rotates (yellow arrow) and fluid enters the pump, centrifugal force, hydraulic pressure, and/or pushrods push the vanes to the walls of the housing. The tight seal among the vanes, rotor, cam, and sideplate is the key to the good suction characteristics common to the Vane pumping principle.
2. The housing and cam force fluid into the pumping chamber through holes in the cam (small red arrow on the bottom of the pump). Fluid enters the pockets created by the vanes, rotor, cam, and sideplate.
3. As the impeller continues around, the vanes sweep the fluid to the opposite side of the crescent where it is squeezed through discharge holes of the cam as the vane approaches the point of the crescent (small red arrow on the side of the pump). Fluid then exits the discharge port.
Rexroth is a major manufacturer of vane pumps [link Point to another website Only the registered members can access]
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[hr][/hr] Vapor pressure: The pressure at which a liquid boils for a specific temperature.
Figure 16 The boundary between liquid and vapor phase of a fluid. A fluid can be vaporized by increasing the temperature or decreasing the pressure.
Figure 17 Vapor pressure vs. temperature for various fluids.
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[hr][/hr] Venturi (Bernoulli's law): a venturi is a pipe that has a gradual restriction that opens up into a gradual enlargement. The area of the restriction will have a lower pressure than the enlarged area ahead of it. If the difference in diameters is large you can even produce a very high vacuum (-28 feet of water). I use a cheap plastic venturi made by Fisher or Cole Palmer for an experiment that I do to demonstrate vapor pressure during my training seminars and it is very easy to create very high absolute vacuum.
In certain locations I can't do this experiment, because hey don't have a source of water in hotel suites, too bad because it's always a winner, so I have to revert to a [link Point to another website Only the registered members can access]
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It is not easy to understand why low pressure occurs in the small diameter area of the venturi. I have come up with this explanation that seems to help.
It is clear that all the flow must pass from the larger section to the smaller section. Or in other words, the flow rate will remain the same in the large and small portions of the tube. The flow rate is the same, but the velocity changes. The velocity is greater in the small portion of the tube. There is a relationship between the pressure energy and the velocity energy, if velocity increases the pressure energy must decrease. This is the principle of conservation of energy at work which is also Bernoulli's law. This is similar to a bicycle rider at the top of a hill. At the top or point 1 (see Figure 18 below), the elevation of the cyclist is high and the velocity low. At the bottom (point 2) the elevation is low and the velocity is high, elevation (potential) energy has been converted to velocity (kinetic) energy. Pressure and velocity energies behave in the same way. In the large part of the pipe the pressure is high and velocity is low, in the small part, pressure is low and velocity high.
Figure 18 The venturi effect.
Bernoulli's law is a relationship between two points within a system that states that the sum of the energies that correspond to pressure, velocity and elevation must be conserved.
The general form of the law (neglecting friction) is:
where p1 is the pressure, v1 the velocity and h1 the elevation at point 1 and the same parameters are used at point 2. Gamma 
is the fluid density and g the acceleration due to gravity.
In the case of the cyclist there is no pressure and only the velocity and elevation can vary, so that Bernoulli's law becomes:
as the cyclist goes down the hill h2 becomes smaller than h1 and to balance the equation then v2 must be larger than v1.
In the case of the venturi tube there is no elevation change and only the velocity and pressure can vary, so that Bernoulli's law becomes:
We can clearly see that if v2 is greater than v1 then p2 must be smaller than v1 to balance the equation.
for an article on this and related subjects see[link Point to another website Only the registered members can access]
[hr][/hr] Viscosity: A property from which a fluid's resistance to movement can be evaluated. The resistance is caused by friction between the fluid and the boundary wall and internally by the fluid layers moving at different velocities. The more viscous the fluid the higher the friction loss in the system. Centrifugal pumps are affected by viscosity and for fluids with a viscosity higher than 10 cSt, the performance of the pump must be corrected. [link Point to another website Only the registered members can access]
The following figure which you can find in the Goulds pump catalogue in the Technical Section shows the effect of viscosity on pump performance.
This next figure is a chart of values for viscosity for different liquids which you can find in the Cameron Hydraulic data book.
The basic unit of viscosity is known as the Poise or centiPoise (cP) named after the French scientist Poiseuille who discovered a practical method of measuring viscosity. The greek letter 
is used to represent viscosity. There are two types of viscosity, the first just mentioned is known as absolute viscosity and the other for which the greek letter nu 
is used is called the kinematic viscosity. The unit of kinematic viscosity is the centiStoke (cSt) named after the English scientist Stokes.
The relationship between the two is:
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[hr][/hr] Viscosity correction: [link Point to another website Only the registered members can access]
[hr][/hr] Viscous drag pump: a pump whose impeller has no vanes but relies on fluid contact with a flat rotating plate turning at high speed to move the liquid.
Viscous drag pump
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[hr][/hr] Volute: syn casing.
[hr][/hr] Vortex: see [link Point to another website Only the registered members can access]
[hr][/hr] Vortex pump: see [link Point to another website Only the registered members can access]
[hr][/hr] Water hammer (pressure surge): If in systems with long discharge lines,(e.g. in industrial and municipal water supply systems ,in refineries and power stations) the pumped fluid is accelerated or decelerated, pressure fluctuations occur owing to the changes in velocity. If these velocity changes occur rapidly , they propagate a pressure surge in the piping system, originating from the point of disturbance ; propagation takes place in both directions (direct waves),and these waves are reflected (indirect waves) at points of discontinuity ,e.g. changes of the cross sectional area ,pipe branches, control or isolating valves, pumps or reservoir. The boundary conditions decide whether these reflections cause negative or positive surges. The summation of all direct and indirect waves at a given point at a given time produces the conditions present at this point.
These pressure surges, in addition to the normal working pressure ,can lead to excessive pressure and stresses in components of the installation . In severe cases such pressure surges may lead to failure of pipe work, of fittings or of the pump casings. The minimum pressure surge may, particularly at the highest point of the installation ,reach the vapor pressure of the pumped liquid and cause vaporization leading to separation of the liquid column. The ensuing pressure increase and collision of the separated liquid column can lead to considerable water hammer .The pressure surges occurring under these conditions can also lead to the failure or collapse of components in the installation.
For the maximum pressure fluctuation the JOUKOWSKY pressure surge formula can be used:
Δp = ρ . a . Δv
Where ρ = density of the pumped liquid
a = velocity of wave propagation
Δv = change of velocity of the flow in the pipe.
The full pressure fluctuation corresponding to the change of velocity Δv occurs only if the change of velocity Δv takes place during the period.
t ≤ reflection time tr = 2.l /a
where l = distance between the nearest discontinuity (point of reflection ) and the point of disturbance .
A contribution from Moshe Shayan of the pump discussion forum.
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