SImply, the vortex breaker keeps vapor from being sucked into the piping by the "vortex" formed at the inlet- same as observed when water drains from a sink. A vortex breaker will greatly reduce the level needed to keep from pulling in vapor. This vapor would cause a loss of pump suction or result in unsteady flow in gravity flow systems. Since the cost is nearly nothing, a vortex breaker is almost always included.
Even if your flow is not going directly to a pump, the vapor pulled into the piping leaving the vessel would cause a two phase flow situation that would be detrimental to process flows. Plus, the vortex itself is a significant pressure loss in the piping at that point.
There can also be a process safety piece to having a vortex breaker if you are counting on a liquid seal in your vessel. For example, to prevent undercarry of vapors to a downstream atmospheric tank.
It is not that important you have vortex breakers. All of what has been said is correct, A vortex broker will seldom hurt, but is by no way mandatory.
If your pump is fed with enough heigth you can spare it.
But if for some reason your fluid wants to gas out in the pump, a vortex breaker will not do (much) good.
It should also be pointed out that vortex generation depends on the flow and outlet pipe size. If you have low velocities, a vortex will not occur.
Inadequate submergence can result in rotation of the water in the tank, resulting in the formation of strong free-surface air core vortices and the entrance of air into the pump suction inlet. This phenomenon is commonly called vortexing.
Vortexing can cause unstable pump operation, vibration, pulsation and severe mechanical damage.
The U.S. based Hydraulic Institute has produced the following guidelines for recommended minimum submergence of the pump suction inlet to reduce the probability that strong free-surface air core vortices will occur:
S = Minimum submergence to prevent vortexing, in inches
D = Pump suction inlet diameter in inches
Q = Pump design flow rate, in USGPM
S = D + [( 0.574 x Q) /( D^1.5)]
Source: American National Standard for Pump Intake Design, Hydraulic Institute, ANSI/HI 9.8-1998,
Section 9.8.7
Q = 3200 GPM
D = 16”
S (Minimum submergence) = 44.7”
Q = 1000 GPM
D = 16”
S (Minimum submergence) = 25”
A vortex braker is to avoid the swirling of the flow and air bobbles which can damage the suction pump impeller. The vortex breaker transforms a big vortex into smaller vortexes to protect the suction pump
Practical design guides based on fluid dynamics for vortex breakers are hard to find since vortex breaker designs and dimensions are generally "jury rigged" types of devices.
One design is a crossed plate inserted into the throat of the outlet pipe in a tank; the length of which is roughly 1.5 times the diameter. This setup is typically used if the outlet pipe is on the side of a tank. A design guide is listed in ANSI/HI 1.1-1.5-1994 Centrifugal pumps for Nomenclature, definitions, applications and Operation. No design dimensions are given.
If the outlet from a tank is on the bottom, a baffle plate can be placed over the mouth of the pipe. Installing the baffle plate above the pipe opening will simulate a larger intake area, thereby reducing the vortex and air entrainment.
The paper that can be accessed at the link below indicates that the cross type vortex breakers do not work and provides some practical experience with vortex breakers:
A flat plate vortex breaker will simulate the function of a pipe reducer and therefore reduce the velocity into the outlet pipe. The cross vortex breaker probably functions as a flow straightener and is not that effective at reducing fluid velocities (and vortexes).
