Jet,
set, go
MC
Singhal throws light on the correct method of operating and selecting
jet pumps for applications that use various operating mediums
Also
known as eductors, jet pumps are simple devices that provide a cost
effective way to pump, mix or heat fluids, solids and gases. Reliable
operation from a variety of power sources allows jet pumps to perform
effectively in a wide array of process applications.
Jet pumps can be used to perform not only singular duties such as pumping
liquids to drain sumps and tanks, or heating liquids in-tank for cooking
or circulating, but can also be used to achieve these functions simultaneously.
They can evacuate gases, create a vacuum, boost suction pressures, mix
granular solids with liquids and move granular solids with compressed
air. In fact, a new user is likely to be surprised at what a jet pump
can do to solve problems in a cost effective and simple way.
How jet pumps operate
All jet pumps operate on the principle of a fluid entraining
a second fluid. Although design and construction may vary, this applies
to all jet pumps. All jet pumps have three common features: inlet, suction
and discharge. Here is how these function: Inlet (Motive): Air operating
fluid medium (liquid, gas, or steam), which is referred to as motive
under pressure, enters the inlet and travels through the nozzle into
the suction chamber. This function is the power phase of pumping operation.
At this stage, the velocity of motive media increases as it passes through
a nozzle. The nozzle converts the pressure of the operating medium into
a high velocity stream. This phase of pumping operation takes advantage
of the kinetic properties of motive media, whether it is liquid, steam
or gas. Due to this design, differences may exist within the motive
connection of the jet pump. For instance, jet pumps with liquid motives
use a convergence nozzle, since liquids usually cannot be compressed.
On the other hand, jet pumps with gas or steam motives use converging/
diverging nozzles to achieve trans-sonic flow velocities. Suction: This
connection of the jet pump is where the pumping action takes place.
The high velocity stream of motive causes a drop in pressure in the
suction chamber. This allows pressure in the suction vessel to push
a liquid, stream or gas into the suction chamber of the jet pump. This,
in turn, is entrained by high-velocity motive stream emerging from the
inlet nozzle.
Discharge: As the motive flow combines with the suction medium, some
kinetic energy of the motive is transferred to the suction, mixing and
discharging at a reduced pressure. The amount of pressure that can be
recovered depends on the ratio of motive flow to suction flow, plus
the amount of suction pressure built up in the suction vessel. Kinetic
energy is converted back to pressure as the mixed media passes through
the diverging caper and is discharged out of the pump.
Utility:
The following discussion deals
with the use of jet pumps in various operating mediums, with reference
to the medium of transport -–
1) Where liquid is both the operating and transport medium:
Liquid transfer
Pump from tank or sump
Dilute in-line
Mix or blend in-line
Lift or elevate liquids
Boost suction pressure to centrifugal pump
In-tank heating
Destration.
2) Where liquid is the operating medium and steam is the transport
medium:
Heat liquids in-line
Exhaust from vessel
Evacuate from vessel. ....
....CONTD
