1. Shaft
axial channeling large
Mechanical seal sealing surface have a certain specific pressure,
so as to play a seal, which requires the mechanical seal spring to have a
certain amount of compression to the seal faces a thrust, spin up the sealing
surface to produce the desired ratio of seal pressure. In order to ensure that
a specific pressure, mechanical shaft seal requires channeling can not have too
much volume, usually to ensure that less than 0.5 mm. But in the actual
designs, due to improper design, often channeling shaft have a huge amount, the
use of mechanical seals is very unfavorable. This phenomenon often occurs in a
multi-stage centrifugal pumps, especially during startup of the pump,
channeling a greater amount.
Automatically
changing the axial ring balance disc and balance between work time balance disc
space b, thereby changing the pressure on both sides of the front and rear
balance disc, resulting in an axial force in the opposite direction of the
force to balance the axial force. Due to fluctuations in the rotor inertia of
the traverse and transient operating conditions of the pump, the operation of
the rotor is not in a static axial equilibrium position. Balance disc always
ran around in the state. Balance disc in normal operation of the axial
channeling only 0105 ~ 011 mm, to meet the mechanical seal to allow the amount
of 015 mm axial channeling requirements, but the balance disc at pump start,
stop, axial channeling conditions upheaval when possible greatly exceeds the
amount of axial channeling mechanical seal allowed.
After a
long-running industrial pumps, balance disc and balance ring friction and wear,
the gap b with the increase, the mechanical seal axial channeling increasing.
Due to the axial force to the suction side of the pressing force of the sealing
surface increases, the sealing surface wear and tear, until the sealing surface
is damaged, lost seal. The discharge side of the mechanical seal, with the
balance disc wear axial rotor parts is greater than the axial channeling
channeling sealing requirements, the pressing force of the sealing surface is
reduced, reach sealing requirements, and finally to both sides of the pump
Mechanical seal all lost seal.
2. Axial
force is too large
Mechanical
seal during use is not able to withstand the axial force, if there is an axial
force, the impact of the mechanical seal is serious. Sometimes due to pump
axial force balance mechanism design unreasonable and manufacture,
installation, use and other aspects, resulting in an axial force is not
balanced out. Mechanical seals to withstand an axial force, when the high
temperature operation of the gland, the polypropylene material, which is melted
at high temperatures, so the pump starts soon lost the sealing effect, the seal
faces the pump still appear intermittent spray drain phenomenon.
3. Shaft
deflection is too large
Mechanical
seals, also known seal, is a rotary seal axially movable contact, which is
under the action of the elastic element and the fluid medium, the two seal
faces perpendicular to the axis line of close contact, relative rotation, so as
to achieve sealing effect, thus requiring uniform force to the seal between the
two. However, due to the pump design is unreasonable, when the operation shaft
deflection at the mechanical seal installation produces large, so that
discontinuity between the seal faces, resulting in poor sealing effect.
4. No
secondary irrigation system or the auxiliary processing system is unreasonable
Auxiliary
mechanical seal flushing system is very important, it can effectively protect the
sealing surface, play a cooling, lubrication, wash away debris and so on.
Sometimes designers no reasonable allocation assisted flushing system, reach
the sealing effect; sometimes though designers to the auxiliary system, but
because of the flushing fluid impurities, fluid flow, the pressure is not
enough, rinse mouth position design unreasonable reasons likewise reach the
sealing effect.
5.
Vibration is too large
Mechanical
seal vibration is too large, resulting in the loss of the sealing effect. But
the mechanical seal is often not the cause of the vibration is too large
mechanical seal reason itself, and the other parts of the pump is the source of
vibration, such as the shaft design is unreasonable, processing reasons, lack
of precision bearings, parallel coupling poor, radial force and other factors.
6. Cause
pump cavitation
Since
the device operating system and the pump inlet unreasonable cavitation
performance is not good, high pump speed, take place at the entrance of the
local pump cavitation, cavitation occurs after the water will bubble one hand,
it will impact the mechanical seal faces the outer surface, so that the surface
damage; on the other hand would fit surface movement flow membrane ring also
contains air bubbles can not form a stable flow membrane, causing the static
ring of consistent surface dry friction, mechanical seal damage.
7.
Machining precision is not enough
Machining
precision is not enough, for many reasons, some precision mechanical seals
itself is not enough reason for this is easy to arouse people's attention, but
also easy to find. But sometimes other parts of precision pump is not enough,
because this area is not easy to attract attention. For example: shaft,
bushings, pump, seal the cavity to increase the accuracy is not enough other
reasons. The presence of these reasons for mechanical seal sealing effect is
very negative.
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