Steps for replacing mechanical shaft seals and overhaul misconceptions

When disassembling the mechanical seal, it is strictly prohibited to use hand hammer and flat shovel to avoid damaging the sealing element. If there are mechanical seals at both ends of the pump, care must be taken during disassembly to prevent loss of one or the other. The mechanical seal has worked, if the sealing surface moves when the gland is loosened, the dynamic and static ring parts should be replaced, and should not be re-tightened to continue to use. Because after loosening, the friction vice original running trajectory will change, the sealing of the contact surface will be easily damaged.

If the sealing element is dirt or cohesion bonding, should be removed after the condensation of mechanical seal disassembly.

(I) Mechanical seal disassembly

Mechanical seal disassembly order and installation order is reversed. In the process of dismantling mechanical seals must be careful, not with a hammer, flat shovel, shall not knock the seal, can not damage the seal moving, static ring sealing surface, if too much dirt because of oil, etc., can not be dismantled, must first be cleaned with paraffin, etc. and then dismantled, so as to keep the parts of the seal intact.

(ii) Overhaul of mechanical seal

After removing the mechanical seal, firstly check the pump body with organic seal installed, and then overhaul the mechanical seal:

(1) check the mechanical seal components. Components shall be complete, no damage, dynamic and static ring sealing surface without scratches, bruises and other defects, if found damaged, shall be repaired or re-replaced mechanical seal;

(2) Check whether the spring elasticity is small, such as small to replace the spring;

(3) Check the seal body wall, seal end cap surface damage, if found timely maintenance.

(C) the mechanical seal of the installation of the preparatory work and precautions

After the above overhaul work is completed, it is necessary to reinstall the mechanical seal, and preparatory work must be done before installation:

1, if the replacement of the new seal, must check the mechanical seal type, specification is correct, whether the quality is in line with standards;

2, static ring tail anti-rotation groove end and the top of the anti-rotation pin should maintain 1mm-2mm axial clearance, so as to avoid buffer failure;

3, dynamic and static ring end face cleaned with alcohol, the rest of the metal parts with gasoline cleaning and clean compressed air blow dry, carefully check to ensure that the dynamic and static ring sealing surface without any damage. Before assembly, two pieces of “O” shaped rubber seal should be coated with a layer of lubricant paste, dynamic and static ring end face is not allowed to apply oil.

(D) mechanical seal installation

Mechanical seal installation order and precautions are as follows:

1, in the rotor and the pump body after the relative position is fixed, to determine the installation position of the mechanical seal, according to the installation size of the seal and the static ring in the position of the gland, measured out the seal in the shaft or shaft sleeve positioning dimensions;

2、Installation of the seal moving ring, the moving ring must be installed to ensure that it can move flexibly on the shaft;

3、Assemble the assembled static ring part and dynamic ring part;

4, the seal end cap installed in the seal body, and tighten the screws.

(E) mechanical seal maintenance misunderstanding

1, the greater the spring compression, the better the sealing effect

In fact, not, spring compression is too large, can lead to friction vice sharp wear, instantaneous burn; excessive compression makes the spring lose the ability to adjust the moving ring end face, resulting in seal failure.

2、The tighter the dynamic ring seal, the better.

In fact, the dynamic ring seal is too tight harmful. One is to exacerbate the wear and tear between the sealing ring and the sleeve, premature leakage; two is to increase the dynamic ring axial adjustment, mobile resistance, in the frequent changes in working conditions can not be adjusted in time; three is the spring excessive fatigue easy to damage; four is to make the dynamic ring sealing ring deformation, affecting the sealing effect.

3, the static ring seal the tighter the better

Static ring seal is basically in a static state, relatively tight sealing effect will be better, but too tight is also harmful. One is to cause the static ring seal due to excessive deformation, affecting the sealing effect; two is the static ring material to graphite mostly, generally brittle, excessive force is very easy to cause cracking; three is difficult to install, disassemble, very easy to damage the static ring.

4, multi-stage centrifugal pump impeller lock mother the tighter the better

Mechanical seal leakage, the leakage between the shaft sleeve and the shaft (inter-axial leakage) is relatively common. Generally believe that the inter-axis leakage is the impeller lock nut did not lock, in fact, leading to inter-axis leakage of more factors, such as inter-axis pad failure, offset, impurities in the inter-axis, shaft and shaft sleeve with a large form error, contact surface damage, the gap between the parts of the shaft, the shaft head thread is too long, etc. will lead to inter-axis leakage. Lock mother locking excessive will only lead to premature failure of the inter-axis pad, on the contrary, moderate locking lock mother, so that the inter-axis pad always maintain a certain degree of compression elasticity, in operation, the lock mother will automatically lock at the right time, so that the inter-axis is always in a good state of sealing.

5, new than the old good

Relatively speaking, the pump using the new mechanical seal is better than the old, but the quality of the new mechanical seal or material selection is not then, with a large error in size will affect the sealing effect; in the polymerisation and permeability of the medium, static ring such as no excessive wear and tear, or not to be replaced as well. Because the static ring in the static ring seat for a long time in a static state, so that the polymer and impurities deposited as a whole, play a better sealing effect.

6, dismantling is better than not dismantling

Once there is a mechanical seal leakage will be eager to dismantle the repair, in fact, sometimes the seal is not damaged, only need to adjust the working conditions or proper adjustment of the seal can eliminate leakage. This not only avoids waste but also can verify their ability to determine the fault, accumulate maintenance experience to improve the quality of maintenance.

Leave a Reply

Your email address will not be published. Required fields are marked *