Mechanical seal is the best answer by a pair or several pairs of perpendicular to the axis of relative sliding of the end for the fluid pressure and the compensation mechanism in the elastic (or magnetic) to keep under seal affixed to merge to achieve together with auxiliary shaft seal leakage resistance device.
Mechanical seal structure used by the geostationary ring (stationary ring) 1, rotating ring (ring) 2, the elastic element 3, the spring seat 4, 5, set screws, rotating ring supporting ring 6 and the stationary ring composed of auxiliary components such as seals 8 , 7 fixed to the gland against resellers to prevent the stationary ring 9 on the turn. Rotating ring and stationary ring often can be compensated according to whether they have the ability to axial or non-compensation is also known as the compensation ring.
Mechanical seal leakage of fluid channels may have A, B, C, D four channels.
C, D leak paths are stationary ring and the gland, the seal between the shell gland, the two are static seal. B-channel is the axis of rotation between the ring and the seal, when the face friction and wear, it can follow only compensate for the small amount of ring movement along the axis, in fact, still a relatively static seal. Therefore, these leaks are relatively easy to block channels. The most commonly used static sealing rubber O-ring or PTFE V-ring, and as compensation for the rotation of ring secondary seal rings or still rings, and sometimes both elastic element functions using rubber, PTFE or metal bellows structure.
A channel is a rotating ring and stationary ring affixed to end cooperation with each other relative sliding seals, mechanical seal device which is the main seal, also decided to mechanical seal performance and longevity of the key. Therefore, the processing requirements of seal face very high, between the seal faces in order to maintain the necessary lubrication film, the system must be strictly cavity-side surface of the unit area pressure, the pressure is too large and difficult to form a stable lubricating film, will accelerate the end wear; pressure is too small, increase of leakage. Therefore, to obtain good sealing performance and a sufficient life, in the design and installation of mechanical seals, we must ensure that the pressure per unit area of face value in the most appropriate range.
Mechanical seals compared with the soft packing seal, has the following advantages: a reliable sealing in the long period of operation, the sealed state is very stable, very small amount of leakage, according to rough statistics, the leakage of soft packing seal is typically only 1 / 100; as long service life in the oil and water based medium, usually ranging from 1 to 2 years or more, usually in the chemical medium can reach more than six months; a friction power consumption of a small mechanical seal friction power is only the soft packing seal 10% to 50%.
The mechanical seal in the pump is widely used products, and its prospects will be even brighter. This author, based on actual work, of what the pump mechanical seal problems.
The current pump mechanical seal in a wide range of products, and as raising the level of product technology and energy conservation requirements, the mechanical seal will be more extensive application prospects. Also known as seal mechanical seal, which has a rotating axis perpendicular to the face, the face in the fluid pressure and external elastic compensation machinery under the influence of co-dependent on secondary seal to keep fit with the other side, and sliding, to prevent fluid leakage. Daqing Petrochemical Plant Bandung property company to use the boiler circulation pump light, model 200LGY75A, flow rate 275 m3 / h, working pressure 0.4MP, working temperature is 95, medium is water, seal mechanical seal pumps, the author of this article actual work, of what the pump sealing problems.
A water pump mechanical seal and the reasons for the leakage phenomenon, leakage due to pressure generated .
The vacuum caused by the mechanical seal leakage operation
Pump at the start, stop the process, clogging the pump inlet, pumping medium containing gas and oher reasons, there may be negative pressure to the sealed chamber, the seal cavity if the negative pressure, can cause seal face friction, will have built-in mechanical seal leak (water) phenomenon, vacuum seal and pressure seal sealing the object is different from the direction of differences, and mechanical seal has its adaptability to a certain direction.
I. Pump mechanical seal Basics:
1. Centrifugal pump mechanical seal of the basic concepts:
Mechanical seal is defined as at least one rotation axis perpendicular to face compensation mechanism in the fluid pressure and stretch (or magnetic) and the secondary seal under the action of the Post merged with the relative sliding to maintain, constitute a device to prevent fluid leakage. Compensation for the auxiliary seal ring metal bellows mechanical seal, called bellows.
2. Mechanical seal consists of:
There are four main parts:
a. Main Seal: rotating ring and stationary ring.
b. Secondary seals: seals.
c. Compression parts: spring, pushing ring.
d. Transmission Parts: Kei Block and bomb key or screw
II. Mechanical seal should pay attention to the problem:
1. Installation Notes
a. should be very careful to avoid installation misalignment generated
(1) the gland coupling alignment should be carried out after the bolts should be evenly supported to prevent the gland face skewed, with a feeler check points, the error is not greater than 0.05 mm.
(2) Check the gland and the shaft or sleeve diameter with the gap (ie concentric), four weeks should be uniform, with a feeler points tolerance no more than 0.01 mm.
b. the amount of compression according to the provisions of the spring, allowed the phenomenon is too large or too small to require error 2.00 mm. Than the pressure may increase the end, the other face wear rate. Too small will cause less than the pressure seal and can not play a role.
c. ring installed in the shaft after the beard to ensure that mobile and flexible, the pressure to the ring after the spring should be able to automatically bounces back.
2. Disassembly Note
a. When the demolition of the mechanical seal carefully, non-use of hand-hammer and flat blade, so as not to damage the sealing elements. To do a pair of wire hook, stretching in the direction of self-financing gap in the drive seat, pull out the seal. If the scale demolition of no less than should be cleaned before demolition.
b. If the pump mechanical seal both ends, in the assembly, the demolition process to take care of each other, to prevent the other.
c. mechanical seal on the run-off, where a loose gland seal is moved to the situation, the static rings parts must be replaced, not re-tighten the continued use. Ying move because of the sample, the friction will be a change in the original running track, the contact surface of the seal is very easily damaged.
III. Mechanical seal running and maintenance issues:
1. Before the start of the preparatory work and notes
a. comprehensive inspection of mechanical seals and ancillary equipment and piping installation is complete, compliance with technical requirements.
b. mechanical seal before the start of the static pressure test, check whether the mechanical seal leakage. If the leak more, should find out the reason for trying to eliminate. If still ineffective, should be demolished and re-check the installation. General static test pressure for 2 to 3 kg / square centimeter.
c. rotation by turning the pump, check whether the light evenly. Such as turning difficult or does not move when the assembly should check whether the size error, the installation is reasonable.
2. Installation and outage
a. shall remain sealed before the start of cavity filled with fluid. Solidification of the medium for transmission, the application will be sealed vapor chamber heat to medium melt. Start before turning to prevent a sudden start caused by soft ring fragmentation.
b. For use outside the seal oil system pump mechanical seal, seal oil system should be launched. After stopping the last stop the seal oil system.
c. heat pump can not immediately stop after the outage seal oil and seal chamber cooling water should be at the oil seal when down to 80 degrees below, we can stop the cooling water to avoid damage to the seal parts.
a. If pump starts minor leakage should be observed for some time. 4 hours continuous operation, such as, leakage is still not reduced, they should check the pump stops.
b. the operation of the pump pressure should be stable, the pressure fluctuation is less than 1 kg / square centimeter.
c. pump in operation, should avoid taking the time to the phenomenon of dry friction in order to avoid sealing surface and seal damage.
d. Always check the seal condition. Operation, when the leakage exceeds the standard, heavy oil is not more than 5 drops / min, light oil is not more than 10 / min, still no signs of improvement, such as 2-3 days, you should check the pump stops bolt seals.
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