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Selection and application of mechanical seals
- Sep 06, 2018 -

Mechanical seals belong to the fine, relatively complex structure of the mechanical base of one of the components, is a variety of pumps, reactors, turbomachinery, diving motor mechanical seals and other equipment key components.Its sealing function and service life depend on many factors, such as selection, precision of machine, accurate equipment application, etc.

<1>.Selection method

Mechanical seal according to the operation conditions and mechanical sealing properties of different media, there are high temperature resistant, resistant to low temperature mechanical seal, mechanical seal, high pressure resistance and corrosion resistance of granules medium mechanical seal and adapt to vaporize the mechanical seal of light hydrocarbon medium, etc., should choose different in terms of the use of different tectonic pattern and the materials of mechanical seal.

Selection of main parameters are: seal cavity pressure (MPA), fluid temperature (℃), the operation speed (M/S), fluid properties and device sealing useful space, etc.

The basic principles of type selection are:

1.According to the pressure of the sealing chamber, it determines that the sealing structure should be of balanced or non-balanced type, single or double face.

2.According to the working speed, decide to choose rotary type or stop type, fluid dynamic pressure type or non-touch type.

3.Based on the properties of temperature and fluid, it determines the data of collision and auxiliary seals, and select the circulation maintenance system of mechanical seals such as smooth, scour, heat preservation and cooling accurately.

4.Use multiple spring or single spring or wave spring, internal or external, according to the space available for sealing the device.

<2>.Equipment and operation request of mechanical seal

1. Requirements of mechanical seal on machine accuracy (taking mechanical seal for pump as an example)

(1) the maximum radial runout tolerance of the shaft (or shaft sleeve) at the mechanical seal part of the device shall not exceed 0.04 ~ 0.06MM.

(2) axial movement of rotor does not exceed 0.3mm.

(3) the maximum beating tolerance of the positioning end connected with the sealing end cover to the outer surface of the shaft (or shaft sleeve) shall not exceed 0.04 ~ 0.06MM.

2. Seal recognition

(1) admit whether the seal of the device is common with the type of request.

(2) carefully check with the final assembly drawing before installation to see if the number of parts is complete.

(3) mechanical seal with spring drive is selected, and the spring is divided into left and right rotation, which shall be selected according to the rotation of the rotating shaft.

3. installation

The device method varies with the type of mechanical seal and type of machine, but the device method is almost the same. The device steps and considerations are as follows:

(1) determination of device scale

When the device is installed, the device scale of mechanical seal shall be ensured according to the operation manual or sample of the product.

(2) before loading, the shaft (shaft sleeve) and gland should be free of burrs, and the bearing is in good condition;Seal, shaft, seal cavity and gland should be clean.To reduce conflict resistance, the mechanical seal part of the shaft shall be lightly coated with a layer of oil for smoothing. Considering the solubility of rubber O ring, if not oil, soapy water can be applied.Floating - mounted static ring without pin structure, should not be oil, should be dry loaded gland.

(3) first install the static ring and the gland together on the shaft, and pay attention not to touch the shaft, and then load the moving ring assembly.The set screws of the spring or drive seat should be tightened evenly several times.

Before the gland is not fixed, the counterbalance ring is pushed by hand for axial contraction. After release, the counterbalance ring can spring back to the scene without sticking, and then the screw bolt of the gland is locked evenly.

4. application

(1) when the transport medium is too hot, too low, or rich in impurity particles, flammable, explosive and toxic, it is necessary to take corresponding measures such as blocking, flushing, cooling and filtration.

(2) before operation, drive the car by hand. Pay attention to whether the torque is too large, and whether there is any rubbing and abnormal sound.

(3) pay attention to the rotation direction, whether the coupling is right, whether the smooth oil addition in the bearing part is appropriate, and whether the piping is accurate.

(4) before operation, first open the dielectric and cooling water valves, check whether the air in the sealed cavity is fully discharged, avoid leakage caused by static pressure, and then start up the operation.

(5) the operation after driving is not normal and stable, with abnormal torque caused by axis rotation, abnormal sound and overheating.