How to Install the Double Mechanical Seal

Author:Site Editor     Publish Time: 2021-01-13      Origin:Site

The double-end mechanical seal has the characteristics of short seal axial size and compact structure, so it is especially suitable for occasions where the axial size is restricted. Due to the complex structure of the double mechanical seal, high technical requirements, and strict sealing performance requirements, the technical requirements and work quality of the on-site installation should be strictly controlled. In this article, we introduced in detail the preparations to be done before installing the double acting mechanical seal, the necessary system conditions for the mechanical seal, and the detailed installation steps.

 

Preparation before install mechanical seal


  1. Before installing the mechanical seal, it must be ensured that the related equipment and the system are out of service or in a non-working state, and have reached the ambient temperature. The pressure part has been released to normal pressure to ensure personal safety during the installation of the double cartridge mechanical seal.

  2. Check whether the mechanical seal model matches the pump model used and whether the installation and connection dimensions are correct, and check whether the mechanical seal device is damaged or deformed.

  3. After preparing the seals to be installed, refer to the seal work diagram, pay attention to the order of disassembly and assembly of the parts when disassembling the pump, and remove the old double mechanical seal.

  4. Check whether the surface of the metal parts in contact with the shaft sleeve and gland on the pump are intact.

  5. In order to avoid damage to non-metallic components (such as the "O" ring), a 2x30 ° chamfer should be machined on all shoulders where non-metallic components slide, and all sharp corners should be rounded and smoothed. All edges and corners are discarded at the keyway or counterbore, and the metal surface roughness Ra should be less than 1.6um at the diameter where the seal ring slips. The metal surface roughness Ra at the static seal ring should be less than 3.2um.

  6. Clean the sealed cavity and check whether there are any traces of damage on the installation surface.

  7. Check whether the installation and connection dimensions related to the mechanical seal are consistent with the working drawing of the mechanical seal.

  8. Check the axial and radial runout of the rotating and stationary parts in the sealed cavity, and do not exceed the limit value specified by the national standard. The runout of the shaft end is less than 0.1 mm, the radial runout of the shaft is less than 0.03 to 0.05 mm, and the perpendicularity between the end face of the seal cavity and the shaft is less than 0.05 mm. If the requirements are not met, the bearings should be replaced or related parts adjusted.

  9. Wipe all parts, and add lubrication to the removed parts. Lubricants are recommended: soapy water, water, silicone grease, ethylenedioxide, or glycerin.

 

pump


System conditions necessary for dual mechanical seal


  • In order to improve the use environment of mechanical seals, sealing water must be used.

  • A water blocking port must be installed on the pump body seal cavity or seal gland.

  • The blocking water system is composed of pipelines, pressure gauges, regulating valves, etc. In order to correctly reflect and adjust the pressure of the blocked water system, the pressure gauge and the regulating valve must be installed at the end of the blocked water outlet.

  • The sealing water pressure must be higher than the pump chamber pressure 0.03~0.05Mpa. Its calculation formula is: P = (P1+ P2) / 2 * 1.2 + 0.05

P: Sealing water pressure

P1: Pump inlet pressure

P2: Pump outlet pressure

 

Assembly process of double mechanical seal


  1. The assembly of the double-acting mechanical seal must be carried out in a clean environment.

  2. Disassemble the mechanical seal package and pay attention to the seal end face not to touch hard objects.

  3. Determine the working length of the sealing according to the working drawing of the sealing.

    The working length of the sealing elastic component (including the moving ring) is calculated, that is, the length that can maintain a proper end-face specific pressure and elastic compensation within the specified operating life. The difference between the working length and the free state length is the compression of the seal. During installation, the actual compression amount needs to be calculated. A small amount of seal compression can be increased or decreased according to use experience. Otherwise, the size of the seal work diagram must be guaranteed. Blindly or excessively increasing or decreasing the amount of compression, and not installing according to the size of the seal working drawing will cause the seal to fail to work or prematurely fail.

  4. After measuring the size of the gland (including the stop pad), install the static ring and the static ring seal into the gland and pay attention to the groove at the back of the static ring to the anti-rotation pin on the gland. If the static ring sealing ring is an "O" ring, apply lubricant to the surface of the sealing ring, and then set it on the static ring, and then lay the static ring flat and press it into the gland by hand. If the static ring sealing ring is PTFE or flexible graphite, first install the sealing ring on the static ring, then lay it flat in the gland and align it with the anti-rotation pin on the gland. Note that the chamfering direction on the inner and outer circles of the sealing ring facilitates installation. Lay the end face flat, and put a soft cloth underneath, and slowly press the static ring into the gland with a press or drilling machine that can generate pressure. The force on the end face must be uniform, and the measured size must meet the requirements and be consistent. Do not apply force locally to the static ring, or knock on the static ring. If it can't move or the pressure is high, stop immediately. Measure the size of the gland, seal ring, and static ring, trim the unsuitable size before assembling.

  5. Clean the end faces of the dual mechanical seals, and carefully close the sleeves with the movable ring and the shaft seal and the glands with the static ring and the stop seal ring, and together them to make the end faces stick together. If it is an integrated seal with a limit plate, the limit plate can be installed and fixed at this time. Then install the remaining parts. If it needs to be tightened, the screws should be tightened evenly. If the shaft sleeve tightening method adopts the nut (that is, the transmission ring) tightening key transmission form (usually a double support pump), the correct thread direction should be selected. That is, the tightening direction of the sleeve tightening nut is opposite to that of the shaft. Note: In this case, there must be a keyed drive sleeve.

  6. The shaft sleeve of the general cantilever pump is directly pressed and fixed by the impeller and is driven by a key. When installing, according to custom, the complete set of seals can be set on the shaft first, then on the pump cover, and the seal gland should be fixed. It is also possible to install the complete set of seals on the pump cover first and fix the sealing gland, and then install it on the pump shaft. Note that the shaft seal gasket and gland gasket should be installed in place. After the pump cover is fixed to the suspension, other accessories such as the impeller key and impeller can be installed.

    double mechanical seals

  7. Install the seal of the double support pump. Sleeve the complete double-end mechanical seal from the shaft end and push it slowly into the seal cavity. Note that the keyway of the sleeve should be aligned with the key on the shaft. After pushing the sleeve in place, fix the gland, and install the shaft seal after the gland is fixed. Push the entire double mechanical seal into place, the gland enters the stop and presses the gland gasket, and then fix the gland. For the shaft sleeve that is positioned and driven by the transmission ring, or the shaft sleeve that is fixed by the expansion ring, evenly tighten the screws on the transmission ring to fix the shaft sleeve. Finally, don't forget to remove the limit plate.

  8.  When installing the dual mechanical seal with the pumping ring, install it step by step according to the seal work diagram. Note the direction of rotation of the axial screw pumping ring, which should be consistent with the working drawing. If the shaft rotates clockwise, a left-handed pumping ring should be installed. If the shaft is rotating counterclockwise, a right-handed pumping ring should be installed. Use radial pumping ring mechanical seals, when installing, pay attention to the direction of the buffer outlet on the gland should be consistent with the shaft rotation direction, which should facilitate the buffer outflow.

  9. When tightening the nuts for fixing the gland, tighten the nuts evenly to prevent the gland from a deflection. After tightening the nut, check whether the gap between the gland and the shaft is even. If there is a gap, it needs to be disassembled and adjusted to avoid spraining the seal.

  10. After installing, assemble the rest of the pump. Rotate the pump shaft to check whether there is friction between the static ring, the gland and the shaft sleeve, and between the rotating part and the sealing cavity. The pump shaft should feel evenly exerted after one revolution. If the shaft cannot be rotated, or the local force is too strong during one revolution, check whether there is an installation problem with the seal. If necessary, disassemble the pump to find the problem and reinstall it.

  11. Connect the pipeline of the sealing auxiliary system according to the pump or seal work drawing. At the same time, it is necessary to ensure that the piping system is clean and the working environment of the double mechanical seal is tidy. Pay attention to the piping arrangement to prevent local trapped gas from affecting the circulation.

 

The above is all our knowledge of installing dual mechanical seals, including the preparations to be done before installing the double mechanical seal, the necessary system conditions for the mechanical seal, and the detailed installation steps. If you want to know more information about other mechanical seals, please contact us now! 

 

Wendong is a professional mechanical seals company and mechanical seals distributor in China, having experienced workers and providing high-quality various mechanical seals.


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