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Maintenance requirements for various parts of chemical pump

Maintenance of chemical pump coupling

Chemical pump couplings mainly include rigid couplings and toothed couplings.
(1) Rigid coupling
Rigid couplings are generally used on centrifugal pumps with small power. During maintenance, first remove the connecting bolts and rubber elastic rings. For liquids with low temperature, the plane gap between the two couplings is 2.2 ~ 4.2mm. When the temperature is high, it shall be greater than the front displacement of 1.55 ~ 2.05mm. The rubber elastic ring of the coupling shall be 0.15 ~ 0.35mm smaller than the perforation diameter. At the same time, special tools must be used during disassembly and assembly to keep them clean and free of bumps and scratches.
(2) Toothed coupling
The toothed coupling has good flexibility and automatic centering performance. The maintenance is generally carried out according to the following methods:

  • ① Check the meshing condition of the coupling tooth surface, the contact area along the tooth height shall not be less than 50%, the tooth width shall not be less than 70%, and the tooth surface shall be free of serious pitting corrosion, wear and crack;
  • ② The radial runout of the outer gear ring of the stainless steel pump coupling shall not be greater than 0.03mm, and the end face circular runout shall not be greater than 0.02mm;
  • ③ If the gear ring needs to be removed, special tools must be used instead of knocking to avoid bending or damage to the shaft. When reassembling, heat the gear ring to about 200 ℃ and then install it on the shaft. The interference between the outer gear ring and the shaft is generally 0.01 ~ 0.03mm;
  • ④ When reassembling the intermediate barrel or other parts, it shall be assembled according to the original marks and data;
  • ⑤ Tighten the bolts evenly with the torque handle.

Maintenance of dynamic seal

The dynamic seal of centrifugal pump refers to the seal at the impeller mouth ring. Generally, the radius direction shall be controlled within 0.20 ~ 0.45mm. If the clearance is too small, it is difficult to turn after assembly; The clearance is too large, which is easy to cause pump vibration. The clearance radius direction of shaft sleeve and lining ring is generally 0.2 ~ 0.6mm.

Maintenance of static seal

The static seal part of the chemical pump includes the split joint surface of the pump body, the joint surface between the bearing gland and the bearing box, the joint of the lubricating oil system, the flange of the inlet and outlet pipe, etc. if the maintenance can not ensure no leakage, the pump can not run. The sealing of the above parts can ensure no leakage as long as the applicable adhesive and gasket are selected according to the medium. At present, the commonly used adhesive for split joint surface is NANDA 703 and NANDA 704.

Maintenance of impeller and rotor

Most of the commonly used corrosion-resistant chemical pumps are single-stage impeller or single-stage double suction rotor. During maintenance, first check the appearance of the impeller and clean it. Whether it is to replace spare parts, install a new impeller or clean the old impeller, static balance shall be done after reinstallation, and dynamic balance shall be done if necessary. The matching of impeller and shaft adopts H/h, and the key and keyway shall be in correct contact when installing the impeller. The allowable bending of the shaft diameter of the rotor shall not be greater than 0.013mm, the maximum bending of the low-speed shaft shall be less than 0.07mm, and the maximum bending of the high-speed shaft shall be less than 0.04mm. The assembly of shaft sleeve and shaft adopts H/h.
For the shaft of rotor part, after maintenance, the radial runout of shaft shall not be greater than 0.013mm, the shaft sleeve shall not be greater than 0.02mm, the impeller mouth ring shall not be greater than 0.04mm, and the end face runout of impeller shall not be greater than 0.23mm. The shaft diameter at both ends shall not be greater than 0.02mm. However, for the centrifugal pump with complex structure, the above data change according to the condition standard of the pump.

Maintenance of mechanical seal

During the maintenance of the mechanical seal of the chemical process pump, the dynamic and static rings of the mechanical seal shall be removed correctly with special tools, and the wear of the end face shall be checked. The dynamic or static balance test shall be conducted for the pump rotor installed with the mechanical seal regardless of the power. In order to ensure that the seal does not leak, the dynamic and static surfaces can be pressed on the fitter platform, and water can be poured for leakage test. If the static water does not leak, it indicates that the surface roughness and flatness of the sealing surface meet the requirements. During installation, the perpendicularity deviation of the end face shall not be greater than 0.015mm. The radial runout values of some shafts or shaft sleeves are shown in Table 5.

Speed/(r.min – 1) Radial runout tolerance/mm Speed/(r.min – 1) Radial runout tolerance/mm
7501200 ≤0. 08 35007200 ≤0. 03
12001500 ≤0. 06 720010000 ≤0. 02
15003500 ≤0. 05

After installation, the axial displacement of the shaft shall not be greater than 0.45mm. It should be emphasized that after the mechanical seal is installed as required, it must be turned, and check whether the cooling water part is reliable to prevent leakage or damage to the mechanical seal end face after rotation. The mechanical seals of pumps used in chemical plants are mostly single-stage, double-stage and series sealing arrangements, but no matter which sealing arrangement can have leakage.

(1) Pump single stage seal arrangement
During the installation of single-stage seal, the dynamic and static rings must be parallel, and the shaft sleeve and journal shall be free of burrs and scratches.
(2) Two stage sealing arrangement of pump

When installing the two-stage arrangement seal, ensure the size and clearance of the locating ring, and push it to the position at one time. The O-ring cannot fall out of the groove, otherwise the sealing surface of the mechanical seal will be damaged.

Source: Network Arrangement – China Pipe Fitting Manufacturer – Yaang Pipe Industry (www.epowermetals.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@epowermetals.com

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