Gate Valve Maintenance Quality Standards

Gate Valve Maintenance Quality Standards

3.1 Valve Body:

3.1.1 The valve body should be free from sand holes, cracks, erosion, and other defects. If any are found, they should be addressed promptly.

3.1.2 The valve body and internal piping should be free of debris, and the inlet and outlet should be unobstructed.

3.1.3 The bottom plug of the valve body should ensure a reliable seal, with no leakage.

3.2 Valve Stem:

3.2.1 The deflection of the valve stem should not exceed 1/1000 of its total length. If it does, the stem should be straightened or replaced.

3.2.2 The trapezoidal threads of the valve stem should be intact, with no broken or jammed threads. The wear on the threads should not exceed 1/3 of the thickness of the trapezoidal threads.

3.2.3 The surface should be smooth, free from rust or scale, and there should be no flaky corrosion or surface delamination in the area where the stem contacts the packing seal. Any corrosion deeper than 0.25 mm should result in replacement. The surface finish should meet a roughness of Ra 6 or better.

3.2.4 The connection threads should be intact, and the pins should be securely fixed.

3.2.5 After assembly with the valve stem nut, the valve stem should rotate smoothly, without binding, throughout its entire stroke. The threads should be lubricated with lead powder for protection.

3.3 Packing Seal:

3.3.1 The packing material should meet the pressure and temperature requirements for the valve’s medium, and the product should be accompanied by a certificate of conformity or undergo necessary testing.

3.3.2 The packing specifications should match the size requirements of the sealing chamber. Overly large or small packing should not be substituted, and the packing height should conform to the valve’s dimensional requirements, leaving adequate thermal expansion clearance.

3.3.3 The packing joints should be cut at a 45° angle, and the joints of each ring should be staggered by 90°–180°. The cut length of the packing should be appropriate, and there should be no gaps or overlapping at the joint when placed into the packing chamber.

3.3.4 The packing seat ring and packing gland should be in good condition, free from rust or scale. The inside of the packing chamber should be clean and smooth, with a gap of 0.1–0.3 mm between the stem and the seat ring, not exceeding 0.5 mm. The gap between the packing gland, seat ring, and the inner wall of the packing chamber should be 0.2–0.3 mm, not exceeding 0.5 mm.

3.3.5 After tightening the hinge bolts, the pressure plate should remain flat, with even tightening force. The clearance between the pressure plate’s inner hole and the valve stem should be uniform. The packing gland should occupy 1/3 of the height of the packing chamber when inserted.

3.4 Sealing Surface:

3.4.1 After maintenance, the sealing surfaces of the valve disc and valve seat should be free from spots, grooves, and should occupy at least 2/3 of the valve seat width. The surface finish should meet a roughness of Ra 10 or better.

3.4.2 During assembly, when the valve disc is inserted into the valve seat, the valve stem should be raised by 5–7 mm above the seat to ensure a tight closure.

3.4.3 When assembling the left and right valve discs, they should adjust flexibly on their own, and the anti-drop mechanism should be intact and reliable.

3.5 Valve Stem Nut:

3.5.1 The internal sleeve threads should be intact, without broken or misaligned threads. The connection to the outer housing should be secure, with no loosening.

3.5.2 All bearing components should be in good condition and rotate smoothly. The inner and outer sleeves, as well as the steel balls, should be free from cracks, rust, or significant surface defects.

3.5.3 The coil spring should be free from cracks or deformation; otherwise, it should be replaced.

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