Core features of the LN87 series sleeve control valve in China: High-pressure compatibility, sealing performance and fault diagnosis

Core features of the LN87 series sleeve control valve in China: High-pressure compatibility, sealing performance and fault diagnosis

Product Positioning

The LN87 series sleeve control valves of China are a new generation of balanced cage-type control valves specifically designed for high-pressure difference, high-temperature, and high-noise working conditions. They cover the9 full range from DN25 to DN400 and from PN25 to PN420 (Class 150-2500), and are widely used in key positions such as the main feedwater of thermal power plants, LNG high-pressure transportation, black water from coal chemical industry, and gas injection on offshore platforms. The keywords "China LN87 series sleeve control valves" have become a frequent focus in search engines and bidding documents for domestic substitution and energy-saving and noise reduction projects.

Core Technologies for High-Pressure Adaptation

. Four-stage labyrinth sleeve

• Each stage's pressure reduction ratio ≤ 1/4, the maximum allowable pressure difference is 40 MPa, the outlet flow velocity is < 30 m/s, fundamentally suppressing cavitation and flash evaporation.
• The labyrinth discs are made of Inconel 625 laser etched, with a thickness of only 0.8 mm, and the anti-corrosion life is ≥ 70,000 h.

. Pressure balance seal

• The difference in the area of the valve core top and bottom is < 3%, the thrust is 60% lower than that of a single-seat valve, and with the selection of a rocker-type or rocker-wheel-type pneumatic actuator, it can be driven, saving 30% of air source consumption.
• Double sealing with piston ring and graphite enhanced ring, the leakage level can be selected as ISO 5208 A grade (zero leakage) or API 598 soft seal VI grade, suitable for SIL 3 safety circuits.

. High-pressure self-sealing valve cover

• The higher the pressure, the tighter the seal; at the maximum design pressure of 42 MPa, the pad pressure is ≥ 200 MPa, and no secondary tightening is required.
• The valve cover and bracket are formed by one-piece forging, avoiding flange leakage caused by high-temperature and high-pressure alternating stress.

. Quick replacement structure

• The design of the pressure plate + U-shaped groove allows for on-site replacement of the sleeve in 5 minutes, suitable for maintenance windows with extremely short time in scenarios such as offshore platforms and underground wellheads.

Sealing Performance Test Data

At a temperature of -196 ℃ in liquid nitrogen conditions, the China LN87 series sleeve control valve maintains pressure for 30 minutes, with a leakage volume of < 0.6 mL/min, which is superior to the ISO 15848-1 BH level standard.

In a 400 ℃ superheated steam condition, after continuous operation for 8000 hours, the concentration of the effusion at the valve stem packing area is < 1×10⁻⁴ mg/(s·m), meeting the latest EPA 40 CFR Part 60 environmental emission requirements.

Selecting Table for Speed Calculation

DN | Kv max | Allowable ΔP (MPa) | Noise reduction (dB(A)) | Recommended actuator

25 10.5 35 -18 LPD-160 50 34 35 -20 LPD-280

100 135 30 -22 LPD-630

200 550 25 -25 LPD-1000

≥300 1000 20 -28 LPD-1600+ Compressed Air Tank

Installation and High-Pressure Commissioning Process (Key Words Repeatedly Inserted)

. Welding end bevels in accordance with ASME B16.25 U-type, argon arc base welding, post-weld heat treatment at 620 ℃ for 2 hours, Brinell hardness ≤ 200 HB, to prevent stress cracking of the valve body welds in the Chinese LN87 series sleeve control valve.

. Hydrostatic strength test 1.5×PN, hold pressure for 30 minutes; gas tightness 0.6 MPa ammonia leak detection, detection rate ≤ 1×10⁻⁶ Pa·m³/s.

. Cold-state no-load: five-point deviation from 0-25-50-75-100%, linear error ≤ ±1%.

. Hot-state with load: temperature rise at 2 ℃/min to rated temperature, actuator air source pressure step ±10%, valve position stable time <2 s, overshoot ≤ 2%.

. Anti-condensation: add valve stem electric heating in cold regions, maintain surface temperature >5 ℃, to avoid the packing of the Chinese LN87 series sleeve control valve freezing and causing leakage.

List of Common Fault Location

Fault phenomenon → Possible cause → Troubleshooting method → Resolution cycle

. Valve position oscillation

• Proportional band of the positioner too low → Set the hand controller to PB ≥ 8% → 10 minutes
• Hole erosion of the sleeve causing gain drift → Inspect the edge round corner of the endoscope > 0.3 mm → Replace the labyrinth disc → 30 minutes

. High-pressure difference whistling

• Outlet flow velocity > 120 m/s → Need to add a diffuser for ultrasonic thickness measurement < 3 mm → Install downstream orifice plate → 2 hours

. Zero leakage failure

• Gap of the piston ring → Check the misalignment of the ring opening should be <1 mm → Replace the new Inconel ring → 45 minutes

. Actuator thrust insufficient

• Air source moisture freezing → Check the pressure drop of the three-way assembly > 0.15 MPa → Replace the dry filter → 20 minutes

. Hot-state jamming

• Thermal expansion difference between the valve stem and the sleeve → Measure the gap with laser < 0.05 mm → Perform online grinding of the packing sleeve → 1 hour

Preventive Maintenance and Longevity Tips

. Perform actuator cleaning monthly： Open the bottom screw plug to discharge condensate water to prevent ice blockage of the gas path in winter for the Chinese LN87 series sleeve control valve.

. Conduct wall thickness scanning quarterly： UT thickness measurement focuses on the 0-2 points of the labyrinth section， a reduction rate > 20% indicates inclusion in the replacement plan.

. Perform self-calibration of the positioner annually： Use the Smart+ APP to automatically set， record the deviation curve to warn of wear.

. Conduct annual spectral verification： Perform PMI component re-inspection on the valve core and sleeve to prevent hardness reduction > 8% due to mixed materials.

. Recommended spare parts package： Keep 1 set of labyrinth disc + 1 pair of piston rings + 2 pieces of graphite packing on hand. Any high-pressure leakage at the site can be restored within 1 hour to ensure the online rate of the Chinese LN87 series sleeve control valve ≥ 99.5%.

Conclusion

Whether it is the 40 MPa feed water for ultra-supercritical units or the -196 ℃ LNG high-pressure transportation， the Chinese LN87 series sleeve control valve， with its four-level labyrinth pressure reduction， zero-leakage sealing， and five-minute quick repair structure， has become a benchmark product for domestic control valves in high-pressure conditions. If you are searching for technical samples， 3D models， or SIL certification documents of "Chinese LN87 series sleeve control valve"， please download immediately or call the official hotline. Let our high-pressure application engineers customize an energy-saving， noise reduction， long-life， and zero-emission complete solution for you！