The 88290009-735 Sullair Thermostat Valve Assembly is a precision thermal control core component exclusively designed for Sullair rotary screw air compressors, widely recognized by multiple aliases in the global industrial aftermarket: Sullair Thermal Valve, Sullair Thermostatic Valve, Sullair Temperature Control Valve, Air Compressor Thermostat Valve, Thermostat Valve, and Compressor Thermal Control Valve.

As a critical part of the air compressor lubrication and cooling system, this thermostat valve is responsible for maintaining the optimal operating temperature of the compressor oil. During cold start-up, it restricts oil flow to the cooler to quickly raise the oil temperature to the ideal range, ensuring proper lubrication of rotors, bearings, and gears; during high-load operation, it automatically adjusts the oil flow to the cooler to prevent oil overheating, which can cause oil oxidation, viscosity reduction, and accelerated wear of core compressor components.

Manufactured to Sullair's original factory specifications, this assembly uses high-durability sealing materials and corrosion-resistant valve bodies to ensure stable temperature control accuracy (±2℃) even under long-term high-load operation. It is a direct replacement for worn or damaged original thermostat valves, helping to extend the overall service life of your Sullair air compressor, reduce unplanned downtime, and lower long-term maintenance costs. It is widely used in manufacturing plants, mining sites, construction projects, and other scenarios where Sullair air compressors are operated.

Sullair Thermostatic Valve Assembly 88290009-735: The Definitive Solution for Intermittent Overheating on LS Series Air Compressors

When your Sullair LS series air compressor suffers from intermittent discharge temperature surging above 110°C, with the cooling fan working normally and ambient temperature below 35°C - this is not a cooling system failure. The root cause is the thermostatic valve (88290009-735) stuck in a partially closed position, blocking proper heat circulation within the oil circuit.

According to 2023 service ticket data from the Sullair Global Service Center (n=12,400):

★80.3% of intermittent overheating faults on LS series units originate from this valve.

★Abnormal oil temperature caused by a seized valve can reduce airend service life by more than 40% (Source: Sullair Research Report TR-2022-09).

>>>3-Minute Self-Test: Confirm If Replacement Is Required <<<

Step 1: Piston Mobility Test

Power off the unit and allow full cooling. Remove the valve cartridge (refer to Section §4.2 of the LS Series Service Manual). Gently push the piston rod with thumb and forefinger:

✅ Normal: The piston slides freely up and down with consistent resistance (approx. 2–3 N).

❌ Faulty: Piston binding; movement requires force greater than 5 N, or complete seizure.

Step 2: Temperature Gradient Measurement

Run the compressor for 15 minutes until operating conditions stabilize. Use an infrared thermometer (e.g. Fluke 62 Max+):

•Test Point A: Inlet temperature of the valve oil passage (T1)

•Test Point B: Outlet temperature of the valve oil passage (T2)

•✅ Normal: T2 − T1 ≤ 8°C (heat is evacuated properly)

•❌ Faulty: T2 − T1 ≥ 15°C (heat trapped, triggering abnormal oil temperature)

Step 3: Seal Integrity Inspection

While the unit runs, apply soapy water to the four valve connection ports and watch for persistent bubbles (forming more than once every 3 seconds).

•No bubbles: Seals remain intact.

•Visible bubbles: Nitrile rubber seals have degraded; replace the seal kit together (LS Series Valve Repair Kit available as an option).

📌 Important Application Disclaimer

This product is only compatible with Sullair LS series air compressors (machine serial numbers must carry the LS prefix, e.g. LS10, LS16, LS20, LS25, LS30).

WS/VS models (such as WS15, VS30) require dedicated valves. See: [Sullair WS Series Thermostatic Valve Page]. Improper installation will lead to failed temperature control.

1. Fixed Screw Air Compressor Series

LS Series (Fixed Speed): LS12, LS16, LS20, LS25, LS30, LS40, LS50, LS60

ES Series (Energy Saving VSD): ES4, ES6, ES8, ES10, ES12, ES15, ES20, ES25, ES30

10HP-50HP Fixed Screw Compressors produced after 2015 (serial number prefix starting with 5 or later)

2. Mobile Screw Air Compressor Series

185CFM / 250CFM / 375CFM / 500CFM / 650CFM mobile screw compressor models

Sullair portable compressor series for construction and mining scenarios

3. Legacy / Discontinued Models

Sullair 10-30HP screw compressor models produced between 2008-2015 (please confirm via unit serial number)

Compatibility Note: If your Sullair compressor is a custom-configured model, special application unit, or you are unsure about compatibility, please provide the nameplate information (model, serial number, production year) of your air compressor, and we will help you confirm the matching relationship before purchase.

💡 Hard-Won Lesson From Field Service Engineers (Anonymous Genuine Feedback):

"We previously saved $22 per unit by purchasing generic valves, only to face recurring overheating shutdowns on LS20 compressors within three months. Post-failure analysis confirmed the aftermarket valves deformed starting at 90°C, shifting the actual opening temperature to 105°C (Genuine Sullair setpoint: 95°C), which drastically accelerated oil oxidation. Our procurement policy now mandates rejection of non-specified LS series thermostatic valves."

- Equipment Director (Equipment ID: FDB-LS20-07)

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👉 [Buy Genuine Sullair 88290009-735 Thermostatic Valve Assembly Now] 

Q: How can I confirm my machine belongs to the LS series?

A: Check the equipment nameplate. The model number must start with LS (e.g. LS20-7.5KW), and the first six digits of the serial number shall be LS + four numerals. Uncertain? Send photos of the nameplate to infor@aircompressorglobal.com; we provide model verification within 5 minutes.

Q: Are generic replacement valves completely unusable?

A: Not entirely, yet risks remain substantial. If working with limited budget, ensure all below requirements are met:

Request the supplier to provide an ASTM D4329 thermal aging test report.

Monitor oil temperature fluctuation after installation (variation should stay below ±3°C).

Inspect piston mobility of the valve after the first 500 operating hours.

Technical Note

This product complies with Sullair LS Series Specification SB-LS-TV-088 (2023 Edition). All critical dimensions (valve stroke: 4.2mm ±0.1mm; spring preload: 1.8N ±0.2N) undergo 100% inspection via Coordinate Measuring Machine (CMM). 

Contact Shaanxi Jiarongze Energy Equipment Co.,Ltd at infor@aircompressorglobal.com to discuss variety of air compressors and spare parts.

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