1. Basic Structure Overview

The complete valve set consists of four key components:

1. Temperature bulb (sensing probe): Immersed in the controlled medium to detect temperature, filled with temperature-sensing liquid inside;
2. Capillary tube: Sealed pressure transmission line, transferring pressure generated by expansion or contraction inside the bulb to the actuator head;
3. Actuator and spring assembly: The sensing pressure counteracts spring force to drive the valve stem;
4. Valve body and plug: Throttling parts to control the flow of heating or cooling medium.

The target set temperature can be preset via the adjusting knob on the top.

2. Heating Type Self-operated Temperature Control Valve｜Valve closes as temperature rises

Heating types are commonly installed on pipelines carrying heating media such as steam, hot water and thermal oil. Its purpose is to maintain the controlled medium at the set value: the higher the temperature, the more the valve closes.

✅ Operating sequence:

• When controlled temperature ＜ set temperature: The sensing liquid inside the bulb contracts, and the thrust transmitted to the actuator drops. The return spring pushes the valve plug open to increase the flow of heating medium, heating the system and raising the temperature.
• When controlled temperature = set temperature: The expansion force balances the spring force, and the valve plug stays at a fixed opening to maintain constant temperature.
• When controlled temperature ＞ set temperature: The sensing liquid expands upon heating, pressure rises and overcomes the spring force to throttle the valve plug, reducing steam or hot water flow and stopping further temperature increase.

👉 Simple rule: Opens at low temperature, closes at high temperature, for heating medium control. 👉 Typical applications: Constant temperature control for heat exchangers, storage tank tracing, heat exchange units for heating, domestic hot water systems.

3. Cooling Type Self-operated Temperature Control Valve｜Valve opens as temperature rises

Cooling types are used for cooling media such as cooling water and chilled water. Its operating logic is the opposite of the heating type: the higher the temperature, the more the valve opens, increasing the flow of cooling medium to remove heat.

✅ Operating sequence:

• When controlled temperature ＜ set temperature: The sensing liquid contracts, thrust decreases, and the spring closes the valve plug to reduce cooling water supply and prevent overcooling.
• When controlled temperature = set temperature: The expansion pressure balances the spring force, and the valve plug remains stable.
• When controlled temperature ＞ set temperature: The temperature bulb expands under heat, pushing the valve plug open to increase cooling water flow and rapidly remove heat to bring temperature back to the target range.

👉 Simple rule: Closes at low temperature, opens at high temperature, for cooling medium control. 👉 Typical applications: Lubricating oil cooling, hydraulic station cooling, process medium cooling, jacket water temperature control for engines.

4. Comparison: Heating Type vs Cooling Type

表格

⚠️ Key note for selection: The valve bodies look almost identical. The difference lies in the internal actuator action mode and spring configuration. You must clearly specify heating type or cooling type when placing orders. Wrong selection reverses the control logic and may cause process runaway and overtemperature accidents.

5. Advantages and Limitations of Self-operated Temperature Control Valves

✅ Advantages

1. Energy-independent operation: Works without electricity or instrument air, ideal for explosion-proof zones, remote sites and pump houses with no power supply.
2. Simple and reliable structure with low failure rate and low maintenance cost.
3. Built-in proportional regulation for small temperature fluctuation, easy installation and commissioning.

⚠️ Limitations It is a mechanical proportional regulator. Not suitable for conditions with sharply fluctuating heat load or high-precision control (within ±0.5℃). For such cases, electric temperature control valves paired with temperature transmitters and closed-loop control are recommended.

6. Summary

Heating type and cooling type self-operated temperature control valves share the same fundamental physical principle — thermal expansion and contraction of sensing fluid. The essential distinction is the opposite direction of valve plug movement:

• Heating type: Close when hot, reduce heating medium supply;
• Cooling type: Open when hot, increase cooling water supply.

During selection for chemical, thermal, oil & gas and metallurgical projects, do not rely only on model numbers. Always verify the action mode and confirm fail-open / fail-close status according to safety requirements upon loss of control.