What is the function of capillary tube in refrigeration, Air conditioning

--Key Roles in Throttling, Pressure Reduction & Refrigerant Flow Metering

Learn the critical functions of capillary tubes in HVAC/R systems. 

This guide explains their role in pressure control and flow metering for stable, efficient cooling.

In refrigeration and air conditioning systems, capillary tubes, as throttling elements, play a crucial role in controlling refrigerant flow and balancing system pressure. This article will clearly explain the functions of capillary tubes, helping you understand how they ensure stable and efficient operation of the entire system.

Throttling & Pressure Reduction Function

When high-temperature, high-pressure liquid refrigerant from the condenser flows through a narrow capillary tube, its pressure drops rapidly due to the significant flow resistance created by the extremely small tube diameter. This process is crucial because only when the refrigerant's pressure is reduced to its evaporation pressure can it boil (evaporate) at a low temperature in the subsequent evaporator. During evaporation, the refrigerant absorbs heat from the surrounding environment, thereby achieving the core purpose of cooling or heating.

Refrigerant Flow Metering Function

Because capillary tubes have no moving parts, flow control relies entirely on their fixed physical properties: precise inner diameter and length.

Under specific system operating conditions (i.e., a fixed high and low pressure differential), a capillary tube of a specific specification can only allow a specific mass of refrigerant to pass through. This design ensures that, during stable operation, the refrigerant quantity entering the evaporator matches the compressor displacement, maintaining system balance and design efficiency.

Why use capillary tubes in specific systems?

In addition to fulfilling the two core functions mentioned above, capillary tubes are widely adopted due to their simplicity, low cost, high reliability, and automatic pressure balancing.

MTSCO's Capillary Tube Solutions

To ensure that capillary tubes accurately perform their throttling and flow control functions, manufacturing tolerances and material purity are crucial. MTSCO's Siri Tubing facility manufactures capillary tubes, which are ISO/PED certified and 100% high-pressure tested (up to 15,000 psi), suitable for the rigorous operating conditions of refrigeration and air conditioning systems. We provide stable and reliable metal tubing support to customers worldwide.