High Precision Copper Capillary Tubes
Copper tubes are easy to install, inexpensive to transport and have long life spans with low maintenance. Because they are compatible with a large range of liquids and are so resistant to a wide variety of environmental conditions, tubes made of copper provide a long term performance that is extremely cost effective over long periods of time. They form piping systems both above and below ground, in freezing temperatures as well as in high heat applications. Fire sprinkler systems, cryogenic plants, air conditioning and refrigeration systems, hospital oxygen systems, gas and steam heating systems and drain/vent systems all use copper tubes as pipes. They also take up less space than other metal pipes.
How Capillary Tube Works?
When the refrigerant leaves the condenser and enters the capillary tube its pressure drops down suddenly due to very small diameter of the capillary. In capillary the fall in pressure of the refrigerant takes place not due to the orifice but due to the small opening of the capillary.
The decrease in pressure of the refrigerant through the capillary depends on the diameter of the capillary and the length of the capillary. Smaller is the diameter and more is the length of the capillary more is the drop in pressure of the refrigerant as it passes through it.
In the normal working conditions of the refrigeration plant there is drop in pressure of the refrigerant across the capillary but when the plant stops the refrigerant pressure across the two sides of the capillary equalize. Due to this reason when the compressor restarts there won’t be much load on it. Also, due to this reason one cannot over-charge the refrigeration system with the refrigerant and no receiver is used.
The capillary tube is non-adjustable device that means one cannot control the flow of the refrigerant through it as one can do in the automatic throttling valve. Due to this the flow of the refrigerant through the capillary changes as the surrounding conditions changes. For instance as the condenser pressure increases due to high atmospheric pressure and the evaporator pressure reduces due to lesser refrigeration load the flow of the refrigerant through the capillary changes. Thus the capillary tube is designed for certain ambient conditions. However, if it is selected properly, it can work reasonably well over a wide range of conditions.
The length of the capillary of particular diameter required for the refrigeration applications cannot be found by fixed formula rather it is calculated by the empirical calculations. Some approximate length required for certain application is found out and it is then corrected by the experiments.
Important Points to Remember when Installing Refrigeration Plants with Capillary Tube
Since the pressure on the two sides of the capillary equalizes when the refrigeration plant is stopped, one should not overcharge the system with the refrigerant. Due to this reason the receiver is also not installed in the refrigeration system with the capillary. If the system is overcharged the discharge pressure from the compressor will be high and the compressor would get overloaded. Thus the refrigerant charge in the refrigeration and air conditioning systems with the capillary tube is critical.
The technician should be very careful while brazing the capillary to the condenser and the evaporator coil. Since the diameter of the capillary is very small the capillary may get blocked if the brazing is done deep inside. Brazing the capillary requires lots of expertise and patience.
In most of the cases, when the fresh refrigerant is charged into the refrigerator or the deep freezers, the capillary of the system should also be changed. This is because when the machine is stopped some oil particles may clog the capillary as the refrigerant leaks to the atmosphere.