What Is a Suction Line?

A suction line is a pipe, hose, or tube that delivers a fluid to the suction or inlet side of a pump or compressor. These sorts of devices are used in a variety of different settings, and can look and function slightly differently depending on the core machine at issue. In general, these lines supply fluids for chemical processing, refrigeration systems, and vacuum pump applications, and can also provide fluids key to oil and water well drilling. They can be thin or thick, long or short; some or optimized for harsh or corrosive fluids, while others carry primarily water. The lines can deliver basically any product that a pump or compressor can handle, including gases and petroleum products. Well drilling mud or other liquid-solid mixtures may also be transported in this way, along with adhesives and epoxies.

The main job of any suction hose or line is to help facilitate the movement of fluids from one place to another. There are usually several reasons why this is important. Fluids are often used as coolants, and may also be used as a source of energy. In storage situations, the lines can act as dispensers, allowing operators to test or release certain measured amounts without disrupting the main well. Lines often look like simple tubes, but they’re almost always pressurized and can usually work as valves, stopping or alternatively triggering flow. When they’re working properly, they can regulate temperature and pressure with a great deal of precision.

Design of suction lines involves both a determination of required flow and adequate pressure drop to prevent what’s known as “starvation” of the pump or compressor. The viscosity or thickness and the weight of the fluid being pumped are key variables for design. Often, design engineers are concerned with net positive suction head. This means having enough positive pressure of fluid at the pump suction to prevent the formation of gas bubbles, called cavitation, which can damage a pump.

Pump suction can be compromised if the supply point for the pump is lower in elevation than the pump or if the suction lines are too small. Also of concern, a large number of fittings or bends can cause pressure to drop, and incorrect sizing can also compromise suction. Regular maintenance of suction devices such as filters or traps is usually recommended to prevent clogging and starving the pump.

Oil drilling makes use of suction line piping to supply drill mud to the rig. Drill mud is a mixture of clay and water that's used to cool and lubricate the drill head, and to remove waste material from the drill hole. A mud pit or mud tank holds the drill mud, and a line of suction is connected from the mud tank to the mud supply pump to supply pressurized mud to the drill assembly.

Chemical processing may involve the pressurization and movement of gases or liquids. The gas compressor or liquid pump takes material from storage or an earlier processing step through a line, discharging the fluid to a downstream processing step or storage. Many liquid chemicals can vaporize easily if positive pressure is not maintained on the pump, so a suction tank may be installed prior to the line to ensure adequate pressure and supply.

Refrigeration and air conditioning systems also use these lines to deliver refrigerant gas from the evaporator to the compressor. Most refrigeration systems circulate a mixture of refrigerant liquid or gas and a liquid lubricating oil for the compressor. Reciprocating compressors can be damaged by excess liquid returning through the line, so an accumulator is normally added to trap liquid and provide a more constant liquid flow.