What Is a Bleeder Screw? Definition, Meaning and Concept

A bleeder screw is a screw that allows people to relieve pressure from a closed system by turning it to create a small outlet. This is known as "bleeding" the system, and when the bleed is done, the bleeder screw can be tightened to close the system again. A classic example can be found in steam radiators in many regions of the world. They can also be seen in pressurized systems like car brakes, as well as other types of hydraulic systems.

The bleeder screw typically has a specialized head to distinguish it from other system components. People may need a key or special tool to open it, depending on the design. This ensures that it can only be opened when needed and not accidentally released. For radiators, a small wrench is commonly used to loosen the bolt.

Closed systems can become contaminated over time as the seal is not perfect. Water, air, and other materials can get in, making the system less effective and causing problems like shock and poor performance. The user needs to bleed the lines to relieve excess pressure and remove the contaminant. Air in a radiator, for example, can prevent fluid circulation and keep the unit cool. Brake fluid can collect water over time or air can end up in the lines after a service appointment.

Bleeding is often difficult, as the contents of the system can squirt out under high pressure. The user can place a bag or container around the opening to catch the spray and minimize mess, especially if the contents of the system are potentially toxic. Once the system is fully vented, the operator can tighten the bleeder screw. It is important to use the proper tool to avoid removing it, as this could make it difficult or impossible to open the system again in the event of a repeated pressure build-up.

Spare bleeder screws are available, in case someone strips, loses, or damages a screw. It is important to get the correct size one to make sure the seal is tight. Many companies produce standardized screws and openings, and people are welcome to bring in the old screw, if possible, to compare with available replacements. It is also possible to order a replacement part directly from the original manufacturer to ensure it is the correct component. In cases where it is impossible to remove an old screw, it is possible for a technician to drill a new hole in the system and install a replacement screw.