NCCER Millwright Practice Exam

If the discharged air of a reciprocating compressor is below its rated capacity, what could be a possible cause?

1. Blocked air filter

2. Low oil level

3. Worn piston rings

4. Improper voltage supply

The correct answer is: Worn piston rings

In a reciprocating compressor, the efficiency and capacity of the discharge air depend on several factors, one of which is the condition of the piston rings. Worn piston rings can lead to a loss of compression. When the rings are worn, they no longer create a proper seal between the piston and the cylinder wall. This wear allows air to leak past the piston during the compression stroke, reducing the amount of air that is effectively compressed and discharged. As a result, the discharged air falls below the compressor’s rated capacity. While other factors such as a blocked air filter, low oil level, or improper voltage supply can impact the overall performance of a compressor, they do not directly affect the sealing mechanism between the piston and the cylinder in the same manner. A blocked air filter might restrict airflow, causing performance issues, but this does not specifically relate to capacity being lower than rated. Similarly, low oil levels may lead to inadequate lubrication, which can cause operational problems but won't necessarily result in reduced discharge capacity as a direct consequence. Improper voltage supply can result in operational failures or reduced efficiency, but the direct effect on discharge air capacity is not as pronounced as with worn piston rings. Thus, the specific issue of worn piston rings directly leading to decreased discharge capacity