🔍 Key Concepts

• Properties of lubricants used on reciprocating (back-and-forth) motion parts • How different oils react with water, heat, and metal surfaces • Why some lubricants are better for reducing wear and preventing rust on exposed rods

💭 Think About

• Think about what happens to a pump rod that moves in and out of packing or guides all day long—what kind of lubricant will stay in place and still protect the metal? • Consider which option is least likely to wash away, gum up, or attract dirt, yet still provides a smooth sliding surface. • Ask yourself which lubricant is commonly used on sliding/reciprocating rods rather than on high‑speed rotating machinery.

✅ Before You Answer

• Compare which lubricant will resist being washed off by water or liquid being pumped. • Consider which lubricant is least likely to form sticky deposits or varnish over time on exposed rods. • Think about which choice is specifically suited to sliding surfaces rather than general engine lubrication.