Cap
Cap turns up in 3 fields: welding, HVAC, geosynthetics. Here is what it means to the people in each one.
Cap in welding
Shop word for the final layer of passes on the face of a groove weld, the cover pass in code language.
Last pass or passes that finish the weld face, set the reinforcement height and tie into both edges of the bevel. On pipe it is laid with weaves or overlapping stringers a little wider than the groove. The cap is what inspectors and customers see first, and codes limit reinforcement height, undercut and overlap at its toes.
"Cap it with stringers, the WPS limits the weave to three rod diameters."
Cap in HVAC
Short for capacitor, the part that gives compressor and fan motors the phase shift they need to start and run.
Run caps stay in the circuit and are rated in microfarads, often a dual cap serving both compressor and fan, such as 45 and 5 MFD, typically within plus or minus 6 percent. Start caps give a brief boost and drop out. A weak or failed cap is one of the most common no-cool calls: the motor hums, overheats or won't start. A bulged top is a sure giveaway, but techs test with a meter rather than trusting looks.
"Fan's not spinning and the compressor's tripping on overload, cap reads 28 on the 45 side, there's your problem."
Cap in geosynthetics
Final cover system placed over a closed landfill or waste area to keep water out and control gas.
A typical cap stacks a gas venting layer, a barrier such as LLDPE geomembrane or a GCL, a drainage layer and cover soil that supports vegetation. It must tolerate settlement as the waste decomposes, so flexible geomembranes and textured surfaces for slope stability are common. Caps usually fail by sliding on a weak interface, losing cover soil to erosion or drowning a drainage layer in storm water.
"Cap goes in this summer, 40-mil textured LLDPE with a drainage composite and two feet of cover."