Some points deserve repeating — and then repeating again. Few plants or “general purpose” machine shops can manufacture engineered replacement parts at a quality and cost competitive with those from an original equipment manufacturer (OEM). In extremely rare cases, delivery problems may justify trying to make parts locally. But even then, know exactly what you’re doing before you start. And realize that unless you’re experienced in making the specific type of engineered equipment you’re replacing, you’re highly unlikely to know what you’re doing. Failure will result. [pullquote] One plant that attempted to manufacture replacement spray nozzles learned that lesson. Effective spray nozzles are highly engineered. A specific nozzle has close fabrication tolerances to achieve the correct flow rate, pressure drop, spray pattern and droplet size distribution. Manufacturing efficiencies are high. Delivery times usually are short for all except nozzles of the most exotic materials. Indeed, expedited shipping can get parts for most applications to a site within one to two days. In spite of this, a few years ago the plant put homemade spray nozzles into heat-transfer service — spraying subcooled liquid into a vapor stream. The OEM nozzles cost around $50 each and are made of a standard-stock material considerably superior for the service than the material of the homemade replacement. They could have been delivered overnight. Figure 1 shows the fabrication drawing for the homemade spay nozzles. Given the components and labor required, they must have cost more than OEM ones and taken a significant time to make. The homemade version started with a ¾-in.-to-2-in. concentric diffuser. Three slots, each 1 9/16-in. wide and ¾-in. tall, were cut in the end. A welded-on ¼-in.-thick plate sealed the 2-in.-wide end of the diffuser. The dimensions shown on the drawing aren’t fully consistent and don’t agree with standard piping. For example, a ¾-in. schedule 40 pipe has an inside diameter of 0.824 in.