In general terms, a flow restrictor does just that … restricts the flow of gas or liquids. They can be made from a variety of metals, metal alloys, and plastics.      Hydronamic Engineering Corporation uses a stainless steel material in the fabrication of its orifice-style metering device. This is done as an in-house manufacturing operation where Hydronamic Engineering controls product quality from punching out the die-cut orifice from the stainless steel material to determining and calibrating the desired rate of flow restriction.      The mls/minute rate of flow restriction is initially established by sample testing restrictors assembled to meet a particular ml flow restriction. Testing is done in house at a static flow rate of 60psi using lab-quality graduated cylinders. Once the rate of flow restriction (in milliliters) has been fixed and verified, it is easily duplicated (within ±10 percent) using custom tools to effect the opening in the formed stainless steel orifice. A chart that shows static and dynamic flow rates, pressure drop, variance, and the custom tool to be used for each established restrictor rating is used for reference. Additionally, Hydronamic Engineering does random testing with each batch of restrictors assembled to maintain its high level of quality control and product excellence.      Currently Hydronamic Engineering has an available range of flow restrictors from 150ml to 3300ml generally at in-between increments of 50mls. The larger restrictors may or may not be assembled with pre- or post-filters depending on the design.      Orifice metering by its very design tends to have a high rate of accuracy and, most importantly, repeatability in a flow restrictor appliance. In addition, Hydronamic Engineering relies heavily on its testing and quality control procedures to ensure a quality product and preserve customer satisfaction and confidence.