The following set of formulas and charts have been formulated to be useful to the fluid power professional. The units provided are those commonly used in our industry and not necessarily the units used in engineering terms. For instance, air pressure-drop through a sharp-edged orifice is given in flow per minute based on the diameter of the orifice, instead of weight per second based on the area of the orifice opening. Each chart shows the equation(s) used in both metric and US Customary units.
A “K” value (constant) is often provided to solve the equations. This “K” value has been derived by reducing the formulas and combining all the constants to simplify the equation. As a result, some of the “K” values may be different than in some commonly used equations. For example, the common equation for finding the velocity of fluid in US Customary terms is , where V = velocity in inches/sec, Q = flow rate in gpm, A = the inside cross-sectional area of the tube and K = 0.3208. In practice, we are usually given the inside diameter of the tube or hose and so the area must first be calculated before the common equation can be used. By changing the formula to Q = K x V x dsq, the K value changes to 0.204 and the equation can be solved without having to first find the area. The engineer who may want to see the entire justification for the “K” values may be disappointed, but the charts are intended for ease of use, not for detailed analysis. If someone wants to know how the “K” values were derived, just drop me a note and I will respond.
Disclaimer: Information and any recommendations set forth at this website are offered free of charge and are designed for persons having some knowledge and technical skill regarding hydraulics and pneumatics. While effort has been made to provide accurate equations and explanations, additional information may be required when making decisions based on the data supplied here. In addition, new information or corrections may not immediately be reflected at the website. The information and recommendations are furnished only on the condition that the reader assumes full responsibility for any use that may be made of it. Your use of this website is at your own risk.