 Welcome back MechanicalEI! Did you know that valves are found in virtually every industrial process including water processing and power generation? This makes us wonder, what are valves? Before we jump in, check out the previous part of this series to learn about what pipe joints are. Now, a valve is a device that regulates, directs or controls the flow of a fluid by opening, closing or partially obstructing various passageways. There are three basic types of valves. First is the shut off valve which helps to control the escape or entrance of fluid into a plumbing system or gas line. These valves can save time by helping provide quick and easy turn on and off. Second comes the check valve or non-return valve which is a valve that allows fluid to flow through it in only one direction. An important concept in check valves is the cracking pressure which is the minimum differential upstream pressure between inlet and outlet at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure. Shown here is a check valve deployed beside a shut off valve used for domestic heating purposes. A gate valve can be defined as a type of valve that uses a gate or wedge type disk and the disk moves perpendicular to the flow direction of fluid to start or stop the fluid flow. A gate valve is the most common type of valve that is used in any process plant. In service, these valves are either in fully open or fully closed position. When the gate valve is fully open, the disk of a gate valve is completely removed from the flow. Due to this, there is a very little pressure drop when fluid passes through a gate valve. Shown here are gate valves upon whom stem cap and T key are being installed for easy access while opening and closing the valve from a distance. Hence, we first saw what valves are, then saw what shut off and non-return valves are and then went on to see what gate valves are. So, here are the top mechanical EIs of our last videos. In the next episode of Mechanical EI, find out what major parts of an IC engine are.