In order to most effectively work with valves, you need to know the most important components of valves. Valves are assembled products that consist of 7 major parts so today, you will learn about the different parts and what each component does.

Valve Body

The valve body not only houses other valve parts including the disk and seat but it also is the main pressure-retaining part of the valve. It is also where fluid passes through the valve as both ends of the valve body are connected with piping. The ends can either be threaded or flanged or finished with butt-welding types that depend on the size and pressure of the piping system. Valve bodies come cast or forged in a variety of materials including cast steel, stainless steel, and alloy steel depending on the requirements of the valve as a whole.

Bonnet

The bonnet is the second pressure-retaining component of a valve and is also referred to as the cover. It is connected to the valve body to create the valve enclosure. In the case of globe, diaphragm, gate, or stop check valves, it has an opening where the valve stem passes through and provides access to the internal parts of the valve when maintenance is needed.

Stem

The valve stem’s purpose is to transfer the required motion to either the disc, plug, or the ball in order to open and close the valve. It is connected to the valve actuator, lever, or handwheel at one end and the valve disc at the other end.

In a gate or globe valve, the stem uses the linear motion of the disc to open or close the valve while in plug, ball, and butterfly valves, the disc is rotated to open or close it.

Disc

The disc is the part of the valve that either allows or stops the flow, depending on where it’s positioned. A valve disk can be forged, fabricated, or cast.

Seat

The seat is one of the main parts of the valve that directly affects the rate at which the valve leaks and is an integral part of the valve body. Valves can have one or more seats depending on the type of valve. For example, a gate valve has two seats, one that sits on the upstream side and the other on the downstream side.

Trim

Valve trim is the collective term for the removable or replaceable internal parts that come into contact with the flow medium. These parts include the valve seat, disc, glands, spacers, guides, bushings, and internal springs.

Actuator

The actuator is the mechanism that operates the valve and is connected to the stem and disk assembly. It can be manually operated by a handwheel, lever, gear, chain, or through the motor, solenoid, pneumatic, or hydraulic mechanism.

Automatic Transmission Valves

At the heart of the automatic transmission's hydraulic control system is the valve body. It consists of several parts: the separator or transfer plate, valves, and valve body. A gasket and a separator plate separate the upper and lower halves. It's installed onto the transmission as a single unit and can be constructed of iron or, on most transmissions, aluminum.

The valve body contains different valves for different purposes: the poppet, the check ball, and the spool valve

The poppet valve can be a ball or a flat disc. It typically has a stem that acts as a guide for the valve's opening or closing. This valve acts as a port, blocking or allowing fluid flow.

A check ball valve sits in a seat in the valve body. It allows or blocks fluid flow according to the direction of flow. Depending on the application and manufacturer, they are either normally open or closed.

The spool valve is the most common valve found in automatic transmissions. They resemble a spool of thread with large areas used to block fluid flow called lands and stemmed areas called valleys. At each end of the valve is a reaction area. It's where fluid pressure, linkage, or a spring act as a force to activate the valve.