Parts of a Valve

A globe valve cut down the middle, open.

Parts of a Valve

Name Date

Tap any part to read, rename or leave it out

1 2 3 4 5 6 7 8 9
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Write the name of each numbered part.Answer key

  1. Body
  2. Ports
  3. Seat
  4. Disc
  5. Stem
  6. Bonnet
  7. Packing
  8. Gland nut
  9. Handwheel

Drawn for this site by script, 2026-09-27. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Next: a faucet, a valve at the sink

All 9 parts on the diagram

Show the list

Start here: 6 main parts 6

  1. Body The outer casing that holds the working parts inside. It is usually brass, bronze, iron, steel or plastic.
  2. Ports The openings the fluid flows in and out through. Joined to the pipes. Most valves have two.
  3. Seat The ring the disc presses against to close the valve.
  4. Disc The movable part that blocks the flow. Screwed down onto the seat, it shuts the valve. It is also called the valve member.
  5. Stem The threaded rod that joins the handwheel to the disc. Turning it moves the disc up or down.
  6. Handwheel The wheel you turn to open or close the valve by hand. Some valves have a handle or an actuator instead.

Bonnet and stem seal: 4 3

  1. Bonnet The cover on top of the body that the stem passes through. It guides and seals the stem, and comes off for maintenance.
  2. Packing Soft sealing material packed around the stem. Fluid then cannot leak out along it.
  3. Gland nut Presses down on the packing to keep it tight around the stem.

How this list was compiled: Read 2026-09-27. Wikipedia, Valve, https://en.wikipedia.org/wiki/Valve : its cross-section of an open globe valve names the body, ports, seat, stem, disc, handle or handwheel, bonnet, packing and gland nut; the body is the outer casing holding the internal parts, usually metal (brass, bronze, cast iron, steel) or plastic; the bonnet covers the body, guides and seals the stem, and is taken off for maintenance; ports are the passages the fluid flows through, most commonly two, joined to pipes; the disc (valve member) is a movable obstruction that restricts flow; a handle controls a valve by hand, an actuator automatically. Licence: own work

The drawing: Drawn for this site by script, 2026-09-27. Own work, nothing traced. Licence: own work

How it works

These are the parts of a valve on a globe valve, the kind textbooks use, cut down the middle and open. Start with the 6 main parts, then the parts on top.

Read the full guide

Following the flow

Fluid comes in one port, passes under the wall inside the body and up through the opening in the middle, then leaves by the other port. The seat is the ring round that opening.

Opening and closing

Turning the handwheel turns the stem, which screws the disc down onto the seat to shut the valve, or lifts it to open it. The bonnet guides the stem, and packing held by the gland nut stops leaks round it.

  • Not every valve has a bonnet: plug valves and many ball valves are built without one.

Questions and answers

What are the main parts of a valve?

The body, the ports the fluid flows through, the seat, the disc that closes against it, the stem that moves the disc, the bonnet on top, and a handle, handwheel or actuator to work it.

What is the bonnet of a valve?

The cover on top of the valve body. The stem passes through it, and it is taken off to reach the parts inside.

What is the disc in a valve?

The movable part inside that blocks the flow, also called the valve member. It is often not shaped like a disc at all.

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