"D valve" meaning in English

{
  "etymology_text": "Named after the hollow central D-sectioned piston.",
  "forms": [
    {
      "form": "D valves",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "D valve (plural D valves)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English entries with language name categories using raw markup",
          "parents": [
            "Entries with language name categories using raw markup",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms with non-redundant non-automated sortkeys",
          "parents": [
            "Terms with non-redundant non-automated sortkeys",
            "Entry maintenance"
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          "source": "w"
        }
      ],
      "glosses": [
        "A slide valve with a cup-like cavity in its face, through which exhaust steam passes."
      ],
      "id": "en-D_valve-en-noun-tYQBMCei",
      "links": [
        [
          "slide valve",
          "slide valve"
        ],
        [
          "cup",
          "cup"
        ],
        [
          "cavity",
          "cavity"
        ],
        [
          "exhaust",
          "exhaust"
        ],
        [
          "steam",
          "steam"
        ]
      ]
    }
  ],
  "word": "D valve"
}

{
  "etymology_text": "Named after the hollow central D-sectioned piston.",
  "forms": [
    {
      "form": "D valves",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "D valve (plural D valves)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English entries with language name categories using raw markup",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms derived from the shape of letters",
        "English terms with non-redundant non-automated sortkeys"
      ],
      "glosses": [
        "A slide valve with a cup-like cavity in its face, through which exhaust steam passes."
      ],
      "links": [
        [
          "slide valve",
          "slide valve"
        ],
        [
          "cup",
          "cup"
        ],
        [
          "cavity",
          "cavity"
        ],
        [
          "exhaust",
          "exhaust"
        ],
        [
          "steam",
          "steam"
        ]
      ]
    }
  ],
  "word": "D valve"
}