PURPOSE:To prevent sludge from being collected or trapped in a valve cavity, by forming a gate hole at an upper part of a gate adapted for opening and closing a fluid passage, and forming a solid part at the lower upper part of the gate. CONSTITUTION:The gate hole 12b is formed at part of the gate 11 which is adapted for opening and closing a fluid passage 5. When the upstream side of the valve and a valve cavity 10 are communicated to each other as the gate 11 is opened gradually, sludge tends to be left on the upstream side of the gate 11 by reason of its own weight or otherwise to flow toward the downstream side of the gate 11 immediately over the lower end part of the gate hole 12b. Therefore, the amount of sludge entering into the valve cavity 10 is extremely small. When the gate 11 is fully opened, on the other hand, no sludge enters into the cavity 10 since it is closed completely.
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