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Subject: back seat Пожалуйста, помогите перевести.Выражение встречается в следующем контексте:
A back seat rising stem gate valve has a valve body with a flow passageway through it and an open top, a gate that is vertically positioned to open and close the passageway, a stem extending upwardly from the valve body, the lower end of the stem being attached to the gate, a bonnet secured to the valve body by which the valve body open top is closed, the stem extending through an opening in the bonnet, a packing box slidably positioned in an opening in the bonnet and receiving the stem, the packing box having a back seat circumferential sealing surface surrounding the valve stem, and the valve stem having an integral enlarged diameter shoulder so that when the stem is in the full upward position the packing box can be displaced downwardly forcing the back seat sealing surface to seal against the stem shoulder to seal against fluid leakage along the valve stem. In one embodiment the packing box is downwardly displaced by hydraulic pressure, such as hydraulic pressure supplied from within the valve body. Заранее спасибо
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