| 摘要 |
A valve for shutting off or closing a main fluid flow comprises a valve stem (28) having a valve head (48), which may engage a valve seat (18). At the end remote from the valve head the valve stem carries a piston (36), which can be actuated by a closing fluid to shut off the main fluid flow. The valve is characterized in that the valve stem (28) is hollow and at the end at which the valve head (48) is provided, is open, and at the opposite end has openings (46) opening into the interior of the hollow valve stem (28), and that the piston (36) is mounted for axial movement on the valve stem (28) to allow further movement towards the valve seat (18) against spring action when the valve head (48) has engaged the valve seat (18) and the valve stem (28) has therefore come to a halt, said further movement relative to the valve stem (28) opening a passage (45) into the openings (46) in the valve stem (28), whereby closing fluid will be injected into the main flow passage (32) through the valve stem. The valve can be used for hot gas defrosting of an evaporator with automatic circulation in a freezing or cooling installation comprising also a compressor (3), a condenser (4) and a liquid separator (2), the valve (9) being connected into a return flow passage (8) from the evaporator (1) to the liquid separator (2). The valve (9) can then periodically close the main fluid flow through the return flow passage and inject hot gas into the evaporator (1) for defrosting purposes. Hot gas from the pressure side of the compressor (3) is used to effect the closing. A closing of the main fluid flow in the return passage (8) and an injection of hot gas in the opposite direction is thereby obtained by means of one and the same valve, merely by opening the hot gas supply. |
