Ventilation device for a hydraulic cylinder

A ventilation device for a hydraulic cylinder connectable to a member to be actuated, comprising:

• a body having a chamber provided with a first port communicable with said hydraulic cylinder and a second port exclusively communicable with a selected space;
• a closure member disposed in said chamber, displaceable along a line of travel into sealing engagement with either of said ports and being laterally spaced from a surface of said chamber, relative to said line of travel to allow the passage of a fluid;
• and
• a prestressed member disposed in said chamber between said body and said closure member, along said line of travel,
• wherein said body includes a portion projecting into said prestressed member, providing said second port engagable by said closure member, and the force exertable by said prestressed member is greater than the force of a fluid at a first pressure applied to said first port, urging said closure member into sealing engagement with said first port, the force exertable by said prestressed member is less than the force of a fluid at a second pressure applied to said first port, urging said closure member into sealing engagement with said second port, and between the force of a fluid at a third pressure between said first and second pressures applied to said first port, urging said closure member out of sealing engagement with both of said ports.